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



Incidence 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).



We 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.



Our findings provide insight into understanding the seasonal pattern and associated climate risk factors.
International Livestock Research Institute, Regional Office for East and Southeast Asia, Room 301-302, B1 Building, Van Phuc Diplomatic Compound, 298 Kim Ma Street, Ba Dinh District, Hanoi, Vietnam. H.S.Lee@cgiar.org.
Hu Suk
HS
Lee
International Livestock Research Institute, Regional Office for East and Southeast Asia, Room 301-302, B1 Building, Van Phuc Diplomatic Compound, 298 Kim Ma Street, Ba Dinh District, Hanoi, Vietnam.
Hung
H
Nguyen-Viet
Vector Borne Diseases and Training, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
Vu Sinh
VS
Nam
Medical microbiology Department, The Royal Bournemouth Hospital, Bournemouth, UK.
Mihye
M
Lee
Graduate School of Public Health, Seoul National University, Seoul, Korea.|Interdisciplinary Program of Bioinformatics, Seoul National University, Seoul, Korea.|Institute of Health and Environment, Seoul National University, Seoul, Korea.
Sungho
S
Won
Center for Public Health and Ecosystem Research (CENPHER), Hanoi School of Public Health, Hanoi, Vietnam.
Phuc Pham
PP
Duc
International Livestock Research Institute, Nairobi, Kenya.
Delia
D
Grace
D002947:Cities / Q000706:statistics & numerical data*; D002980:Climate; D021821:Communicable Diseases, Emerging / Q000453:epidemiology* / Q000517:prevention & control / Q000821:virology; D003715:Dengue / Q000453:epidemiology* / Q000517:prevention & control / Q000821:virology; D004196:Disease Outbreaks / Q000517:prevention & control / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D015233:Models, Statistical; D012307:Risk Factors; D012621:Seasons; D014744:Vietnam / Q000453:epidemiology
Climate factors; Dengue fever; Monthly incidence rate; Seasonality; Temperature and precipitation; Vietnam