as well as number and proportion of ILI cases admitted to the hospital. We were also able to evaluate trends over time to compare current ILI activity and age distributions with previous influenza seasons. We observed a good correlation between syndromic ED ILI trends and laboratory-based surveillance data, and between hospitalized confirmed H1N1 cases and syndromic ED admissions among patients with ILI, suggesting that ED ILI data tracked the novel influenza A H1N1 outbreak well. Resources necessary to manage the syndromic surveillance system are provided through federal preparedness funding. Limitations of syndromic surveillance include the inability to do case follow-up easily (because data are deidentified), missing data (e.g., disposition), absence of standardized chief complaint categories or terms resulting in potential misclassification, and variable definitions of ILI used in syndromic systems around the country. Until syndromic ILI and pneumonia data can be validated, their sensitivity and specificity remain unknown.
School absenteeism reporting is a commonly employed indirect indicator of seasonal influenza activity and had special prominence during the spring 2009-H1N1 influenza A outbreak. The increased focus on absenteeism reporting highlighted the limitations of our current system and potential areas for improvement.
Until recently, school absenteeism reporting has been a passive, manual system, in which school personnel are requested to report weekly absenteeism. Participation in this system has been variable and inconsistent across King County’s 19 public school districts (with 525 schools) and 225 private schools. Consequently, there are no reliable historical data to allow analysis of absenteeism trends over time. Absenteeism rates are reported at the school level. Data on grade-level rates are not provided, definitions of absence are not standardized, and the threshold for reporting (traditionally 10 percent) is arbitrary and not adjusted for baseline levels of absenteeism.
To promote increased participation in absenteeism reporting, in 2008 we developed a web-based reporting system that requested the following information: a weekly absenteeism report with peak absenteeism for the week, whether more than half of absenteeism was due to illness, and the predominant reasons for absenteeism. However, many schools did not report because of resource and staff constraints, and consistency of reporting was poor. To further simplify reporting and relieve schools of the associated administrative burden, after the spring 2009-H1N1 influenza A outbreak we implemented district-level automated electronic absenteeism reporting to collect aggregate counts of the daily absences by school and grade level. This system is made possible through collaboration among public health, school districts, and a cooperative of districts and educational service districts that were already collecting electronic data. Strengths of the system include complete data collection from participating school districts, the ability to analyze trends over time, establish baseline levels of absenteeism and define increases above baseline, and inclusion of grade level data. Limitations include