Evaluation of the Norovirus Sentinel Testing and Tracking Network, Tennessee *

BACKGROUND:  Norovirus is the most common cause of foodborne disease outbreaks in the United States, causing up to 21 million cases of acute gastroenteritis every year. The Norovirus Sentinel Testing and Tracking (NoroSTAT) Network was established in 2012 through the Centers for Disease Control and Prevention (CDC) to improve the timeliness, completeness, and consistency of norovirus outbreak reporting to CDC. The NoroSTAT surveillance system in Tennessee was evaluated to assess local utility and whether CDC’s objectives are being met.

METHODS:  NoroSTAT was evaluated according to the guidelines described in the CDC “Updated Guidelines to Evaluating Public Health Surveillance Systems: Recommendations from the Guidelines Working Group” (CDC, 2001). Interviews were conducted with key stakeholders at CDC and the Tennessee Department of Health. Epidemiologic data from the National Outbreak Reporting System (NORS) and laboratory data from CaliciNet were used to evaluate norovirus outbreak reporting in Tennessee from August 2012- July 2014.  NORS and CaliciNet data from August 2009- July 2012 were used to assess Tennessee norovirus outbreak reporting prior to the establishment of NoroSTAT.

RESULTS:  During August 2012 through July 2014, 115 confirmed or suspect norovirus outbreaks were reported in Tennessee. Epidemiologic data were determined to have good completeness, with 5 out of 6 of the required NoroSTAT data fields having no missing data. Since joining NoroSTAT, only 12 (10.4%) outbreaks had missing data for outbreak “setting” compared to 39 (43.8%) outbreaks prior during August 2009-July 2012. Seventy-three percent of norovirus outbreaks had confirmed etiology during NoroSTAT participation years, with the remaining 27% of outbreaks having 1 or no samples positive for norovirus. The majority of norovirus outbreaks (98 outbreaks, 85.2%) had missing information on the median incubation period, likely decreasing the positive predictive value for suspect outbreaks using the Kaplan criteria. The average number of days between notification of an outbreak and reporting initial epidemiologic data into NORS was 2 days. Prior to NoroSTAT, the average number of days before documenting the outbreak in NORS was 16.7 days.

CONCLUSIONS:  NoroSTAT participation has greatly increased the completeness and timeliness of norovirus reporting in Tennessee. The surveillance system provides close to real-time situational awareness of norovirus activity in Tennessee and contributes to national data. Improving the reporting of outbreak characteristics, such as median incubation period, severity indices, and stool sample collection can further enhance our ability to monitor norovirus trends within Tennessee.