Estimated Hospitalization Rates for Seasonal Influenza in Adults and Children in Middle Tennessee using a Capture-Recapture Method

Abstract Background Ongoing surveillance of influenza activity is important to monitor variation in disease severity and vaccine effectiveness, but surveillance systems have limitations. The capture-recapture method aims to more comprehensively estimate disease burden by combining data from independent studies. Methods Residents of 8 counties in Middle TN hospitalized with influenza during the 2015-16 influenza A(H1N1pdm09)-predominant season were identified using data from 3 independent CDC-sponsored programs. The Influenza Hospitalization Surveillance Network/Emerging Infections Program (FluSurv-Net/EIP) identifies adult and pediatric cases based on a positive clinician-ordered influenza test. The U.S. Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) and the New Vaccine Surveillance Network (NVSN) enroll adults (3 hospitals) and children (1 hospital), respectively, with respiratory symptoms with/without fever, and obtain nasal/throat swabs to identify cases of influenza; 2015–2016 was a pilot year for HAIVEN. Using the numbers of matched and unmatched cases detected by two studies, a capture-recapture analysis estimated the total number (N) of influenza-related hospitalizations in the population (Table 1). Due to small sample size, the Chapman equation was used, where N = ((a + b + 1)(a + c + 1)/(a + 1)) – 1. The capture–recapture estimates were adjusted for the hospitals’ market share for acute respiratory illness in middle TN residents (69.2% for children and 23.9% for adults) based on hospital discharge data. Table 1. Sample 2 × 2 table for capture–recapture Analysis HAIVEN or NVSN FluSurv-Net/EIP Detected Missed Detected A b Missed c z a = cases identified by both studies (matches); b = cases identified by EIP only; c = cases identified by HAIVEN or NVSN only; z = estimated number of patients hospitalized with influenza not captured by either study. N = a + b + c + z Results Capture-recapture analyses based on unadjusted crude data are shown in Figure 1A and 1B. Age-specific rates of hospitalization were then calculated (Figure 1C). Conclusion Using a capture–recapture method, we estimated influenza hospitalization rates of 0.87 (95% CI 0.06–1.68) and 0.80 (95% CI 0.62–0.98) per 1,000 persons among children and adults, respectively. Disclosures N. B. Halasa, sanofi pasteur: Research Contractor, Research support. Astra Zeneca: Research Contractor, Grant recipient. W. Schaffner, Pfizer: Scientific Advisor, Consulting fee. Merck: Scie