Epidemic resurgence of dengue fever in Singapore in 2013-2014: A virological and entomological perspective

Abstract

BackgroundDengue resurged in Singapore during 2013-14, causing an outbreak with unprecedented number of cases in the country. In the present study, we summarise the epidemiological, virological and entomological findings gathered through the dengue surveillance programme and highlight the drivers of the epidemic. We also describe how the surveillance system facilitated the preparedness to moderate epidemic transmission of dengue in the country.MethodsThe case surveillance was based on a mandatory notification system that requires all medical practitioners to report clinically-suspected and laboratory-confirmed cases within 24 hours. The circulating Dengue virus (DENV) populations were monitored through an island wide virus surveillance programme aimed at determining the serotypes and genotypes of circulating virus strains. Entomological surveillance included adult Aedes surveillance as well as premise checks for larval breeding.ResultsA switch in the dominant serotype from DENV-2 to DENV-1 in March 2013 signalled a potential spike in cases, and the alert was corroborated by an increase in average Aedes house index. The alert triggered preparedness and early response to moderate the impending outbreak. The two-year outbreak led to 22,170 cases in 2013 and 18,338 in 2014, corresponding to an incidence rate of 410.6 and 335.0 per 100,000 population, respectively. DENV-1 was the dominant serotype in 2013 (61.7 %, n = 5,071) and 2014 (79.2 %, n = 5,226), contributed largely by a newly-introduced DENV-1 genotype III strain. The percentage of houses with Ae. aegypti breeding increased significantly (p < 0.001) from 2012 (annual average of 0.07 %) to 2013 (annual average of 0.14 %), followed by a drop in 2014 (annual average of 0.10 %). Aedes breeding data further showed a wide spread distribution of Ae. aegypti in the country that corresponded with the dengue case distribution pattern in 2013 and 2014. The adult Aedes data from 34 gravitrap sentinel sites revealed that approximately 1/3 of the monitored sites remained at high risk of DENV transmission in 2013.ConclusionsThe culmination of the latest epidemic is likely to be due to a number of demographic, social, virological, entomological, immunological, climatic and ecological factors that contribute to DENV transmission. A multi-pronged approach backed by the epidemiological, virological and entomological understanding paved way to moderate the case burden through an integrated vector management approach.

Assessing the interplay between human mobility and mosquito borne diseases in urban environments

“…More than 80% of the world's population is at risk from at least one vector-borne disease 3 . The populations most at risk are those living in poverty in the tropical and subtropical areas, but as the case of Singapore shows, highly developed cities and countries still need continued efforts to prevent outbreaks 34 . The rapid urbanization, the increase in international travel and trade, the modification of agriculture and environmental changes have increased the spread of vector populations, putting more and more people at risk.…”

Patterns of Urban Housing Shape Dengue Distribution in Singapore at Neighborhood and Country Scales

“…Two epidemiological data sets were obtained for this study: (1) dengue cases in Geylang neighborhood (2010–2015), received from the Ministry of Health (MOH), Singapore; this data set includes the number of reported cases by location (i.e., street address) and epidemiological week for the period; and (2) dengue cases in Singapore (2013–2015), retrieved mainly from a recent report by Hapuarachchi and others (Hapuarachchi et al, ). This article provides the spatial distribution of dengue in 2013–2014 using four quantiles of cases densities: two cases/km 2 , 16–25 cases/km 2 , 56–61 cases/km 2 , and >217 cases/km 2 .…”

Using spatial genetics to quantify mosquito dispersal for control programs

“…We analyzed the genotyped and geo-referenced Aedes aegypti individuals collected in two densely populated areas of Singapore with a homogeneous distribution of high-rise apartment blocks. Aedes aegypti is the primary vector of dengue virus in Singapore that, despite having a low Aedes house index (2%) and an extensive vector surveillance and control program [22], continues to experience regular dengue outbreaks [23,24]. This dataset offered an opportunity to characterize Ae.…”