WEST NILE ENCEPHALITIS EPIDEMIC IN SOUTHEASTERN ROMANIA

Background West Nile fever (WNF) is a mosquito-borne flavivirus infect ion endemic in Africa and Asia. In 1996, the first major WNF epidemic in Europe occurred in Romania, with a high rate of neurological infect ions. We investigated the epidemic to characterise transmission patter ns in this novel setting and to determine its origin. Methods Hospital -based surveillance identified patients admitted with acute aseptic me ningitis and encephalitis in 40 Romanian districts, including Buchares t. Infection was confirmed with IgM capture and indirect IgG ELISAs. I n October, 1996, we surveyed outpatients in Bucharest and seven other districts to estimate seroprevalence and to detect infected patients n ot admitted to hospital. We also measured the rates of infection and s eropositivity in mosquitoes and birds, respectively. Results Between J uly 15 and Oct 12, we identified 393 patients with serologically confi rmed or probable WNF infection, of whom 352 had acute central-nervous- system infections. 17 patients older than 50 years died. Fatality/case ratio and disease incidence increased with age. The outbreak was conf ined to 14 districts In the lower Danube valley and Bucharest (attack rate 12.4/100 000 people) with a seroprevalence of 4.1%. The number of mild cases could not be estimated. WN virus was recovered from Culex pipiens mosquitoes, the most likely vector, and antibodies to WN virus were found in 41% of domestic fowl. Interpretation The epidemic in Bu charest reflected increased regional WNF transmission in 1996. Epidemi cs of Cx pipiens-borne WNF could occur in other European cities with c onditions conducive to transmission.