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González-Fernández A, Symonds EM, Gallard-Gongora JF, Mull B, Lukasik JO, Rivera Navarro P, Badilla Aguilar A, Peraud J, Mora Alvarado D, Cantor A, Breitbart M, Cairns MR, Harwood VJ. Risk of Gastroenteritis from Swimming at a Wastewater-Impacted Tropical Beach Varies across Localized Scales. Appl Environ Microbiol 2023; 89:e0103322. [PMID: 36847564 PMCID: PMC10057883 DOI: 10.1128/aem.01033-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Accepted: 01/21/2023] [Indexed: 03/01/2023] Open
Abstract
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.
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Affiliation(s)
| | - Erin M. Symonds
- College of Marine Science, University of South Florida, Saint Petersburg, Florida, USA
- Department of Anthropology, Southern Methodist University, Dallas, Texas, USA
| | | | - Bonnie Mull
- BCS Laboratories, Inc., Gainesville, Florida, USA
| | | | - Pablo Rivera Navarro
- Laboratorio Nacional de Aguas, Instituto Costarricense de Acueductos y Alcantarillados, Tres Ríos, Cartago, Costa Rica
| | - Andrei Badilla Aguilar
- Laboratorio Nacional de Aguas, Instituto Costarricense de Acueductos y Alcantarillados, Tres Ríos, Cartago, Costa Rica
| | - Jayme Peraud
- Department of Integrative Biology, University of South Florida, Tampa, Florida, USA
| | - Darner Mora Alvarado
- Laboratorio Nacional de Aguas, Instituto Costarricense de Acueductos y Alcantarillados, Tres Ríos, Cartago, Costa Rica
| | - Allison Cantor
- Department of Anthropology, Southern Methodist University, Dallas, Texas, USA
| | - Mya Breitbart
- College of Marine Science, University of South Florida, Saint Petersburg, Florida, USA
| | - Maryann R. Cairns
- Department of Anthropology, Southern Methodist University, Dallas, Texas, USA
| | - Valerie J. Harwood
- Department of Integrative Biology, University of South Florida, Tampa, Florida, USA
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