Exposure to the risk of dengue virus infection in an urban setting: ecological versus individual heterogeneity

The dynamics of dengue virus circulation in the intra-urban spaces of large cities and the risk factors for the occurrence of such infections are still not well known. Although it has been established that poverty is one of the determinants of the majority of infectious and parasitic diseases, in the case of dengue this is still a matter of some controversy. This study had the objective of describing the distribution of dengue seroprevalence and seroincidence in different intra-urban spaces within a large and complex city in north-eastern Brazil. The study investigated whether there is any relationship between the intensity of virus circulation and the population’s living conditions or between group immunity and Aedes aegypti infestation rates. The variability in the risk of such infections was also examined. A prospective study was conducted by means of serological investigations among a sample of people living in 30 different spaces (“sentinel areas”) in the city of Salvador, which was selected according to extreme differences in living conditions. High rates of seroprevalence (67.7%) and seroincidence (70.6%) were found for the circulating serotypes (DENV-1 and DENV-2). Similar to what has been occurring in south-east Asia, the seroincidence was high (55%) even when the group immunity had already been partially established (42%) and the Ae. aegypti infestation rates were relatively low (<3%). Contrary to the ecological analysis, at the individual level, substantial heterogeneity in dengue exposure was observed. This paper discusses this apparent contradiction, highlighting its implications for the effectiveness of vector control strategies.