Community-Acquired Pneumonia Requiring Hospitalization among U.S. Adults

Abstract

Background: Community-acquired pneumonia is a leading infectious cause of hospitalization and death among U.S. adults. Incidence estimates of pneumonia confirmed radiographically and with the use of current laboratory diagnostic tests are needed.

Methods: We conducted active population-based surveillance for community-acquired pneumonia requiring hospitalization among adults 18 years of age or older in five hospitals in Chicago and Nashville. Patients with recent hospitalization or severe immunosuppression were excluded. Blood, urine, and respiratory specimens were systematically collected for culture, serologic testing, antigen detection, and molecular diagnostic testing. Study radiologists independently reviewed chest radiographs. We calculated population-based incidence rates of community-acquired pneumonia requiring hospitalization according to age and pathogen.

Results: From January 2010 through June 2012, we enrolled 2488 of 3634 eligible adults (68%). Among 2320 adults with radiographic evidence of pneumonia (93%), the median age of the patients was 57 years (interquartile range, 46 to 71); 498 patients (21%) required intensive care, and 52 (2%) died. Among 2259 patients who had radiographic evidence of pneumonia and specimens available for both bacterial and viral testing, a pathogen was detected in 853 (38%): one or more viruses in 530 (23%), bacteria in 247 (11%), bacterial and viral pathogens in 59 (3%), and a fungal or mycobacterial pathogen in 17 (1%). The most common pathogens were human rhinovirus (in 9% of patients), influenza virus (in 6%), and Streptococcus pneumoniae (in 5%). The annual incidence of pneumonia was 24.8 cases (95% confidence interval, 23.5 to 26.1) per 10,000 adults, with the highest rates among adults 65 to 79 years of age (63.0 cases per 10,000 adults) and those 80 years of age or older (164.3 cases per 10,000 adults). For each pathogen, the incidence increased with age.

Conclusions: The incidence of community-acquired pneumonia requiring hospitalization was highest among the oldest adults. Despite current diagnostic tests, no pathogen was detected in the majority of patients. Respiratory viruses were detected more frequently than bacteria. (Funded by the Influenza Division of the National Center for Immunizations and Respiratory Diseases.).

Figure 1. Screening, Eligibility, and Enrollment of Patients with Pneumonia

CT denotes computed tomography.

Figure 2. Pathogen Detection among U.S. Adults with Community-Acquired Pneumonia Requiring Hospitalization, 2010–2012

Panel A shows the numbers (above the bars) and percentages of all adults in whom a specific pathogen was detected. A total of 966 pathogens were detected in 853 of 2259 hospitalized adults with radiographic evidence of pneumonia who had tests available for the detection of both bacterial and viral pathogens. The proportions of viral, viral–viral, bacterial–viral, bacterial, and fungal or mycobacterial pathogens detected and no pathogen detected are shown in the pie chart. Percentages may not sum as expected owing to rounding. A total of 76 pathogens other than those listed here were detected in 74 patients, including Haemophilus influenzae (in 12 patients), Chlamydophila pneumoniae (in 9), Mycobacterium tuberculosis (in 8), pseudomonas (in 8), Streptococcus pyogenes (in 7), viridans streptococci (in 7), other streptococcus species (in 7), nontuberculous mycobacterial species (in 4), fusobacterium (in 3), Pneumocystis jirovecii (in 3), and bacteroides, coccidioides, histoplasma, pasteurella, both H. influenzae and Neisseria meningitidis, and both viridans streptococci and other streptococcus species (in 1 each). Panel B shows, according to month and year, the number of hospitalized adults who had pneumonia from any cause; patients in whom human rhinovirus, influenza virus, human metapneumovirus, and respiratory syncytial virus were detected; and patients in whom S. pneumoniae and Staphylococcus aureus were detected. Note the difference in scale of the y axis for each line graph.

Figure 3. Estimated Annual Pathogen-Specific Incidence Rates of Community-Acquired Pneumonia Requiring Hospitalization, According to Age Group

Circles indicate the annual number of hospitalizations for pneumonia per 10,000 adults, and the horizontal lines 95% confidence intervals. Rates are based on 10,511,911 person-years of observation. Note the differences in the scale of the x axis for the groups of patients 65 to 79 years of age and 80 years of age or older, as compared with the groups of patients 18 to 49 years of age and 50 to 64 years of age.