The Impact of Flooding on Infectious Diseases: Insights from a Decade of Data

Floods are becoming more frequent worldwide. Between 1990 and 2022, 4,713 floods in 168 countries affected more than 3.2 billion people and caused over 218,000 deaths. Beyond the immediate destruction, floods create ideal conditions for disease when floodwater contaminates water supplies, damages sanitation infrastructure, displaces populations, and leaves stagnant water where mosquitoes breed.

To bring together fragmented evidence on how flooding affects waterborne and vector-borne diseases, Luangnara et al. analyzed 71 studies (most of them observational) published between 2014 and 2024, covering 30 countries. Flooding was consistently associated with increases in waterborne infections, including cholera, bacillary dysentery, leptospirosis, and hepatitis A and E, as well as vector-borne diseases such as dengue and malaria. The lag period between flooding and outbreak emergence varied by disease: cholera typically emerged 1–2 weeks after flooding, leptospirosis after 1–12 weeks, dengue after 5 days to 3–4 weeks, and malaria after 1–6 months. These delays varied by region, flood characteristics, and the strength of existing public health infrastructure. Diarrheal infections were common after flooding in low- and middle-income countries, whereas severe outbreaks were rare in high-income countries (1).

The cholera examples are striking. After Hurricane Matthew in Haiti in 2016, average daily cholera cases rose from 92 to 138, and daily deaths more than doubled. After Cyclone Kenneth in Mozambique in 2019, two doses of oral cholera vaccine, combined with early health messages, quick case detection, and rapidly established treatment centers, helped control the outbreak. In Uganda in 2019, rapid vaccination reaching over 90% coverage ended an outbreak within 10 weeks.

Building on the authors’ recommendations, the response should be tailored to the type of infection and local context. For waterborne diseases, short-term priorities are emergency water, sanitation, and hygiene measures; health communication; and oral rehydration points. Targeted measures include oral cholera vaccination and, for people exposed to floodwater, doxycycline chemoprophylaxis against leptospirosis. Over the longer term, improved water infrastructure and latrine reconstruction are needed. For vector-borne diseases such as dengue and malaria, the authors highlight early mosquito control: removing breeding sites and distributing insecticide-treated bed nets. To reduce the impact of outbreaks, preparedness is key: linking flood forecasts to disease surveillance and pre-positioning supplies enable a rapid response.