Epidemiology and Infection

Rota- and noroviruses

Norovirus outbreak associated with undercooked oysters and secondary household transmission

E. ALFANO-SOBSEYa1 c1, D. SWEATa2, A. HALLa3, F. BREEDLOVEa4, R. RODRIGUEZa5, S. GREENEa2, A. PIERCEa4, M. SOBSEYa5, M. DAVIESa2 and S. L. LEDFORDa1

a1 Wake County Human Services, Raleigh, NC, USA

a2 North Carolina Division of Public Health, Raleigh, NC, USA

a3 Centers for Disease Control and Prevention, Atlanta, GA, USA

a4 Wake County Department of Environmental Services, Raleigh, NC, USA

a5 University of North Carolina, Gillings School of Global Public Health, Chapel Hill, NC, USA

SUMMARY

During December 2009, over 200 individuals reported gastrointestinal symptoms after dining at a North Carolina restaurant. An outbreak investigation included a case-control study of restaurant patrons, a secondary household transmission study, environmental assessment of the restaurant facilities and operations, and laboratory analysis of stool and food samples. Illness was primarily associated with consumption of steamed oysters (odds ratio 12, 95% confidence interval 4·8–28) and 20% (8/41 households) reported secondary cases, with a secondary attack rate of 14% among the 70 susceptible household contacts. Norovirus RNA was detected in 3/5 stool specimens from ill patrons; sequencing of RT–PCR products from two of these specimens identified identical genogroup II genotype 12 sequences. Final cooked temperatures of the steamed oysters were generally inadequate to inactivate norovirus, ranging from 21°C to 74°C. Undercooked contaminated oysters pose a similar risk for norovirus illness as raw oysters and household contacts are at risk for secondary infection.

(Accepted March 16 2011)

(Online publication April 28 2011)

Correspondence:

c1 Author for correspondence: E. Alfano-Sobsey, Ph.D., Wake County Human Services, 10 Sunnybrook Rd, Room 301, Raleigh, North Carolina, 27610, USA. (Email: Edie.AlfanoSobsey@wakegov.com)

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