Quantification of Human Health Risks in Longitudinal Studies from Multimedia Exposure Pathways

Probabilistic modeling is a powerful tool in the estimation of public health risks associated with the presence of pathogenic microorganisms in surface waters. Three quantitative microbial risk assessment studies were performed to evaluate (1) viral risks associated with water-based recreational exposures in a watershed in southern California using three scenarios: adults by primary contact, children by primary contact, and secondary contact regardless of age; (2) the risks from accidental ingestion of recreational water associated with protozoal pollution in surface waters in Salta City, Argentina; and (3) the human health risks associated with the nematode Ascaris lumbricoides in surface water in Salta, Argentina arising from incidental recreational ingestion of contaminated surface water, consumption of raw produce irrigated with contaminated surface water and incidental ingestion of irrigation spray by vegetable growers using contaminated water for irrigation.;In the first study, a site-specific quantitative microbial risk assessment (QMRA) model to estimate the adenovirus disease burden associated with a multi-use coastal watershed in California in different scenarios was constructed. Children were at a higher risk compared to both adults and secondary contact exposure, with an individual illness risk per exposure event (IIR) of 3.5% from incidental ingestion of recreational waters assuming that 100% of adenovirus 40/41 genome detections in watershed samples were the infectious adenovirus 4 sub-type. In addition, the risk estimates changed appreciably when different statistical distributions were used to describe virus concentrations in ingested surface waters affected by fecal pollution from various sources (agricultural, industrial, combined sewer overflows etc.) in the watershed.;The second study was aimed at, on a theoretical level and utilizing QMRA to estimate infection risk at a site in Salta province of northern Argentina from water-borne intestinal protozoa in Arenales River due to primary and secondary recreational exposure. QMRA was used to quantify the recreational gastrointestinal infection risks in the community of Salta City from the parasitic protozoa Giardia lamblia and Entamoeba coli under different scenarios. The uncertainty in the dose-response parameter "r" for Giardia lamblia was also included in the uncertainty analysis using an empirical distribution for "r" based on likelihood confidence intervals where "r" is defined as the pathogen infectivity constant. The different simulations were run to evaluate single exposure, yearly, and seasonal (dry versus wet) risk of infection. Since many assumptions were used in the risk scenarios, calculations of both the "realistic" risks and worst-case scenario risks were also possible.;In the third study, probabilistic models were developed to quantify the human health risks associated with Ascaris lumbricoides detected in Arias-Arenales river in Salta, Argentina from three different exposure pathways, consisting of i) accidental ingestion of polluted surface water during recreation; ii) consumption of raw uncooked produce irrigated with polluted water, and iii) incidental ingestion of contaminated irrigation spray by farmers while irrigating with polluted water . The produce consumption related health risks were dependent on the type of ingested raw vegetable (cucumber, lettuce, cabbage, water-cress, and broccoli) and the results indicated that the annual risk in the community was highest for water-cress consumed 100 g/day and lowest for cucumber consumed 28 g/day, each produce consumed 7 times per week on average, assuming that 100% of detected Ascaris eggs detected in polluted water used to irrigate these vegetables were viable and became infectious once attached to produce. (Abstract shortened by UMI.).