Influenza associated hospitalizations among elderly patients has increased substantially over the past two decades

The estimated number of influenza-associated hospitalizations among elderly patients has increased substantially over the past two decades, according to an article in the September 15 issue of JAMA.

Although national estimates of influenza-associated deaths have been important in understanding the epidemiology of influenza over time and in planning for future epidemics and pandemics, “mortality incompletely reflects the severity of influenza infections because many severe illnesses do not result in death,” according to background information in the article.

William W. Thompson, Ph.D., of the Centers for Disease Control and Prevention, Atlanta, and colleagues estimated the annual average number of hospitalizations associated with the circulation of the influenza virus over two decades. The researchers used data from the National Hospital Discharge Survey (NHDS) and World Health Organization Collaborating Laboratories to make estimates for the influenza seasons during 1979 – 1980 through 2000 – 2001.

The researchers analyzed hospitalizations in several different ways and found there were 226,054 primary and 294,128 any listed respiratory and circulatory hospitalizations associated with influenza virus infections on average each season (and annual averages of 94,735 primary and 133,900 any listed pneumonia and influenza hospitalizations associated with the influenza virus infections). Highest rates of influenza-associated primary respiratory and circulatory hospitalizations were found in persons 85 years and older.

After adjusting for length of each influenza season, influenza-associated rates of primary pneumonia and influenza hospitalizations increased over time among elderly. There were no significant increases in the rates of influenza-associated primary respiratory and circulatory hospitalizations after adjusting for the length of the influenza season. Children younger than five years had rates similar to those found among the 50 through 64 year-old age group. Persons aged five years through 49 years had the lowest rates of hospitalizations associated with influenza.

The authors write: “Currently, we estimate that more than 200,000 respiratory and circulatory hospitalizations are associated with influenza each year in the United States, substantially more than estimates of pneumonia and influenza hospitalizations.”

They conclude by saying: “Significant numbers of influenza-associated hospitalizations in the United States occur among the elderly, and the numbers of these hospitalizations have increased substantially over the last two decades due in part to the aging of the population. … These findings highlight the need for improved influenza prevention efforts for both young and older U.S. residents.”