Are Atypical Pathogens Important for Patients with Community-Acquired Pneumonia?

Abstract

The term “atypical pathogens” refers to a variety of organisms, including Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella spp., that can cause community-acquired pneumonia (CAP). This designation was developed when investigators realized that some patients with pneumonia had a clinical picture and natural history that differed from that seen in patients with pneumococcal infection. The syndrome, initially associated with M. pneumoniae [1], is characterized by gradual onset of illness, with low-grade fever, mucoid sputum and a non-toxic presentation, with a chest radiograph that shows more severe involvement than indicated by the patient’s findings. Over the years, the frequency of pneumonia due to atypical pathogens has been widely variable in clinical series, the need for therapy of these pathogens has been questioned, the role of these organisms in severe ICU-treated CAP has been controversial, and the definition of the patient most at risk has been uncertain. In addition, there has been debate about whether identifying the presence of the “atypical pneumonia syndrome” has any diagnostic value and whether clinicians should use the presence or absence of this syndrome to guide initial empiric antibiotic therapy of CAP [2–4].