Short-term Effects of Moderate and Severe Floods on Infectious Diarrheal Diseases in Anhui Province, China

Background: Previous studies showed that floods can lead to diarrheal diseases outbreaks; however, the short-term effects of different severity floods on diarrheal diseases are not clear. This study aims to examine 0-14 days lagged effects of moderate and severe floods on diarrhea in Anhui Province, one heavily flood-prone area in China.

Methods: Daily diarrheal cases from January 1, 2013 to August 31, 2017 in 16 cities of Anhui were extracted from the National Notifiable Disease Surveillance System. Meteorological data were obtained, and moderate or severe floods were identified according to Comprehensive Study Group of Major Natural Disasters of the State Science and Technology Commission in China. The quasi-Poisson generalized linear models were applied to evaluate effects of floods on daily diarrheal cases in each city with 0-14 days lag, and we divided post-flood periods into week 1 and week 2, further conducted provincial-level meta-analysis.

Results: Immediate effects of floods on diarrheal diseases were observed within 7 days, and at provincial level moderate floods had a RR of 1.05 (95% CI: 1.02-1.09) and severe floods RR = 1.04 (95% CI: 1.01-1.08) controlling for population size, temperature and relative humidity etc., but less effects appeared in the second week. Impacts of flooding on diarrheal diseases varied among cities. Moderate floods in week 1 had a RR of 1.51 (95% CI: 1.29-1.78) in Bozhou, and severe floods had a RR = 1.31 (95% CI: 1.05-1.64) in Chuzhou. The severe floods may have higher RR in week 1 compared with moderate floods in Anqing (1.10 vs 1.06), Chuzhou (1.31 vs 1.07) and Luan (1.18 vs 1.00).

Conclusions: Both moderate and severe floods can significantly increase diarrheal risks in one week with regionally varied effects, and severe floods may lead higher risks. The findings have implications for preparing emergent interventions in hazard periods to reduce health risks of floods.