A prospective epidemiological study of gastrointestinal health effects due to the consumption of...

Correspondence to P. Payment.

0960-3123/97/010005-27 � 1997 Journals Oxford Ltd

International Journal of Environmental Health Research 7, 5±31 (1997)

A prospective epidemiological study ofgastrointestinal health effects due to theconsumption of drinking waterPIERRE PAYMENT1 , JACK SIEMIATYCKI1 , LESLEY RICHARDSON1, GILLES

RENAUD1, EDUARDO FRANCO2 and MICH ÁELE PR� VOST3

1Institut Armand-Frappier, 531 boulevard des Prairies, Laval H7N 4Z3, 2Department of Oncology, McGill

University, 546 avenue des Pins, ouest, Montr…al H2W 1S6 and 3Chaire en eau potable, � cole Polytechnique de

Montr…al, CP 6079, Succ A, Montr…al H3C 3A7, Canada

The objective of this study was to assess if drinking water meeting currently accepted microbiological

standards is the source of gastrointestinal illnesses and to attempt to identify the source(s) of these

illnesses. A randomized prospective study was conducted over a period of 16 months (September

1993±December 1994) in a middle class suburban community served by a single water filtration plant. A

representative sample of 1400 families were selected and randomly allocated in four groups of 350, to the

following regimens: (1) tap water; (2) tap water from a continuously purged tap; (3) bottled plant water;

(4) purified bottled water (tap water treated by reverse osmosis or spring water). The water treatment plant

produced wather that met or exceeded current North American regulations for drinking water quality. The

distribution system was found to be in compliance for both coliforms and chlorine. Using the purified

water group as the baseline, the excess of gastrointestinal illness associated with tap water was 14% in the

tap group and 19% in the tap-valve group. Children 2±5 years old were the most affected with an excess

of 17% in the tap group and 40% in the tap-valve group. Mottled plant water was not the source of any

increase in the incidence of gastrointestinal illnesses, even if it contained very high levels of heterotrophic

bacteria after two weeks. The data collected suggest that 14±40% of the gastrointestinal illnesses are

attributable to tap water meeting current standards and that the water distribution system appears to be

partly responsible for these illnesses.

Keywords : drinking water; waterborne disease; gastrointestinal illness; health effects; epidemiologic study.

Introduction

The notion that coliform-free drinking water is pathogen-free is being seriously questioned as

is the value of current water quality indicators (Craun 1990). Several outbreaks of gastroenteritis

and hepatitis (Wilson et al. 1982, Bloch et al. 1990, Mackenzie et al. 1994, Kramer et al. 1996),

giardiasis and cryptosporidiosis (Hayes et al. 1989, Smith et al. 1989, Smith and Sm ith 1990)

in communities with water meeting current regulations (Federal Register 1989a, Anonymous

1994), have brought to the public attention the fact that current standards may not provide

complete protection (Batik et al. 1983, Craun 1990) .

Any estimation of the waterborne fraction of disease is impaired by their low incidence in the

population (Payment et al. 1991b) and it is only in outbreak situation that detailed analyses can

6 Payment et al.

be performed (Batik et al. 1979, Collin et al. 1981, Zmirou et al. 1987). The estimation of a

waterborne fraction of water-related diseases myst often rely on events that occur rarely and

retrospective epidemiological studies are often difficult to interpret because of multifactorial

disease etiology and confounding variables (Crump and Guess 1982, Morris et al. 1992, Riley

1995). Gastrointestinal symptoms offer a more frequent and easier to measure indicator of health

effects: diarrhea and vomiting occur in most normal individuals at a rate of about once a year.

We have relied on this normally high rate of occurrence of these symptoms to attempt to

evaluate the level of water attributable of gastrointestinal illnesses.

The estimated annual incidence of highly credible gastro-intestinal (HCGI) illness was

evaluated in a previous study (Paym ent et al. 1991b) at 0.76 episode/person-year among tap

water drinkers as com pared with 0.50 among filtered water drinkers. It was estimated that 35%

of the reported GI illnesses among the tap water drinkers was attributable to tap water and thus

preventable. The rate of disease increased with the amount of tap water consumed (Payment et

al. 1991b) and with distance of the household from the plant (Payment et al. 1993). Bacterial

regrowth in tap water was suggested as an explanation and later studies on the virulence of

bacteria isolated from tap water revealed that a small fraction of these bacteria could be

considered as opportunistic pathogens as they exhibited several virulence characteristics

(Payment et al. 1994). Attempts were made to determine the etiology of the observed illnesses,

but there was no serological indication of water-related infections due to enteroviruses, hepatitis

A virus, rotavirus (Paym ent 1991) or Norwalk virus infections (Paym ent et al. 1994). The

societal cost of these `mild illnesses’ has been estimated to be several orders of magnitude

higher than the costs associated with acute hospitalized cases or deaths. In the US, the annual

cost to society of gastrointestinal infectious illnesses was estimated to $19 500 million dollars

(Garthright et al. 1988, Roberts and Foegeding 1991).

The objective of the current study was to reevaluate the level of gastrointestinal illnesses

attributable to tap water in a population consuming drinking water meeting current regulations

and to determine the source of these illnesses.

Methods

General design

A randomized intervention trial was carried out in an area served by a single water treatment

plant and its distribution system. This system and the area under study are the same that were

studied previously (Payment et al. 1991b). A representative sample of families with young

children was selected and they were randomly assigned into four groups to experience one of

the following drinking water regimens for a period up to 16 months (September 1993±Decem-

ber 1994): (1) unmodified tap water as distributed by the local public water supply (tap group);

(2) tap water with a purge valve installed on the cold water line under the kitchen sink (tap-valve

group); (3) bottled water consisting of fully treated plant water (plant group) or (4) purified

bottled water consisting of spring water or reverse-osmosis treated filtered plant water (purified-

water or PW group). Water for groups 3 (plant) and 4 (PW) was bottled and delivered every 2

weeks to the subjects. Gastrointestinal and respiratory symptoms of all participating family

members were recorded via a diary procedure for the duration of the study.

The tap water group was intended to establish a baseline value of the level of illness in the

general population. The tap-valve group served to establish the contribution of microbial

regrowth in household plumbing to the illness rate. It was postulated that, by maintaining a

constant flow of water in the household pipes, water consumed by the subjects would be close

Gastrointestinal health effects of tap water 7

in quality to water in the distribution system mains. Plant water and purified-water were bottled

and delivered to participating families in unmarked containers effectively blinding the

consumers to the type of water they consumed. Plant water obtained directly at the treatment

plant was unmodified by the distribution system. Purified-water provided an uncontaminated

water source of drinking water and was a way to repeat our previous study in which each

individual households had been fitted with reverse-osmosis domestic filters as a barrier to all

contaminants (Payment et al. 1991a,b).

Water treatment plant

The population selected is served by a single water treatment plant and is located in the same

area that was studied during our previous study (Payment et al. 1991b). The watershed is over

300 km long and drains both rural and urban areas. A large relatively unpolluted lake acts as a

buffer zone before the river enters the suburban area under study which is polluted by untreated

sanitary and storm sewer discharges. The capacity of the water treatment plant is 130 000 cubic

meters per day and water is treated by a complete conventional treatment (alum flocculation,

settling, filtration on sand-anthracite, ozonation and a final chlorination).post-chlorination).

Fluoride is usually added to tap water and tracer experiments were performed using fluoride

concentration to assess residence in the plant and contact times for the oxidants.

Reverse-osmosis unit

A reverse-osmosis (RO) unit rated at a product flow rate of 120 l/min at 4ÊC was leased from

Airableau Inc. (Qu…bec, Canada) and installed at the water treatment plant. The unit was

composed of hydronautics membranes (10 cm dia.) in two sets of 10 modules. The unit was

connected through sanitary tubing to a high pressure main at the water treatment plant.

Efficiency of the unit was monitored by on-line by conductivity and pressure controls and

samples were taken at each use for bacteriological analysis of the product water.

Water consumed by each group

Tap-water and tap-valve groups. Subjects in these two groups consumed tap water and did not

change their normal consumption pattern. To evaluate if bacterial regrowth in household

plumbing plays a role in gastrointestinal health effects, purge valves were installed by

professional plumbers in a randomly chosen sub-group of households. These valves maintained

a sufficient flow rate to the drain to equilibrate the water quality in the household with the water

quality in the main. The diversion valve was installed under the kitchen sink, 30 ±60 cm from the

tap on the cold water line, with a continuous discharge to the sewer. The valve was fitted with

back-flow preventers according to local building codes. The valve was adjusted to deliver

100 ±500 ml/min with minimal background noise due to the flowing water.

Bottling of plant and purified water. Water was bottled by a commercial facility located

100 km from the water treatment plant. A sanitary stainless steel tanker truck dedicated to

drinking water transport was used to haul water from the treatment plant or the spring. Sanitary

connections to the tanker from the main water line or the RO-unit were provided and all water

lines were flushed for 10 min before the actual loading.

Plant finished water was bottled without further treatment while purified water, Spring water

or plant water treated by reverse osmosis were ozonated before bottling. Water was bottled in

standard 4-l plastic bottles marked only with a code that included the date, the time of bottling,

the work shift, and our own code. Bottled water was packaged in cases of four bottles which

8 Payment et al.

were delivered to a warehouse where they were kept at room temperature until delivery in the

next 2±4 days.

The study began in September 1993, however purifed water (RO-treated) was not available

until February 1994 and during spring water was obtained from the bottling company as a

replacement. This water is certified by the Ministry of Environment of Quebec and is obtained

from a protected underground aquifer which has no history of any contamination. This water

was ozonated at the time of bottling and was delivered to the subjects in the PW group until

February 1994.

Bottled water (purified or plant) was picked-up at the warehouse and delivered to the subjects

within 2±4 days of bottling. Subjects were instructed to use this water for the following 2 weeks

and were requested to discard left-over bottles from the previous delivery. Enough water was

provided to each family for a 2-week period. If they did not have sufficient water during this

2-week period, they could call our offices and obtain supplementary water from the same

production lot.

Popula tion evaluated

The study was planned to include 4 groups of 350 families followed for 16 months (September

1993±December 1994). The purpose of the study was not to evaluate the susceptibility of groups

at special risk such as immunosuppressed, immunocom promised, elderly, etc., thus the

individuals selected were in good health with no known medical conditions that may affect the

outcome. The study was carried out in a suburban area of average socio-economic level. Apart

from the fact that most of the population of this area is French-speaking, it is quite typical of

an average socioeconomic level, the subjects were in good health and should reflect an average

North American community.

Selection process

Four eligibility criteria were established for participation in the study: residence located within

the zone of influence of the water filtration plant, being a usual consumer of tap water supplied

by the city, at least one child aged 2 ±12 years living full-time in the household and ability to

communicate in French. The sampling frame was the list of families residents in the study area

and benefiting from a government-run income supplement program for families with children

under 18 years. The program is independent of incom e and does not denote a lower economic

class. The government agency responsible for the program provided us a list of 4800 qualifying

families residing in the area.

Families were first contacted by mail to inform them of the study and that someone would be

calling them within a few days. Within the next week, telephonists contacted the family to assess

eligibility. If the family satisfied the eligibility criteria and agreed to participate in the study, it

was assigned randomly to one of the four groups. This process of screening and random

allocation was continued until there were approximately 350 households per group. This number

of families was chosen in the hope that by the end of the follow-up period while there would

remain at least 250 families per group.

W hile subjects knew from the introductory letter that there would be four groups, they were

given no choice as to the group they could participate. They were however always given the

possibility to refuse to participate at any step of the selection process as well as during the

observation period.

All families were visited to explain the study and to obtain written consent forms from all

members of the family that agreed to participate, answer basic questions and explain to them the

Health Watch Calendar. Further sociodemographic and water consumption data were obtained on

two other occasions, in June and December 1994, from self-completed questionnaires which were

returned to us by mail. The baseline questionnaire included sociodemographic information, as

well as information on place of work, school or day-care attendance, trips, chronic medical

conditions and use of medication. Arrangements were made with each family to agree on a

convenient time for delivery of the water if they were in the bottled water groups. For those in the

tap-valve group, we made arrangements for a plumber to install the valve at the kitchen tap.

Health survey

Survey calendar and incentives. A simple diary-type questionnaire with a list of symptoms

was distributed to all subjects and one parent was designated to record daily symptoms

experienced by members of the family. The diary was distributed as a spiral bound booklet 8.5

3 11 in. containing an `Introductory Letter ’ and all 2-week questionnaires for the observation

period. Each record sheet was printed on both sides and could be used to record the events of

four individuals during each 2-week period. If there were more than four subjects in the

household, a second booklet was provided. The subjects were asked to record on the day it

occurred if they had experienced nausea, vomiting, diarrhea, cold or flu. A list of subsidiary

symptoms was also to be completed (see list in Table 5).

Every 2 weeks, families were contacted by telephone to obtain the information recorded on the

diary. The telephonist was only required to record the information already on the daily diary. As

most weekly reports were negative and the information sought fairly simple, telephone calls were

relatively short. The telephonist asked the designated person (i.e. informant) if any of the subjects

had experienced cold or flu, vomiting, diarrhea or nausea. If any of these symptoms were reported,

the telephonist requested the com plementary information recorded on the questionnaire (i.e. all

other symptoms experienced). Participants were also asked what was the perception of the family

of the water quality during the period. School or day-care attendance, trips out of the country or

absence from home were also noted on this diary. To minimize information bias, each telephonist

received alternatively a different subgroup of subjects to contact.

To maintain the level of participation and maximize contact with the participating families, a

lottery ticket was sent to each family every month with a short note thanking them for their

continued participation.

Water consumption surveys. Three water consumption surveys were done during the course of

thet study, one as part of the baseline survey at the time of enrollment, one in June 1994 and one

in December 1994. The questionnaire was designed to establish an estimate of the amount and

type of water, where it was consumed and whether it was consumed unmodified or was used for

preparing tea, coffee or juices.

Data entry and statistical analysis. The database was prepared using FileMaker Pro for the

Macintosh. All data on each member of the participating families were entered in this database,

verified and validated. Discrepancies were resolved. Data entered in the database were further

cross checked and re-verified to ensure its accuracy. All data were first analyzed using SAS

Software and SPSS Software installed on a SUN Microstation and stratified according to the

variables entered.

For analysis purposes two periods were distinguished: the 1993±94 school year from

September 1993 until June 1994 and the remaining months from July 1994 to December 1994.

In the Province of Quebec, the end of June marks the end of the school year as well as the period

10 Payment et al.

in which a relatively large proportion of the population moves from one household or apartment

to another.

Highly credible gastrointestinal (HCGI) episodes were defined as: (1) vomiting or liquid

diarrhea alone; or (2) soft stools or nausea with abdominal cramps. This is the same definition

that was used during our initial study (Payment et al. 1991b). The time criteria for inclusion in

the analysis and acceptance as a credible episode was a period of at least 6 consecutive

symptom-free days between the episodes. Symptom occurrence and HCGI rates were calculated

for each group and stratified according to the collected variables. Estimates of incidence of

HCGI illnesses in the groups were derived by means of Poisson regression methods (Frome

1983). Since this technique counts each episode as an independent event, a correction had to be

made for the correlation between repeat episodes by the same unit of observation. This was done

using the `quasi-likelihood’ approach (McCullagh and Nelder 1983), which amounts to reducing

the nominal significance of each result by a factor related to the amount of this correlation.

Some analyses were based on the entire famikly as the unit of observation, while others were

based on selected individuals within the family. In addition to group membership, som e

covariates were included in the corresponding models in order to adjust for any imbalance in the

groups. These covariates were: age, sex, and subregion. When the analyses were carried out for

the entire period of follow-up, the study period was also incorporated as a covariate in the

model. Adjusted rates were estimated from the results of the fitted models. Each regression

model gave an estimate of the p-value associated with group membership.

Poisson regression was also used to establish whether there was a dose-response relationship

between tap water consumption and incidence of HCGI in the tap and tap-valve groups. This

was done by adding the number of glasses of water consumed per week as an independent

variable to the models. These analyses were based on unmodified tap water, i.e. water other than

that used in food preparation or cold and hot beverages.

Bacteriological and physico-chemical analyses

Bacteriological and physico-chemical analyses were performed according to standard methods

(APHA 1992) unless otherwise indicated. Total coliforms, HPC, alkalinity, hardness and color

were monitored twice a day at the plant. Turbidity, pH, flow, pressure, temperature and

disinfectant residual are monitored continuously at the water treatment plant. Chlorinated water

samples were collected in bottles containing sodium thiosulfate. Compliance monitoring data

were obtained from the water utility authorities from analysis of samples collected at selected

consumers taps (two mid-point and two at the end of the distribution system). Three sets of

analyses were performed on three to six bottles of each lot of bottled water: at the time of

collection, upon delivery to our warehouse, and after 2 weeks at room temperature to simulate

storage by the subjects. Heterotrophic plate counts bacteria were determined (HPC) on R2A

medium at 20 and 35ÊC, total coliforms on m-Endo, Pseudomonas aeruginosa on m-PA,

Aeromonas hydrophila on Ryan medium, direct counts and viable counts were monitored using

membrane filtration equipment and the indicated medium (APHA 1992). Clostridium

perfringens was enumerated using the membrane filtration method on m-CP medium as

described by Bisson and Cabelli (1979) and modified by Armon and Paym ent (1988).

Virological and parasitological analyses

Raw water (100 l), filtered water (1000 l) and finished water (1000 l) samples were analyzed every

two weeks for the presence of human enteric viruses and parasites according to a single method

developed in our laboratories using electronegative wound fiberglass cartridges. Viruses in

concentrates were detected by two passages on MA-104 cells followed by an immunoperoxidase

test using human gamma globulins. Concentrated samples for parasite analysis were purified by

Sucrose-Percoll flotation, collected on membrane filters and analyzed for Giardia cysts and

Cryptosporidium oocysts by immunofluorescence using monoclonal antibodies (28, 33).

Results

Treatment plant and distribution system

The treatment plant produced water that met and exceeded all current North American drinking

water regulations in application at the time of the study including the Total Coliform Rule and

the Surface Water Treatment Rule. Water entering the plant was at pH 7.4, treated water was at

pH 8.0 and temperature varied from 1ÊC to 23ÊC. Ozone was applied to the filtered water at a

dose of 2±2.5 mg/l resulting in a final concentration of 0.3 ±0.4 mg/l after a 10 min, contact time.

Finished water turbidity was mostly below 0.1 NTU an the level of free chlorine residual

averaged 0.5 mg/l in the clearwell and at the first consum er. Plant effluent water had a biological

oxygen demand content of 0.5 mg/l. Most of the mains were put in place between 1960±70, but

some were as recent as 1990.

A schematic view of the area is presented in Fig. 1. The average residence time of water as

it reached each household was calculated using a model (Piccolo) of the distribution system: the

model predicted residence times of 0.3±34 h.

Bacteriological data from distribution system and plant (compliance monitoring)

Over the period of the study, the quality of the bacteriological quality of the water was within

current North American guidelines. Coliforms were never detected in plant effluent. Fecal

coliforms were never detected in any of the samples requires for com pliance monitoring in the

distribution system and only 4 out of 633 (0.6%) were positive for total coliforms.

Fig. 1. Schematic representation of area studied and estimated residence time of water in each of the

geographical areas (burroughs).

12 Payment et al.

Microbiological data from large volume analyses

River water entering the treatment plant was contaminated by human enteric viruses, Giardia

cysts and Cryptosporidium oocysts (Table 1). Clostridium perfrongens and somatic coliphages

were also found in large numbers. The level of viruses detected in the raw water was relatively

stable until April 1994, when their numbers dropped sharply after the spring run-off (Fig. 2).

Microorganisms were rarely found after filtration and before any disinfection had been applied

(Fig. 3) and none were found in the disinfected finished water.

Fig. 2. Occurrence of selected microorganisms in river water entering the water treatment plant.

Fig. 3. Detection of Clostridium perfringens, somatic coliphages, Giardia cysts and Cryptosporidiumoocysts in filtered water before application of any disinfectant. The flat part of each line indicates detection

limit.

14 Payment et al.

Performance of the plant was evaluated by a private consulting firm whose mandate was to

estimate the CT (disinfectant concentration 3 time) values achieved under operational

conditions using the USEPA data (Federal Register 1989), tracer experiments and data from the

plant. The models predicted CT values of 82 ±221 mg/l.min for ozonation and chlorination

combined (Fig. 4).

Bacteriology of taps with valves

Water samples, collected at three pilot sites where purge-valves had been installed at the onset

of the study, indicated that water quality at the tap was very close to the bacteriological quality

in the pipe feeding the distribution line distribution mains. This was confirmed by samples

obtained during visits to the households: bacterial counts were lower than would have been

expected for normal taps and bacterial counts were low even after a 1 min flush. First flush

samples contained a geometric mean of 288 cfu/ml (HPC at 25ÊC) and 44 cfu/ml (HPC at 35ÊC)

while after a 1 min flush HPC counts were respectively 71 and 3 cfu/ml.

Bacteriology of bottled waters (purified and plant)

RO-treated and spring water were ozonated at bottling, an operation that insured low bacterial

counts at the time of bottling. After 2 weeks at room temperature (Table 2), bottled RO-water

and spring water contained less 10 cfu/100 ml, while bacterial counts in bottled plant water

increased to a geometric mean value of 1 273 700 cfu/100 ml (HPC 25ÊC, 7 days). Total

coliforms, Pseudomonas aeruginosa and Aeromonas hydrophila were rarely detected.

Fig. 4. Monthly average temperature and minimum total CT values at the water treatment plant.

Table 2. Geometric mean number of bacteria in bottled water after 2 weeks at room temperature

Type of bottledwater

Total counts(epifluorescence)

HPC 25ÊC(cfu/100 ml)

HPC 35ÊC(cfu/100 ml)

Pseudomonasaeruginosa(cfu/100 ml)

Aeromonashydrophila

(cfu/100 ml)

Totalcoliforms

(cfu/100 ml)

RO-treated water 3 680 200 0 0 0 0 0

Spring water 1 106 500 8 1 0 0 0Plant water 63 714 300 1 273 700 4997 0 0 0

Recruitment and enrollment

The enrollment process was completed at the end of December 1993 (Fig. 5) and the requisite

quota was achieved in each of the four observation groups (Table 3). The first three groups were

recruited and commenced participation between the 13 September and the end of October 1993.

The fourth group was initiated in November 1993. Recruitment of all groups and the installation

of the purge valves was completed by the end of December 1993. As expected there were some

losses over time. In three of the groups, over 80% of the enrolled families completed the entire

18 month follow-up; however in the Bottled plant water group 50% of the initial subjects

dropped-out during the course of the study mainly because of taste and odor problems associated

Fig. 5. Number of families participating in the study by calendar period and study groups.

Table 3. Response to request to participate in the study in each of the four study groups

Status

Purified(bottled)

Plant(bottled)

Tap-valve

Total number of families randomized to 1206 100 883 100 1203 100 1050 100the group

Unable to reach 86 7.1 11 1.2 57 4.7 10 1.0Not eligible ± drinks modified water 217 18.0 213 24.1 226 18.8 259 24.7

Not eligible ± no child 15 1.2 12 1.4 5 0.4 6 0.6Not eligible ± not able to communicate 8 0.7 9 1.0 13 1.1 11 1.0in French

Refused when first called 257 21.3 141 16 345 28.7 182 17.3

Agreed to participate when first called 387 32.1 373 42.2 419 34.8 369 35.1(September 1993)

Remained committed when visited 371 30.8 360 40.8 405 33.7 355 33.8(September/October 1993)

Participating (December 1993) 339 28.1 346 39.2 354 29.4 330 31.4Participating (December 1994) 270 22.3 296 33.5 215 17.9 281 26.8

16 Payment et al.

with bottled plant water. This water had a distinctive taste and odor that some subjects found

very unpleasant.

Several families moved house during the course of the study. The sharp drop in participation

in July (Fig. 5) is explained by the fact that this is a com mon moving date in Quebec. If the

family moved within the studied area, they were asked to continue participation in the same

observation group. For subjects in the tap-valve group, a new valve was installed in their new

house or apartment.

General observations and rates of symptoms

Subjects were distributed equally in the four participation groups (Table 4).

Cold or flur was by far the most frequently reported symptom however, differences between

the groups were small (Table 5). Diarrhea was frequently reported while bloody diarrhea, back

pains, muscular pains and earaches were rarely reported. Changes in daily activities, absences

from work or school, being bedridden and having to seek medical help were quite frequent,

while hospitalization was a relatively rare occurrence in all groups. Subjects from the tap-valve

and tap groups generally reported events more frequently than those in the bottled water groups.

Bottled plant water consumers reported many of these events less frequently than subjects in the

other three groups.

During the period of observation, between 32 and 49% of the subjects experienced at least

one HCGI episode. The number of episodes reported by each subject varied from 0 to 16 (Table

6) and the duration of episodes ranged from 1 to 35 days (Table 7).

For all groups the highest incidence of HCGI was observed during autumn and winter 1993

and the lowest during the summer 1994 period (Fig. 6). By autumn 1994, the incidence for all

groups was slowly increasing again as expected for these illnesses. The temporal pattern was

similar among children and among all subjects. Average incidence of HCGI was in the range of

Table 4. Distribution of subjects in the four observation groups at the end of the study period by

selected variables

Variable Subgroup Purified Tap Plant Tap-valve Total

Age 0±5 206 166 200 214 7866±20 499 490 476 458 1923

21±49 618 616 591 601 242650 + 37 24 30 27 118

Sex Female 706 678 668 656 2708Male 654 618 629 644 2545

Region #1 159 104 190 96 549

#2* 375 347 309 402 1433#3 348 286 214 376 1224

#4 275 364 273 307 1219#5 203 195 311 119 828

Total 1360 1296 1297 1300 5253

*Location of water treatment plant.

Stratified observations

Variations in the incidence of HCGI was observed when the data was stratified by age, sex,

status and area. These observations were made for all subjects (Table 9) and for children 2±12

years old (data not presented). The incidence was higher for female than for male subjects and

it decreased with age. Proxy-reporting or self-reporting revealed a slight difference which is

compatible with the fact that informants were mainly wom en in the 21±49 years old age group.

Analysis of the ratio of HCGI in the tap water group compared with those in the purified water

group suggest that separate clusters or episodes might have occurred (Fig. 7). The ratio was

higher for tap water consumers in the months of October±December 1993 and in early April

1994. Minor variations were observed during the remaining part of the observation period, but

the low rate of HCGI precludes any significant conclusion.

Table 5. Symptoms and behaviors (number of days reported per 100 person-years) by group for allsubjects and for children 2±12 years

All subjects

Purified(bottled) Tap

Plant(bottled)

Tap-valve

2 ± 12 years old

Plant(bottled)

Tap-valve

Nausea* 22.3 27.7 20.2 32.7 23.3 27.8 15.6 40.2Vomiting* 32.4 35.9 30.9 43.0 51.2 55.2 46.9 62.5

Diarrhea soft* 51.7 69.6 68.1 60.7 54.7 71.2 59.4 52.8Diarrhea liquid* 38.0 44.9 52.4 48.3 41.7 49.2 52.2 44.1

Diarrhea liquid, bloody* 0.6 0.5 0.9 0.2 0.8 0.6 0.7 0.0Fever 44.9 47.7 31.7 57.3 68.2 79.1 53.9 92.6

Abdominal cramps 32.6 38.4 31.7 41.1 41.1 47.2 36.1 50.5

Muscular pains 7.7 16.4 8.8 12.9 4.2 10.1 4.9 7.3Back pains 4.5 9.2 5.0 5.6 2.0 3.5 1.8 2.6

Sore throat 36.1 57.1 34.2 55.0 42.5 60.4 36.5 63.5Headache 31.0 57.1 32.8 53.2 30.1 60.6 28.6 58.0

Cold or flu* 132.1 152.1 126.0 133.9 166.8 195.1 161.4 168.7Earache 9.2 10.1 11.7 10.4 14.1 14.4 14.7 16.2

Changed daily activities 20.8 39.2 11.2 56.5 27.2 53.6 14.1 73.3

Absent (work/school) 25.1 31.7 17.6 36.8 38.5 48.4 28.6 55.4Stayed in bed 15.4 24.9 9.4 31.2 20.6 31.2 11.9 39.6

Consulted physician 19.0 19.4 13.8 23.6 28.0 29.3 23.1 34.0Was hospitalized 0.7 0.5 0.4 0.6 0.9 0.5 0.0 0.6

*Subjects were first asked if they had experienced nausea vomiting, diarrhea, cold or flu (symptoms marked with an

asterisk). If the answer was positive they were then asked to further complete the detailed questionnaire.

0.5±1 episode/person-year (Table 8). For all subjects, the incidence of HCGI was lowest in the

purified water (PW) group at 0.58 episodes/person-year and in the bottled plant water group at

0.60 episodes/person-year. Rates were slightly higher in the tap-valve group at 0.70 episodes/

person-year. Subjects drinking bottled plant water had a tendency to have an equivalent or lower

incidence of HCGI than subjects in the PW group. Children 2 ±12 and 2±5 years who were tap

water consumers experienced 17±40% more HCGI (Table 8).

18 Payment et al.

20 Payment et al.

Analysis by Poisson regression methods

Poisson regression analysis revealed that for all subjects and both periods com bined, group

membership was a significant predictor of the risk of HCGI (Table 10). The difference was 15%

for the tap group and 24% for the tap valve group. Age was a significant variable, with children

experiencing a higher incidence of HCGI. Significant differences were also observed for sex,

observation periods and subregions. When the analysis was restricted to the informants, i.e.

mainly females 21±49 years old, group differences were small. Among children however,

whether youngest or all 2±12 years old, significant differences of 20 ±40% were associated with

group membership. This effect was seen only in period 1.

W henever group membership was significant, it was possible to verify simultaneously that

there were no statistical differences between the two bottled water groups and the two tap water

groups.

Water consumption and water quality perception

The taste of the water was generally reported to be good or excellent (Fig. 8) except by subjects

in the bottled plant water group. Taste and odor problems, mainly chlorine and metallic taste,

were reported by some subjects who drank bottled plant water as evidenced by the 10% who

reported bad tasting water. This occurred sporadically and no apparent reason was found to

explain these occurrences.

Total tap water consumption (Table 11) was similar in the tap and tap-valve groups at

respectively 6.9 glasses per person-day and 7.0 glasses/person-day with little bottled water

Fig. 6. Rate of HCGI (8-week forward moving average) for all subjects in the four study groups.

22 Payment et al.

consumption. The two bottled water groups (PW and plant) reported consumption of bottled

water at a rate of 4.2 glasses/day (PW) and 4.3 glasses/day (plant), but also reported drinking

3.1 and 3.3 glasses/day of tap water. Tap water consumed outside of the home was similar in all

groups at a rate of about 0.7 glasses. About half of the drinking water was unmodified tap water

consumed at home.

Correlation with reisdence time and with water consumption

There was no correlation between the time of residence of the water in the distribution system

and the incidence of HCGI in a family (data not shown). Significant dose-response relationships

Fig. 7. Relative risk (4-week forward moving average) for all subjects using the PW group rate as thereference.

Table 10. Ratio between rates of HCGI by group derived from Poisson regression model, withinsubsets of the study population group and unit of observation with age, sex, group participation and

region as variables

Period Study subjects

Ratio of HCGI rate

Purified Tap Plant Tap-valve p-value

September 93±December 94 All 1.00 1.15 1.00 1.24 0.007

Periods 1 and 2 Informant 1.00 1.23 1.17 1.32 0.216Children 2±12 1.00 1.14 0.94 1.21 0.079

September 93±June 94 All 1.00 1.21 1.06 1.33 0.001

Period 1 Informant 1.00 1.24 1.22 1.40 0.299Children 2±12 1.00 1.20 0.97 1.30 0.008

July 94±December 94 All 1.00 0.99 0.82 1.03 0.204

Period 2 Informant 1.00 1.14 1.06 1.11 0.858Children 2±12 1.00 0.95 0.85 0.98 0.853

p-value for differences between groups.

Excellen t Good Bad No response

Taste of water

Purified

Tap-valv e

24 Payment et al.

Fig. 8. Perception of water quality in the four observation groups based on over 36 000 responses frombiweekly questionnaires.

Table 11. Amount of drinking water consumed (glasses/dry) by group, type of water and location

where it was consumed

Location Type of water

Plant(bottled)

Tap-valve

Home and out of the home Total tap water 3.1 6.9 3.3 7.0

Total bottled water 4.2 0.3 4.3 0.3

Home Tap water, unmodified 1.1 3.2 1.1 3.2Tap water, juices* 0.5 1.4 0.7 1.5Tap water, hot beverages 0.4 1.1 0.5 1.1

Bottled water, unmodified 2.2 0.1 2.1 0.1Bottled water, juices* 1.1 0.0 1.2 0.0

Bottled water, hot beverages 0.7 0.0 0.7 0.0

Out of the home Tap water, unmodified 0.7 0.7 0.6 0.7

Tap water, juices 0.1 0.1 0.1 0.1Tap water, hot beverages 0.4 0.4 0.3 0.4

Bottled water, unmodified 0.2 0.2 0.2 0.2

Bottled water, juices* 0.0 0.0 0.0 0.0Bottled water, hot beverages 0.1 0.0 0.1 0.0

*Water used for the preparation of concentrated fruit juices.

were observed between water consum ption and incidence of HCGI for children and for

informants in the tap group (Table 12). In subjects over 12, including informants, the

relationship was positive and in subjects less than 12 years the correlation was negative. Dose-

response relationships were not observed when the data was analyzed for all subjects or for

subjects in the tap-valve group even if HCGI incidence was higher.

Discussion

Incidence of gastrointestinal illnesses

In the current study, 59 to 67% of the families experienced at least one episode of HCGI over

a 16 month period of observation (Table 13). The rate of HCGI (Table 14) was similar to that

observed during our previous study (Paym ent et al. 1991a,b, 1993). These results are also

comparable to data reported in the early 1950s during the Cleveland studies (Hodges et al. 1956)

and in the 1980’ s during the Tecumseh studies (Monto et al. 1980, Monto et al. 1983). W hile

the annual average rate of gastrointestinal illnesses is relatively constant from year to year,

weekly or monthly rates are unpredictable (Rothbart 1995) .

Table 12. Incidence of HCGI episodes by amount of unmodified tapwater consumed among subjectsconsuming tap water

Tap Tap-valve

Glasses of waterper day

Unit of observation 0 ± 2.7 2.8 ± 4.5 > 4.5 p-value* 0 ± 2.7 2.8 ± 4.5 > 4.5 p-value*

All subjects 1.03** 1.07 1.03 0.975 1.90 1.74 1.68 0.226Informant 0.38 0.60 0.69 0.005 0.60 0.76 0.65 0.788

Child 2±12 1.30 1.04 0.96 0.020 2.21 2.08 2.10 0.724Subjects over 12 0.27 0.40 0.39 0.011 0.42 0.38 0.36 0.279

*p-value for Trend test.

**Annual incidence (HCGI per person-year) derived by Poisson Regression model including age, sex and subregion

as variables.

Table 13. Percentage of families by group of observation with at least one HCGI episode during1988±89 (Payment et al. 1991a) and 1993±94 (current observations)

Observation period Purified Tap Plant Valve

January 1988±June 1989 (18 months) (Payment et al. 1991a) 62.0% 67.7% ND NDSeptember 1993±December 1994 (16 months) (current results) 59.6% 66.9% 61.7% 65.9%

26 Payment et al.

Autumn 1993 was extremely cold and winter came early with record breaking low

temperatures often below ±20ÊC. During this period, we observed high rates of respiratory and

gastrointestinal sym ptoms. While part of this higher level of illness can also be related to the

onset of the study and an eagerness to report, this is true for all groups and should not invalidate

the inter-group differences that we have observed.

Tap water attributable disease

The results are compatible with the hypothesis that tap water is the source of an excess in water-

related gastrointestinal illnesses. The overall relative risk compared to the PW water consum ers

was 14 ±19% for the tap water consumers for the complete observation period and it was 20 and

35% for the period of September 1993 to June 1994. These values are essentially of the same

order of magnitude as those reported for our 1988 ±89 study (Payment et al. 1991b) (Table 14).

No significant relative risk was found later. A significant dose-response relationship was

observed for some groups. While the effect of tap water was seen in all age groups in the earlier

study, data from the present study suggest a higher risk for children consuming tap water. We

can only speculate on the reasons for this increased risk. The fact that children are the most

affected by HCGI is consistent with their developing immunity. The observation that children

who drink more tap water have a lower incidence of HCGI, is also consistent with their

developing immunity because children who drink more water have a higher probability of being

infected. After a first infection, these children will be refractory to infection by the same

microorganism for a period that can range from several months to life (Rothbart 1995) .

Assuming low doses of microorganisms in water, subjects consuming large volumes of water

would be infected more rapidly, but would also be protected for several months from a similar

infection. At the time of enrollment in the study, consum ers of large volume of waters would

already have been less susceptible to infection because of their habit. This is not true for children

2±5 years old who had not yet been affected and who would have been developing water

consumption habits and would be more susceptible to infection.

It was not possible to show a relationship between water consumption and HCGI incidence

derived by Poisson Regression for all subjects. This was to be expected as the positive effect

Table 14. Comparison of 1993±94 (current data) and 1988±89 (Payment et al. 1991b)

Age group Period

HCGI rate(episodes/person-year)

Purified Tap Plant Valve

Percent differencewith purified water

Tap Plant Valve

All Jan. 88±Jun. 88 0.72 0.99 ND ND 38 ND NDSep. 88±Jun. 89 0.48 0.65 ND ND 36 ND ND

Sep. 93±Jun. 94 0.68 0.81 0.73 0.92 19 7 35

Jul. 94±Dec. 94 0.42 0.41 0.36 0.44 ±2 ±14 5

0±5 years old Jan. 88±Jun. 88 1.66 2.48 ND ND 49 ND NDSep. 88±Jun. 89 1.13 1.59 ND ND 41 ND ND

Sep. 93±Jun. 94 1.13 1.54 1.04 1.53 36 ±8 35

Jul. 94±Dec. 94 0.64 0.84 0.48 0.90 31 ±15 41

observed in subjects over 12 years was balanced by the negative effect seen in young children.

The absence of a dose-response effect in subjects from the tap valve group is compatible with

a higher level of exposure during the first months of period 1. This exposure resulted in a higher

HCGI incidence during these months and accounts for less susceptible population for the

following months.

Effect of bacterial regrowth and stagnancy

One of the hypotheses that we were attempting to test in the current study was that there was

a health risk associated with bacterial growth resulting from stagnancy of water in household

pipes. The data collected does not support this hypothesis. If it had been true, the installation of

a valve keeping water running would have resulted in a lower incidence of HCGI. On the

contrary, we observed an increase and subjects in the tap-valve group were affected whatever

their age. Constantly flowing water might have brought pathogens to the consumer before a

significant inactivation occurs due to residual chlorine, especially if these pathogens had been

introduced by breaks in the distribution system.

The fact that subjects who drank bottled plant water with an extremely high bacterial content

had a lower rate of illness is consistent with the hypothesis of inactivation of pathogens by

bacterial growth. Stagnant water in pipes would be subjected to a similar efffect and would thus

have a protective effect on consumers by inactivating pathogens.

The fact that the subjects in the tap-valve group had a higher rate of illness is consistent with

the fact that their tap water had a shortened residence time resulting in reduced exposure to

residual disinfectant and low bacterial regrowth. The fact that water was flowing continuously

in the households with purge valves implies that pathogens, if present, would reach the

consumer faster than if the water is left to stand in pipes for several hours. During stagnation,

pathogens would be exposed to microbial growth, a known inactivating factor for viruses

(Cliver and Herrmann 1972, Hurst 1988a,b). They would also be exposed to leaching chemicals

from pipes. Most of the buging installed was copper and it has been reported that this type of

pipe can inactivate viruses and bacteria (Yahya et al. 1991, Abad et al. 1994).

W hile the water entering the plant was extremely contaminated we were unable to detect

pathogens or indicators in the treated water. Water obtained directly at the plant and bottled was

not affected by the distribution system. Any observed increase in this group would have

indicated that the source of the illnesses was insufficient treatment at the plant resulting in the

introduction of pathogens: this was rarely the case. In a previous study, we have observed a

correlation between disease and bacteria growing at 35ÊC in water produced by domestic

reverse-osmosis units (Payment et al. 1991a). It was thus quite surprising that in fact subjects

in this group generally experienced no increase in illness, but this could be due to different

bacterial populations in the tap and the RO-units. Bacteria detected in the RO-units were mainly

bacteria growing on the rubber substrate in the reservoir provided with these units. Bacteria in

the bottled plant water were bacteria common in tap water and in the distribution system: our

observation might indicate that bacterial regrowth in distribution systems and pipes could be

more beneficial than hazardous.

Significance of group differences

For subjects who drank bottled plant or purified water, it could be argued that their lower level

of reported illness is because they assumed that they were drinking high quality water (i.e. `if

it is bottled, it is better’ ). However, subjects consuming bottled plant water and having the

28 Payment et al.

lowest rate of symptoms ranked their water as of poor quality based on taste and odor while

those in the tap-valve group with the highest rate of symptoms were the ones who ranked their

water as being of `very good quality’ (i.e. continuously flowing water was less likely to have bad

taste or odor).

Subjects in the two bottled water groups were still drinking a significant proportion of tap

water, accounting for about 40% of their water consumption (Table 10). This is higher than

our earlier data which had showed only 20 ±30% tap water consum ption in the RO group

during the 1988±89 study (Payment et al. 1991b). In 1988±89, RO-filters had been installed

under the kitchen sink of each household and RO-treated water was always available from

a small tap located on the sink itself. In the current protocol, subjects had to physically get

a 4-l container of water from the refrigerator or the counter to obtain their drinking water.

It appears that this procedure was more cumbersome and resulted in having many subjects

get their water directly from the tap, a simpler procedure. As all subjects were originally tap

water consumers (one of the criteria for enrollment), it appears that they often reverted to

this source of drinking water. This has an overall conservative effect, as it reduced the

difference that could be observed by exposing subjects in these groups to tap water

contaminants. Any difference reported here or earlier must be recognized as being an

underestimation of any health effects. If our point estimates are accurate, then water-related

illness might have been 50% higher among tap water consumers than among the bottled water

consumers.

The fact that the rate of HCGI in the Plant group was equivalent or less than the PW group

suggests that the distribution system might be the source of the differences observed. Analysis

of the data and correlation of the HCGI rate in the families with the residence time of the

water in the distribution system did not reveal any link. This suggests that bacterial regrowth

in the distribution system is probably not the cause for the illnesses observed. If it were, the

longer residence time and the ensuing bacterial regrowth might have shown some correlation.

While som e regrowth did occur, the residence time never exceeded 34 h, a relatively short

period that would not result in high bacterial counts such as those encountered in the bottled

plant water.

The results of this epidemiological study appear to support and confirm that tap water is a

significance source of gastrointestinal illnesses even if it meets all current drinking water quality

criteria. Over the observation period, the fraction of these illnesses attributable to tap water

consumption was 14 ±19%. During certain subperiods, one in December 1993 and the other in

April 1994, the average monthly relative risk reached 2.0±2.5, sugggesting that part of the effect

observed could be the results of two episodes of contamination of the water. Most of the

observed effects were due to illnesses reported in children 2±5 years old in which an estimated

17±40% of the infections were attributable to drinking water.

Contrary to what was expected, installing a purge valve to enhance water flow and

maintaining water to a quality equivalent to the water in the distribution system resulted in an

increase in reported illnesses. This points to the distribution system as the major source of the

unknown etiologic agent(s) responsible for the reported illnesses. The usually short duration of

the illnesses suggests a viral origin. We were however unable to detect any microorganism in the

finished water and CT values attained at the plant were at the levels currently recommended.

Water from the distribution system did not contain bacteriological indicators of contamination,

but it was not tested for viral and parasitic contaminants. Finally, contrary to our hypothesis that

regrowth of bacterial contaminants in household pipes could be a health risk, we have shown

that it might in fact have a protective effect.

Acknowledgements

The authors want to acknowledge the time and efforts of the members of the project advisory

committee that was formed to review the proposal and numerous reports that were produced

during the course of this study. Their advice and com ments helped make this project a success.

The authors are also indebted to more than 100 individuals who reviewed the original

proposal(s) and helped by providing their constructive comments. The authors also acknowledge

the numerous people who were involved in the technical and daily aspects of this work.

This paper is based upon work supported by the following agencies: United States

Environmental Protection Agency (Cooperative agreement #CR820446-01), American Water

Works Association Research Foundation (Contract #919-93 ), National Water Research Institute

(Award No. HRA 699-510-95), Health Canada, Compagnie G…n…rale des Eaux (France), Institut

Armand-Frappier (Universit… du Qu…bec). Any opinions, findings, conclusions or recom menda-

tions expressed in this material are those of the author(s) and do not necessarily reflect the views

of these agencies.

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