By Dean L. Winslow, MD, FACP, FIDSA
SYNOPSIS: An active population-based surveillance of community-acquired pneumonia (CAP) requiring hospitalization in adults 18 years of age and older was conducted in five hospitals in Chicago and Nashville. The incidence of CAP requiring hospitalization was highest in older adults. Despite extensive diagnostic testing, no pathogen was identified in most patients. Respiratory viruses were identified more frequently than bacteria.
SOURCE: Jain S, et al. Community-acquired pneumonia requiring hospitalization among U.S. adults. N Engl J Med 2015; 373: 415-27.
From January 2010 through June 2012 a total of 2488 (of 3634 eligible) adults were enrolled in an active population-based surveillance of community-acquired pneumonia requiring hospitalization in adult patients. Patients who had recently been hospitalized or who were severely immunosuppressed were excluded. Blood, urine, respiratory, and pleural specimens were systematically collected for testing by culture, serology, antigen detection and molecular diagnostic methods. In addition to routine bacteriological methods and urine antigen testing for S.pneumoniae and Legionella pneumophila, a variety of real-time PCR assays were systematically performed on respiratory samples and pleural fluid (when available).
Of the 2488 enrolled patients, independent review of X-rays by a panel of study radiologists concurred with the radiographic diagnosis of pneumonia in 2320 (93%). Mean age of patients was 57 years. 78% of patients had some underlying medical condition (most commonly chronic lung disease, heart disease, immunosuppression or diabetes). 21% of patients required ICU admission and 2% died. Incidence rates of CAP requiring hospitalization ranged from 6.7 cases/10,000 adults per year in patients ages 18-49 to 164.3 cases/10,000 adults per year in patients 80 years of age or older.
Of the 2259 patients who had radiographic evidence of pneumonia and specimens available for both bacterial and viral testing, a pathogen was detected in 38%, one or more viruses in 23%, bacteria in 11%, bacterial + viral pathogen in 3%, and fungal or mycobacterial pathogen in 1%. Of the potential pathogens identified, the most common were rhinovirus in 9%, influenza virus in 6%, and Streptococcus pneumonia in 5%. Less common pathogens included human metapneumovirus (4%), RSV (3%), and parainfluenza virus (3%). Interestingly, Mycoplasma pneumoniae, Staph aureus, adenovirus, Legionella, and Enterobacteriaceae were each found in <2% of cases. A large peak of infection occurred during the winter of 2010-11 and was associated with a large number of Influenza cases and smaller peaks of S.pneumoniae and S.aureus cases.
COMMENTARY
This is an interesting surveillance study conducted by the CDC in two large U.S. cities over a 2-year period. The study highlights the burden of pneumonia requiring hospitalization, particularly in older adults. This study also emphasizes that, even when extremely sensitive molecular diagnostic tests are used, a pathogen can be identified in only a minority of cases of CAP and that viral pathogens are more common than bacterial ones. This study is a nice companion piece to the paper published by this same group at CDC earlier this year that focused on CAP requiring hospitalization in children (1).
REFERENCE
- Jain S, et al. Community-acquired pneumonia requiring hospitalization among U.S. children. N Engl J Med 2015; 372: 835-845.
