New Report Shows Variability in Annual Rate of Flu-Related Deaths

A new report from the Centers for Disease Control and Prevention (CDC) published in today's MMWR Report, updates the estimates of death associated with seasonal influenza in the United States from 1976 to 2007.

For several decades, the CDC has made annual estimates of influenza-associated deaths, which have been used in influenza research and to develop influenza control and prevention policy. To update previously published estimates of the numbers and rates of influenza-associated deaths during 19762003 by adding four influenza seasons through 20062007, the CDC says it used statistical models with data from death certificate reports. National mortality data for two categories of underlying cause of death codes, pneumonia and influenza causes and respiratory and circulatory causes, were used in regression models to estimate lower and upper bounds for the number of influenza-associated deaths.

David Shay, a medical officer in CDC's influenza division, speaking in a press conference held today, notes, "What the report being issued in today's MMWR has done is really just update previous estimates last made in 2009 using the same methodology, incorporating an additional four years of data. So, this is an update that confirms what we have seen previously in terms of flu. The updated estimates encompass data from 31 seasons from 1976-1977 influenza season to the 2006-2007 influenza season, which is the last date we have death certificate data that we can look at. And that range is from about 3,000 deaths in the 1986-1987 season to a maximum, if you will, of about 49,000 deaths that we saw in the 2003-2004 season. So, our major point today is to point out the incredible variability of influenza seasons."

According to the MMWR Report, the annual rate of influenza-associated death in the United States overall during this period ranged from 1.4 to 16.7 deaths per 100,000 persons. The findings also indicated the wide variation in the estimated number of deaths from season to season was closely related to the particular influenza virus types and subtypes in circulation.

For deaths with underlying pneumonia and influenza causes during 19762007 in the United States, the models estimated an annual overall average of 6,309 influenza-associated deaths. For these underlying causes, the average annual rate of influenza-associated death was 2.4 deaths per 100,000.

Among persons aged <19 years, an estimated annual average of 97 influenza-associated deaths with underlying pneumonia and influenza causes occurred. The average annual rate of influenza-associated deaths for this age group was 0.1 deaths per 100,000 persons. Among adults aged 1964 years, an estimated annual average of 666 influenza-associated deaths with underlying pneumonia and influenza causes occurred. The average annual rate of influenza-associated deaths for this age group was 0.4 deaths per 100,000 persons.

Among adults aged 65 years, an estimated annual average of 5,546 influenza-associated deaths with underlying pneumonia and influenza causes occurred. The average annual rate of influenza-associated deaths for this age group was 17.0 deaths per 100,000. Deaths among persons aged 65 years accounted for 87.9 percent of the overall estimated average annual influenza-associated deaths with underlying pneumonia and influenza causes.

For deaths with underlying respiratory and circulatory causes (including pneumonia and influenza causes) during 19762007, the models estimated an annual U.S. average overall of 23,607 influenza-associated deaths. For these underlying causes, the average annual rate of influenza-associated death was 9.0 deaths per 100,000.

Reference: MMWR Weekly Report. Vol. 59, No. 33. Aug. 27, 2010. Estimates of Deaths Associated with Seasonal Influenza United States, 19762007.