This study found that the 30-day period prevalence of acute diarrhoea was significantly higher among individuals living in households without cisterns when compared to individuals living in households with cisterns. Additionally, children under five years of age (both with and without cisterns) had a significantly higher period prevalence of diarrhoea than all other age groups except when compared to those between the ages of 51 and 65 years old. In this instance, those under 5 did have a higher period prevalence but the difference was not significant which may have been a result of small sample sizes among the 51 to 65 year old age group. It is interesting to see that in most instances children under five years of age had a significantly higher period prevalence compared to other age groups. A possible explanation for this finding could be that children under five years have not had a chance to acquire immunity to the pathogens found in their drinking water. A significant reduction in 30-day period prevalence of diarrhoea among households with cisterns was also found at the household level.
To the authors’ knowledge, this is the first study to estimate the prevalence of diarrhoea with and without the use of cisterns in a developing country and as such, no direct comparisons with other populations can be made. However, there have been studies that have estimated prevalence and incidence of diarrhoea in developing countries. Burden of illness studies in Cuba, Argentina, and Chile have estimated the 30-day period prevalence of diarrhoea to be between 3.44 and 10.6%
[27–29]. Participants from these studies were from a variety of different rural and urban settings, and tended to be older and more educated than the participants in our study. This may help to explain why the 30-day period prevalence was higher (14.5%) in our study.
A literature review of 11 articles on diarrhoeal incidence among children under five years of age in developing countries by the WHO estimated the median incidence for children under five years old in developing countries to be 3.2 episodes per child-year (range = 2.3-6.3 episodes per child year)
. One of the studies included in this review was conducted in an urban slum in northeast Brazil and estimated the under five years old incidence of diarrhoea to be 5.25 episodes per child year
. These estimates are similar to our 3.15 and 4.83 episodes per child-year for those with and without cisterns, respectively.
The reduction of diarrhoea with the use of cisterns is supported by results from previous trials investigating the relationship between rainwater use and diarrhoea
[16, 18]. A quasi-experimental design conducted in rural villages in Kenya, although not specifically looking at cisterns, reported that the use of harvested rainwater as a drinking water source, mostly via all available collection vessels (e.g., buckets and barrels), significantly reduced the risk of diarrhoea by 30%
. This is consistent with a developed country study in Australia that found no significant difference in gastroenteritis rates between children who consumed treated public mains water compared to those who drank household cistern water
Although these studies and our current findings support the use of cisterns to reduce diarrhoea in developing countries, or not to increase diarrhoea in developed countries, studies investigating the microbiological and chemical quality of rainwater from cisterns have found conflicting results. In Bermuda, samples from rainwater tanks have been found to be highly contaminated, with over 90% of samples taken containing more than 10 CFU/100 ml of total coliforms
. However, these results may not have been representative of rainwater tanks in developing countries as the trial was conducted after a hurricane. This may have increased dust and dirt on the rooftops from which the rainwater was collected. In Australia, samples from rainwater cisterns contained E. coli and heavy metals from sediments
. There seems to be a disconnect between reductions in diarrhoea and water quality with respect to rainwater from cisterns. Ahmed et al. (2008) suggest that fecal indicators used in many microbiological water quality studies may not be adequate to assess the microbiological quality of rainwater because of poor correlation between fecal indicators and potential pathogens. In addition, environmental organisms have been found to contribute to the bacterial load in rooftop rainwater in Australia and may be important in processes within the cistern tank that may have a beneficial impact on the microbiological quality of water in the cistern
. Also, these water quality studies were conducted in developed countries using relatively small sample sizes and may not be applicable in rural settings in developing countries. Further work should be conducted to explore the relationship between the use of rainwater from cisterns, reductions in diarrhoea and corresponding microbiological water quality. It is possible that, in the semi-arid region of Brazil, the use of cisterns in place of contaminated surface water would still be beneficial even if there was some contamination of the water from the rooftop, and that this contamination could be reduced using point of use disinfectants, filtering, boiling, or educational methods.
Not all diarrhoea is due to waterborne causes, and therefore, it is not expected that all diarrhoea in northeast Brazil could be prevented or reduced with the use of a household cistern. However, there is evidence to support that reducing waterborne diarrhoeal episodes will have an impact on the reduction of overall diarrhoeal episodes, as the WHO estimates that 88% of the estimated 4.4 billion cases of diarrhoea are attributable to unsafe water, inadequate sanitation and hygiene
Symptomology, duration of diarrhoea and type of health care sought was not significantly different between those with and without cisterns. Hence, although the number of episodes appears to be lower among individuals with cisterns, it does not affect the length and severity of illness when it does occur, nor the types of care sought for diarrhoea. We would expect that people with more severe symptoms for a longer duration would seek medical care more often than those with mild diarrhoea for a short duration. The lack of difference may indicate that these two groups are experiencing diarrhoea caused by similar pathogens, albeit less frequently in the cistern group. Future studies should be implemented to explore this hypothesis; perhaps by investigating the effect of cistern use on diarrhoea while additionally collecting faecal samples to determine the agent responsible. This could also provide further evidence linking the episodes of diarrhoea with a waterborne pathogen.
Gender, mother’s and father’s literacy status and education level, along with several sources of income were not found to be independently significantly associated with diarrhoea. Previous studies conducted in developing countries have also found gender
[9, 28, 29], mother’s education
 and mother’s and father’s literacy status
 not to be risk factors for diarrhoea. In this study, reasons for this could be that our population was relatively uniform in that approximately 70% of mothers and half of fathers were literate, with the majority of the parents who were literate having low levels of education. Also, the majority of household incomes came from self employed farming and/or family assistance. Therefore, differences may not have been found in literacy levels, education and sources of income other than self employed farming or family assistance due to a lack of statistical power.
There are a few limitations to this study, one being that we did not randomly select our households. Randomization was attempted but unsuccessful because there were inconsistencies between the list of cisterns that had been built and the actual number on the cistern at the households. While the total number of cisterns built in each community was known, the authors were not able to determine the specific location and household of cisterns within each community and were therefore unable to create a sampling frame. Controls were selected by interviewers based on proximity to households with cisterns, as the risk of diarrhoea can be dependent on location. Having interviewers select controls could be a source of selection bias however, this approach ensured that those without cisterns were similarly distributed among communities and municipalities as those with cisterns. In addition, households with and without cisterns were selected within each community and municipality in proportion to the number of cisterns that had been built in that particular community and municipality, with a minimum of four households (two with cisterns and two without) selected per community. Every household member within each household was interviewed and included in the study, and a large sample size was achieved. The systematic sampling method, large sample size and a 100% response rate was thought to capture a study group that was representative of the study population of interest.
Secondly, we were unable to compare the demographic characteristics or typical water treatment practices of our study population with the population from which the sample was taken. This is because census information from Agreste Central Region of Pernambuco State is not consistently collected for all municipalities. Due to the large sample size used for this study and the inclusion of all the qualifying municipalities, participants were thought to represent the population who qualify for a cistern from the P1MC. Our study may not be representative of all people who live in rural households as they could have different water needs, income, and socio-economic statuses. It is also expected that participants were on average younger than those in the general population due to the selection criteria of households requiring at least one child less than five years old.
This study used a 30-day recall period so as to be comparable with burden of illness studies in developing countries
[27–29]. There is a potential for recall bias when using a longer recall period, however, population surveys in an Argentine community and a Metropolitan region in Chile have compared 7-day, 15-day and 30-day recall periods for acute gastrointestinal illness and found between 1.7-5.4 times higher annual incidence rates compared to the 30-day recall period. These results suggest an underestimate of the true burden of disease when using a longer recall period. The potential for recall bias should be further explored in future studies, in particular, in the Agreste Central Region of Pernambuco State, Brazil. Finally, it was difficult to determine if families used only rooftop rainwater to fill their cistern. When families receive their cisterns they are informed not to fill it with outside water, such as water that is trucked in from other areas, as it may not be free of contaminants. Despite this instruction, outside water may have been used, although the extent to which this may have occurred was not assessed. Therefore this study may have underestimated the association between the 30-day period prevalence of diarrhoea and the use of cisterns that are only filled with rainwater.
Our study did not analyze additional risk factors for diarrhoea such as presence of a latrine in the home, regular use of soap, point of use disinfectants and practices, whether water was boiled and demographic variables that have been previously shown in other populations to impact the rate of diarrhoea
[2, 15, 16]. Future studies should take into account these risk factors as potential confounders. Our study duration was only 30 days and conducted shortly after the rainy season. This time period was chosen because higher rates of diarrhoea are typically seen and cisterns should have had adequate amounts of water stored. Future studies should estimate the prevalence of diarrhoea in the dry season, or for an entire year, to determine if these differences between groups occur year round.