Demographic profile of sylvatic yellow fever in Brazil from 1973 to 2008.

Background: Yellow fever is an acute, frequently fatal, febrile arbovirosis that in Brazil occurs only in the sylvatic form. Sylvatic yellow fever (SYF) appears in sporadic outbreaks over a large area of Brazil. In this paper, we analyze the demographic profile of 831 SYF cases that occurred between 1973 and 2008, to determine which segments of the exposed population are at greater risk.

Methods: Data were statistically analyzed and were also geo-referenced in order to observe their spatial pattern. The basic reproductive number of infections, R0, was estimated by the ratio between average life expectancy and the average age of the cases.

Results: SYF cases showed a modal profile of young male adults, approximately 30 years of age, living in rural areas of the states of Pará, Goiás, Maranhão and Minas Gerais, who were unvaccinated or whose vaccination was out of date. The disease showed a high mortality rate (51%, 421/831) among the notified cases, with death occurring on around the seventh day of illness for most patients. The R0 for SYF was estimated at approximately 2.4.

Conclusion: The results of this study suggest that lack of vaccination coverage is a major risk factor for SYF, and that the groups most at risk are migrant laborers, farm workers and tourists.