Sapovirus Outbreaks in Long-Term Care Facilities, Oregon and Minnesota, USA, 2002–2009

Sapovirus gives new meaning to the phrase “cradle to grave.” Historically, sapovirus has been associated with gastrointestinal illness in children living in group settings such as hospitals, shelters, or refugee camps. But now, sapovirus outbreaks are occurring among elderly residents of long-term care and similar facilities. These elderly residents are especially vulnerable to rapidly transmitted gastrointestinal viruses and serious complications. This virus has been making the rounds in long-term care facilities since 2002, and outbreaks started increasing in 2007. Sapovirus testing should be added to routine diagnostic workups for gastrointestinal infections, regardless of patient age group. Results can be used to develop prevention, control, and treatment guidelines, especially for vulnerable elderly populations.

Defi ning a sapovirus outbreak in this study as >1 sapovirus-positive fecal sample, 21 (23%) of the 93 norovirus-negative outbreaks were found to be caused by sapovirus. Adenovirus or norovirus were also identifi ed in 4 (19%) of the 21 sapovirus outbreaks ( Table 1). The unexpected norovirus fi nding is likely due to slight variations in testing methods between state public health laboratories and viral loads nearing the detection level of the RT-PCR.
Of 21 sapovirus outbreaks, LTCFs accounted for 12 (66%); grade schools for 2 (10%); and a prison, a large psychiatric hospital, a cruise ship, a restaurant, and a bed and breakfast for 5 (24%). During 2007, 10 outbreaks (48%) occurred; 14 outbreaks (67%) occurred during the colder months (November-March) of each observed year. Person-to-person transmission accounted for 18 (86%) of 21 outbreaks. On the basis of the outbreak setting, foodborne transmission was suspected, but not confi rmed, in 3 (14%) of 21 sapovirus outbreaks; food items were not implicated. Outbreaks involved 5-44 persons (median 34 persons) per outbreak and lasted 1-28 days (median 15 days) (  sapovirus GIV, and 1 (5%) by sapovirus GV (Table 1). The genogroup-specifi c differences between outbreak settings and between the proportions of vomiting, diarrhea, and fever were not statistically signifi cant. Seventy-three percent of sapovirus GIV outbreaks occurred in 2007. A representative sequence from each outbreak was placed in the phylogenic tree (Figure). Of 14 sapovirus outbreaks with >2 sapovirus-positive samples, sequences from 12 were identical within the outbreaks, and 2 had ≈2 different sequences (Figure).

Conclusions
In this study, the high (66%) proportion of sapovirus outbreaks in LTCFs among 21 outbreaks of previously unknown etiologies is likely to be an artifact of legally mandated outbreak reporting by health care facilities rather than the true distribution of sapovirus outbreaks in Oregon and Minnesota. Still, elderly residents of LTCFs are especially vulnerable to rapid transmission of viral enteric pathogens and serious complications from infection with these agents (12), and therefore merit the attention of public health.
Our data, together with a recent study in Canada (7), demonstrate that sapovirus has been circulating among the institutionalized elderly since at least 2002 and that sapovirus outbreaks increased in 2007 as part of a worldwide surge in gastroenteritis outbreaks (2,7,9). Before these retrospective studies, sapovirus infections among adults >65 years old had been reported as single cases at a low (3%) rate in 2002 (13) and as nosocomial outbreaks in 2010 and 2005 (8,14). In 2010, Svraka et al. reported an age distribution shift from younger to older persons (9).
Sapovirus outbreaks occurred in the same settings and had the same seasonal distribution as norovirus outbreaks (2,15). Our study adds clinical details to information provided by studies in Canada and Europe (7,9). The clinical profi le of sapovirus outbreaks in this study (49% vomiting, 88% diarrhea, and 23% fever, plus a median duration of 48 hours) approximates the criteria of Kaplan et al. (3), which are still used to evaluate norovirus outbreaks when laboratory resources are limited. We found, however, that sapovirus and norovirus outbreaks are clinically and epidemiologically similar enough to be indistinguishable without laboratory testing.
This study has at least 3 limitations. First, testing a convenience sample of fecal specimens from norovirusnegative outbreaks might have introduced selection bias, the impact of which is uncertain. Second, because outbreak reporting from institutions other than LTCFs is not legally mandated, outbreaks in these settings are underreported. Third, feces from norovirus-positive outbreaks were not assayed for sapovirus. Previously undetected norovirus GI and GII discovered among 21 sapovirus outbreaks indicates that outbreaks might have had >1 etiology. It is therefore likely that the number of sapovirus outbreaks was underestimated.
In summary, gastroenteritis outbreaks in LTCFs should be investigated by public health departments in conjunction with testing of fecal specimens. Public health laboratories should archive fecal samples from all gastroenteritis outbreaks until a cause is established. As in this study, testing with assays for sapovirus, astrovirus, adenovirus, and rotavirus, should be conducted when standard methods for norovirus and enteric bacterial pathogens fail to identify a causative agent.
In keeping with recent recommendations, at minimum, adding sapovirus to routine diagnostics of infections that occur in any setting and by any mode of transmission will establish etiologies of some norovirus-negative outbreaks and help defi ne the disease impact and clinical characteristics of sapovirus infections (9,10,13). These data can in turn be used to develop and evaluate sapovirus disease management guidelines and sapovirus outbreak prevention and control measures.