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ABSTRACT |
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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128 was detected in 7.1% of group A, 2.5% of group B, 1.8% of group C, and 0.1% of group D (P < 0.0001). The highest seroprevalence (11.2%) was noted among HIV-infected persons who were men having sex with men (MSM) 30–39 years of age. Compared with persons with gastrointestinal symptoms, the adjusted odds ratio for having high IHA titers among HIV-infected persons was 3.206 (95% confidence interval, 1.433, 7.176; P = 0.005). These findings show that HIV-infected persons, especially MSM 30–39 years of age, are at significantly higher risk of E. histolytica infection. |
INTRODUCTION |
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To better understand if HIV-infected persons have a higher seroprevalence rate of E. histolytica infection than persons at low risk of HIV infection, we conducted a serologic study of four different groups of persons: persons with HIV infection, asymptomatic HIV-uninfected persons seeking anonymous HIV testing, persons without HIV infection who presented for medical care because of gastrointestinal symptoms (diarrhea and/or liver abscess), and persons who underwent health check-up at the hospital. We will show that positive amebic serologies are significantly more common in HIV-infected persons, especially MSM.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Four groups of study subjects were defined: group A, 667 consecutive non-hemophiliac HIV-infected adult persons 15 years of age seeking HIV care at the NTUH; group B, 1,311 persons seeking anonymous testing for HIV infection whose test results were negative; group C, 616 patients with gastrointestinal symptoms (diarrhea and/or liver abscess) who sought medical care at the hospital and were tested negative for HIV infection; and group D, 2,500 persons who sought health check-up at the hospital. Persons of group D did not undergo anti-HIV antibody testing and were considered as controls. A standardized case record form was used to collect information of risk behaviors for HIV transmission among persons who were HIV-infected and persons who sought anonymous HIV testing. However, because of the anonymity in the latter study group, we were unable to identify the exact number of persons who might have repeat HIV testing over the 4 study years.
Anti-HIV antibody assays (SERODIA-HIV; Fujirebio, Tokyo, Japan) and indirect hemagglutination antibody (IHA) assays (Cellognostics; Boehhringer Diagnostics, Marburg, Germany) were performed by following the manufacturer’s instructions by research assistants who were blinded to the clinical characteristics of study subjects. A person was considered to have serologic diagnosis of E. histolytica infection when the blood specimens showed a high IHA titer that was defined as 1:128 or greater. The Institutional Review Board of the hospital approved the study protocol.
All statistical analyses were performed using SAS statistical software (Version 8.2; SAS Institute, Cary, NC). Categorical variables were compared using 
2 or Fisher’s exact test. Non-categorical variables were compared using Wilcoxon’s rank-sum test. The multiple logistic regression was used to identify the risk factors associated with high IHA titers. Odds ratios and 95% confidence intervals (CIs) were also calculated. All tests were two-tailed. A P < 0.05 was considered significant.
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RESULTS |
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. HIV-infected persons (group A) and persons who sought anonymous HIV testing (group B) were younger and more likely to be men than persons of the other two groups. Persons who were HIV-uninfected and underwent IHA assays because of gastrointestinal symptoms (group C) were significantly older than those of the other three groups.
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). Of the 667 HIV-infected persons, 47 (7.1%) had high IHA titers, with titers ranging from 128 to 8,192 (median, 128). Of the 1,311 asymptomatic persons at risk for HIV infection, 33 (2.5%) had high IHA titers; all had a titer of 128. Of the persons of the other two groups at low risk of HIV infection, the seropositivity rate of amebic infection caused by E. histolytica was 1.8% (11 of 616) and 0.1% (3 of 2,500) in HIV-uninfected persons with gastrointestinal symptoms and healthy controls whose HIV status was unknown, respectively (Figure 1). Over the 4 study years, there were no trends of increasing seroprevalence of E. histolytica infection in the four study groups (data not shown).
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). More than 80% of the persons with high IHA titers in the group A and B were between 20 and 49 years of age. In contrast, most of HIV-uninfected persons with gastrointestinal symptoms who had high IHA titers were in the age groups of 40–49 years or greater (Table 1). The proportion of male sex in persons with high IHA titers in groups A (100%) and B (93.9%) was significantly higher than persons in groups C (63.6%) and group D (66.7%). In addition, men in groups A and B had statistically significantly higher seroprevalence of invasive amebiasis than women, which was not seen in men of groups C and D (Table 1).
Compared with healthy controls, all of the other three groups of persons were at statistically significantly higher risk for having positive amebic serologies (Table 2). Compared with HIV-uninfected persons who presented with gastrointestinal symptoms, HIV-infected persons remained at a significantly higher risk for having positive amebic serologies with an odds ratio of 3.206 (95% CI, 1.433, 7.176; P = 0.005) after adjustment for age, sex, and year enrolled (Table 2). Compared with HIV-uninfected persons seeking anonymous HIV testing, the odds ratio for having positive amebic serologies among HIV-infected persons after adjustment for age, sex, risk behavior, and year enrolled was 1.349 (95% CI, 0.767, 2.347; P = 0.30), although the seroprevalence of E. histolytica infection of the latter was significantly higher than that of the former (Table 2).
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DISCUSSION |
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The seroprevalence of E. histolytica infection may vary with geographic regions and populations studied. There is a high prevalence of colonization and infection with E. histolytica in developing countries.15–17 For example, 15% of the children in Bangladesh had serologic evidence of prior or current episode of E. histolytica infection, and reinfection was common.15,16 In Vietnam, the prevalence of E. histolytica infection among adults was 11.2%, and the mean half-life of infection was estimated to be 12.9 months.17 In Taiwan, we found that 0 of 144 HIV-uninfected healthy adults was infected with E. histolytica determined by amebic antigen tests of the stool specimens, and 0 of 178 had high IHA titers suggestive of past or current E. histolytica infection.13 These findings of low background seroprevalence of E. histolytica infection in Taiwan was further supported by this study with a larger case number, in which only 3 of 2,500 (0.1%) adults seeking health check-up had high IHA titers.
Despite the fact that prevalence of colonization and infection with E. histolytica has been low in developed countries, E. histolytica seems to be an emerging cause of parasitic infection in MSM in several developed countries. In Italy and Japan, the seropositivity rates of E. histolytica infection have been previously reported to be as high as 20% in MSM whose HIV status was not known; the rates were significantly higher than heterosexuals and female sex workers.7–9 More than 5% (5.7%) of 140 MSM in a study conducted in the United States had serologic evidence of E. histolytica infection, which was found to correlate with intestinal colonization with E. histolytica.18 In this study, we further provided evidence that HIV-infected persons who were MSM at the age of 30–39 years were at particularly higher risk for having serologic evidence of E. histolytica infection (Figure 1).
The higher seroprevalence of E. histolytica infection in HIV-infected persons in our study is related to a higher rate of intestinal colonization with E. histolytica infection,13 which is different from the findings in previous studies from western countries where a substantial proportion of MSM are colonized with E. dispar that does not cause invasive diseases or positive amebic serologies.1–5 Retrospective case reviews in Taiwan and Japan indicated that invasive amebiasis was an emerging parasitic disease among HIV-infected persons who were MSM.10–12 In three metropolitan cities in Japan, MSM and persons with HIV infection accounted for 56% and 45% of the reported cases of symptomatic E. histolytica infection, respectively.12 Of 49 HIV-infected persons with invasive amebiasis in Taiwan, 41 (83.7%) were MSM.13 Both studies indicated that MSM who are HIV-infected are at higher risk for invasive amebiasis. Furthermore, we found that in HIV-infected persons the rate of E. histolytica infection among MSM (8.6%) was significantly higher than heterosexuals (2.0%) and HIV-uninfected healthy controls (0%).12
Among MSM, E. dispar may be transmitted through fecal–oral route and oral–anal sex. Infection with E. dispar is considered as the sentinel sign of oral–anal sex practice in the developed countries where the likelihood of acquisition of amebic infection through contaminated water or food but without foreign travel is low.1–5 Such an association between E. dispar and oral–anal sex practice may also be applied to the case of E. histolytica infection among MSM. In this study, we found that MSM who are HIV-infected are indeed at higher risk for invasive amebiasis, even higher than the HIV-uninfected persons who sought medical care for gastrointestinal symptoms. The findings imply that MSM have to take precautions against acquisition of E. histolytica during oral–anal sex with persons residing in or returning from endemic areas of E. histolytica.
The study has several limitations, and interpretation of the data should be cautious because of selection biases. First, we did not collect the clinical information of HIV-infected persons regarding gastrointestinal symptoms or HIV-uninfected individuals with gastrointestinal symptoms regarding whether their symptomatology was related to E. histolytica infection. We might have overestimated the seroprevalence of E. histolytica infection because the enrolled HIV-infected patients were more immunosuppressive and had more gastrointestinal symptoms. However, our previous study has shown that invasive amebiasis and a high seropositivity rate (10.0%) for E. histolytica occurred when HIV-infected patients had CD4 count of 200/µL or greater when opportunistic infections of the gastrointestinal tract is less likely to develop.13 Compared with the persons seeking medical care because of gastrointestinal symptoms, seroprevalence of E. histolytica infection remained significantly higher in HIV-infected persons. Second, we might have underestimated the seroprevalence of those persons who sought anonymous HIV testing because we were not able to exclude the possibility of repeat HIV testing. However, in a recent study of 213 MSM who frequented gay bathhouses in Taiwan, the estimated seroprevalence of E. histolytica infection was 5.6%,19 a rate similar to that of the study by Sorvillo in the United States.18 Third, the study was conducted in a metropolitan city where invasive amebiasis is rare in the general population. The findings may not be generalized to developing countries that are endemic for E. histolytica infection and having rapid increase of case numbers of HIV infection,17,20 although E. histolytica and E. dispar infection is also more prevalent in persons with HIV infection and AIDS.20
In conclusion, our study suggests that HIV infection is associated with increased risk of serologic evidence of amebic infection caused by E. histolytica in persons who are MSM.
Received November 15, 2005. Accepted for publication February 19, 2006.
Acknowledgment: We thank Dr. Victor L. Yu of University of Pittsburgh for review of the manuscript.
Financial support: This study was supported by the Center for Disease Control, Department of Health, Executive Yuan, Taiwan (DOH94-DC-1017).
* Address correspondence to Chien-Ching Hung, Department of Internal Medicine, National Taiwan University Hospital, 7 Chung-Shan South Road, Taipei 100, Taiwan. E-mail: hcc0401{at}ha.mc.ntu.edu.tw 
Authors’ addresses: Jih-Jin Tsai, Liang-Yin Ke, and Jeng-Hsien Yen, 100 Tzyou 1st Road, Kaohsiung, Taiwan 807. Hsin-Yun Sun, Keh-Sung Tsai, Sui-Yuan Chang, Szu-Min Hsieh, Chien-Ching Hung, and Shan-Chwen Chang, 7 Chung-Shan Road, Taipei, Taiwan 100. Chin-Fu Hsiao, 35 Keyan Road, Zhunan Town, Miaoli County, Taiwan 350.
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