Increases in Entamoeba histolytica Antibody–Positive Rates in Human Immunodeficiency Virus–Infected and Noninfected Patients in Japan: A 10-Year Hospital-Based Study of 3,514 Patients

Serological evidence of the epidemiological trends in Entamoeba histolytica infection is scarce, especially in nonendemic countries. We aimed to determine the antibody-positive rates over a 10-year period, and compare the trends between human immunodeficiency virus (HIV)-infected and -noninfected patients. We reviewed 3,514 patients who underwent antibody testing during the study periods, which were divided into five annual categories: 2004-2005, 2006-2007, 2008-2009, 2010-2011, and 2012-2013. Anti-E. histolytica antibody was assessed by indirect immunofluorescence assay. The antibody-positive rate increased yearly from 2004-2005 to 2012-2013 (P < 0.001), although there was no increase in the annual number of antibody tests. This trend was seen among males (18.6-28.3%; P < 0.01), females (5.4-28.2%; P < 0.01), HIV-infected patients (18.4-26.9%; P < 0.001), and non-HIV-infected patients (14.6-36.8%; P < 0.001), and HIV-infected men who have sex with men (19.4-29.1%; P < 0.001). Among antibody-positive patients, there was a significant increase in the proportion of patients with high (≥ 1,600) titers (0.7-12.9%; P < 0.001), whereas this trend was not seen in patients with low (100) or intermediate (200-800) titers (P = 0.282 and 0.409, respectively). This large hospital-based study demonstrated that positive anti-E. histolytica antibody rates increased over 10 years, even though the annual number of antibody tests remained constant. Moreover, this trend was identified in non-high-risk patients (females and non-HIV-infected patients) as well as in high-risk patients. The proportion of patients with high antibody titers significantly increased among the antibody-positive patients.