BACKGROUND: Norovirus is the leading cause of acute gastroenteritis (AGE) and foodborne disease outbreaks in the United States. Since 2009, epidemiologic and laboratory data on norovirus outbreaks are reported to CDC through the National Outbreak Reporting System (NORS) and CaliciNet, respectively. Data from these systems are used collectively to monitor norovirus activity and trends, identify emerging strains and their impacts, and to potentially link outbreaks to a common source. In 2012, to encourage more complete, timely and better linked norovirus outbreak reporting, the CDC launched NoroSTAT, a collaborative network of 5 states (Minnesota, Ohio, Oregon, Tennessee and Wisconsin).
METHODS: We evaluated NORS and CaliciNet per capita reporting rates, report timeliness, and data completeness for the 5 states participating in NoroSTAT, compared with all other US states. The three-year period since introduction of NoroSTAT (August 2012– July 2015) was compared with the preceding three-year period (August 2009 – July 2012). We also determined the number of outbreaks that could be directly linked in NORS and CaliciNet by reporter-supplied identification numbers.
RESULTS: The median reporting rate for norovirus outbreaks in NORS among the 5 NoroSTAT-participating states increased from 41.5 to 60.7 per 1,000,000 person-years since NoroSTAT introduction in 2012, compared to a smaller increase from 10.2 to 13.4 per 1,000,000 person-years for all other US states. The median reporting lag for NORS reports decreased from 22 to 2 days for NoroSTAT states, while remaining unchanged at 26 days for all other states. NORS reports with all required fields completed increased from 71% to 84% for NoroSTAT states, compared to an increase from 30% to 52% for all other states. The CaliciNet reporting rate for NoroSTAT states increased from 20.1 to 30.9 per 1,000,000 person-years, compared to a smaller increase from 6.7 to 7.8 per 1,000,000 person-years for all other states. The median reporting lag for CaliciNet reports decreased from 21 to 3 days for NoroSTAT states, compared to a smaller decrease from 21 to 11 days for all other states. CaliciNet reports that were linkable to NORS reports increased from 81% to 96% for NoroSTAT states, compared to an increase from 27% to 38% for all other states.
CONCLUSIONS: This evaluation demonstrates substantial improvements in norovirus outbreak reporting with the advent of NoroSTAT. Data collected through this network can effectively evaluate current norovirus outbreak activity and assess the impact of new strains.