Table 1.
Diagnostic features of the nonzoonotic atypical pneumonias
| Key Characteristics | M pneumoniaea | Legionnaires' Disease | C pneumoniae |
|---|---|---|---|
| Signs | |||
| • Rash | ±b | − | − |
| • Nonexudative pharyngitis | + | − | + |
| • Hemoptysis | − | ± | − |
| • Wheezing | − | − | + |
| • Lobar consolidation | − | ± | − |
| • Cardiac involvement | ±c | −d | − |
| • Splenomegaly | − | − | − |
| • Relative bradycardia | − | + | − |
| Laboratory abnormalities | |||
| • WBC count | ↑/N | ↑ | N |
| • Acute thrombocytosis | ± | − | − |
| • Hyponatremia | − | + | − |
| • Hypophosphatemia | − | + | − |
| • ↑ AST/ALT | − | + | − |
| • ↑ CPK | − | + | − |
| • ↑ CRP (>30) | − | + | − |
| • ↑ Ferritin (>2 × n) | − | + | − |
| • ↑ Cold agglutinins (≥1:64) | + | − | − |
| • Microscopic hematuria | − | ± | − |
| Chest radiograph | |||
| • Infiltrates | Patchy | Patchy or consolidation | “Circumscribed” lesions |
| • Bilateral hilar adenopathy | − | − | − |
| • Pleural effusion | ± (small) | ± | − |
| Diagnostic tests | |||
| • Direct isolation (culture) | ± | + | ± |
| • Serology (specific) | CF | IFA | CF |
| • Legionella IFA titers | − | ↑↑↑ | − |
| • Legionella DFA | − | + | − |
| • Legionella urinary antigen | − | +e | − |
Abbreviations: CF, complement fixation; CPK, creatinine phosphokinase; CRP, C-reactive protein; CYE, charcoal yeast agar; DFA, direct fluorescent antibody; IFA, indirect fluorescent antibody; N, normal; WBC, white blood cell; +, usually present; ±, sometimes present; −, usually absent; ↑, increased; ↓, decreased; ↑↑↑, markedly increased.
Adapted from Cunha BA, editor. Pneumonia essentials. 3rd edition. Sudbury (MA): Jones & Bartlett; 2010.
Mental confusion only if meningoencephalitis.
Erythema multiforme.
Myocarditis, heart block, or pericarditis.
Unless endocarditis.
Often not positive early, but antigenuria persists for weeks. Useful only to diagnose L pneumophila. (serogroups 01–06), not other species/serogroups.