Risk of Gastroenteritis from Swimming at a Wastewater-Impacted Tropical Beach Varies across Localized Scales.

Population growth and changing climate are expected to increase human exposure to pathogens in tropical coastal waters. We examined microbiological water quality in three rivers within 2.3 km of each other that impact a Costa Rican beach and in the ocean outside their plumes during the rainy and dry seasons. We performed quantitative microbial risk assessment (QMRA) to predict the risk of gastroenteritis associated with swimming and the amount of pathogen reduction needed to achieve safe conditions. Recreational water quality criteria based on enterococci were exceeded in >90% of river samples but in only 13% of ocean samples. Multivariate analysis grouped microbial observations by subwatershed and season in river samples but only by subwatershed in the ocean. The modeled median risk from all pathogens in river samples was between 0.345 and 0.577, 10-fold above the U.S. Environmental Protection Agency (U.S. EPA) benchmark of 0.036 (36 illnesses/1,000 swimmers). Norovirus genogroup I (NoVGI) contributed most to risk, but adenoviruses raised risk above the threshold in the two most urban subwatersheds. The risk was greater in the dry compared to the rainy season, due largely to the greater frequency of NoVGI detection (100% versus 41%). Viral log10 reduction needed to ensure safe swimming conditions varied by subwatershed and season and was greatest in the dry season (3.8 to 4.1 dry; 2.7 to 3.2 rainy). QMRA that accounts for seasonal and local variability of water quality contributes to understanding the complex influences of hydrology, land use, and environment on human health risk in tropical coastal areas and can contribute to improved beach management. IMPORTANCE This holistic investigation of sanitary water quality at a Costa Rican beach assessed microbial source tracking (MST) marker genes, pathogens, and indicators of sewage. Such studies are still rare in tropical climates. Quantitative microbial risk assessment (QMRA) found that rivers impacting the beach consistently exceeded the U.S. EPA risk threshold for gastroenteritis of 36/1,000 swimmers. The study improves upon many QMRA studies by measuring specific pathogens, rather than relying on surrogates (indicator organisms or MST markers) or estimating pathogen concentrations from the literature. By analyzing microbial levels and estimating the risk of gastrointestinal illness in each river, we were able to discern differences in pathogen levels and human health risks even though all rivers were highly polluted by wastewater and were located less than 2.5 km from one another. This variability on a localized scale has not, to our knowledge, previously been demonstrated.

Assessing the defecation practices of unsheltered individuals and their contributions to microbial water quality in an arid, urban watershed.

Outdoor defecation by people experiencing homelessness is frequently perceived as a potentially large source of human fecal pollution and a significant source of health risk in urban waterbodies with recreational contact. The goal of this study was to count the number of people experiencing homelessness and quantifies their sanitation habits in an urban river corridor setting, then use this information for estimating human fecal pollutant loading on a watershed scale. Two types of census counts were conducted including periodic point-in-time counts over six years and weekly counts of encampments. While the population census varied from count-to-count, the range of population estimates in the river corridor varied from 109 to 349 individuals during the six-year span, which mirrored the weekly counts of encampments. A face-to-face survey of people experiencing homelessness assessed the sanitation habits of the unsheltered population (N = 63), including outdoor defecation frequency and containment practices. Overall, 95 % of survey respondents reported defecating outdoors; 36 % practiced outdoor defecation between 4 and 7 days/week and 27 % practiced outdoor defecation <1 day/week. Of those that did practice outdoor defecation, 75 % contained their feces in a bucket or bag, thereby limiting fecal material contributions to the river; 6.7 % reported defecating on low ground near the river that could wash off when flood waters rise during a storm event. Only a single survey respondent reported defecating directly into the river. Based on literature values for average HF183 output for an adult human, and the average rainfall in the urban watershed, the total watershed contribution of HF183 averaged 1.2 × 1010 gene copies per storm event (95 % CI: 0.9 × 1010-1.6 × 1010) along the 41 km stretch of river in this study. This human fecal loading estimate is at least two orders of magnitude less than cumulative HF183 loading from all human sources measured at the bottom of the watershed.

The relationship between environmental parameters and microbial water quality at two Costa Rican beaches from 2002 to 2017.

Environmental conditions influence fecal indicator bacteria (FIB) levels, which are routinely used to characterize recreational water quality. This study examined 15 years of environmental and FIB data at Puntarenas and Jacó beach, Costa Rica. FIB relationships with sea level, wave height, precipitation, direct normal irradiance (DNI), wind, and turbidity were analyzed. Pearson's correlations identified lags between 24 and 96 h among environmental parameters and FIB. Multiple linear regression models composed of environmental parameters explained 24% and 27% of fecal coliforms and enterococci variability in Jacó, respectively. Puntarenas's models explained 17-26% of fecal coliforms and 12-18% enterococci variability. Precipitation, sea level anomalies, and wave height most frequently explained FIB variability. Hypothesis testing often identified significant differences in precipitation, wave height, daily sea level anomalies, and maximum sea level 24 h prior between days with and without FIB threshold exceedance. Unexpected FIB interactions with DNI, sea level, and turbidity highlight the importance of future investigations.

Relationships among microbial indicators of fecal pollution, microbial source tracking markers, and pathogens in Costa Rican coastal waters.

Tropical coastal waters are understudied, despite their ecological and economic importance. They also reflect projected climate change scenarios for other climate zones, e.g., increased rainfall and water temperatures. We conducted an exploratory microbial water quality study at a tropical beach influenced by sewage-contaminated rivers, and tested the hypothesis that fecal microorganisms (fecal coliforms, enterococci, Clostridium perfringens, somatic and male-specific coliphages, pepper mild mottle virus (PMMoV), Bacteroides HF183, norovirus genogroup I (NoVGI), Salmonella, Cryptosporidium and Giardia) would vary by season and tidal stage. Most microorganisms' concentrations were greater in the rainy season; however, NoVGI was only detected in the dry season and Cryptosporidium was the only pathogen most frequently detected in rainy season. Fecal indicator bacteria (FIB) levels exceeded recreational water quality criteria standards in >85% of river samples and in <50% of ocean samples, regardless of the FIB or regulatory criterion. Chronic sewage contamination was demonstrated by detection of HF183 and PMMoV in 100% of river samples, and in >89% of ocean samples. Giardia, Cryptosporidium, Salmonella, and NoVGI were frequently detected in rivers (39%, 39%, 26%, and 39% of samples, respectively), but infrequently in ocean water, particularly during the dry season. Multivariate analysis showed that C. perfringens, somatic coliphage, male-specific coliphage, and PMMoV were the subset of indicators that maximized the correlation with pathogens in the rivers. In the ocean, the best subset of indicators was enterococci, male-specific coliphage, and PMMoV. We also executed redudancy analyses on environmental parameters and microorganim concentrations, and found that rainfall best predicted microbial concentrations. The seasonal interplay of rainfall and pathogen prevalence undoubtedly influences beach users' health risks. Relationships are likely to be complex, with some risk factors increasing and others decreasing each season. Future use of multivariate approaches to better understand linkages among environmental conditions, microbial predictors (fecal indicators and MST markers), and pathogens will improve prediction of high-risk scenarios at recreational beaches.