Hepatitis A Outbreak Among Men Who Have Sex With Men in a Country of Low Endemicity of Hepatitis A Infection

To the Editor—We read with interest the recent article by Manor et al [1] on an outbreak of hepatitis A virus (HAV) infection originating among injecting drug users and homeless adults in Tel Aviv, and subsequently spreading to the general population in Tel Aviv metropolitan region. From analyses of clinical and sewage samples, Manor et al presented phylogenetic evidence to suggest that HAV had continued to circulate endemically in Israel despite the universal toddlers’ vaccination (UTV) program in place since 1999, and finally resulted in the outbreak in Tel Aviv in 2012–2013. In the United States [2], Australia [3], and Korea [4], reports have also demonstrated an increase of the seroprevalence of anti-HAV immunoglobulin G (IgG) and a decrease of acute hepatitis A incidence with the implementation of large-scale vaccination programs. In Israel, the seroprevalence of anti-HAV IgG is 80%–90% in children who are covered by the UTV program; in contrast, the seropositivity is only ≤57% in adult populations who are not included in the UTV program. Furthermore, compliance with HAV vaccines was generally low in at-risk groups, such as men who have sex with men (MSM) or injection drug users [5], which may increase the risk of subsequent HAV outbreaks. Before 1980, Taiwan was a country of high HAV endemicity. However, recent surveys suggest that seropositivity has declined significantly among Taiwanese children, with the improvement of sanitation and implementation of HAV vaccination for toddlers in townships with a high incidence of acute hepatitis A after 1995. In a survey conducted in central Taiwan in 2010, the seroprevalence of anti-HAV antibody was only 2.3% among schoolchildren aged <15 years [6]. The incidence of acute hepatitis A declined significantly in both vaccine-covered townships and non-vaccine-covered townships [7]. The seropositivity in young, high-risk populations was also low in Taiwan. The seroprevalence among human immunodeficiency virus (HIV)–infected MSM aged <40 years was 27.5% in a survey between 2004 and 2007 [8]. In another survey conducted among young HIV-infected and HIV-uninfected MSM aged 18–40 years between 2009 and 2010, the overall HAV seroprevalence further decreased to 10.4% [9]. Although HAV vaccination is recommended for high-risk populations by the Adult Committee on Immunization Practices (ACIP) of Taiwan’s Centers for Disease Control (CDC), compliance has been low. Since June 2015, 2 indigenous cases of acute hepatitis A in patients coinfected with HIV were reported to the Taiwan CDC; the number of indigenous cases of acute hepatitis A increased thereafter, with >1000 indigenous cases reported in 2016 (Figure 1), and >70% of the cases concentrated in northern Taiwan [10]. At least 70% of the cases were in MSM; 60% had HIV infection and >60% had syphilis, gonorrhea, or shigellosis; and subgenotype IA was identified as the strain causing the outbreak (Taiwan CDC, unpublished data). In response to this unprecedented outbreak of acute hepatitis A among at-risk populations, a vaccination campaign against HAV was launched in September 2015 at designated hospitals for HIV care, and the Taiwan CDC has, since October 2016, provided free HAV vaccine to HIV-infected patients and those individuals who sought medical attention because of sexually transmitted diseases; this has been associated with gradually decreasing trends of acute hepatitis A (Figure 1). Number of indigenous cases of acute hepatitis A virus (HAV) reported to the Taiwan Centers for Disease Control (CDC) between 2014 and 2016, including among men who have sex with men (MSM). Black arrowhead marks the start of the ongoing outbreak of acute hepatitis A. Both data from Israel and Taiwan demonstrate that outbreaks of acute hepatitis A among high-risk populations may occur even though the incidence of HAV infection is low in the general population. While universal coverage of HAV vaccines decreases the burden of acute hepatitis A in the general population, this benefit may not extend to high-risk groups when vaccination practices are neglected. Awareness of, and adherence to, the recommendations of HAV vaccination should be promoted among the healthcare providers and at-risk populations. Potential conflicts of interest. All authors: No potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.