Using capture-recapture methods to assess varicella incidence in a community under active surveillance

The Varicella (chickenpox) Active Surveillance Project (VASP) has been conducting active surveillance since 1 January 1995 in the high desert community known as Antelope Valley, CA (population 300,000) among 300 public and private schools, daycares, and healthcare providers. Capture-recapture methods were applied to estimate reporting completeness for 1995 varicella incidence data and these were compared with the national average incidence rates by age reported by the National Health Interview Survey (NHIS). Varicella cases reported among individuals aged <20 years reflect under-reporting in excess of 50%. Despite limitations on accuracy, capture-recapture estimates are a reasonably accurate, quick, and inexpensive approach in epidemiologic studies.