Microbial contamination—both bacterial and viral—of flood waters can cause great concern for use of previously flooded outdoor areas. Limited guidance exists on how to determine safe use of these areas. |
Flood waters commonly contain microbial contaminants and can directly affect public health. Increased levels of microbes in floodwaters increase the risk of human exposure and the likelihood for infection.
Floodwater contaminated by microbes may contain bacteria, viruses, protozoa, and helminthes . Exposure to these pathogens can cause illnesses ranging from mild gastritis to serious diseases such as dysentery, infectious hepatitis, and severe gastroenteritis . The concentration of microbes in flood water depends on how many and what kind of sources contributed to the contamination, the volume of contaminants released and the degree of their dispersion in the environment, and the level of treatment of the affected wastewater-treatment facilities before the flooding
Typically, it takes 2–3 months for enteric bacteria to significantly reduce in soil, with certain exceptions . Environmental factors including temperature, soil desiccation, pH, soil characteristics, and sunlight influence microbial survival and persistence . Microbial survival in soil and the resulting potential for human exposure is difficult to predict because of natural variability in those environmental factors and varying microbial susceptibilities. For example, shigella has survived in soil at room temperature for 9–12 days and cryptosporidium oocysts may survive in a moist environment for 60–180 days . Spore-forming microbes such as coccidioides, a fungus that exists in semiarid southwestern U.S. soil , and anthrax spores can survive in soil for many years . Aside from the microbe's ability to survive, availability is another important factor to consider. Certain microbes can sorb to stable soil, which may lengthen their survival time.
Due to different microbial responses to the environment, providing universal guidance is difficult. Intensity of sunlight exposure, level of soil desiccation, and ambient temperatures necessary to effectively kill all microbes within a specified time varies among microbes. Survival characteristics for microbes under specified conditions have been reported, however generalizing study results proves more difficult. The scientific inability to generalize microbial viability reinforces the need to implement a risk-assessment approach that considers all variables that could influence potential exposure.
Exposure risk to microbes in soil after a flood event can be influenced by emphasizing the importance of personal hygiene. Public health education efforts should include personal hygiene precautions and guidance. Education efforts should emphasize proper handwashing and adequate handwashing and drying supplies and equipment in public restrooms and at temporary handwashing facilities should be provided. Education efforts should include cautions to avoid standing water, areas saturated with floodwater, and areas with visible debris. Those areas create concern for microbial exposure and may also cause public safety concerns.
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