Changing Microbiology of Community Acquired Pneumonia

Since the start of pneumococcal conjugate vaccine use for routine childhood immunization, the overall rate of invasive disease and pneumonia among adults has decreased, likely due to herd immunity. We also now have have more sensitive laboratory tests to detect pathogens responsible for pneumonia in adults. This requires an updated assessment of the incidence of pneumonia and causative pathogens.

Seema Jain and her colleagues have recently explored this question in a prospective, multicenter, population-based, active surveillance study, the Centers for Disease Control and Prevention (CDC) Etiology of Pneumonia in the Community (EPIC) study, and published results in the NEJM.

The study enrolled adults 18 years of age or older were enrolled at three hospitals in Chicago (John H. Stroger, Jr., Hospital of Cook County, Northwestern Memorial Hospital, and Rush University Medical Center) and at two in Nashville (University of Tennessee Health Science Center–Saint Thomas Health and Vanderbilt University Medical Center) from January 1, 2010, to June 30, 2012.

There were 2320 cases of pneumonia confirmed with radiographs. Quite interestingly, and in contrast to what would one expect to see, pneumonia were distributed about evenly between younger (18-49) middle (50-64) and older (>64) age groups, roughly one third in each category. Most (78%) had some underlying condition predisposing to pneumonia. Surprisingly, less than half were vaccinated with influenza or pneumococcal vaccine. Only in 38% of patients, a pathogen was detected despite using an extensive battery of laboratory diagnostics. Pathogens detected were as follows: 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 pneumococcus (in 5%).

At a population level, 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).

The results overall reaffirm the common observation that pneumonia incidence is highest in the elderly population. Results further show that despite current diagnostic tests, no pathogen was detected in the majority of patients. The overall pathogens for pneumonia are changing with respiratory viruses being detected more frequently than bacteria.