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RESEARCHrates by gender or HIV status (1,30). The current study didnot include children, which likely explains why previouslyidentified trends of increasing infection levels with agewere not detected. We also did not find a trend of seroprevalenceover time. The only risk factor substantially associatedwith HEV seroprevalence was the METRO studyperiod, 2003–2005, as compared to the ICAR study, whichwas conducted during 1989–1995. Both studies were conductedamong women in Blantyre, Malawi.It is unclear what may have caused the METRO studyparticipants to have higher levels of HEV seroprevalence.We did not collect data on seasonality and source of waterand food; over the years Malawi had fluctuating boutsof drought and food scarcity. We tested diverse studypopulations from rural and urban settings recruited overa period of nearly 20 years, but no clear major trendswere observed.As expected, HAV seroprevalence was nearly universalin this sample of adults, with an overall prevalence of≈100%. In low-resource settings such as Malawi, HAV isa childhood infection, and nearly all persons are infectedwithin the first few years of life. Though children were notincluded in our study, it should be considered that they canbe exposed to HEV because of the high prevalence amongadults we observed. Although HAV and HEV infectiontend to cause mild disease independently, concurrent infectionswith these pathogens in children may lead to accelerateddisease progression (20). The changing epidemiologyof HAV in some settings related to rapid industrializationand urban migration in developing countries may result insome children not being exposed to HAV (10).An overall prevalence of 7.5% (95% CI 5.6%–9.4%)was found for HBsAg and 7.1% (95% CI 5.3%–8.9%) forHCV. The results of the HBsAg and HCV seroprevalencetests are consistent with previously published data fromsub-Saharan Africa. Specifically in Malawi, a study publishedin 2002 reported a prevalence of 14.9% for HBsAgand 10.6% for HCV among the SUCOMA participants(23). In our study, we found a prevalence of 11.8% (95%CI 7.0%–16.6%) and 10.7% (95% CI 6.1%–15.3%) forHBsAg and HCV, respectively, in the SUCOMA studysamples. Women who enrolled in NVAZ had lower oddsof testing positive for HBsAg compared to those in ICAR.The only distinct difference between these studies was theHIV status of the women (some women in the ICAR studywere HIV negative), but because this was included in themultivariate logistic regression, results should not be confoundedby the HIV status. No covariates were found to beassociated with HCV seroprevalence in this study.HEV epidemiology is evolving, and circulating genotypesand modes of transmission appear to be complex inboth developing and industrialized countries (1). We donot know in Malawi if only waterborne HEV genotypesare the source of potential infections or if other less virulentzoonotic HEV genotypes coexist. High seroprevalenceof HEV antibodies does not imply clinical infection or increasedassociation with clinical complications. Nonetheless,some misclassification of acute viral hepatitis is likelyin Malawi where screening for HEV antibodies is not performed.Because the seroprevalence of HEV in this studywas twice that of HBV or HCV, cases of acute hepatitismay frequently be caused by HEV as opposed to HBV orHCV. Notably, 15.7% (95% CI 12.7%–18.7%) of womenin this study cohort had antibodies against HEV, which canpose serious health risks for pregnant women (3).Although no association was found that HIV-positivepersons are at higher risk for anti-HEV than are HIV-negativepersons, the finding that 12.9% (95% CI 9.6%–16.2%)of samples from HIV-positive persons were HEV positiveis of concern. Malawi and other countries in sub-SaharanAfrica have high levels of HIV infection, and co-infectionwith HEV may lead to chronic HEV infection and accelerateddisease progression.The findings from this study should be regarded aspreliminary and require confirmation. Therefore, additionalepidemiologic and virological studies should be conductedin this region. As with all cross-sectional data, inferencesregarding associations should be interpreted with caution.A related limitation is that the samples used for serologictesting in this study included both enrollment and followupsamples (in cohort studies) to maximize availability ofsamples, whereas the covariate data used for all participantswas baseline enrollment data. Despite these limitations,we suspect that many of the covariates used, suchas having running water in the house, did not substantiallychange over time. Very few risk factors associated withHEV, HBV, or HCV seroprevalence were found. This resultmay be because of differences in population characteristicsor definitions used in multiple studies. For example,participants in the SUCOMA study were all men workingin a rural sugar estate occupational setting and may be consideredto be at high risk (23). We also did not have dataon some behaviors associated with HCV seroprevalence,such as intravenous drug use, although the practice is veryrare in Malawi. The lack of association between viral hepatitidesand various risk factors conventionally collected inthese studies suggests that better data collection tools toevaluate potential risk factors and different study designstargeting at risk populations may need to be considered infuture studies.Confirmation of the hepatitis testing results, particularlyHEV seroprevalence, reported in this study will becritical in subsequent studies because each sample wastested once. Retesting of a subset of positive and negativesamples should ideally be done with the same Wantai assayused in this study as well as with other assays. The hepatitis1180 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 21, No. 7, July 2015