Background: Influenza-like illness (ILI) is used for influenza surveillance. Student absenteeism from school associated with ILI (aILI) may be a strong marker for influenza activity in the surrounding community. We monitored aILI and investigated its utility as an early warning signal for influenza outbreaks.
Objective: To evaluate the correlations among: (1) aILI and influenza cases confirmed after home visits in children absent from school for ILI (school-based influenza [SI]), (2) SI and medically attended influenza-positive cases (MAI), and (3) aILI and MAI.
Methods: Daily counts of aILI from all K-12 students in the Oregon School District (OSD) were collected from September 2014 to March 2015 (29 weeks), and summarized as weekly averages. Students absent from school due to ILI from January to March (11 weeks) were visited at home by the study team; oropharyngeal swabs were collected for influenza and other respiratory virus testing using RT-PCR. MAI data were collected for all age groups from September 2014 to March 2015, at five Wisconsin Influenza Incidence Surveillance Project (W-IISP) clinics where the OSD community seeks care. W-IISP conducts surveillance for acute respiratory infections, and similarly tests for respiratory viruses. We evaluated the correlation between the weekly occurrence of aILI to SI and SI to MAI over an 11-week period, and aILI to MAI over a 29-week period using Pearson correlation.
Results: During the school year, aILI and MAI were highly correlated (r=0.77; P<0.001). From January to March, 493 aILI-days were recorded and 115 home visits were conducted. Influenza was recovered from 30 (26%) swabs collected from children during home visits; other respiratory viruses were identified in 46 (40%). High statistically significant correlations were found between aILI and SI (r=0.89; P<0.001), and also between SI and MAI in all age groups in the community (r=0.69; P<0.05).
Conclusion: We demonstrate that ILI-related school absenteeism is highly correlated with influenza infection in school-aged children. Moreover, linkages extend from school absences due to influenza to influenza activity in the community. School absenteeism for ILI may be considered as a powerful surveillance tool for influenza in schools and broader community.
A. Schemmel, None
E. Temte, None
M. Landsverk, None
Y. Zheteyeva, None
A. Fowlkes, None
A. Uzicanin, None