BACKGROUND: Varicella (chickenpox) is an acute infectious disease caused by the varicella zoster virus. Suspect cases are reported to the Arkansas Department of Health (ADH) and entered into the National Electronic Disease Surveillance System (NEDSS) Base System (NBS). Cases are investigated by the ADH Central Office and local health unit staff, managed and stored through NEDSS. An evaluation of the varicella surveillance system was conducted to determine areas that can be improved to ensure cases are reported and investigated in a timely and detailed manner.
METHODS: The varicella surveillance system was evaluated using the 2001 Updated Guidelines for Evaluating Public Health Surveillance Systems published by the Centers for Disease Control and Prevention (CDC) in 2001. The percentage of hospitalized cases, present in the Arkansas’ Hospital Discharge Database, that were detected by the surveillance system was used to calculate sensitivity. Data quality was measured by determining the percentage of case investigations with variables marked as ‘unknown’ or missing. Acceptability was assessed by determining the median number of days it took a source to report a case after diagnosis. To evaluate timeliness, median number of days an investigation was completed and then reported to CDC were calculated, respectively. Surveillance system attributes were discussed with staff who actively participate in varicella surveillance activities.
RESULTS: From 2006 to 2014, a total of 4,601 confirmed or probable cases were reported to ADH, with a dramatic decrease in case numbers over time. Only 13% of hospitalized patients with an ICD-9 code indicative of varicella were reported to ADH. Data quality improved as percentage of case investigations with variables marked as ‘unknown’ or missing decreased. From 2009 to 2014, cases of varicella were consistently reported to ADH at a median of 3 to 4 days after diagnosis. Case investigation completion improved from a median of 28 days in 2009 to 7 days in 2014. Additionally, reporting to CDC substantially improved from a median of 146 days in 2009 to 12 days in 2014.
CONCLUSIONS: Surveillance of varicella in Arkansas has several strengths as well as opportunities for improvement. Overall, the varicella surveillance system is simple and flexible, allowing for changes and adaptations to reporting and investigation processes. Data quality and timeliness of reporting and closing out investigations have greatly improved over time. Reporting from patients and providers remains a challenge, though efforts are being made to encourage more individuals to report.