Viruses, Not Bacteria, Most Common Pathogen in Adult Pneumonia
Viruses, not bacteria, are the most commonly detected respiratory pathogens in adults hospitalized with pneumonia in the United States, according to the results of a multicenter study. However, despite current diagnostic tests, neither viruses nor bacteria are detected in the majority (62%) of these patients (N Engl J Med 2015 July 14. ([Epub ahead of print]).
The findings highlight a need for more sensitive and rapid diagnostic tests to identify pneumonia pathogens and choose appropriate treatments, the researchers said.
“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 Tom Frieden, MD, MPH, the director of the Centers for Disease Control and Prevention (CDC), which led the study. “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 Etiology of Pneumonia in the Community (EPIC) study was a prospective, multicenter, population-based study that used chest x-ray and extensive diagnostic methods to determine the incidence and etiology of community-acquired pneumonia hospitalizations. Patients were enrolled from Jan. 1, 2010 to June 30, 2012, at three pediatric hospitals in Memphis and Nashville, Tenn., and Salt Lake City, and five adult hospitals in Chicago and Nashville. This study looked at results in adults.
The EPIC study team enrolled 2,488 eligible adults, of which 2,320 (93%) had pneumonia that was confirmed by chest radiography and extensive diagnostic methods, including culture, serologic testing, antigen detection and molecular diagnostic testing. The median age of the participants was 57 years.
The researchers detected viruses in 27% of patients and bacteria in 14%. Human rhinovirus (HRV) was the most commonly detected virus among pneumonia patients.
Influenza virus was the second most common viral pathogen detected, and there were twice as many pneumonia hospitalizations related to influenza as any other viral pathogen (except HRV) in adults aged 80 years or older, underscoring the need for improvements in influenza vaccine uptake and effectiveness, they said.
Altogether, 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 aged 65 years 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 ICU patients compared with 6% among non-ICU patients.
“We studied about 2,400 patients hospitalized with community-acquired pneumonia at five hospitals to understand if pneumonia continues to be a significant public health burden and to investigate what pathogens are causing pneumonia in our communities,” said Wesley Self, MD, MPH, assistant professor of emergency medicine at Vanderbilt University Medical Center, in Nashville, Tenn.
Even though routine administration of pneumococcal conjugate vaccine to children has reduced the overall rate of invasive pneumococcal disease and pneumonia among children and adults, pneumonia is still a serious problem in this country, the researchers said. “We found that community-acquired pneumonia remains a very common reason for hospital admission in the U.S. We also found that viruses were more commonly associated with pneumonia than bacteria in our study,” Dr. Self said, reiterating Dr. Frieden’s call for better diagnostic tests.
“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 Seema Jain, MD, a 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% 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.”