| Temporal Trends and Climatic Factors
Associated with Bacterial
Enteric Diseases in Vietnam,
1991–2001 Louise A. Kelly-Hope,1 Wladimir J.
Alonso,1 Vu Dinh Thiem,2 Do Gia Canh,2 Dang Duc Anh,2 Hyejon Lee,3 and Mark A. Miller1 1Division
of International Epidemiology and Population Studies, Fogarty
International Center, National Institutes of Health, Department
of Health and Human Services, Bethesda, Maryland, USA; 2National
Institute of Hygiene and Epidemiology, Hanoi, Vietnam; 3International
Vaccine Institute, SNU Research Park, Seoul, Korea Abstract
Objective: In Vietnam, shigellosis/dysentery, typhoid fever, and cholera are important enteric diseases. To better understand their epidemiology, we determined temporal trends, seasonal patterns, and climatic factors associated with high risk periods in eight regions across Vietnam. Methods: We quantified monthly cases and incidence rates (IR) for each region from national surveillance data (1991–2001) . High- and low-disease periods were defined from the highest and lowest IRs (1 SD above and below the mean) and from outbreaks from positive outliers (4 SDs higher in 1 month or 2 SDs higher in ≥ 2 consecutive months) . We used general linear models to compare precipitation, temperature, and humidity between high- and low-risk periods. Results: Shigellosis/dysentery was widespread and increased 2.5 times during the study period, with the highest average IRs found between June and August (2.1/100,000–26.2/100,000) . Typhoid fever was endemic in the Mekong River DeltaDelta ; and emerged in the Northwest in the mid-1990s, with peaks between April and August (0.38–8.6) . Cholera was mostly epidemic along the central coast between May and November (0.07–2.7) , and then decreased dramatically nationwide from 1997 onward. Significant climate differences were found only between high- and low-disease periods. We were able to define 4 shigellosis/dysentery, 14 typhoid fever, and 8 cholera outbreaks, with minimal geotemporal overlap and no significant climatic associations. Conclusions: In Vietnam, bacterial enteric diseases have distinct temporal trends and seasonal patterns. Climate plays a role in defining high- and low-disease periods, but it does not appear to be an important factor influencing outbreaks. Key words: cholera, climate, dysentery, enteric disease, epidemiology, outbreaks, seasonality, shigellosis, typhoid fever, Vietnam. Environ Health Perspect 116: 7–12 (2008) . doi:10.1289/ehp.9658 available via http://dx.doi.org/ [Online 16 October 2007]
Address correspondence to L.A. Kelly-Hope, Division of International Epidemiology and Population Studies, Fogarty International Center, 16 Center Dr., National Institutes of Health, Bethesda, MD 20892 USA. Telephone: (301) 496-3110. Fax: (301) 496-8496. E-mail: kellyhopel@mail.nih.gov We thank the International Vaccine Institute (Korea) for providing disease data. We also thank C. Schuck Paim (University of São Paulo, Brazil) for assistance with statistical methods. This study was funded by the Fogarty International Center and the Bill and Melinda Gates Foundation. The authors declare they have no competing financial interests. Received 28 August 2006 ; accepted 15 October 2007.
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