April 11, 2012 — In a collaborative study between the Oregon Public Health Division, the Minnesota Department of Health, and the US Centers for Disease Control and Prevention, Lore E. Lee, MPH, from the Oregon Public Health Division in Portland, and colleagues found that gastroenteritis in long-term care facilities (LTCFs) may be caused by sapovirus, an organism not routinely tested. The findings, published online April 11 in Emerging Infectious Diseases, underscore the need for multiorganism testing during gastroenteritis outbreaks, as the exact etiology of the outbreak can be difficult to discern on the basis of clinical profile alone.
Using data from the Oregon and Minnesota public health departments, the researchers investigated 2161 gastroenteritis outbreaks between 2002 through 2009. Of these, 142 outbreaks (7%) were found to be norovirus-negative, and 93 of these were further tested for other gastrointestinal viruses including sapovirus, astrovirus, adenovirus, and rotavirus. Sapovirus was identified in 21 outbreaks (23%), with 66% of these occurring in LTCFs. Close to half of these cases occurred in 2007 alone.
Using data from 14 of the 21 outbreaks, for which clinical data on 141 to 269 patients were available, symptoms appeared to last from 24 to 105 hours (median duration, 48 hours), and the clinical profile included vomiting (49%), diarrhea (88%), and fever (23%).."Four (19%) of 21 sapovirus outbreaks were caused by sapovirus [genogroup I (GI)], 1 (5%) by sapovirus GII, 15 (71%) by sapovirus GIV, and 1 (5%) by sapovirus GV," the authors report. The clinical symptoms and outbreak settings were not statistically different among genogroups.
The researchers note that the clinical findings are similar to the criteria used to evaluate norovirus outbreaks in settings where laboratory resources are limited. "We found, however, that sapovirus and norovirus outbreaks are clinically and epidemiologically similar enough to be indistinguishable without laboratory testing," write the authors.
The high proportion of sapovirus outbreaks among LTCFs may not represent a true distribution of sapovirus outbreaks in Oregon and Minnesota, discuss the authors. Rather, these findings may be artifactual as a result of legally mandated outbreak reporting by healthcare facilities.
The authors note that the spike in sapovirus gastroenteritis cases in 2007 may have been part of a worldwide surge in gastroenteritis outbreaks that year; however, sapovirus infections among patients aged 65 years or older do appear to have been trending upward since 2002.
The researchers acknowledge study limitations such as selection bias, possible underreporting from institutions where outbreak reporting is not legally mandated, and the fact that norovirus-positive samples were not tested for sapovirus, which may have led to sapovirus outbreaks being underestimated.
"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 define the disease impact and clinical characteristics of sapovirus infections," conclude the authors. "These data can in turn be used to develop and evaluate sapovirus disease management guidelines and sapovirus outbreak prevention and control measures."
The authors have disclosed no relevant financial relationships.
Emerg Infect Dis. Published online April 11, 2012. Full text
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