Quantifying the Emergence of Dengue in Hanoi, Vietnam: 1998–2009

Hoang Quoc Cuong,Nguyen Tran Hien,Peter Horby,Jeremy Farrar,Tran Nhu Duong,Vu Sinh Nam,Khoa T D Thai,Nguyen Nhat Cam,Tran Vu Phong,Scott B Halstead

doi:10.1371/journal.pntd.0001322

Abstract

BackgroundAn estimated 2.4 billion people live in areas at risk of dengue transmission, therefore the factors determining the establishment of endemic dengue in areas where transmission suitability is marginal is of considerable importance. Hanoi, Vietnam is such an area, and following a large dengue outbreak in 2009, we set out to determine if dengue is emerging in Hanoi.Methods and Principal FindingsWe undertook a temporal and spatial analysis of 25,983 dengue cases notified in Hanoi between 1998 and 2009. Age standardized incidence rates, standardized age of infection, and Standardized Morbidity Ratios (SMR) were calculated. A quasi-Poisson regression model was used to determine if dengue incidence was increasing over time. Wavelet analysis was used to explore the periodicity of dengue transmission and the association with climate variables. After excluding the two major outbreak years of 1998 and 2009 and correcting for changes in population age structure, we identified a significant annual increase in the incidence of dengue cases over the period 1999–2008 (incidence rate ratio = 1.38, 95% confidence interval = 1.20–1.58, p value = 0.002). The age of notified dengue cases in Hanoi is high, with a median age of 23 years (mean 26.3 years). After adjusting for changes in population age structure, there was no statistically significant change in the median or mean age of dengue cases over the period studied. Districts in the central, highly urban, area of Hanoi have the highest incidence of dengue (SMR>3).ConclusionsHanoi is a low dengue transmission setting where dengue incidence has been increasing year on year since 1999. This trend needs to be confirmed with serological surveys, followed by studies to determine the underlying drivers of this emergence. Such studies can provide insights into the biological, demographic, and environmental changes associated with vulnerability to the establishment of endemic dengue.

Highlights

Dengue is caused by infection with one of four genetically related but serologically distinct dengue virus serotypes, which are transmitted by the bite of an infected female Aedes mosquito
Hanoi is a low dengue transmission setting where dengue incidence has been increasing year on year since 1999. This trend needs to be confirmed with serological surveys, followed by studies to determine the underlying drivers of this emergence. Such studies can provide insights into the biological, demographic, and environmental changes associated with vulnerability to the establishment of endemic dengue
To explore disease dynamics we describe the temporal patterns of dengue incidence and its association with local climate variables

Summary

Introduction

Dengue is caused by infection with one of four genetically related but serologically distinct dengue virus serotypes, which are transmitted by the bite of an infected female Aedes mosquito. It is the most common vector borne viral disease of humans with an estimated 50 million infections every year and around 3.6 billion people living in areas at risk [1,2]. Albopictus, a secondary vector of dengue, has expanded dramatically [5] Both Aedes vectors are adapted to peridomestic urban habitats that are expected to burgeon over the four decades, with the urban populations of Africa and Asia predicted to treble and double respectively [6]. Vietnam is such an area, and following a large dengue outbreak in 2009, we set out to determine if dengue is emerging in Hanoi

Methods

Results

Discussion

Conclusion