Thanks to Melissa McMahon MPH, Melissa McMahon MPH, Karen G Martin MPH, Nancy Bollman, Anna Strain PhD, Leslie Kollmann, and Ruth Lynfield MD at MDH
MDH Infectious Disease, Epidemiology, Prevention and Control Division (MDH IDEPC) routinely tracks influenza-associated deaths in Minnesota, relying heavily on the information provided by the Office of Vital Records (OVR) staff. Methods for identifying cases and describing the partnership between MDH IDEPC and OVR has been previously described in February 2018 Vital Records News.
MDH IDEPC recently completed an analysis looking at characteristics of influenza-associated deaths in adults. We focused on adults >18 years of age for this analysis to help fill gaps in the knowledge regarding influenza-associated deaths. Among adults, we found that most deaths were associated with Influenza A (particularly H3), a little more than half occurred in hospitals, almost all had medical comorbidities, and a high proportion lacked documentation of vaccination.
Influenza-Associated Death Surveillance and Partnering with OVR:
Influenza-associated deaths are reportable for all ages in Minnesota. These deaths are tracked via a number of reporting sources, including laboratory-confirmed hospitalized cases, outbreak reports in long-term care facilities, and unexplained death and critical illness surveillance (UNEX). Death certificates are queried daily by OVR staff and forwarded to MDH IDEPC staff. Influenza-associated deaths are defined as deceased individuals who meet any of the following criteria: “influenza” listed on the death certificate, death following a laboratory-confirmed influenza hospitalization ≤30 days post-discharge, influenza-like illness or confirmed influenza in a resident of a skilled nursing facility experiencing an influenza outbreak, influenza positive results from post-mortem testing, or death occurring ≤60 days after positive influenza test if symptoms did not resolve before death. Vaccination history is obtained through review of the immunization registry and medical charts. Influenza strain type and subtype are included where available.
Results:
There were 1,621 adult influenza-associated deaths reported during the 2010-11 through the 2018-19 influenza seasons (October through mid-May). The initial reporting source for most cases was death certificate queries from OVR (72%), followed by hospital surveillance (22%), skilled nursing facility reports (3%) and UNEX (2%). Case counts per season ranged from 42 in 2011-12 to 434 in 2017-18. Cases were 95% White (87% of Minnesota population >18 years is White).
Influenza test results were found for 86% of cases, with 85% positive for influenza A (6% H1, 38% H3), 15% for influenza B (28% Yamagata, 0% Victoria), and 0.6% for both A and B. The median age of death was 85 years (Inter-Quartile Range [IQR] 91-74) for H3, 63.5 years (IQR 54-72.5) for H1 and 82 years (IQR 71-89) for B. Underlying condition status was available for 1,284 (79%) cases. Of those, 829 (96%) had at least one known underlying medical condition. Documentation of current season vaccine was found for 829 (51%) of cases. The most common death location was hospital inpatient (861 [53%]), followed by skilled nursing facility (460 [28%]), private residence (206 [13%]), and emergency room (32 [2%]).
Conclusions:
Although deaths are likely underreported, having case-based data enables an improved understanding of fatalities associated with influenza and can help refine and target prevention education and interventions. Our collaboration with MDH OVR and having consistent and timely access to death certificates allows us to easily identify trends in influenza death, and therefore, better understand the burden of influenza disease in Minnesota.
Email melissa.mcmahon@state.mn.us if you have questions.
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