Introduction In Brazil, three serotypes of dengue virus (DENV1 to 3) circulate. The incidence of dengue fever (DF) was greater in adults and was lower than the proportion of dengue haemorrhagic fever (DHF). However, since 2007 this has changed. This study describes and discusses some of the determinants of this change.
Method Data from 1990 to 2010, recorded in the Notification and Hospital Information Systems, were used. The incidence of DF and the number of hospitalisations for DHF were represented in time trends curves, by age-group.
Results Until 2000, the proportion of DHF was 0.06%; In 2002 and 2009 it was 0.34% and 0.46%, respectively. Between 1998 and 2006, DF and DHF were concentrated in individuals over 14 years old, particularly between 20 and 40 who represented more than 50% of the cases. In 2007, there was substantial increase in hospitalisations for DHF of individuals under 15. Between 1998 and 2006, the proportion in this age-group varied from 9.5% (1998) to 22.6% (2001, and in 2007 reached 53% (p<0.05). This trend increased in 2008, and has remained until 2010.
Conclusions There was a significant increase of DHF and in the ratio DF/DHF in Brazil, especially by age-group pattern. A more virulent DENV-2 serotype, responsible for outbreaks from 2007 to 2008, could have occurred, but there was no change in phylogenetic DENV2 that circulates in Brazil since 1990. It is possible the sequence of the three DENV is a important factor in determining the changes in epidemiology in this country.
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