Large-scale hepatitis E virus genotype 3 outbreak on new caledonia island

Background and Aim: Several symptomatic cases of hepatitis E virus (HEV) infections were reported to the New Caledonia Island Public Health Service between August and December 2023. This prompted epidemiological and virological investigations to identify the source of infection. Approach and Results: HEV RNA was assessed in symptomatic patients, various food items and pig farms on the island. HEV strains were characterised by sequencing. A seroprevalence study was also conducted on asymptomatic blood donors before and after the outbreak. 127 symptomatic cases were reported. Hospitalisation was required for 29/127 patients (22.8%). Hospitalised patients presented more frequently with comorbidities including liver and cardiovascular diseases, (80.7% vs. 27%, p<0.01) and 3 persons died (2.3%). Among the 100 HEV RNA-positive samples received at the French National Refence Centre for HEV, viral sequencing was possible for 76 samples. All strains were identified as HEV genotype 3 and 74/76 strains were grouped together (nucleotide identity: 98-100%). Full-length sequencing indicated a new HEV-3 subtype within HEV-3 subclade abk. Only genotype 3f strains were detected on the island’s pig farms. No food items tested positive for HEV RNA. The seroprevalence of HEV IgG and IgM in blood donors was 9.2% (9/98) and 0%, respectively, in 2020, rising to 17.3% (17/98) and 2% (2/98) in 2024. Conclusions: Although all previous large-scale epidemics in Asia and Africa were associated with HEV-1 or 2, the New Caledonia outbreak was linked to HEV-3. A high number of symptomatic cases were admitted to hospital with a case fatality rate of 2.3%.