5. Nonbacterial community – acquired pneumonia (atypical, viral)
Covers atypical and viral community-acquired pneumonia, starting with the definition and the organisms involved, including Mycoplasma, Chlamydophila, Legionella, Coxiella and respiratory viruses. It then sets out how these infections spread and how they differ clinically from typical bacterial pneumonia, using a comparison table. Each important atypical bacterium and the main viruses, such as influenza and COVID-19, are described with their presentation and treatment, followed by diagnosis, drug choices in a table, and complications.
Topic 5 of 139 in the MU Sofia syllabus for Internal Diseases and Therapy (Medicine, Years 4 and 5). The free AceMed note covers it in 9 sections, about 945 words (8 min of reading), with 16 flashcards.
In this note
Definition
Etiology
Pathogenesis
Clinical presentation (compared with typical pneumonia)
Important atypical bacteria
Viral pneumonia
Diagnosis
Treatment
Complications and prognosis
Definition
Atypical pneumonia is pneumonia caused by organisms that are not seen on Gram stain, do not grow on routine culture and are not covered by β-lactams: the "atypical" bacteria (Mycoplasma, Chlamydophila, Legionella, Coxiella) and respiratory viruses. They usually cause an interstitial pneumonia with an indolent course and prominent extrapulmonary symptoms ("walking pneumonia").
Etiology
Viruses are found in up to a third of adults with CAP; a viral infection often paves the way for a secondary bacterial pneumonia (S. pneumoniae, S. aureus, H. influenzae).
Pathogenesis
Most are spread by droplets person to person (Mycoplasma, Chlamydophila, viruses); Legionella, psittacosis and Q fever come from the environment or animals and are not transmitted between people.
Mycoplasma has no cell wall (so β-lactams do not work); it attaches to ciliated epithelium (P1 adhesin), damages the cilia and causes inflammation of the bronchioles and interstitium.
Chlamydophila and Legionella are intracellular (Legionella multiplies in alveolar macrophages) → need drugs that enter cells (macrolides, tetracyclines, fluoroquinolones).
Viruses infect and destroy respiratory epithelium → interstitial mononuclear infiltrate, oedema of the alveolar walls, hyaline membranes in severe cases (diffuse alveolar damage → ARDS).
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