Risk assessment of selected opportunistic pathogens in drinking water.

Water as a route of opportunistic bacterial disease transmission has not been well established. The use of epidemiological evidence linking drinking water bacterial contamination to health effects in a population is lacking and very costly to obtain. Also, the significance of exposure to low-level contamination is difficult to determine epidemiologically. This makes it difficult to estimate the impact on a community. The use of risk assessment approach allows an understanding of low-level exposure; and to define it in a more quantitative fashion. Microbial risk assessment was employed to determine the risks associated with exposure to selected opportunistic bacterial pathogens (Aeromonas hydrophila and Pseudomonas aeruginosa) present in drinking water from various sources. An extensive analysis was conducted on drinking water obtained from various sources including point-of-use (POU)-treated water, tap water with POUconnection, tap water, bottled water, and water from vending machines and storage tanks. Enumerated bacteria included: A. hydrophila, heterotrophic plate count (HPC) bacteria, Mycobacteriuni spp., Plesiomonas shigelloides, P. aeruginosa, and total and fecal coliforms. It was found that opportunistic pathogens were present in small numbers in drinking water. Neither fecal coliforms nor P. shigelloides were found in the drinking water samples. The annual risks of colonization based on the consumption of 2L/day/person for drinking water were determined to be as high as 7.9x10⁻⁵ and 9.9x10⁻⁴ for A. hydrophila and P. aeruginosa, respectively at exposure levels ranging from 90 to 10 CFliimL. respectively. The results obtained indicates that the risk of colonization is a transient process, and the probability of infection may be very but could result in the most vulnerable (very young, the elderly and immunocompromised). More studies are needed on the occurrence of opportunistic pathogens in drinking water from various sources and animal andjor human feeding studies to better define dose-response in both healthy and immunocomprimised individuals. There is no doubt that the greatest need for microbial risk assessment is the occurrence data. Therefore, national surveys in drinking water from various sources will help in the developing of microbial risk assessment for opportunistic bacterial pathogens. The use of conventional methods as well as molecular approaches are recommended in order to obtain a more accurate identification of waterborne bacterial pathogens.hydrology collectio