Association between climate variability and hospital visits for non-cholera diarrhoea in Bangladesh: effects and vulnerable groups
Masahiro Hashizume1,2,*, Ben Armstrong1, Shakoor Hajat1, Yukiko Wagatsuma3, Abu SG Faruque4, Taiichi Hayashi5 and David A Sack4
1Public and Environmental Health Research Unit, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
2Research Center for Tropical Infectious Diseases, Institute of Tropical Medicine, Nagasaki University, Sakamoto 1-12-4, Nagasaki City, Nagasaki 852-8523, Japan.
3Department of Epidemiology, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaragi 305-8575, Japan.
4ICDDR,B: Centre for Health and Population Research, Bangladesh, Mohakhali (GPO Box 128, Dhaka 1000) Dhaka 1212, Bangladesh.
5Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
* Corresponding author. Research Center for Tropical Infectious Diseases, Institute of Tropical Medicine, Nagasaki University, Sakamoto 1-12-4, Nagasaki City, Nagasaki 852-8523, Japan. E-mail: firstname.lastname@example.org
Background We estimated the effects of rainfall and temperature on the number of non-cholera diarrhoea cases and identified population factors potentially affecting vulnerability to the effect of the climate factors in Dhaka, Bangladesh.
Methods Weekly rainfall, temperature and number of hospital visits for non-cholera diarrhoea were analysed by time-series regression. A Poisson regression model was used to model the relationships controlling for seasonally varying factors other than the weather variables. Modifications of weather effects were investigated by fitting the models separately to incidence series according to their characteristics (sex, age, socio-economic, hygiene and sanitation status).
Results The number of non-cholera diarrhoea cases per week increased by 5.1% (95% CI: 3.3–6.8) for every 10 mm increase above the threshold of 52 mm of average rainfall over lags 0–8 weeks. The number of cases also increased by 3.9% (95% CI: 0.6–7.2) for every 10 mm decrease below the same threshold of rainfall. Ambient temperature was also positively associated with the number of non-cholera diarrhoea cases. There was no evidence for the modification of both ‘high and low rainfall’ effects by individual characteristics, while the effect of temperature was higher amongst those individuals at a lower educational attainment and unsanitary toilet users.
Conclusions The number of non-cholera diarrhoea cases increased both above and below a threshold level with high and low rainfall in the preceding weeks. The number of cases also increased with higher temperature, particularly in those individuals at a lower socio-economic and sanitation status.
Keywords Bangladesh, diarrhoea, non-cholera, rainfall, season, temperature, time-series, weather
International Journal of Epidemiology 2007 36(5):1030-1037. Published by Oxford University Press on behalf of the International Epidemiological Association. An Open Access Article.
Diarrhoea is one of the principal causes of mortality and morbidity especially in developing countries. Some data suggest that 4 billion episodes of diarrhoea occurred each year, of which more than 90% occurred in developing countries.1 Many investigations have reported seasonal coincidence of the peak of diarrhoea incidence with the rainy season in tropical regions.2 However, these studies did not address the direct association between rainfall and diarrhoea allowing for the potential confounding by seasonally varying factors other than rainfall. Ambient temperature could also contribute to the incidence of diarrhoea.3 Clarifying the potential role of weather on the transmission of diarrhoeal diseases could help by bringing a deeper insight into the mechanisms of the seasonality of the disease. This study quantifies the impacts of rainfall and temperature on the number of non-cholera diarrhoea cases. Overall relationships of non-cholera diarrhoea are particularly focused on here because cholera has been known to have a strong link to weather factors,4 while that of the rest of diarrhoeal diseases is less clear.5 Population factors potentially affecting vulnerability to the effect of the climate factors are also examined. To have some insight into the causal pathways between rainfall and diarrhoea, the association with river levels was also investigated.