Norovirus outbreak associated with an elementary school: Use of absentee data and electronic meal records for hypothesis generation

Background: In October 2010, the Oklahoma State Department of Health was notified of increased absenteeism in an elementary school. An epidemiologic investigation was initiated. Methods: A random sample of children absent on October 13, 2010 was interviewed for symptoms, activities, and to request stool specimens. Student absentee records were obtained for October 12th - 14th and electronic meal ticket records for October 11th and 12th. Absentee lists, electronic meal ticket data, and total number students were used as a cursory surrogate to determine if illness was associated with consuming school meals. Results: Eighteen (86%) of 21 interviewed from the October 13th absentees reported symptoms consistent with norovirus; one was confirmed with norovirus G1 by reverse transcriptase-polymerase chain reaction (RT-PCR). The only common setting or activity among ill was attendance at the elementary school. An epidemiologic curve demonstrated an increase in absenteeism on October 13th. Of 453 students with records showing meal purchase on October 11th (exposed), 85 (19%) were absent October 12th or 13th compared with 46 (15%) among 301 unexposed on October 11th (Odds Ratio 1.28; 95% CI: 0.85, 1.93). Conclusions: Epidemiologic and laboratory findings indicated an outbreak of norovirus. Although not conclusive, analysis of electronic school records indicated absenteeism was not significantly associated with consumption of school meals 48 hours after meal time. This investigation revealed the utility of school electronic records during the hypothesis-generating phase to determine if further epidemiological investigation or in-depth case-control studies are warranted and for better allocation of time and resources designated to outbreak investigation.