Yellow fever: reemerging in the state of Sao Paulo, Brazil, 2009

OBJECTIVE: To describe the investigation of a sylvatic yellow fever outbreak in the state of Sao Paulo and the main control measures undertaken.METHODS: This is a descriptive study of a sylvatic yellow fever outbreak in the Southwestern region of the state from February to April 2009. Suspected and confirmed cases in humans and in non-human primates were evaluated. Entomological investigation in sylvatic environment involved capture at ground level and in the tree canopy to identify species and detect natural infections. Control measures were performed in urban areas to control Aedes aegypti. Vaccination was directed at residents living in areas with confirmed viral circulation and also at nearby cities according to national recommendation.RESULTS: Twenty-eight human cases were confirmed (39.3% case fatality rate) in rural areas of Sarutaia, Piraju, Tejupa, Avare, and Buri. The deaths of 56 non-human primates were also reported, 91.4% were Allouatta sp. Epizootics was confirmed in two non-human primates in the cities of Itapetininga and Buri. A total of 1,782 mosquitoes were collected, including Haemagogus leucocelaenus, Hg. janthinomys/capricornii, and Sabethes chloropterus, Sa. purpureus and Sa. undosus. Yellow fever virus was isolated from a group of Hg. Leucocelaenus from Buri. Vaccination was carried out in 49 cities, with a total of 1,018,705 doses. Nine serious post-vaccination adverse events were reported.CONCLUSIONS: The cases occurred between February and April 2009 in areas with no recorded yellow fever virus circulation in over 60 years. The outbreak region occurred outside the original recommended vaccination area with a high percentage of susceptible population. The fast adoption of control measures interrupted the human transmission within a month and the confirmation of viral circulation in humans, monkeys and mosquitoes. The results allowed the identification of new areas of viral circulation but further studies are required to clarify the dynamics of the spread of this disease.