Study published analysing infectious disease risks following the October 2024 flash flood in Valencia

The massive flood caused by the weather phenomenon known as DANA that struck Valencia on 29 October 2024 was unprecedented in its devastation, catastrophic effects and potential impact on public health. The research team launched an initiative to assess the risks of individual infections and infectious epidemics in the extensive area affected. “This work has been led from the outset by the Unit of Health Parasitology of the University of Valencia, internationally recognised as an official collaborating centre of the World Health Organization and a global reference centre of the FAO/United Nations. The complexity of the infectious agents involved required a multidisciplinary approach, prompting close collaboration between different teams who responded promptly to this initiative. To this end, our unit is coordinating a joint effort with other expert groups”, explained María Dolores Bargues.The study was carried out in collaboration with the University Institute of Tropical Diseases and Public Health of the Canary Islands, part of the University of La Laguna, led by Jacob Lorenzo-Morales, and the MiniAging group of the INCLIVA Health Research Institute, led by Consuelo Borrás. Additionally, several teams from other Spanish centres are currently engaged in further research in the affected area, which will yield results to be published in the coming months.

WHO expert Santiago Mas-Coma described how the search for infectious agents was conducted using environmental samples of water, mud and soil from flooded areas, collected during the first three weeks after the disaster. The focus was primarily on affected core areas. The evolving scenario was analysed across the days prior to the catastrophe, the day of the cold front and the following weeks. The entire affected geography was mapped to trace the paths taken by water and mud flows and to understand the multidisciplinary circumstances related to short-, medium- and long-term risks of infection. The analyses and surveys enabled the identification of a 4x4 grid-like pattern, consisting of four independent watercourses — rivers and/or ravines — each comprising four distinct types of zones from inland to the sea: first, wild areas, followed by rural zones with agricultural fields and livestock farms, then urban areas, and finally the vast Albufera lake zone with its surrounding rice fields and the recreational and ecological strip between the lake and the beaches.

Mas-Coma explained that “to help follow the study’s progress, we have created an illustrative diagram showing how the analytical procedures were carried out. The surveys revealed a wide variety of infectious agents, with significantly higher concentrations found in the mud than in flood waters, which is both interesting and noteworthy. The environmental samples contained viruses, bacteria, parasitic protozoa, opportunistic free-living amoebae and helminths, as well as vector groups of various infectious diseases such as mosquitoes, phlebotomine sandflies (also known as midges or gnats) and freshwater snails”.

For each infectious agent detected, the article summarises the disease transmission characteristics, sources or routes for human infection, and pathogenicity. Potentially emerging vector-borne diseases were analysed, and it was confirmed that the microorganisms detected involve various transmission types — from direct to zoonotic — and different routes of infection, including oral, transcutaneous and through wounds. Their biological cycles range from short to long and transmission may be permanent or seasonal. Faecal contamination was shown to be high, originating from both human and animal sources, with potential reservoirs such as sheep, goats, pigs, horses, dogs and cats. It is particularly noteworthy that all the microorganisms detected have the capacity to cause disease in humans, with varying degrees of pathogenicity depending on the agent involved.

Consuelo Borrás referred to the significant importance of the initiative in relation to the impact of the cold front on the elderly. The consequences for this vulnerable segment of the affected population have been enormous — both on a personal and family level as well as economically, psychologically and emotionally. Many elderly residents lived on ground floors in the central streets of the flooded towns, where damage and losses were most severe. This initiative also includes an experimental study to analyse how the pathogens detected may affect older individuals.

The vast flooded area calls for a multidisciplinary One Health approach. Many lessons must be learned, both by professionals across the disciplines involved and by government authorities. The great heterogeneity, complexity and far-reaching health consequences of the disaster have been thoroughly analysed to develop a transferable baseline model that can be extrapolated to deal with similar catastrophic climate events in the future — particularly those expected to occur according to current climate change trends, both throughout the Mediterranean and elsewhere.

Santiago Mas-Coma concluded by stressing: “It is important to bear in mind that studies from other countries and continents affected by water-related disasters have shown that the greatest risks of individual infections and infectious outbreaks or epidemics do not occur in the short term, i.e., in the weeks immediately following the catastrophe, but rather in the medium to long term, after several months or even years. That is why surveys in the affected area must be planned over the long term, for at least three years”.

The study received funding from the University of Valencia — specifically through the Office of the Vice-Rector for Research —, the CIBER network for Infectious Diseases of the Spanish Ministry of Health (with five research groups coordinated by Professor María Dolores Bargues), a PROMETEO Project of the Generalitat Valenciana, as well as other sources such as European funds from the Marie Skłodowska-Curie Actions Programme (Horizon Europe) of the European Commission, and from the Island Council of Tenerife.

The Rector concluded the press conference by highlighting the University of Valencia’s commitment to supporting the efforts of its experts in the recovery of the area affected by this unprecedented catastrophic event.

Published article:

Mas-Coma S., Artigas P., Cuervo P.F., De Elías-Escribano A., Fantozzi M.C., Colangeli G., Córdoba A., Marquez-Guzman D.J., Mas-Bargues C., Borrás C., Pérez-Pérez P., Bethencourt-Estrella C.J, Rodríguez-Expósito R.L., Peña-Prunell M.D., Chao-Pellicer J., García-Pérez O., Domínguez de Barros A.T., García-Ramos A., Sirvent-Blanco C., Gajeta-Arenas M., Córdoba-Lanús A.E., Piñero J.E., Valero M.A., Lorenzo-Morales J., Bargues M.D., 2025.- Infectious disease risk after the October 2024 flash flood in Valencia, Spain: Disaster evolution, strategic scenario analysis, and extrapolative baseline for a One Health assessment. One Health, Volume 21, Article No. 101093, https://doi.org/10.1016/j.onehlt.2025.101093 (24 pp. + 16 pp. in Supplements 1-4; 1 Table, 1 Schema, 1 Graph, 5 Maps, 116 Figures, 197 References).