Exposure to Schistosoma mansoni infection in a rural area of Brazil. I: Water contact

Abstract

SummaryThe study of water contact patterns in rural Brazil presents unique challenges due to widely dispersed settlement patterns, the ubiquity of water contact sites, and the privatization of water resources. This study addresses these challenges by comparing the two most widely used methods of assessing water contact behaviour: direct observation and survey. The results of a 7-day direct observation of water contact were compared with water contact surveys administered 1 week after and then 1 year after the direct observation study. The direct observation study recorded a water contact rate higher than reported by other investigators (3.2 contacts per person per day); however, 75% of these contacts were for females and consisted mainly of domestic activities occurring around the household. A comparison of the frequency of water contact activities between the direct observation and the two surveys revealed several important points. First, no signi®cant differences were found between methods for routine water contact activities (e.g. bathing), indicating that participants were able to accurately self-report some types of water contact activities. Second, signi®cant differences were found in the recording of water contact activities that took place outside the observation area, indicating that direct observation may under-report water contact activities in areas where contact sites are dispersed widely. Third, signi®cant differences between the direct observation and the survey method were more common for males than for females, indicating that the combination of widespread water contact sites and gender-speci®c division of labour may result in under-reporting of male contacts by direct observation methods. In short, despite the limitations in the recording of duration and body exposure, the survey method may more accurately record the frequency of water contact activities than direct observation methods in areas of widely dispersed water contact sites. Hence, surveys may be more suitable for the unique challenges of water contact in rural areas of Brazil.

Exposure to Schistosoma mansoni infection in a rural area in Brazil. II: Household risk factors

“…household worth index, number of rooms per house, or the ownership of land. Finally, the three water contact behaviours were characterized by similar duration and body immersion values as seen in Gazzinelli et al (2001). All of them result in prolonged exposure of large parts of the body to possible cercarial invasion.…”

“…Another strength of the study was the survey instrument. It was derived from extensive preliminary observations on water usage and accessibility in the study area (Gazzinelli et al 2001). This preliminary work gave us insights into water contact behaviours and resources that would not be yielded by conventional surveys, which are often structured around questions imposed by outside researchers and, hence, dislocated from Figure 2 The relationship between ln(epg + 1) and 10 year age intervals by gender.…”

“…The determination of infected or safe was based on the presence (infective) or absence (safe) of snail intermediate hosts by malacological surveys undertaken at each contact site. Water contact frequencies that occurred at potentially infective sites were then multiplied by standardized duration and body immersion values from Gazzinelli et al (2001). The residence of the survey team in the study area made it possible to check the quality of data collection and correct data at once by revisiting the household concerned.…”

Additive host genetic factors influence fecal egg excretion rates during Schistosoma mansoni infection in a rural area in Brazil.

“…A detailed description of the area is available elsewhere. 7,19 The household was the main sampling unit, with the research team visiting all houses within the 100-square kilometer area of the study site to obtain informed consent using a verbal consent form approved by the National Ethics Committee of Brazil and the Internal Review Board of the State University of New York at Buffalo, New York. At this time, each house was assigned a unique household identification number (HHID), and each resident, a unique personal identity number (PID).…”

“…Initially, direct observation studies were conducted in the area to determine the most frequent water contact activities in the study area. 19 These data were then used to construct a survey on the weekly frequency and source of water for these common water contact activities (Table 1). 7 The survey was then administered individually to each participant in the sample.…”