title: Comparing active and passive varicella surveillance in Philadelphia, 2005-2010: recommendations for the transition to nationwide passive varicella disease surveillance.
abstract: OBJECTIVE
  The Philadelphia Department of Public Health (PDPH) conducts active surveillance for varicella in West Philadelphia. For its approximately 300 active surveillance sites, PDPH mandates biweekly reports of varicella (including zero cases) and performs intensive case investigations. Elsewhere in Philadelphia, surveillance sites passively report varicella cases, and abbreviated investigations are conducted. We used active varicella surveillance program data to inform the transition to nationwide passive varicella surveillance.
  
  
  METHODS
  We compared classification of reported cases, varicella disease incidence, and reporting completeness for active and passive surveillance areas for 2005-2010. We assessed reporting completeness using capture-recapture analysis of 2- to 18-year-old cases reported by schools/daycare centers and health-care providers.
  
  
  RESULTS
  From 2005 to 2010, PDPH received 3,280 passive and 969 active surveillance varicella case reports. Most passive surveillance reports were classified as probable cases (18% confirmed, 56% probable, and 26% excluded), whereas nearly all of the active surveillance reports were either confirmed or excluded (36% confirmed, 11% probable, and 53% excluded). Overall incidence rates calculated using confirmed/probable cases were similar in the active and passive surveillance areas. Detection of laboratory-confirmed, breakthrough, and moderate-to-severe cases was equivalent for both surveillance areas.
  
  
  CONCLUSIONS
  Although active surveillance for varicella results in better classified cases, passive surveillance provides comparable data for monitoring disease trends in breakthrough and moderate-to-severe varicella. To further improve passive surveillance in the two-dose-varicella vaccine era, jurisdictions should consider conducting periodic enhanced surveillance, encouraging laboratory testing, and collecting additional varicella-specific variables for passive surveillance.
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, PA.
authors.forename: Kendra
authors.initials: K
authors.lastname: Viner
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, PA.
authors.forename: Dana
authors.initials: D
authors.lastname: Perella
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA.
authors.forename: Adriana
authors.initials: A
authors.lastname: Lopez
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bialek
authors.affiliation: Food and Drug Administration, Rockville, MD.
authors.forename: Michael
authors.initials: M
authors.lastname: Nguyen
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, PA.
authors.forename: Niya
authors.initials: N
authors.lastname: Spells
authors.affiliation: Philadelphia Department of Public Health, Philadelphia, PA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Watson
mesh_terms: D000293:Adolescent; D002644:Chickenpox / Q000145:classification / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D006801:Humans; D015994:Incidence; D009111:Local Government; D019221:Mandatory Reporting; D015143:Philadelphia / Q000453:epidemiology; D011159:Population Surveillance / Q000379:methods*; D011635:Public Health Administration