Enhanced Surveillance of Norovirus Outbreaks of Gastroenteritis in Georgia

Abstract

SYNOPSISObjectives. The role of noroviruses in both foodborne and person-to-person outbreaks of acute gastroenteritis (AGE) has been difficult to determine in the U.S. because of lack of routine norovirus testing and of national reporting of person-to-person outbreaks. We conducted a prospective study in one state in which enhanced testing for noroviruses was performed to better understand the relative contribution of all gastroenteric pathogens.Methods. During the two-year period, 2000-2001, we took all fecal specimens from AGE outbreaks reported in Georgia that were negative for bacteria and tested these for norovirus.Results. We investigated 78 AGE outbreaks, from which suitable fecal samples were collected from 57 of them. Norovirus was identified in 25 (44%) outbreaks, bacteria in 20 (35%) outbreaks, and parasites in one (2%) outbreak. Forty-three (75%) of the outbreaks tested were foodborne, of which 17 (40%) were attributable to norovirus and 18 (42%) were attributable to bacteria. Adjusting for incomplete testing, we estimated that 53% of all AGE outbreaks were attributable to norovirus. A total of 2,674 people were reported ill in the 57 outbreaks, and norovirus infections accounted for 1,735 (65%) of these cases. Norovirus outbreaks tended to be larger than bacterial outbreaks, with a median number of 30 vs. 16 cases per outbreak, respectively (p0.057).Conclusions. This study provides further evidence that noroviruses are, overall, the most common cause of AGE outbreaks in the U.S. Improved specimen collection, reporting person-to-person outbreaks, and access to molecular assays are needed to further understand the role of these viruses and methods for their prevention.

Incidence of and Factors Associated with False Positives in Laboratory Diagnosis of Norovirus Infection by Amplification of the RNA-Dependent RNA Polymerase Gene

“…This method can detect NV with high sensitivity and readily differentiate the two major genogroups of NV [5] , [11] . The assay had been widely implemented in laboratory diagnosis and various epidemiology studies of human NV infections [7] , [12] , [13] , [25] . Misinterpretation of electrophoresis results due to the similar size of the PCR products between nonspecific amplification and virus-specific amplicons has not been reported for this assay, although the phenomenon has been recognised in other RT-PCR methods of NV detection [26] .…”

“…RdRp is a highly conserved region in the NV genome, and primer sets designed to amplify this allele have been shown to be able to detect NV with satisfactory sensitivity [11] . The assay remains used in the diagnosis of NV infection in clinical laboratories, surveillance studies and epidemiology studies [7] , [12] , [13] .…”