Norovirus Outbreak in a Public School: Use of Environmental Sampling to Target Control Measures *

BACKGROUND: Norovirus is easily transmitted in the school setting through multiple routes of exposure, and outbreaks have led to campus closures.  Ensuring implementation of transmission-prevention measures is challenging in large secondary schools, where exclusion criteria for ill persons may be limited, and sufficient environmental surface disinfection may be difficult to achieve.  During a 2014 norovirus outbreak in a Dallas County public high school, supplemental approaches to outbreak control were assessed, including environmental testing.

METHODS: Students and staff with self-reported vomiting or diarrhea were interviewed with standardized questionnaires.  Surveys were also administered to all 2500 students to gather exposure data.   A case-control analysis included a randomly selected sample of 300 cases and 600 controls frequency-matched on gender.  Multiple logistic regression was performed using SAS 9.4 (Cary, NC).  Stool samples from cases and environmental surface swabs were tested for norovirus by RT-PCR assay. 

RESULTS: An overall attack rate of 32% occurred over 4 weeks, with a peak in cases on January 30, the day of initial report to public health.  Cases reported vomiting (83%), diarrhea (57.3%), and fever (40.3%). Norovirus genogroups GI.B3 (n=4) and GII (n=1) were identified in stool samples.   Ongoing new cases 5 days following public health notification prompted environmental sampling.  Norovirus GI. B3 (n=8) and GII (n=2) were identified from multiple surfaces, including:  door handles, stair rails, computer keyboards, and a water cooler spigot.  Numbers of new cases declined after enhanced cleaning targeting these fomites.  In the case-control analysis, statistically significant exposures included:  water fountain use (OR=1.79, p= 0.004); and participation in the dance team (OR=1.91, p= 0.03) or theater (OR=1.78, p= 0.02).

CONCLUSIONS: Routine public health interventions to control norovirus outbreaks are often difficult to implement in public secondary schools.  Environmental surface testing for norovirus during persistent outbreaks may be useful in the development of enhanced disinfection strategies that best utilize limited school resources.