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Hospitalization risk persists for up to 210 days after floods for ten health conditions
Research in over 700 communities shows that people exposed to flooding suffer longer-term impacts from all kinds of diseases; diabetes posed the highest hospitalization risk
Operação de resgate durante enchentes no Rio Grande do Sul, Brasil, em maio de 2024, considerada a maior catástrofe climática da história do Estado – Foto: Ministério da Defesa – Operação Taquari 2/Wikimedia Commons
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An international team of researchers investigated the long-term public health impacts of floods and inundations. Scientists analyzed daily hospitalization counts between 2000 and 2019 in 747 cities and communities in Australia, Brazil, Canada, Chile, New Zealand, Taiwan, Thailand, and Vietnam. According to the study, hospitalization risks increased and persisted for up to 210 days after flood exposure for as many as ten specific causes.
Beyond direct consequences of contact with floodwaters, such as drowning, electrocution, and hypothermia, the study calculated the Cumulative Relative Risk (CRR) for ten different conditions and diseases in populations exposed to heavy rainfall events. In locations affected by floods, the overall disease incidence risk increased by 26%.
“These are delayed-onset diseases, because the rain ends, but the problem doesn’t. First come the fevers: leptospirosis, diarrhea, hepatitis. Then you find yourself in a place where you’ve lost everything. At first, you just want to survive, but then you realize that everything you built is gone. That doesn’t do the heart any good, it brings stress, sadness, depression, and alters our biology,” says Paulo Saldiva, pathologist and professor at the USP Medical School (FM), to Jornal da USP.
Saldiva co-authored the research published in Nature Water. “There are people who know how to crunch numbers, people who know how to build statistical models and gather huge databases. I’m the old-timer doctor who tries to explain why it all happens,” he jokes.
Paulo Saldiva - Photo: Marcos Santos/USP Imagens
To calculate the Cumulative Relative Risk (CRR)—a measure used to assess the impact of flood exposure on hospitalization risk over a specific period—the group considered the potential delayed effects of flood exposure in long-term associations with hospitalizations.
Yuming Guo, Monash University - Photo: Michelle McFarlane/Monash University
According to the study, 210 days after flood exposure, the CRR was highest for diabetes (61%), kidney diseases (40%), injuries and cardiovascular diseases (35%), and cancer and nervous system disorders (34%). Risks were also identified for respiratory and digestive diseases (30%), infectious diseases (26%), and mental disorders (11%).
Overall, we found that the risk of hospitalization, both for all health conditions combined and for specific ones, increased after flood exposure for up to 210 days, except for hospitalizations due to infectious diseases and mental disorders, for which the increases persisted for around 90 and 150 days, respectively,” explains Yuming Guo, the first author of the article, to Jornal da USP. “Due to climate change, floods will occur more frequently, with greater duration and intensity, as a result of more frequent extreme precipitation events and rising sea levels caused by global warming,” he adds.
Most affected countries
According to Yuming Guo, professor of Global Environmental Health and Biostatistics at Monash University, Australia, the countries were selected through a collaborative network of researchers, thereby facilitating access to data. The cities were chosen based on rainfall and health data availability for the same location.
“In general, we don’t have meteorological stations and rainfall measurements in every city in Brazil, for example. And often, rainfall may be intense in one neighborhood and lighter in another. Note that we only selected heavy rainfall events,” says Micheline Coelho, one of the study’s authors. She is a researcher at Monash University, a physician, mathematician, and meteorologist. Along with Saldiva, she coordinates the Brazilian team of the Multi-Country Multi-City (MCC) project, an international research network on climate impacts in urban health.
Micheline Coelho is a researcher at FM and Monash University - Photo: Personal Archive
Micheline highlights that Thailand, Vietnam, Brazil, and Australia were the countries most affected by heavy rainfall and the extended consequences of flooding: communities in northeastern New South Wales, along the Amazon River, southern Brazil, the Mekong River Basin in Vietnam, and southern Thailand experienced flooding more frequently. However, Brazil, Canada, and Taiwan showed the largest increases in hospitalization risks for all causes and most specific causes after floods.
“In Brazil, rain has changed its ZIP code. It hit regions that didn’t use to face this; take Rio Grande do Sul, for instance,” says Saldiva. According to the professor, Brazil’s greatest ongoing challenge remains sanitation and drainage, especially in chronic situations like Jardim Pantanal in São Paulo.
“Urban drainage has lagged behind the public health system. Brazil has invested more in organizing healthcare, with national programs integrating various areas of the state. We inherited a public health surveillance system dating back to yellow fever in the 19th century. In such scenarios, we’re more prepared to support civil defense and set up field hospitals, but health doesn’t regulate drainage. That depends on intersectoral actions, and that’s a weakness in Brazil"
Long-lasting effects
One of the researchers’ hypotheses to explain the floods’ prolonged health effects is contamination of the water supply system, which can increase the risk of digestive diseases and help spread infectious diseases. Floods also create environments conducive to the proliferation of fungi, bacteria, and vectors like mosquitoes and rats.
Although overcrowding in health services was considered a worsening factor for health post-floods, the study found an unexpected result: more severe floods presented lower hospitalization risks. “This is an unusual finding, as more severe floods usually have a greater impact on the environment and infrastructure,” the researchers stated in the article.
One possible reason is that more severe floods had a greater impact on the capacity of healthcare and transportation systems, preventing many patients from even being admitted or leading to deaths before hospitalization. Another possible explanation is the evacuation process itself, with people being admitted or hospitalized in locations other than the community where the flooding originally occurred.
“Each region has its own problem: in one, it may be sewage, and in another, it may be landslides and housing. So, you need to make fine adjustments, and for that, you need to talk to local authorities. In our work, everyone is a scientist. This needs to be brought to the management level,” says Saldiva.
The article Hospitalization risks associated with floods in a multi-country study is available online and can be read here.
For more information: yuming.guo@monash.edu, with Yuming Guo; coelhomicheline@gmail.com, with Micheline Coelho, and pepino@usp.br, with Paulo Saldiva.
*Intern under the supervision of Moisés Dorado
English version: Nexus Traduções, edited by Denis Pacheco
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A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.