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CDC Study Highlights Burden of Pneumonia Hospitalizations

Pathogens undetectable in 62% of patients

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 most of these patients, according to a study by the Centers for Disease Control and Prevention (CDC) published in the New England Journal of Medicine.

This 2½-year study, conducted at three hospitals in Chicago and at two hospitals in Nashville, estimated the burden of community-acquired pneumonia (CAP) hospitalizations among U.S. 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, MD, MPH. “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’s study was a prospective, population-based investigation that used chest radiographs and extensive diagnostic methods to determine the incidence and etiology of hospitalizations for CAP among U.S. adults from January 2010 through June 2012. Study participants provided specimens that were tested for viral and bacterial respiratory pathogens.

During the study, the CDC team enrolled 2,488 eligible adults, of whom 2,320 (93%) had radiographically confirmed pneumonia. The participants’ median age was 57 years.

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

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

Together, human metapneumovirus, respiratory syncytial virus, parainfluenza virus, coronavirus, and adenovirus were detected in 13% 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 of age and older than in younger adults. Mycoplasma pneumoniae, Legionella pneumophila, and Chlamydophila pneumoniae combined were detected in 4% of patients. Overall, Staphylococcus aureus was detected in 2% 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% of detections among intensive care unit (ICU) patients compared with 6% among non-ICU patients.

“The frequency with 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 lead author Dr. Seema Jain. “However, what’s most remarkable is that despite how hard we looked for pathogens, no discernible pathogen was detected in 62% of adults hospitalized with pneumonia. This illustrates the need for more sensitive diagnostic methods that can help guide treatment at the individual level as well as inform public health policy for adult pneumonia at a population level.”

Sources: CDC; July 14, 2015; and NEJM; January 14, 2015.

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