Using records of diagnoses from healthcare encounters and laboratory test results to estimate the incidence of norovirus infections, active component, U.S. Armed Forces, 2007-2016: limitations to this approach.

During the 10-year surveillance period, there were 709 incident cases of norovirus (NoV) infection identified among active component service members, with an overall crude incidence rate of 5.7 cases per 100,000 person-years (p-yrs). The overall incidence rate of NoV infection was slightly higher among female service members than males. Compared to their respective counterparts, service members aged 24 years or younger, members of the Army, junior enlisted, and recruits had the highest rates of NoV infection. Overall rates were similar across all race/ethnicity groups. Service members in "other" occupations had the highest overall incidence rate, compared to service members in other occupational groups. Annual incidence rates of NoV infection ranged from a low of 2.5 cases per 100,000 p-years in 2008 to 11.2 cases per 100,000 p-yrs in 2010. The monthly distribution of the cumulative number of incident cases of NoV infection during the surveillance period showed a pattern of seasonality with higher numbers of diagnosed cases from November through March. Comparing the results of this analysis to modeled estimates of the underreported incidence of NoV infections demonstrated the limited utility of using only medical encounter diagnoses, reportable events, and laboratory data to report on NoV incidence. The disparity between such estimates highlights the importance of developing and using other methodologies to derive estimates of norovirus incidence and burden in future analyses.