Among the reported outbreaks, 70.9 percent were water-borne diseases, 2.9 percent water-based, 12.2 percent water-related, 6.8 percent water-washed, and 7.3 percent water-dispersed. Almost half were caused by bacteria, with nearly 40 percent caused by viruses and the rest by parasites.

The analysis also showed that fewer water-washed diseases occurred in places with larger bodies of surface water, and that areas with higher average annual rainfall had fewer outbreaks of water-borne and water-related diseases.

“No single factor can explain this distribution,” Liang said. “And for different categories of diseases, the impact of those factors varies. This is the first time we’ve had large-scale proof of that.

“At this point, we’ve identified all of the reported outbreaks, but not every socio-environmental factor that influenced them.”

The model predicts that Western Europe, Central Africa and Northern India are at higher risk for water-borne diseases, especially E. coli diarrhea, and that the risk in Europe is primarily driven by water-carried diseases that tend to occur in recreational areas. Western Europe, North Africa and Latin America tend to be at higher risk for water-washed diseases, particularly viral conjunctivitis. Risks associated with water-based diseases, especially schistosomiasis, were highest in east Brazil, Northwest and Central Africa and southeast of China.

Even with all of the data available, the researchers suggest that their database and map represent just a fraction of the actual outbreaks that have occurred because the under-reporting of these diseases is a common problem, especially in the developing world.

They also were surprised to find that economic status did not appear to influence risk for water-associated disease outbreaks, at least on a global scale. “When we look specifically at an area on a smaller scale, we might find something different,” Liang said.

Liang and colleagues already have begun to take a closer look at two regions, Africa and Asia, to examine environmental and economic issues that are most likely to influence risks for water-associated infectious disease outbreaks on those continents.

This work is supported in part by the National Institutes of Health and by two Ohio State University programs: Public Health Preparedness for Infectious Diseases and Climate, Water and Carbon.

Co-authors, all from Ohio State, include first author Kun Yang and Bo Lu of the College of Public Health (Yang is now with the Jiangsu Institute of Parasitic Diseases in China); Jeffrey LeJeune of the Ohio Agricultural Research and Development Center and the College of Veterinary Medicine; and Doug Alsdorf and C.K. Shum of the School of Earth Sciences.

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Source: Ohio State University