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Anwar Huq, Mohammed Yunus, Syed Salahuddin Sohel, et
al.
2010. Simple Sari Cloth Filtration of Water Is Sustainable
and Continues To Protect Villagers from Cholera in Matlab,
Bangladesh. mBio 1(1): e00034-10.
doi:10.1128/mBio.00034-10.
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Simple Sari Cloth Filtration of Water Is
Sustainable and Continues To Protect
Villagers from Cholera in Matlab,
Bangladesh
Simple Sari Cloth Filtration of Water Is Sustainable and Continues To
Protect Villagers from Cholera in Matlab, Bangladesh
Anwar Huq,a Mohammed Yunus,b Syed Salahuddin Sohel,b Abbas Bhuiya,b Michael Emch,c Stephen P. Luby,b Estelle Russek-Cohen,d*
G. Balakrish Nair,b* R. Bradley Sack,e and Rita R. Colwella,e,f
Maryland Pathogen Research Institute, University of Maryland, College Park, Maryland, USAa; International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka,
Bangladeshb; Department of Geography, University of North Carolina, Chapel Hill, North Carolina, USAc; Department of Animal and Avian Sciences, University of Maryland,
College Park, Maryland, USAd; Johns Hopkins School of Public Health, Baltimore, Maryland, USAe; and Center for Bioinformatics and Computational Biology, University of
Maryland, College Park, Maryland, USAf
* Present address: Estelle Russek-Cohen, Diagnostics Branch, Division of Biostatistics, Office of Surveillance and Biometrics, U.S. Food and Drug Administration, Rockville, Maryland,
USA; G. Balakrish Nair, National Institute of Cholera and Enteric Diseases, P-33, Cit Scheme XM, Beliaghata, Kolkata, India.
ABSTRACT A simple method for filtering water to reduce the incidence of cholera was tested in a field trial in Matlab, Bangladesh,
and proved effective. A follow-up study was conducted 5 years later to determine whether the filtration method continued to be
employed by villagers and its impact on the incidence of cholera. A total of 7,233 village women collecting water daily for their
households in Bangladesh were selected from the same study population of the original field trial for interviewing. Analysis of
the data showed that 31% of the women used a filter of which 60% used sari filters for household water. Results showed that sari
filtration not only was accepted and sustained by the villagers and benefited them, including their neighbors not filtering water,
in reducing the incidence of cholera, the latter being an unexpected benefit.
IMPORTANCE A simple method for filtering pond and river water to reduce the incidence of cholera, field tested in Matlab, Bangladesh, proved effective in reducing the incidence of cholera by 48%. A follow-up study conducted 5 years later showed that 31%
of the village women continued to filter water for their households, with both an expected and an unexpected benefit that filtration had both a direct and indirect effect in reducing cholera (chi-square statistic of 1,591.94; P ⴝ <0.0001). Results of the study
showed that the practice of filtration not only was accepted and sustained by the villagers but also benefited those who filtered
their water as well as neighbors not filtering water for household use in reducing the incidence of cholera.
Received 25 February 2010 Accepted 22 April 2010 Published 18 May 2010
Citation Huq, A., M. Yunus, S. S. Sohel, A. Bhuiya, M. Emch, et al. 2010. Simple sari cloth filtration of water is sustainable and continues to protect villagers from cholera in
Matlab, Bangladesh. mBio 1(1):e00034-10. doi:10.1128/mBio.00034-10.
Invited Editor Christine Moe, Emory University Editor Keith Klugman, Emory University
Copyright © 2010 Huq et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License,
which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited.
Address correspondence to Rita R. Colwell, [email protected]
D
iarrheal diseases are a major cause of death of children less
than 5 years old in developing countries, and cholera, the
most severe form of diarrhea, is characterized by massive loss of
body fluid and electrolytes. Toxigenic Vibrio cholerae, the causative agent of cholera, is native to the aquatic environment, is
present in Bangladesh (1), and is transmitted to humans, mainly
via contaminated drinking water. According to a recent report,
more than one billion people lack access to safe drinking water
worldwide, and over five million die each year from diseases
caused by unsafe drinking water (2). Recent studies suggest that
improving drinking water quality at the point of use (POU) has a
highly beneficial effect in combating waterborne disease (3, 4).
Several POU technologies that involve both chemical treatment
and filtration of water have become available during the past decade. However, compliance and sustainability are serious challenges because of many factors that range from cost, ease of use,
production of sufficient quantities of clean water with minimal
effort, social acceptance at the end user level, and most importantly, availability under natural disaster conditions when obtaining the bare necessities for daily life is a challenge.
April 2010 Volume 1 Issue 1 e00034-10
Cholera remains a global concern, affecting those most economically deprived who lack access to safe drinking water. As is
the case for diarrheal diseases, cholera is dose dependent, and the
infective dose has been shown to be ca. 103 to 106 Vibrio cholerae
O1 cells. Ingestion of this dose causes clinical symptoms (5, 6).
V. cholerae is commensal to planktonic crustacean copepods, i.e.,
part of the copepod natural microbial flora, with a single copepod
carrying up to 103 to 104 V. cholerae bacteria (7–9).
A method for simple filtration of water for domestic use, including drinking, was devised; this method employs cotton sari
cloth, a material readily available to village women in Bangladesh
(10). When this method was tested in the laboratory, using 1 to 4
layers of sari cloth to filter pond and river water containing
V. cholerae attached to small crustacean zooplanktonic copepods
and particulate matter, this simple procedure successfully reduced
the number of V. cholerae bacteria by 2 log units (10 –12).
Whether 1, 2, 3, or 4 layers of sari cloth was used as a filter, the
number of V. cholerae bacteria in the water was reduced by ca.
90%. Four layers of sari cloth were considered optimal for water
filtration, since it consistently removed ⬎99% of the bacteria, but
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RESEARCH ARTICLE
2 or 3 layers were approximately equally effective (10). After the
laboratory-based tests were completed, a field trial using cotton
sari cloth was performed, and as a reference, a commercially available nylon material that was used to eradicate dracunculiasis in
Africa was included. Both were field tested for efficacy in reducing
cholera in Matlab, Bangladesh. That is, village women responsible
for collecting water, in a population of 30,000 (15,000 in each
group, one group using sari filters and the other using nylon filters), were taught how to use folded cotton sari cloth or nylon
mesh to filter their daily water. A third group of 15,000 villagers,
receiving no instruction with respect to filtration of their water,
served as the control group. Results of the field trial showed that
the number of cholera cases was reduced approximately 50% in
the group using cotton sari cloth to filter water at the time of
collection, with nylon filtration slightly less effective and also very
expensive compared to sari cloth (11).
Although POU technologies have been shown to be effective in
laboratory experiments, they do not necessarily perform equally
well in the field over an extended period of time (13). The objective of the original study was to determine whether the incidence
of cholera could be reduced by sari filtration, since filtering out
plankton and particulate matter removed ⬎99% of V. cholerae
associated with zooplankton. Although 50% reduction in cholera
cases was observed among sari filter users, there was concern that
the practice of sari water filtration would not be sustained among
villagers once the original study had been completed. Hence, the
study reported here was undertaken.
Therefore, 5 years after the original field trial, a follow-up study
was conducted to determine whether sari water filtration continued to be practiced by the same population of participants and, if
it was, whether there would continue to be a beneficial effect of
reduced incidence of cholera. The site of study is located within
the Matlab Demographic Surveillance System of the International
Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B).
The objective, simply stated, was to determine the sustainability
and efficacy of filtration that was introduced earlier to the community.
RESULTS AND DISCUSSION
From the survey data, 2,207 (31%) of 7,233 interviewed respondents reported using a filter of any type and 1,327 (60%) of the
filter users reported using cotton sari cloth (either one, two, three,
or four layers of cloth). Within the original sari filter group, 635
(74%) of the filter users used sari cloth; of the 635, 117 (18%) used
four layers of sari cloth for filtering, 157 (25%) used three layers,
271 (43%) used two layers, and 90 (14%) used one layer of cloth.
Results of laboratory studies on which the intervention was based
had previously shown that two and three layers of sari cloth were
effective in removing up to 99% of the attached V. cholerae bacteria (10). The intervention recommended for prevention of cholera
based on the laboratory study was four layers of sari cloth because
it was slightly more effective in consistently removing ⱖ99% of
the V. cholerae bacteria (10). In the original field trial, four layers
of sari cloth were used and proved effective in reducing the incidence of cholera by ca. 50% (11). We found that 74% of those
using sari cloth filters, whether one or more layers, in the
follow-up study received a beneficial effect, even though filtration
using the recommended four layers was practiced by only 18% of
the population of the original group of villagers who had been
taught to use a sari cloth filter. Among the 2,351 households orig-
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TABLE 1 Number of households filtering water
No. (%) of households using the
following filter:
Group
Sari filter
Nylon filter
Control
Sari
635 (74.4)
342 (47.8)
350 (54.6)
Nylon
180 (25.3)
Other
218 (25.6)
191 (26.8)
291 (45.4)
Total no. of
households
853
713
641
inally assigned to the nylon filter group, 713 (30%) reported that
they continued filtering their water, of which 342 (48%) used sari
cloth. The numbers of households filtering water from the original
different groups using sari cloth or any other material are shown
in Table 1.
Of 2,426 households from the control group, i.e., those from
the original study not receiving education and training about filtration, 641 (26%) used some kind of filter, of which 350 (55%)
used 1 to 3 layers of sari cloth, but not 4 layers. People have been
filtering water for aesthetic purposes, e.g., to remove leaves, insects, and other visible particulate matter from drinks sweetened
with sugar or molasses (the latter are especially attractive to ants),
but not for the purposes of water safety as they had been taught
during the original field trial. In the follow-up of 11-hrs observation of 50 randomly selected households that reported they filtered their water with cotton sari cloth, only 19 (38%) were observed to consistently filter their water with sari cloth and only 2
(4%) folded the sari cloth into at least four layers. These data
indicate that, although a reduced number of households continued to use sari filtration as originally recommended, i.e., four layers of sari cloth, overall, the use of some kind of filtration was
practiced by 31% of the villagers, of which 60% used sari cloth.
The rate of use of one or more layers of sari cloth showed that the
number of villagers who were sari filter users (n ⫽ 853) surveyed
from the original sari filtration group was significantly higher
(74%) than the number from the control group (54%) (␹2 ⫽
63.91; P ⬍ 0.001) of the original study, indicating the sustainability of the practice of filtering water 5 years after the intervention
was introduced. It is unclear whether control households practicing sari filtration may have done so as a longstanding practice, but
it is highly probable that diffusion of the practice of filtration from
the original groups occurred based on observations made in the
original study, when some of the villagers showed their neighbors
how to filter water and they began to filter their water as well.
From the results of this study, it is clear that the population taught
to use sari filter comprised the largest number of sari filter users
and fewer were from the control group (not taught to use a sari
filter), indicating that training played an important role in the
practice of sari filtration by these villagers. In addition, it is important to note that 25% (180/713) of the nylon filter group were still
using the nylon filters provided 5 years earlier, although its effectiveness was not determined (Table 1). Eighteen percent of the sari
filter group reported using four layers of sari cloth as filter, while
only 1.1% of the control group used three layers and none used
four layers. From the interview, we also determined that when
villagers from the original study who had been instructed to use a
single layer of the nylon filter switched to sari cloth filter, 76.3% of
them continued to use one layer of sari cloth, as they were taught
to do with the nylon filter, and only 0.6% used four layers. This is
a clear indication of both compliance with instructions and the
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Huq et al.
TABLE 2 Neighborhood incidence of cholera in a total population of 7,470 relative to the number of cholera cases per 1,000 individuals not
protected by water filtration
Cholera incidence category
(no. of cases of
cholera/1,000)
0
0.1-5.1
5.1-8.4
8.4-11.5
11.5-33.3
No. (%) of cases of cholera in neighborhoods with a water filtration rate of:
0%
34 (3.8)
114 (12.8)
94 (10.6)
150 (16.9)
496 (55.9)
0.1 to 8.4%
178 (10.8)
174 (10.6)
415 (25.2)
537 (32.6)
342 (20.8)
sustainability of the method, but it also shows the need for continuing education in the appropriate use and benefits of simple
filtration.
Determining the sustainability of this method was the primary
objective of the study. However, although not statistically significant, a reduced incidence (25%) of hospitalization for cholera was
observed for the evaluation period (2003 to 2006) among households filtering their water compared to those households not filtering. With the lower rate of filtration in this follow-up study, it is
not surprising that the observed reduction in disease rate was not
as high as the 48% observed in the original trial (11), suggesting
that active reinforcement would have been effective in ensuring
higher protection.
Additional analysis that was not part of the original study plan,
was employed to explore the potential for indirect protection
from cholera of households using sari cloth filtration, was done
based on an earlier report (19). The percentage of villagers using
some kind of filtration (sari, nylon, or gamcha, the local name for
a thin towel) and living in proximity to participants of the original
study was also calculated. Table 2 presents the 7,470 neighborhood clusters as five levels of cholera incidence (range, 0 to 33.3
per 1,000) stratified by neighborhood filtration percentage (range,
0 to 54.3%). Categories of approximately equal size were used,
with zero values restricted to those neighborhoods with no cases as
a separate category. Households not filtering water and located in
neighborhoods where water filtration was not practiced were
more likely to be in the highest incidence category (11.5 to 33.3 per
1,000). Households not filtering their water and in neighborhoods
where water filtration was practiced (30.0 to 54.3%) rarely fell into
the highest cholera incidence category and more than 50% of the
time had an incidence rate lower than 5.1/1,000. This inverse relationship between neighborhoods where filtration was practiced
and the incidence of cholera in the unprotected group is shown in
Fig. 1. Figure 1 is a graphic presentation of data taken from Table 2
to illustrate the incidence of cholera by neighborhood filtration
rate. The distribution shown is unlikely to have occurred by
chance (chi-square statistic of 1,591.94; P ⱕ 0.0001). Moreover, it
is important to note that filtration was carried out by many households employing two or three layers of sari cloth, not the recommended four layers. Thus, this effect, although significant, could
be further improved by reinforcement of the recommended practice.
Examination of the practice of filtration relative to household
socioeconomic status, measured by asset index (with the lowest
quintile representing the lowest socioeconomic level and the highest quintile representing the most affluent) revealed a statistically
significant negative association between socioeconomic status
and the use of filtration. The most affluent quintile used filtration
April 2010 Volume 1 Issue 1 e00034-10
8.4 to 22.3%
173 (10.51)
398 (24.2)
237 (14.4)
371 (22.5)
467 (28.4)
22.3 to 30.9%
118 (7.2)
437 (26.6)
495 (30.1)
434 (26.4)
161 (9.8)
30.9 to 54.3%
389 (23.6)
523 (31.8)
405 (24.6)
173 (10.5)
155 (9.4)
the least (22.1%), followed by the second most affluent group
(28%), whereas the lowest, second lowest, and middle economic
groups filtered their water the most with values of 34%, 36%, and
32%, respectively. Affluent people usually have the resources to
boil their water or have access to safe drinking water, e.g., bottled
water.
Interestingly, during the original trial, several families had to
be removed from the control group because they became convinced filtration would protect their children from contracting
cholera and began using sari filtration (11). The study team complied with their wishes for ethical reasons, despite its effect on the
study. It is important to note that the filtration method did not
require financial resources or extensive training on the part of the
village women, and it was easy to include in their daily activity.
Shallow tube well water, once considered a source of safe drinking
water, has unfortunately been found to contain high levels of arsenic in many regions of Bangladesh, with the concentration of
arsenic in the tube well water exceeding 50 ppb and concentrations 10 times higher in some areas of Bangladesh (15, 16). In the
affected geographic regions, the population returned to surface
water for household use, making simple filtration an important
consideration.
In summary, the primary goal of this study was achieved,
namely, to determine compliance in practicing simple filtration.
Subsequent reduced incidence of cholera in the households filtering water was expected. Of the 2,456 women included in the original study who were taught to use sari cloth as a filter, 853 (35%)
reported that they consistently used some kind of filter and 635
(26%) reported that they continued to use sari cloth filtration. A
minority of the women who reported that they used sari filtration
actually did so during the 11 h of structured observation, suggest-
FIG 1 Incidence of cholera in non-water-filtering households by neighborhood use of water filtration. The number of cases of cholera per 1,000 individuals (Cases/1000) is shown in the key to the right of the graph.
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Simple Sari Filtration of Water Can Reduce Cholera
ing that, like other behavior changes, the practice of filtration
would benefit from a focused effort to enhance its sustainability
and provide a further reduction in the incidence of cholera. Sari
filtration is easy to use, does not require extensive training, is
socially acceptable, and, most importantly, involves no additional
cost to the household. Where conditions of extreme poverty or
local disasters prevent access to potable water, notably in areas
where cholera is endemic and areas subject to social disruptions,
simple filtration can be deployed with a beneficial outcome to
public health.
MATERIALS AND METHODS
Study site. The study, conducted in Matlab, Bangladesh, at the same location of the original sari filtration field trial, was carried out September
1999 through July 2002. The largest continuously operating Health and
Demographic Surveillance System (HDSS) in the world, first established
in 1966, is located in Matlab, Bangladesh, providing an eminently suitable
site for both the original field trial and the present survey (14). The original field trial included a population of approximately 45,000 individuals
(assigned in equal numbers to sari or nylon filtration groups and the
control group) from a total population of more than 220,000 under the
HDSS in Matlab, Bangladesh. In this follow-up study, a total of 7,470
village women responsible for collecting water for their household and
available to participate in this study were selected from the original field
trial population. Also, 772 neighboring households not part of the original
study were also included to determine whether the practice of filtering
diffused by social contact and had become part of the daily routine. In
addition, 50 households were randomly selected 1 month after completion of the interviews from among the group of households reporting that
they were using sari filtration. These households were subjected to structured observation designed to record systematically all water-related activities of each of the 50 households. Field staff members with experience
in qualitative research and recruited from the community were educated
on the topic of the research and trained to carry out the structured observation, with an anthropologist included in the research team overseeing
the study.
Since village women begin their daily household activities, including
collecting water for their family, in these rural Bangladesh villages early in
the morning, structured observations began at 6 a.m. each day and continued until 5 p.m. As in the earlier study, the households observed were
those with children under 5 years of age.
Sample size was calculated using a chi-square 2-by-2 table, where the
total number of households was determined, but specific row and column
totals were random, with the constraint that 50% of the study population
filtered their water and that cases of cholera had been reported in 2.4% of
the households over the previous 2-year period. An odds ratio of 1 under
the null hypothesis and an odds ratio of 1.50 under the alternative were
assumed. In the original study, an odds ratio closer to 2 had been observed. Because in that study the practice of filtration was reinforced by
regular visits of staff, compliance in filtration in this follow-up study was
not expected to be as high as in the original study.
In the Matlab HDSS study area, each household is assigned a unique
identification (ID) code. Thus, every household included in the current
study from the original filtration field trial could be identified. Covariates
specific to each household, such as the number of children less than 5
years old, which treatment group (sari filter, nylon filter, or control) a
given village was assigned to during the previous study, and other covariates were considered when explaining differences in cholera incidence
between the households practicing filtration and those not practicing filtration.
In the original field trial performed in 1999 to 2002, a team of two field
workers visited each participating household every 2 weeks on a regular
basis during the entire period of the study (11). During this visit, the
person responsible for collecting water was interviewed (with a set of
questions in a questionnaire) to determine whether filtration was being
4
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practiced according to previously established instructions. The field
workers examined the condition of the filter, and the filter was replaced if
it was damaged. Any type of illness, including diarrhea, any difficulty in
filtering when following the method taught, any travel by the family members to, or visitors from, other villages, or any major change in water use in
the household was recorded, and records were maintained on a biweekly
basis. In the present study, a similar survey instrument was employed.
This survey or questionnaire included questions concerning personal demographics, level of education, socioeconomic status, water use, and illnesses other than those reported to the hospital, which are recorded by the
ICDDR,B field hospital and available from that data bank. Most importantly, several of the questions were designed to determine water use behavior, namely, source of water, whether filtration or other treatment was
employed, and frequency of use. It should be noted that the major difference in this study from the original was that each family was interviewed
once during the 8 months of the survey. Hospital reports of confirmed
cases of cholera, based on laboratory confirmation and covering a period
of 4 years after completion of the original field trial, were examined to
measure effectiveness, that is, severity of illness as recorded in the hospital
records or hospitalization reports. Eight teams, each of which comprised
two field workers, visited 10 households per day, requiring 8 months to
complete the survey. To assess the validity of reported behavior, 50 households that reported using sari cloth filter in the interview were randomly
selected and revisited 1 month later. This was a one-time revisit by a
female observer who stayed with the family and observed all water-related
activities during the day from 6 a.m. to 5 p.m.
Using the ICDDR,B geographic information system (GIS), households in close proximity to those households in Matlab, Bangladesh,
drawing on a common source of water and included in the earlier study
were also queried to determine whether diffusion of the innovation had
occurred. Also, using GIS, the incidence of cholera was calculated for
7,470 non-water-filtering villagers in a 1-kilometer neighborhood cluster
in the Matlab area, Bangladesh, employing a method described elsewhere
(17–19). These 1-km Euclidean distance neighborhoods were used as
proxy for the local-level area of influence of each household.
Data forms from the field workers, hospitals, and laboratories were
scanned, and the data were entered into the computer at the Matlab
Project Office. The results of the questionnaires were reviewed in detail,
and if concerns were raised or additional information was required, the
forms were returned to the specific field worker for correction and/or
update. All data were entered in repositories at both the ICDDR,B and
University of Maryland. All forms and data collection procedures were
approved by the Institutional Review Board (IRB) at the ICDDR,B and the
Western Institutional Review Board assigned by the University of Maryland.
ACKNOWLEDGMENTS
The original study to develop sari filtration was supported by the Thrasher
Research Fund (grant no. 02903-3) and the field trial was supported by the
National Institute of Nursing Research of the National Institutes of Health
(grant RO 1 NR0427-01A1). This research activity was supported by the
Thrasher Research Fund through the University of Maryland Biotechnology Institute to carry out the follow up study (grant GR-00443/01). We
acknowledge with gratitude the commitment of the Thrasher Research
Fund to the research efforts of the ICDDR,B. We are indebted to the
Thrasher Research Fund (2005 to 2006) for generous support to carry out
this follow-up study.
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Simple Sari Filtration of Water Can Reduce Cholera
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