BACKGROUND: Norovirus is the most common acute gastroenteritis (AGE) outbreak etiology identified among vulnerable long-term care facility populations (LTCF). Timely risk communication and prevention efforts in LTCFs could mitigate norovirus outbreaks. Data analyzed from a sporadic AGE surveillance system among children in Davidson County, TN and outbreak data reported to the Norovirus Sentinel Testing and Tracking Network were used to assess the predictive ability of sporadic norovirus surveillance for norovirus outbreaks in middle Tennessee.
METHODS: Sporadic norovirus cases were identified among children ≥15 days and ≤17 years that were enrolled from Vanderbilt Children’s Hospital through AGE surveillance from December 2012- July 2015. The association between weekly number and percent of AGE cases testing positive for norovirus and the occurrence of outbreaks from selected middle Tennessee counties were analyzed using logistic regression models. Receiver operating characteristic curves were constructed to evaluate potential thresholds of number and percent positive of sporadic norovirus infection to signal increased risk of an outbreak occurring. Comparisons of sensitivities and relative risk ratios were used to inform the selection of a threshold value.
RESULTS: During December 2012- July 2015, 490 (14%) of the 3431 children enrolled with AGE tested positive for norovirus. During the same time, 32 confirmed and probable norovirus outbreaks occurred in middle TN counties, with 56% occurring in LTCFs. Increases during winter months in sporadic norovirus cases preceded an increased frequency in reported outbreaks. We found that the factors most highly correlated with the occurrence of an outbreak were the number and percentage of norovirus cases in the preceding two week period. Using logistic models, a 71% sensitivity in predicting an outbreak was observed when ≥ 3 cases (or 15% of specimens) tested norovirus-positive. When that threshold was exceeded, the risk of an outbreak occurring in the next 2 week period rose 2.9 times over the baseline (95% CI: 1.5-5.4).
CONCLUSIONS: AGE and norovirus sporadic illness among children in clinical settings may potentially serve as an early warning system for norovirus outbreaks in communities to trigger risk communication and implementation of scalable risk-reducing measures in LTCFs. Our findings provide key insights into norovirus transmission dynamics in the community and potential opportunities for targeted interventions (i.e., vaccines). Our findings also highlight the importance of laboratory testing of AGE by providers and the potential for sharing data between public health and clinical institutions.