(See the Editorial Commentary by Holmberg, on pages 782–3.)
Background. A large outbreak of hepatitis A affected individuals in several Australian states in 2009, resulting in a 2-fold increase in cases reported to state health departments compared with 2008. Two peaks of infection occurred (April–May and September–November), with surveillance data suggesting locally acquired infections from a widely distributed food product.
Methods. Two case-control studies were completed. Intensive product trace-back and food sampling was undertaken. Genotyping was conducted on virus isolates from patient serum and food samples. Control measures included prophylaxis for close contacts, public health warnings, an order by the chief health officer under the Victorian Food Act 1984, and trade-level recalls on implicated batches of semidried tomatoes.
Results. A multijurisdictional case-control study in April–May found an association between illness and consumption of semidried tomatoes (odds ratio [OR], 3.0; 95% CI 1.4–6.7). A second case-control study conducted in Victoria in October–November also implicated semidried tomatoes as being associated with illness (OR, 10.3; 95% CI, 4.7–22.7). Hepatitis A RNA was detected in 22 samples of semidried tomatoes. Hepatitis A virus genotype IB was identified in 144 of 153 (94%) patients tested from 2009, and partial sequence analysis showed complete identity with an isolate found in a sample of semidried tomatoes.
Conclusions. The results of both case-control studies and food testing implicated the novel vehicle of semidried tomatoes as the cause of this hepatitis A outbreak. The outbreak was extensive and sustained despite public health interventions, the design and implementation of which were complicated by limitations in food testing capability and complex supply chains.