A large outbreak of epidemic polyarthritis (EPA) caused by the arbovirus Ross River virus (RRV) occurred in the south west of NSW during the summer of 1993. A total of 312 cases was reported by laboratories ip contrast to 33 cases in 1991 and 29 cases in 1992. Cases occurred from January to June, with 64 per cent occurring in ,January and February. The outbreak followed heavy rains between October and December 1992. This report describes the outbreak of RRV disease which was the largest in the south west since the Statewide RRV outbreak in 1984 (Figure 5). The major inland vector of RRV in NSW is the mosquito Cuiex annulirostris and the major coastal vector is Aedes vigilax. The clinical symptoms of RRV infection vary but commonly include rash, lethargy and myalgia followed by arthralgia, joint stiffness and joint swelling. A follow-up study of REV patients in a Western Australian outbreak in 1988-89 showed that only 27 per cent of cases had fully recovered within six months. In addition, more than 33 per cent of cases had at least one month off work'. The economic consequences of RRV are likely to be large as attack rates are highest in the working-age groups. METHODS Notifications were received from five main laboratoriestwo in NSW and three in Victoria. We defined a case as a resident of the South West Districts whose paired sera showed a fourlbld or greater rise in antibody titre, or whose single serum specimen demonstrated RRV-speci be 1gM antibody.

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