Contaminated Water and Enteric Infections

This document discusses the association between contaminated water and enteric infections. It explores the prevalence of enteric diseases, the nature of the association between contaminated water and enteric infections, and the evidence base for this relationship. The document also highlights the methodological limitations in interpreting this association.

Assignment 1

Contents
QUESTION 1..................................................................................3
QUESTION 2..................................................................................6
References........................................................................................9

QUESTION 1
(A) Identification of a contemporary exposure-outcome
association
The outcome is the enteric diseases/infections.Enteric disease will
include three or more unformed stools daily and any documented
intestinal infection related to disordered intestinal absorptive
and/or barrier function. The outcome when found in young
children population, it may lead to hindrance of growth and
cognitive functioning.It was found that diarrhoeal ailments were
the second most common acute disorders in 2013, which led to 2.7
billion cases across the globe (1). A decrease of 7.9% is observed
in their incidence from 1990 to 2013, these are still regarded as one
of the most significant communicable diseases worldwide. By
2013, these diseases were placed among all the etiologies of death
globally (2). Moreover, diarrhoeal diseases lead to huge negative
socioeconomic effect. These were ranked among the top 50 causes
of Years of Life Lost (YLL) across the globe by 2013.There are
various causes of diarrhoeal diseases such as infections,
malnutrition, etc. but exposure to contaminated water is one of the
most significant causes due to a range of infectious agents such as
bacteria, protozoa, viruses, etc.The enteric illnesses are public
health issue in Australia. 33% of working population of Australian
miss on average one day of work each year (3). These disorders are

burden to the health care system, estimated around 1.2 billion
Australian dollars every year (3).
The prevalence of the outcome may vary with specific socio-
demographic groups or populations.Like the regions living at
regions which has contaminated supply of water will be most
frequently exposed to the pathogens present in the water and
thereby, the outcome will also be frequently observed in that
region. The low and middle income countries usually fail to
provide safe drinking water to their population and therefore, low
and middle income countries are most exposed. Further, in
developed countries people living in deprived areas belonging to
low socio-economic status have higher prevalence of the outcome.
Among the various population, the outcome predominantly relates
to the children population. It is mainly because this population is
most commonly exposed due to their ignorance while drinking
with water or playing near waterandbtheir low immunity. Among
them, though the scholar-age children were the most affected, but,
children under five years old also demonstrated high prevalence
showcasing the significance of paying attention to this group when
examining the epidemiology and interventions (4). There are other
main determinants of the outcome such as female gender, rural
dwellings and low socioeconomic status and poor personal
hygiene. These determinants have been considerably related to the
enteric parasitic infections.

(B) Nature of association between the selected exposure and
the outcome
In a cross-sectional study, the exposure is the drinking water
sources in Buea, Cameroon and the outcome is the presence of
enteric pathogenic protozoa.155 water samples were collected
from a range of drinking sources such as boreholes, springs, taps
and wells. Physicochemical investigation and parasitological
analysisof the samples were doneto ascertain the presence of
enteric pathogenic protozoa. The overall prevalence of enteric
pathogenic protozoa in water sources was 62.6 %. The study found
8 species of enteric protozoa. The most commonly found species
was Cryptosporidium parvum (45.8 %). The contaminated source
with enteric protozoa was springs (85.7 %) while pipe borne water
had all the identified eight species of protozoa. The only
significant factor related to the prevalence of the identified
pathogens in the sources of water was a pH of 6. There is strong
relationship between exposure and outcome. The results are
consistent within the study.
(C) Summary of the evidence-base upon which this association
is based

A range of studies can be found in the literature on the topic of
contaminated water-enteric infection association. All types of
studies can be found in the literature. However, the most frequently
observed type of study are cross-sectional studies (5) (6). Different
population bases such as food handlers, agricultural communities,
hospitalized patients, etc. however, the most predominant
population found in the epidemiology literature is of the children.
It is probably because this outcome is most found in this
population group. So, it can be said that the findings across these
studies are consistent. The results are plausible in terms of
biological mechanism (7).
QUESTION 2
(A) Summary of the key methodological limitations in
interpreting the association
Measurements of exposure and disease condition must be made in
the study populationat the same time minimising the different
kinds of error that maytake place. The individuals from the
population must come in contact with water, for exposure to take
place.Preference is given to measuring the exposure at individual
level, but in several studies, the exposure is measured at a group
level. Measuring the exposure status at group level may cause
misclassification of exposure for specific individual. For example,

in those studies which measure exposure to particular contaminant
from wastewater irrigation, exposure status can bedetailed at the
collective level and no differences in individual exposure status is
measured. In studies where the misclassification is not based on
disease condition, then the bias would be towards the null, which
makes it more challenging to examineactual associations between
exposure and outcome (enteric infections). It must be particularly
considered in studies which investigate the validity of particular
microbiological quality guideline levels, because those studies can
fail in demonstrating an effect of exposure to the guideline level
while a true effect may actually be present.
Differentialmisclassification has the issue of either overestimating
or underestimating the effect of exposure on outcome. One of the
contributor of misclassification of exposure occur due to the
restricted accuracy of recent techniques to enumerate the indicator
microorganisms.However, it was found in the epidemiology
literature review that this is not taken into account in majority of
the epidemiological studies based on the topic. The bias comprises
of selection bias, information bias, recall bias, and confounding.
While sampling, it must be ensured that the populations of the
exposed and control groups must be chosen to be possibly most
similar in every factorexcept the factor of mattersuch as socio-
economic status. However, the samples can never be completely
similar, possible confounding factors must be recorded and

controlled to be analysed. For enteric infections occurring due to
exposure to contaminated water, these factors will becleanliness,
personal hygiene, drinking-water source, food hygiene, and
travelling. It is significant that both exposure and outcomemust be
measured as precisely as possible in the selected samples. Like, in
studies based on drinking water, the source of drinking water
source for all the householdsmust be identifies accurately. In the
epidemiology literature, majority of the studies, samples are
chosen from a larger population which has exposure to the factor
of interest, by utilising a sampling frame. It is done as the chosen
sample represents the larger population. In this process, barriers of
selection bias and insufficient sample size usually occur. The
selection of study population must be based on the kind of
epidemiological study chosen. Confounding takes place when the
association between the exposure and outcome can be attributed
partly or completely to the impact of other risk factors which are
the confounders. It occurs when the confounder is an autonomous
risk factor for the outcome and is also related to the exposure. It
can result in an overor underestimate of the relationship between
exposure and disease.Like, personal hygiene can be a confounder
of the association between quality of water and enteric infection
status.So such factors which may be confounding needs to be
measured during the research and regulated for using statistical
analysis. For example, logistic regression analysis can be utilised

to accommodate the quantification of association between
exposure and outcome for the impact of the other risks factors.
It can be said that there is a consensus in the literature as the
evidence consistent and coherent. The association is of cause and
effect’ nature. Majority of the epidemiological studies verified the
relationship between the chosen exposure and outcome. The
biological mechanism also confirm that exposure to contaminated
water leads to enteric infections.

References
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1. Vos T, Barber , Bell. Global, regional, and national incidence,
prevalence, and years lived with disability for 301 acute and
chronic diseases and injuries in 188 countries, 1990-2013: a
systematic analysis for the Global Burden of Disease Study
2013. Lancet. 2015; 386(9995): p. 743-800.
2. Naghavi M, Wang H, Lozano R. Global, regional, and national
age-sex specific all-cause and cause-specific mortality for 240
causes of death, 1990-2013: a systematic analysis for the Global
Burden of Disease Study 2013. The Lancet. 2015; 385(9963): p.
117–171.
3. Fletcher S, Merif J, Ellis J, Hal V, Andresen D, Rawlinson W,
et al. Descriptive epidemiology of infectious gastrointestinal
illnesses in Sydney, Australia, 2007–2010. Western Pac Surveill
Response J. 2015; 6(4): p. 7-16.
4. Worrell , Wiegand , Davis , Odero , Blackstock , Cuellar. A
Cross-Sectional Study of Water, Sanitation, and Hygiene-
Related Risk Factors for Soil-Transmitted Helminth Infection in
Urban School- and Preschool-Aged Children in Kibera, Nairobi.
PLoS ONE. 2016; 11(3).

5. Knee J, Bruijn Ed, Schmidt WP, Nalá R, Cumming O, Brown J,
et al. Risk factors for childhood enteric infection in urban
Maputo, Mozambique: A cross-sectional study. PLoS Negl Trop
Dis. 2018; 12(1).
6. Rivero MR, Angelo CD, Nuñez P, Salas M, Motta CE, Chiaretta
A, et al. Environmental and socio-demographic individual,
family and neighborhood factors associated with children
intestinal parasitoses at Iguazú, in the subtropical northern
border of Argentina. PLoS Negl Trop Dis. 2017; 11(11).
7. Ramírez-Castillo FY, Harel J, Guerrero-Barrera AL, Jacques M,
Garneau P, Avelar-González FJ, et al. Waterborne Pathogens:
Detection Methods and Challenges. Pathogens. 2015; 4(2): p. 307-
334.
8. Fletcher , Boonwaat , Moore , Chavada , Conaty. Investigating an
outbreak of staphylococcal food poisoning among travellers across
two Australian states. Western Pac Surveill Response J. 2015; 6(2): p.
17-21.
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