From the CDC website at http://www.cdc.gov/nceh/drought/infectious.htm
Increases in infectious disease can be a direct consequence of drought.
- Viruses, protozoa, and bacteria can pollute both groundwater and surface water when rainfall decreases. People who get their drinking water from private wells may be at higher risk for drought-related infectious disease. Other groups also at increased risk include those who have underlying chronic conditions.
- Acute respiratory and gastrointestinal illnesses are more easily spread from person to person when hand washing is compromised by a perceived or real lack of available water. During water shortages, the risk for infectious disease increases when hygiene is not maintained.
- E. coli and Salmonella are examples of bacteria that during drought can more readily contaminate food and cause infectious disease. Food can serve as a vehicle for disease transmission during a drought because water shortages can cause farmers to use recycled water to irrigate their fields and process the food they grow. When used to grow crops, improperly treated water can cause a host of infectious diseases (such as those caused by toxin-producing E. coli and Salmonella), which can be life-threatening for people in high-risk groups. In addition, the likelihood of surface runoff, which can occur when rain fails to penetrate the dry and compacted soil that often accompanies drought, can cause the inadvertent contamination of crops.
- Other infectious disease threats arise when drought leads to the contamination of surface waters and other types of water that are used for recreational purposes. When temperatures rise and rainfall declines, people are more likely to participate in water-related recreation. Persons exposed to contaminated recreational waters are more likely to become infected with pathogens that thrive in the shallow warm waters that exist during drought conditions.