In this setting of VCT that may provide as an entry point for prevention and care for HIV infection and other sexually transmitted diseases, we found that MSM were at significantly higher risk for E. histolytica
infection either by serologies or specific amebic antigen assays compared with those persons who were not MSM in Taiwan; in addition, intestinal infection with E. histolytica
was also associated with HIV infection when .specific antigen assays were used to detect E. histolytica
. These findings are of particular public health concerns and continued surveillance is indicated because male homosexual contact remains the leading route of HIV transmission and other STD in many developed countries and transmission of E. histolytica
or other intestinal pathogens and HIV may be potentially facilitated in settings where unprotected oral-anogenital sex among MSM is likely to occur.22
In this study, the overall prevalence of amebiasis by serologies is estimated 1.2% in persons seeking VCT services and 1.5–2.6% in MSM, which is lower than that in HIV-infected MSM seeking HIV care at our hospital (7.2%).9
The lower prevalence of amebiasis in those persons seeking VCT services than HIV-infected patients may be caused by referral bias in that most of the patients newly diagnosed with HIV infection referred to this hospital were at late stage of HIV infection.9
The other possible explanation may be that HIV-infected patients may have had increased frequency or intensity of risky exposure to both HIV and E. histolytica
because both older age and HIV infection are associated with amebiasis in our study, though HIV infection itself did not reach statistical significance in multivariate analysis.
In this case-control study, our findings provide further support to the observation that MSM remain at significantly higher risk for amebiasis than heterosexuals in Taiwan, probably because of infrequent use of condoms during oral-anogenital sexual contact among MSM, which may increase risk for E. histolytica
In this study, less than 5% of the case subjects who were predominantly MSM used condom consistently in oral-anogenital sexual contact. However, we were not able to show the statistical significance in this study, probably because of the small sample size or low specificity or sensitivity of the queries with respect to sexual practices and the time frame of the unprotected behaviors listed in the questionnaire. In this study, we did not specifically inquire and examine the interval between the latest risky sexual contact for HIV infection and amebiasis and seeking VCT services.
Oral-anal sexual contact with persons that are intestinal carriers of E. dispar
appears to be the route of transmission in MSM who seek medical attention for STD in western countries.1,3,4,6,7
Because E. dispar
and E. histolytica
share the same transmission route, it is not unexpected that risk of E. histolytica
infection will also increase in persons with risky sexual contact with individuals who reside in or travel to areas that are endemic for E. histolytica
Most of the infections with E. histolytica
are asymptomatic and carriage of E. histolytica
may be prolonged,23
and therefore, spread of E. histolytica
is likely to occur in the gay community in endemic areas for E. histolytic
a infection when unprotected oral-anogenital sexual practices are adopted. In previous study, we have demonstrated that case cluster of E. histolytica
infection might have occurred in HIV-infected patients in Taiwan.9
Similarly, case clustering may also occur in this high-risk population who sought VCT, although we did not further analyze the genetic relatedness of the isolates of E. histolytica
. Because of the association between HIV infection and intestinal infection with E. histolytica
, invasive amebiasis, which may be life-threatening, may be more likely to develop once HIV infection and progressive immunosuppression occur. Therefore, similar to other STD, screening and counseling for E. histolytica
infection among MSM should be provided to prevent infection and development of invasive diseases because those carriers of E. histolytica
may potentially serve as a reservoir to transmit E. histolytica
to other MSM by oral-anaogenital sexual contact.
There are several limitations in our study and interpretation of the results should be cautious. First, amebiasis was defined as presence of an IHA titer of
128 in this study. Antibodies can persist for years after infection and this fact limits their usefulness for diagnosing currently active disease in endemic countries. Second, although the specificity of IHA for E. histolytica
is very high, the sensitivity of IHA is low compared with specific amoebic antigen assays, which could lead to an information bias that would affect both the selection of cases and the controls. Third, the association between seropositivity for E. histolytica
infection and homosexuality is only reported in East Asia (Taiwan and Japan); more studies from other countries are needed to confirm our findings using both serologies and specific amoebic antigen assays. Fourth, limited by the design questionnaire, we are not able to explain why older age and lower education achievement were associated with amebiasis, although we postulate that increased cumulative exposure to E. histolytica
with age and poorer adherence to hygiene among subjects with lower education achievement may be contributory.
In conclusion, male homosexuality, older age, and lower education achievement were associated with higher risk for amebiasis in persons who sought VCT services. It is important for health care providers to diagnose amebiasis and provide appropriate treatment and counseling to MSM in preventing development of invasive amebiasis and transmission of E. histolytica.