An outbreak of acute gastroenteritis in a geriatric long-term-care facility: Combined application of epidemiological and molecular diagnostic methods

OBJECTIVE: To assess possible transmission modes of, and risk factors for, gastroenteritis associated with Norwalk-like viruses (NLVs) in a geriatric long-term-care facility. METHODS: During a prolonged outbreak of acute gastroenteritis, epidemiologi cal data on illness among residents and employees ere collected in conjunct ion with stool, vomitus, and environmental specimens for viral testing. NLV s were identified by electron microscopy in stool and vomitus specimens, an d further characterized by reverse-transcriptase polymerase chain reaction and nucleotide sequencing. Potential risk factors were examined through med ical-record review, personal interview, and a self-administered questionnai re sent to all employees. RESULTS: During the outbreak period, 52 (57%) of 91 residents and 34 (35%) of 90 employees developed acute gastroenteritis. Four case-residents were h ospitalized; three residents died at the facility shortly after onset of il lness. A point source was not identified; no association between food or wa ter consumption and gastroenteritis was identified. A single NLV strain gen etically related to Toronto virus was the only pathogen identified. Residen ts were at significantly higher risk of gastroenteritis if they were physic ally debilitated (relative risk. [RR], 3.5; 95% confidence interval [CI95], 1.0 12.9), as were employees exposed to residents with acute gastroenterit is (RR, 2.6; CI95, 1.1-6.5) or ill household members (RR, 2.3; CI95, 1.4-3. 6). Adherence to infection control measures among the nursing staff may hav e reduced the risk of gastroenteritis, but the reduction did not reach stat istical significance. CONCLUSIONS: In the absence of evidence for foodborne or waterborne transmi ssion, NLVs likely spread among residents and employees of a long-term-care facility through person-to-person or airborne droplet transmission. Rapid notification of local health officials, collection of clinical specimens, a nd institution of infection control measures are necessary if viral gastroe nteritis transmission is to be limited in institutional settings.