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 (CAP) 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%). The mean age of patients was 57 years. Seventy-eight percent of patients had some underlying medical condition (most commonly chronic lung disease, heart disease, immunosuppression, or diabetes). Twenty-one percent of patients required intensive care unit (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 plus 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 pneumoniae in 5%. Less common pathogens included human metapneumovirus (4%), respiratory syncytial virus (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 Centers for Disease Control (CDC) in two large U.S. cities during a two-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

  1. Jain S, et al. Community-acquired pneumonia requiring hospitalization among U.S. children. N Engl J Med 2015;372:835-845.