Immunity to Hepatitis A among men who have sex with men attending a large sexual health clinic in Melbourne, Australia, 2012-2018

Background: Outbreaks of hepatitis A are being reported more commonly among men who have sex with men (MSM) globally. Australia has also reported a sharp increase in the number of cases of hepatitis A in 2017. This study aimed to determine the level of immunity to hepatitis A among MSM attending a large urban sexual health clinic in Victoria in the lead up to recent outbreak. Methods: This was a retrospective audit of serological testing data from first-time MSM attendees at Melbourne Sexual Health Centre (MSHC) in Australia from 1 January 2012 to 31 December 2018. We determined the proportion of MSM who were tested and who had serological detection of hepatitis A IgG, stratified by age and calendar year. We used univariable and multivariable logistic regression to investigate factors associated with testing for and detection of hepatitis A IgG. Results: There were 16 609 first-time MSM attendees at MSHC over the 7-year period, of which 9718 (59%, 95% CI 58% to 60%) were tested for hepatitis A IgG. There was a 2% annual increase in the proportion of men tested (from 60% in 2012 to 69% in 2018; OR=1.02, 95% CI 1.00 to 1.03, p=0.025). Men born outside of Australia/New Zealand, and younger men <30 years had higher odds of being tested. Of those tested, 44% (n=4304, 95% CI 43% to 45%) had hepatitis A IgG detected at their first visit, with no change over time (OR=1.01, 95% CI 0.99 to 1.03, p=0.210). Detection of hepatitis A IgG was associated with being aged 30 years or older (adjusted OR=2.06, 95% CI 1.89 to 2.24, p<0.001) or being born overseas versus Australia/New Zealand (AOR=1.21, 95% CI 1.11 to 1.31, p<0.001). Conclusion: Hepatitis A immunity among MSM remains below the estimated 70% required to prevent outbreaks. Measures including increased testing and higher vaccination coverage are needed to prevent outbreaks and to limit the number of cases and deaths.