511. The Total Burden of H1N1 Influenza by Capture-Recapture Analysis
Session: Poster Abstract Session: Influenza and other Respiratory Viral Infections Epidemiology Studies
Friday, October 21, 2011
Room: Poster Hall B1
Background: To estimate the total burden of H1N1 influenza disease by combining data from two independent surveillance systems using capture-recapture analysis.

Methods: We prospectively and systematically enrolled persons from Forsyth County, NC of all ages from September 2009 through mid-April 2010 who presented to the ED or were admitted to the hospital with fever and/or acute respiratory symptoms. After informed consent, nasopharyngeal swabs were obtained and tested for H1N1 influenza by virus culture and RT-PCR. Physician-ordered testing for H1N1 influenza was independently performed based on clinical indications. We combined results from both systems identifying H1N1 influenza in a capture-recapture analysis to estimate the total number of county residents with H1N1 influenza that were seen in the ED or admitted to our hospital.

Results: Among 595 prospectively enrolled county residents (70% of those eligible and approached), 38 (6%) were H1N1 positive--68% of whom were identified during the peak (September 9 - December 4, 2009). Influenza-positive patients were 4 months to 68 years (47% <18 years, 39% 18-49 years, 13% ≥50 years). 39% were male; 39% black, 37% white, 21% Hispanic and 3% unknown; 87% were never hospitalized.

Physician-ordered influenza testing identified 102 H1N1 positive county residents who were 5 months to 76 years (47% <18 years, 25% 18-49 years, 29% ≥50 years)--79% of whom were identified during the peak. 48% were male; 45% were black, 28% white, 21% Hispanic, and 6% other/unknown; 4% were never hospitalized.

Capture-recapture analysis combines the 38 H1N1 positive patients identified by prospective surveillance and the 102 positive patients independently identified by physician-ordered testing to estimate the total burden. We estimate that 969 county residents had H1N1 and were seen in our hospital, of which 86% were missed by both systems.

Conclusion: The burden of H1N1 influenza disease in the ED and inpatient settings during this influenza season was much larger than that detected by either surveillance system alone. The ability to estimate the total burden, including that not detected by any system, makes capture-recapture analysis useful for diseases such as H1N1 influenza when many symptomatic persons were not tested.

Subject Category: N. Hospital-acquired and surgical infections, infection control, and health outcomes including general public health and health services research

Timothy Peters, MD, Elizabeth Blakeney, BS, Tammy Bischoff, BSN, MPH, Werner Bischoff, MD, PhD, Elizabeth Palavecino, MD, Robert Sherertz, MD, FIDSA, Snively Beverly, PhD, Suerken Cynthia, MS, Lauren Vannoy, BA and Katherine Poehling, MD, MPH, Wake Forest School of Medicine, Winston-Salem, NC


T. Peters, None

E. Blakeney, None

T. Bischoff, None

W. Bischoff, None

E. Palavecino, None

R. Sherertz, None

S. Beverly, None

S. Cynthia, None

L. Vannoy, None

K. Poehling, None

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