You are here:
Asymptomatic norovirus infection associated with swimming at a tropical beach: A prospective cohort study
Citation:
Wade, Tim, S. Augustine, S. Griffin, E. Sams, K. Oshima, A. Egorov, K. Simmons, T. Eason, AND A. Dufour. Asymptomatic norovirus infection associated with swimming at a tropical beach: A prospective cohort study. PLOS ONE . Public Library of Science, San Francisco, CA, 13(3):e0195056, (2018).
Impact/Purpose:
We used a novel, salivary immunoassay to determine whether norovirus infection was associated with swimming at a tropical marine beach in Puerto Rico. Higher rates of infection were observed in swimmers compared to non-swimmers, although most infections were asymptomatic. This study provides evidence that asymptomatic norovirus infections may be transmitted via swimming in the absence of an outbreak and provides insight into the transmission dynamics of norovirus infection. It is expected that these findings may be used to help shape and inform EPA regulations for recreational waters.
Description:
Background Swimming in fecally-contaminated waterbodies can result in gastrointestinal infections. However, the pathogenic microorganisms responsible are not well understood because sporadic cases of illness are not reported completely, exposure information is often not collected, and epidemiology studies rely on self-reported symptoms. Noroviruses are considered a likely cause because they are found in high densities in sewage, resistant to wastewater treatment and survive in the environment. In this study, saliva samples were collected from subjects at a beach in Puerto Rico and tested for evidence of norovirus-specific IgG responses as an indicator of incident norovirus infection. Methods Saliva samples were collected from 1298 participants using an oral swab. Samples were collected on the day of the visit (S1); after 10-12 days (S2); and after three weeks (S3). Saliva was tested for IgG responses to GI.1 and GII.4 noroviruses using a microsphere based multiplex salivary immunoassay. Immunoconversion was defined as a four-fold increase in median fluorescence intensity (MFI) from S1 to S2 with the S3 sample at least three times above the S1 MFI. Results Thirty-four subjects (2.6%) immunoconverted to GI.1 or GII.4 norovirus. Swimmers who immersed their head in water had a higher rate of immunoconversion (3.4%), compared to beach goers who did not (0.4%, Odds Ratio: 5.07, 95% Confidence Interval:1.48-17.00). Immunoconversion was not associated with gastrointestinal symptoms. Conclusions This is the first study to demonstrate an association between swimming at a beach impacted by fecal contamination and asymptomatic norovirus infection. The findings implicate recreational water as an important transmission pathway for norovirus infection.
