Background:Jishou and Huaihua,two cities in the west of Hunan Province,had suffered from severe floods be-cause of long-lasting and heavy rainfall during the end of June and July 2012.However,the Disability Adjusted of Life Years(DALYs)of bacillary dysentery caused by the floods have not been examined before.The study aimed to quantify the impact of the floods on the burden of bacillary dysentery in Hunan.China.Methods:A unidirectional case-crossover study was firstly conducted to determine the relationship between daily cases of bacillary dysentery and the floods in Jishou and Huaihua of Hunan Province in 2012.Odds ratios(ORs)estimated by conditional logistic regression were used to quantify the risk of the floods on the disease.The years lived with disability(YLDs)of bacillary dysentery attributable to floods were then estimated based on the WHO framework to calculate potential impact fraction in the Burden of Disease study.Results:Multivariable analysis showed that floods were significantly associated with an increased risk of the number of cases of bacillary dysentery(OR = 3.270,95%Cl:1.299-8.228 in Jishou;OR = 2.212,95%Cl:1.052-4.650 in Huaihua).The strongest effect was shown with a 1-day lag in Jishou and a 4-day lag in Huaihua.Attributable YLD per 1000 of bacillary dysentery due to the floods was 0.0296 in Jishou and 0.0157 in Huaihua.Conclusions:Our study confirms that floods have significantly increased the risks of bacillary dysentery in the study areas.In addition,a sudden and severe flooding with a shorter duration may cause more burdens of bacillary dysentery than a persistent and moderate flooding. Public health preparation and intervention programs should be taken to reduce and prevent a potential risk of bacillary dysentery epidemics after floods.