Flu-related hospitalizations have risen among elderly

Sep 23, 2004 (CIDRAP News) – The graying of America is leading to an increase in hospital stays related to influenza, according to a research report in the Sep 15 issue of the Journal of the American Medical Association.

Many flu-related hospitalizations occur among the elderly, and the number of such hospitalizations has increased "substantially" in the last 20 years as the population has aged, say William W. Thompson, PhD, of the National Immunization Program of the Centers for Disease Control and Prevention in Atlanta, and six other researchers.

They estimate that more than 200,000 respiratory and circulatory hospitalizations are associated with the flu each year in the United States, substantially more than previous estimates of hospitalizations attributed specifically to pneumonia and flu.

While national mortality estimates have been important for influenza planning, the article says those estimates don't fully reflect the incidence of severe flu infections, because many severe illnesses aren't fatal.

The study drew upon 22 years' worth of data in the National Hospital Discharge Survey (NHDS). Using the NHDS data, as well as flu surveillance data from World Health Organization collaborating laboratories, the researchers estimated the annual average numbers of hospitalizations for primary and any listed pneumonia and influenza and for overall respiratory hospitalizations from 1979-80 through 2000-01.

The investigators found that people 85 and older had the highest rates of flu-linked hospitalizations, at 1,194.9 hospitalizations per 100,000. Children younger than 5 had the same rates of flu-associated hospitalization as people aged 50 to 64 years. People between the ages of 5 and 49 had the lowest rates of flu-related hospitalizations, the study showed.

The data link the dominant type of flu in a given season and hospitalization rates. When A(H3N2) viruses predominated, there were 43.5 primary pneumonia and influenza and 99.0 primary respiratory and circulatory hospitalizations per 100,000 person-years associated with flu viruses. When B viruses were predominant, the respective hospitalization rates were 37.7 and 81.4. When A(H1N1) predominated, 22.6 pneumonia and flu and 55.9 respiratory and circulatory hospitalizations were found per 100,000 person-years.

The increase in flu-related hospitalizations and deaths was due to several factors, including the prevalence of A(H3N2) viruses in many recent flu seasons and a trend for longer flu seasons during the 1990s, the article adds.

The findings highlight the need to improve flu prevention among the very young and the very old, the authors conclude. Recommendations for flu vaccine for high-risk individuals, household contacts of high-risk people, healthcare workers, and young children must be implemented, they write.

One limitation of the study is that NHDS data don't include patients' previous health history or vaccination status, which could be used to measure vaccine effectiveness, the authors write.

Thompson WW, Shay DK, Weintraub E, et al. Influenza-associated hospitalizations in the United States. JAMA 2004:292(11):1333-40 [Abstract]