Academic journal article Environmental Health Perspectives

Temporal Trends and Climatic Factors Associated with Bacterial Enteric Diseases in Vietnam, 1991-2001

Academic journal article Environmental Health Perspectives

Temporal Trends and Climatic Factors Associated with Bacterial Enteric Diseases in Vietnam, 1991-2001

Article excerpt

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 [greater than or equal to] 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 Delta 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]

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In Vietnam, shigellosis (bacillary dysentery), typhoid fever, and cholera are enteric diseases of significant public health concern (DeRoeck et al. 2005). They are primarily caused by the bacterial pathogens Shigella spp., Salmonella typhi, and Vibrio cholerae, respectively, and transmission occurs through fecal contamination of food or water or by person-to-person contact (Bhan et al. 2005; Crump et al. 2004; Kindhauser 2003; Kotloff et al. 1999; Lanata et al. 2002). Infection rates and outbreaks are highest where the standards of living, water supply, and human behaviors related to personal hygiene and food preparation are poor. The distribution and ecologic determinants of shigellosis/dysentery, typhoid fever, and cholera have recently been described from surveillance data in Vietnam (Kelly-Hope et al. 2007). The data show that each disease varies in magnitude and has a distinct spatial pattern, which appears to be driven by a combination of human and environmental factors, including poverty, water sources, and climate.

Many infectious diseases, including shigellosis/dysentery, typhoid fever, and cholera, are influenced by climate. Specifically, climate plays an important role in the transmission process and can influence spatial and seasonal distributions, as well as interannual variability and long-term trends [Burke et al. 2001; Kovats et al. 2003; World Health Organization (WHO) 2004]. Although climate is one aspect of the complex epidemiology of these enteric diseases, it can help to define high-risk periods. Few studies conducted in Asia have described the temporal patterns and outbreaks of shigellosis/dysentery and typhoid fever, and no study has specifically examined the impact of climate on these diseases. In general, cholera has been studied more widely, and formal and informal listings of outbreaks and putative risk factors are available from various sources (Griffith et al. …

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