Summary Viruses are believed to be a significant cause of recreationally associated water‐borne disease. However, they have been difficult to document because of the wide variety of illnesses that they cause and the limitations in previous detection methods. Noroviruses are believed to be the single largest cause of outbreaks, which have been documented in the published literature 45% (n = 25), followed by adenovirus (24%), echovirus (18%), hepatitis A virus (7%) and coxsackieviruses (5%). Just under half of the outbreaks occurred in swimming pools (49%), while the second largest outbreak occurred in lakes or ponds (40%). The number of reported outbreaks associated with noroviruses has increased significantly in recent years probably because of better methods for virus detection. Inadequate disinfection was related to 69% (n = 18) of swimming pool outbreaks. A lack of required reporting and nonuniform water quality and chlorination/disinfection standards continues to contribute to water‐borne recreational disease outbreaks.

An outbreak of suspected norovirus gastroenteritis among three consecutive groups of houseboaters on a large recreational lake in Arizona was investigated to assess the role of fomite contamination, and to provide recommendations for prevention of future outbreaks. Interior boat surfaces were sampled for norovirus using transport swabs. Onboard toilet reservoirs were swabbed as a surrogate for stool samples from ill participants, since none were available, and onboard potable water supplies were sampled for norovirus. All samples were analyzed using RT-PCR with primers specific for human norovirus. Widespread fomite contamination was documented in the houseboats; 83% (5/6) of bathroom surface samples, 40% (2/5) of kitchen surface samples, and 100% (3/3) of doorknob samples were positive for the presence of norovirus. Samples of onboard potable water supplies were all negative. One of the participants on the first boating trip arrived already displaying symptoms of gastrointestinal illness prior to boarding the boat. This investigation demonstrates the potential role of widespread fomite contamination in outbreaks in confined spaces. To prevent or minimize future outbreaks in confined spaces, the adoption of practices such as surface disinfection and the utilization of methods to identify and exclude those with gastroenteritis from trips or activities in confined spaces, where others may become infected, are recommended.

Background Every year over 22 000 people raft the Colorado River through the Grand Canyon in Arizona. Since 1994, over 400 rafters in 6 separate outbreaks have become ill with norovirus while rafting this stretch of the river. Objectives To assess potential causes of these outbreaks, Colorado River water, water from nearby wastewater treatment plants, and a drinking water source were sampled and tested for norovirus and other water quality indicators. Methods Colorado River water was collected and sampled during the 2004 rafting season. Water from wastewater treatment plants near the Lee's Ferry launch site and drinking water from the Lee's Ferry launch site were also examined during the 2003 and 2004 rafting seasons. Stool samples from ill rafters and composite stool samples from onboard toilet-cans were tested for the presence of norovirus during the 2003 and 2004 outbreaks. Parameters examined included the following: norovirus by reverse transcriptase– polymerase chain reaction, coliforms, Escherichia coli, temperature, turbidity, and pH. Results No norovirus was detected in the Colorado River during the 2004 field sampling. Norovirus was detected in the Glen Canyon Dam Wastewater Treatment Plant on one occasion in 2004. Drinking water from the Lee's Ferry launch site was negative for norovirus in 2003, and Colorado River water from the Lee's Ferry launch site was negative for norovirus in 2004. In 2003, 3 of 10 stool samples from ill rafters or onboard toilet-cans were positive for norovirus. Neither of 2 stool samples collected in 2004 was positive for norovirus. Conclusions Colorado River water tested during nonoutbreak periods was negative for norovirus, indicating that there is not an ongoing high level of norovirus contamination in the river. No source or sources of contamination could be identified from the testing. Potential sources of norovirus outbreaks among rafters include drinking contaminated river water, consuming contaminated foodstuff, rafter importation of the virus and subsequent person-to-person spread, and contaminated fomites, campsites, or equipment. It is likely outbreaks are the result of more than one source of norovirus, and the exact source remains unknown for several outbreaks.

The tested unit complied with the criteria guidelines for virus removal under the US Environmental Protection Agency's "Guide Standard and Protocol for Testing of Microbiological Water Purifiers."