Seroprevalence of Entamoeba histolytica at a voluntary counselling and testing centre in Tokyo: a cross-sectional study

Abstract

Background: Amebiasis, which is caused by Entamoeba histolytica, is a re-emerging public health issue owing to sexually transmitted infection (STI) in Japan. However, epidemiological data are quite limited.

Methods: To reveal the relative prevalence of sexually transmitted E. histolytica infection to other STIs, we conducted a cross-sectional study at a voluntary counselling and testing (VCT) centre in Tokyo. Seroprevalence of E. histolytica was assessed according to positivity with an ELISA for E. histolytica-specific IgG in serum samples collected from anonymous VCT clients.

Results: Among 2083 samples, seropositive rate for E. histolytica was 2.64%, which was higher than that for HIV-1 (0.34%, p<0.001) and comparable to that for syphilis (rapid plasma reagin (RPR) 2.11%, p=0.31). Positivity for Chlamydia trachomatis in urine by transcription-mediated amplification (TMA) was 4.59%. Seropositivity for E. histolytica was high among RPR/Treponema pallidum hemagglutination (TPHA)-positive individuals and it was not different between clients with and without other STIs. Both seropositivity of E. histolytica and RPR were high among male clients. The seropositive rate for anti-E. histolytica antibody was positively correlated with age. TMA positivity for urine C. trachomatis was high among female clients and negatively correlated with age. Regression analysis identified that male sex, older age and TPHA-positive results are independent risk factors of E. histolytica seropositivity.

Conclusions: Seroprevalence of E. histolytica was 7.9 times higher than that of HIV-1 at a VCT centre in Tokyo, with a tendency to be higher among people at risk for syphilis infection. There is a need for education and specific interventions against this parasite, as a potentially re-emerging pathogen.

Keywords: diagnostic microbiology; epidemiology; parasitology; public health; sexual medicine; tropical medicine.

Figure 1

Proportion of clients in each age group among men and women. The average age among female clients was significantly lower than that in male clients (p<0.001). The proportion of clients aged 29 years or less among female clients was 53.4%, whereas that in male clients was only 29.6%.

Figure 2

Seropositivity for Entamoeba histolytica and other sexually transmitted infections (STIs) in Tokyo. Serologic testing results (anti-E. histolytica antibody, HIV-1, RPR and TPHA) were obtained for 2083 clients of a voluntary counselling and testing centre in June and December 2017. Results of urinary TMA for Chlamydia trachomatis and Neisseria gonorrhoeae were available for 1437 clients who agreed to testing. All statistics were calculated using Fisher’s exact test. (A) The seropositive rate for E. histolytica was compared with those of other STIs. (B) Comparison of seropositivity for E. histolytica, with and without other STIs. RPR, rapid plasma reagin; TPHA, Treponema pallidum hemagglutination; TMA, transcription-mediated amplification.

Figure 3

Positive rate of sexually transmitted infections (STIs) by sex and age group. (A) Positive rate of Entamoeba histolytica and other STIs were compared between male (n=1474) and female (n=609) clients using Fisher’s exact test. (B) Seropositive rates for E. histolytica and RPR, and TMA positivity for Chlamydia trachomatis were calculated for clients of different age groups (serum, urine samples): 29 years or younger (752, 503), 30–39 years (666, 453), 40–49 years (443, 315), and 50s or older (222, 167). Correlation between age and positivity was calculated using the χ² test for trend. RPR, rapid plasma reagin test; TPHA, Treponema pallidum hemagglutination; TMA, transcription-mediated amplification.