The seroprevalence of antibodies to Japanese encephalitis virus in five New South Wales towns at high risk of infection, 2022: a cross-sectional serosurvey

Abstract

Objectives: To determine the proportion of people in New South Wales towns at high risk of Japanese encephalitis virus (JEV) infections during the 2022 outbreak; to identify risk factors for JEV infection.

Study design: Cross-sectional serosurvey study of the seroprevalence of JEV-specific antibodies in NSW.

Setting, participants: Convenience sample of people (all ages) from five regional NSW towns deemed to be at high risk of JEV infections after first outbreak of Japanese encephalitis in southeastern Australia in early 2022 (Balranald, Corowa, Dubbo, Griffith, Temora), 21 June - 22 July 2022.

Main outcome measures: Proportion of people seropositive for JEV total antibody, assayed by defined epitope-blocking enzyme-linked immunosorbent assay; prevalence odds ratios for exposure risk factors and protective behaviours.

Results: Eighty of 917 eligible participants (559 girls or women, 61%; 42 Aboriginal and Torres Strait Islander people, 4.6%; median age, 52 years [IQR, 37-62 years]) were seropositive for JEV-specific total antibody (8.7%); the median age of seropositive people was 61 years (IQR, 48-70 years). The seropositivity proportion was largest for people aged 65 years or more (30 of 192; weighted proportion, 13.7%) and larger for male than female participants (30 of 358, 10.6% v 50 of 559, 7.5%). Five of 42 samples from Aboriginal and Torres Strait Islander participants were seropositive (12%). We found mixed associations with a range of potential risk factors.

Conclusion: We found evidence for a substantial number of JEV infections in five regional NSW towns during a single arbovirus season in 2022. Public health responses, including effective surveillance, vaccination against JEV, and mosquito management, are critical for controlling outbreaks. Promoting behaviours that reduce exposure to mosquitoes is a core component of prevention, particularly when the vaccine supply is limited.

Keywords: Arbovirus infections; Disease transmission, infectious; Encephalitis, viral; Epidemiology; Public health; RNA virus infections; Surveys and questionnaires; Vaccine preventable disease; Zoonoses.