May 9, 2012 (CIDRAP News) – The role of fomites in norovirus outbreaks has been difficult to pin down, but Oregon health officials today described how a reusable grocery bag left in a bathroom where a patient was sick spread the virus to members of a girls' soccer team and their chaperones.
The outbreak came to the attention of the Oregon Public Health Division when they learned that a group of girls and their chaperones got sick after participating in a soccer tournament in King County, Wash. Officials noted that the outbreak was unusual, because the index patient had no contact with her teammates after she got sick, and the public health investigation didn't find links to other illnesses at the team's hotel, the tournament, or the restaurants where they had dined.
Reporting their findings today in the Journal of Infectious Diseases were Kimberly Repp, PhD, MPH, from the department of public health and preventive medicine at Oregon Health and Science University, and William Keene, PhD, MPH, senior epidemiologist with the Oregon Public Health Division in Portland.
The initial case-patient started feeling ill in the evening and went to a chaperone's room, where the girl started vomiting and having diarrhea in the bathroom after midnight. The next morning the girl was driven home to Oregon by the chaperone, who later became ill.
Neither of the two had rejoined the group the following day, which was Sunday. Other group members, however, got sick on Tuesday after they had returned home. In total, 9 of the 21-member team delegation got sick.
During the investigation, interviews with the girls and chaperones revealed that eating sealed packaged cookies during a Sunday lunch was significantly associated with illness. Seven of 11 members at the lunch got sick. The cookies and other lunch supplies had been bought in Oregon and stored at the hotel.
Upon further questioning, group members told public health officials that the items had been stored in a reusable open-top grocery bag that had been stored in the hotel bathroom where the first girl repeatedly vomited and had diarrhea. The girl said she never touched or handled the grocery bag.
Hours after the sick girl had departed for home, the grocery bag was taken to another hotel room, where its contents—packaged cookies, chips, and grapes—were eaten for lunch.
Three stool specimens from sick patients were positive for norovirus genotype GII.2. Two of 10 swabs taken from the grocery bag 2 weeks after the team meal was consumed were positive for genogroup GII norovirus, though they were insufficient for sequencing.
Looking back at the investigation, Repp and Keene said incubation time suggested most members of the group were exposed during the Sunday lunch, but the first girl's illness was puzzling, because she didn't have direct contact with teammates or the food after she started vomiting and having diarrhea. "Only when we learned about the bag in the bathroom did a coherent story emerge," they wrote.
Aerosolized virus in the hotel bathroom probably settled on the grocery bag and its contents, and touching the bag and consuming its contents appeared to facilitate transmission. "Incidentally, this also illustrates one of the less obvious hazards of reusable grocery bags," the authors noted.
The event confirms the potential for aerosol contamination of fomites in norovirus outbreaks, which has been suspected, but difficult to prove in other outbreak settings such as cruise ships and nursing homes, they wrote.
A take-home message from the event is, of course, not storing food in bathrooms and where aerosol exposure may have occurred. It's important to disinfect not only exposed surfaces, but objects that may have been in the area, Repp and Keene concluded.
In an editorial that accompanied the report, Aron Hall, DVM, MSPH, from the division of viral diseases at the Center for Disease Control and Prevention's (CDC's) National Center for Immunization and Respiratory Diseases, wrote that taking on the overwhelming burden of norovirus infections requires understanding the complex ways the viruses spread, especially given their strikingly low infectious dose and how high the viral load is in infected patients' vomit and feces.
He wrote that Repp and Keene's report is a fascinating example of how unique situations can lead to a norovirus outbreak. "The chain of events in this outbreak demonstrates how this tenacious virus finds a way to move from host to host, even when those hosts have no direct contact with one another," Hall added.
The report shows that not only can noroviruses be aerosolized and dispersed onto fomites, exposure to contaminated fomites can lead to disease, Hall said. It also emphasized the importance of environmental sampling and considering fomites as potential exposures in outbreak investigations, though he cautioned that results should be interpreted with caution, because diagnostic techniques detect viral RNA, which doesn't always indicate presence of infectious virus.
Repp KK, Keene WE. A point-source norovirus outbreak caused by exposure to fomites. J Infect Dis 2012 Jun;205(11):1639-41 [Abstract]
Hall AJ. Noroviruses: the perfect human pathogens? (Editorial) J Infect Dis 2012 Jun;205(11):1622-4 [Extract]
May 9 Infectious Diseases Society of America press release