Addition of an active surveillance component to influenza-like illness surveillance in Pennsylvania, 2003–2004

Purpose The Pennsylvania Department of Health (PADOH) has participated in the CDC Influenza Surveillance Provider Network (ISPN) since 1997. In 2003, we added an active surveillance component in an effort to improve the consistency with which providers submit weekly reports of influenza-like illness (ILI) seen in their practices. Because active surveillance entailed nontrivial costs for PADOH, some measurement of its benefits was necessary to facilitate policy decisions regarding use of active ILI surveillance in future influenza seasons. Methods Each Tuesday from November 3, 2003, through March 2, 2004 (CDC weeks 200345 through 200409), a list of ISPN providers who did not submit an ILI report for the previous week was generated from the CDC ISPN website. Immunization nurses in the local health districts phoned these providers and offered assistance with ILI data entry. Primary measure: the difference in the percentage of ISPN providers submitting reports in 50% or more of CDC-defined influenza surveillance weeks in the 2002–2003 influenza surveillance season (no active surveillance) and the 2003–2004 season (with active surveillance). Subsidiary measure: change in reporting consistency for individual providers who participated in ISPN during both seasons, as measured by the mean and median change in % of surveillance weeks for which providers submitted reports. Results Forty-two sentinel providers participated in the entire 2003–2004 surveillance season and 66 in 2002–2003. Active surveillance resulted in an absolute increase of 46% (from 23% to 69%) in proportion of ISPN providers reporting in 50% or more of surveillance weeks. Among the 37 providers who participated during both seasons, reporting consistency improved a mean of 31% (95% CI = 20%, 43%), median 30%. Conclusion Active surveillance was a valuable addition to Pennsylvaniaʹs ISPN. Consideration of the improvement achieved versus cost incurred will be incorporated into decision making regarding future use of this active surveillance technique by PADOH.