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Study Highlights Burden of Pneumonia Hospitalizations Among US Adults

When U.S. adults are hospitalized with pneumonia, viruses are more often to blame than bacteria. However, despite current diagnostic tests, neither viruses nor bacteria are detected in the majority of these patients according to a study released today by the Centers for Disease Control and Prevention (CDC).

This two-and-a-half year study published in the New England Journal of Medicine and conducted by researchers at CDC, three hospitals in Chicago, and two hospitals in Nashville estimated the burden of community-acquired pneumonia hospitalizations among U.S. adults.

University of Utah professors of pediatrics Andrew Pavia, M.D., and Krow Ampofo, M.D., contributed to study design and interpretation based on their lead roles in a part of the study that examined pneumonia in children. "The findings emphasize the need for better diagnostic tools so we can provide the right treatment for patients with pneumonia, and only use antibiotics when they are needed," said Pavia, also chief of the division of pediatric infectious diseases.

The study showed that found that viruses, rather than bacteria, were the most commonly detected respiratory pathogens in adults hospitalized with pneumonia. However, the researchers were unable to detect a pathogen in the majority of hospitalized adults.

"Pneumonia is a leading cause of hospitalization and death among adults in the United States and in 2011 the medical costs exceeded $10 billion," said CDC Director Tom Frieden, M.D., M.P.H. "Most of the time doctors are unable to pinpoint a specific cause of pneumonia. We urgently need more sensitive, rapid tests to identify causes of pneumonia and to promote better treatment."

The CDC Etiology of Pneumonia in the Community (EPIC) study was a prospective, multicenter, population-based study that used chest x-rays and extensive diagnostic methods to determine the incidence and etiology of community-acquired pneumonia hospitalizations among U.S. adults. Participants in the study were enrolled from January 2010 through June 2012 in three hospitals in Chicago and two in Nashville. Study participants provided specimens that were tested using a range of laboratory tests for viral and bacterial respiratory pathogen detection.

During the study period, the EPIC study team enrolled 2,488 eligible adults, of which 2,320 (93 percent) had radiographically-confirmed pneumonia. The median age of study participants was 57 years.

The researchers detected viruses in 27 percent of patients and bacteria in 14 percent of patients. Human rhinovirus (HRV) was the most commonly detected virus among pneumonia patients.

Influenza (flu) was the second most common pathogen detected, and there were twice as many pneumonia hospitalizations due to influenza than any other pathogen (except HRV) in adults 80 years or older, underscoring the need for improvements in flu vaccine uptake and effectiveness.

Together, human metapneumovirus, respiratory syncytial virus, parainfluenza virus, coronavirus, and adenovirus were detected in 13 percent of patients.

Of bacterial pathogens, Streptococcus pneumoniae was the most commonly detected bacterium, causing an estimated five times more pneumonia hospitalizations in adults 65 years and older than in younger adults. Mycoplasma pneumoniae, Legionella pneumophila, and Chlamydophila pneumoniae combined were detected in 4 percent of patients. Overall, Staphylococcus aureus was detected in 2 percent of patients and was found less frequently than S. pneumoniae or viruses.

S. pneumoniae, S. aureus, and Enterobacteriaceae were significantly more common among severely ill patients, accounting for 16 percent of detections among intensive care unit (ICU) patients compared with 6 percent among non-ICU patients.

"The frequency in which respiratory viruses were detected in adults hospitalized with pneumonia was higher than previously documented. This may be due to improved molecular diagnostics for viruses and also to the benefits of bacterial vaccines," said Dr. Seema Jain, lead author of the paper and medical epidemiologist in CDC's Influenza Division. "However, what's most remarkable is that despite how hard we looked for pathogens, no discernible pathogen was detected in 62 percent of adults hospitalized with pneumonia in the EPIC study. This illustrates the need for more sensitive diagnostic methods that can both help guide treatment at the individual level as well as inform public health policy for adult pneumonia at a population level."

The CDC EPIC study is one of the largest population-based pneumonia studies ever conducted in the United States. It has helped improve understanding of the burden pneumonia places on U.S. adults and children. For more information on the EPIC study, visit's CDC's EPIC website. This EPIC study is available from the New England Journal of Medicine's website.


Modified and reproduced with permission from the CDC