Seasonal patterns of dengue fever and associated climate factors in 4 provinces in Vietnam from 1994 to 2013

Abstract

BackgroundIn Vietnam, dengue fever (DF) is still a leading cause of hospitalization. The main objective of this study was to evaluate the seasonality and association with climate factors (temperature and precipitation) on the incidences of DF in four provinces where the highest incidence rates were observed from 1994 to 2013 in Vietnam.MethodsIncidence rates (per 100,000) were calculated on a monthly basis from during the study period. The seasonal-decomposition procedure based on loess (STL) was used in order to assess the trend and seasonality of DF. In addition, a seasonal cycle subseries (SCS) plot and univariate negative binomial regression (NBR) model were used to evaluate the monthly variability with statistical analysis. Lastly, a generalized estimating equation (GEE) was used to assess the relationship between monthly incidence rates and weather factors (temperature and precipitation).ResultsWe found that increased incidence rates were observed in the second half of each year (from May through December) which is the rainy season in each province. In Hanoi, the final model showed that 1 °C rise of temperature corresponded to an increase of 13% in the monthly incidence rate of DF. In Khanh Hoa, the final model displayed that 1 °C increase in temperature corresponded to an increase of 17% while 100 mm increase in precipitation corresponded to an increase of 11% of DF incidence rate. For Ho Chi Minh City, none of variables were significant in the model. In An Giang, the final model showed that 100 mm increase of precipitation in the preceding and same months corresponded to an increase of 30% and 22% of DF incidence rate.ConclusionOur findings provide insight into understanding the seasonal pattern and associated climate risk factors.

Impact of Climate Variability and Abundance of Mosquitoes on Dengue Transmission in Central Vietnam

“…The incidence of dengue increased significantly in Da Nang and Khanh Hoa during the study period. Before 2009, the respective monthly numbers of dengue cases reported in Da Nang and Khanh Hoa were usually <500 and 1200 [38]. Compared with the rates reported in 1994-2013, the annual incidence of dengue in Khanh Hoa increased by approximately 1.6-fold [38].…”

“…Before 2009, the respective monthly numbers of dengue cases reported in Da Nang and Khanh Hoa were usually <500 and 1200 [38]. Compared with the rates reported in 1994-2013, the annual incidence of dengue in Khanh Hoa increased by approximately 1.6-fold [38]. Notably, the massive outbreaks that occurred after 2015 in these two hotspots might have been triggered by climate changes that have already impacted neighboring countries [25,64,65].…”

“…In Hanoi, where more than 75 % of dengue cases in northern Vietnam occur, dengue fever transmission showed a seasonal pattern, with a gradual increase in incidence from April to August and a peak in September and October [38,62]. Southern Vietnam is known to be a hyperendemic area where dengue transmission occurs all year round [34,63] with a particularly high incidence from August to November [38]. In central Vietnam, there is a difference in dengue transmission between the north-central and south-central coast regions.…”

“…During 1980-2010, Vietnam reported nearly 2.5 million cases and six major outbreaks [36]. Most dengue studies conducted in Vietnam focused on the northern area (Hanoi) and southern regions [34,[37][38][39]. The central region of Vietnam is also an endemic area for dengue; however, there is little relevant research in this region [40,41].…”

Whole genome sequencing and genetic variations in several dengue virus type 1 strains from unusual dengue epidemic of 2017 in Vietnam

“…Dengue in Vietnam has a year-round occurrence, usually increasing in the rainy season with peak numbers of cases observed between June and October [18]. The disease occurs in both children and adults with an increasing number of cases and associated complications.…”