514. The Changing Epidemiology of Influenza-Related Deaths in Minnesota from the 2009-2010 to 2010-2011 Influenza Seasons
Session: Poster Abstract Session: Influenza and other Respiratory Viral Infections Epidemiology Studies
Friday, October 21, 2011
Room: Poster Hall B1

Minnesota Dept. of Health established a statewide surveillance system during the 2009 H1N1 pandemic to identify influenza-related deaths occurring in hospital and community settings using a standardized definition.


The case definition for influenza-related death was a decedent with influenza-like-illness (ILI) that did not return to baseline and a positive influenza test or direct contact with a lab positive case. Cases were reported through surveillance of hospitalized patients with lab-confirmed influenza, medical examiner-based surveillance (MED-X), clinician based unexplained death surveillance (UNEX), lab confirmed nursing home outbreaks and death certificates with influenza noted as a cause of death or matched to lab-positive case.  Deaths with ILI during the 2009-10 and 2010-11 seasons (9/1-4/30) were investigated through medical record review and interviews with healthcare providers.


During the 2009-10 season, 2009 H1N1 accounted for 59/65 (91%) deaths vs. 7/55 (13%) during 2010-11.  In 2010-11, 18/55 (33%) were influenza A-H3, and 26/55 (47%) were influenza A-unidentified. Median age was 50 years during 2009-10 compared to 85 years for 2010-11 (Wilcoxon rank sum, p<0.001), and 20% were 65+ years in 2009-10 vs. 80% in 2010-11. In 2009-10, 68% were identified via hospital surveillance vs. 42% in 2010-11, 12% vs. 4% via UNEX/Med-X, 5% vs. 40% via death certificates and 15% for both seasons via other methods. 78% of 2009-10 deaths occurred in hospitals compared to 49% of 2010-11 deaths (χ² 11.3, p<0.001). Autopsies were performed in 32% (21/65) of 2009-10 cases vs. 5% (3/55) 2010-11 cases (p<0.001). 57 (88%) of 2009-10 and 50 (91%) of 2010-11 cases had underlying conditions. 1/7 children in 2009-10 and 1/2 in 2010-11 had no co-morbidities.


Due to the differences in circulating strains and host immunity, the age distribution and source of case identification was significantly different from the 2009-10 to 2010-11 influenza seasons. Influenza-related death investigation using multiple sources that includes deaths outside of hospitals is needed for a more complete capture of deaths and this provides a useful and timely understanding of the relationship between circulating strains and populations at risk.

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

Christine Lees, RN, MPH1, Craig Morin, MPH1, Richard Danila, PhD, MPH1, Aaron DeVries, MD, MPH1, David Boxrud, MS2, Catherine Lexau, PhD, MPH1 and Ruth Lynfield, MD3, (1)Infectious Disease Epidemiology Prevention and Control, Minnesota Department of Health, St. Paul, MN, (2)Public Health Laboratory, Minnesota Department of Health, St. Paul, MN, (3)Minnesota Department of Health, St. Paul, MN


C. Lees, None

C. Morin, None

R. Danila, None

A. DeVries, None

D. Boxrud, None

C. Lexau, None

R. Lynfield, None

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