Seroprevalence and risk factors for dengue infection in socio-economically distinct areas of Recife, Brazil
Introduction
Dengue is a vector-borne disease considered a global public health threat in tropical and subtropical countries. Approximately 2.5 billion people – two fifths of the world population – are at risk of infection, mostly in urban regions given that the main vector (Aedes aegypti) is widespread and well adapted to such environments (Gubler, 1998, WHO, 2009). South-east Asia is one of the most affected regions, where dengue haemorrhagic fever (DHF) has been a leading cause of hospitalization and death among children (WHO, 2009). In the Americas, where all four serotypes (DENV 1–4) circulate, dengue incidence has increased dramatically in the last two decades (PAHO, 2008, Torres and Castro, 2007). From 2001 to 2008, more than 5 million cases of dengue were reported, including approximately 100,000 cases of dengue hemorrhagic fever and 1500 deaths (PAHO, 2008). Brazil currently accounts for the majority (∼80%) of the cases reported in Latin American, with co-circulation of three serotypes (DENV 1–3) in most of the country, with sporadic epidemic waves in several urban areas (Teixeira et al., 2009, PAHO, 2008, Siqueira et al., 2005).
Dengue has a broad spectrum of manifestations and the number of reported cases underestimates the number of infections, because most are asymptomatic and not all symptomatic ones are reported (Kyle and Harris, 2008). Hence, serosurveys and longitudinal studies are used to assess past and current dengue infection and transmission rates at the population level (Thai et al., 2005, Endy et al., 2010, Teixeira et al., 2002).
The spatial distribution of dengue infection can vary greatly between neighboring areas in urban settings (Vanwambeke et al., 2006, Reiter et al., 2003, Vallee et al., 2009, Almeida et al., 2007). Among possible individual and household risk factors, predictors of infection have included higher age (Yew et al., 2009), low socio-economic status (Vasconcelos et al., 1998, Siqueira et al., 2004), lower education level (Teixeira et al., 2002, Silva-Nunes et al., 2008) and lack of household protective measures such as unscreened houses or absence of air-conditioning (Ko et al., 1992, Reiter et al., 2003) In turn, this shows the importance of understanding small-scale variation in dengue infection when formulating control strategies.
The aim of the current population-based household study, conducted in the city of Recife in the Northeast of Brazil, was to estimate the prevalence of dengue infection between privileged and non-privileged areas and identify individual and area-level risk factors for infection in three urban areas. In addition, we describe the spatial distribution of risk of dengue infection to explore intra-urban variations in dengue infection that could be valuable in suggesting alternative control strategies.
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Study settings
Recife (1.5 million inhabitants) lies on the Atlantic coastal plain (8°03′S 34°52′W) at a mean altitude of 5 m above sea, level and is relatively flat. The city's area of 217 km2 is divided in 94 neighborhoods (IBGE, 2009) as shown in Fig. 1. Its climate is tropical humid, with average temperature of 25 °C and rainfall of around 2000 mm per year, with no major variation between neighborhoods (ITEP, 2009). Dengue vector surveillance and control covers the whole city and relies on premise visits for
Results
A total of 2819 individuals, approximately half of them aged 5–14 years, were analyzed in the three areas. Participants living in the high and intermediate socio-economic status areas were, on average, more highly educated and more likely to commute outside their home area (Table 1). Around 90% of people lived in houses in the deprived and intermediary areas, compared to more than 40% in apartment buildings in the high socio-economic area. Around 25% of the dwellings in the high socio-economic
Discussion
This household survey of a Northeastern Brazilian city found dengue seroprevalence ranging from 74% to 91%, with the risk being inversely associated with socio-economic status. This variation in prevalence is unlikely to be explained by climate, because local temperature, rainfall, humidity and altitude are similar among these three areas of the city. Further, entomological research found that infestation rates of Aedes aegypti are similarly high in the three study areas (Regis et al., 2008).
In
Acknowledgments
The authors acknowledge the support of the National Institute of Allergy and Infectious Diseases (NIAID/NIH), Grant U19 AI56541 and PDTIS RVR09-FIOCRUZ. Martelli CMT, Albuquerque MFP and Souza WV were partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico -CNPq (scholarships 307963/2004-7, 305947/2006-0, respectively)
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