Table 1.
Diagnostic features of the non-zoonotic atypical pneumonias. Adapted from Cunha, 2006 [6]
| Key Characteristics | Mycoplasma pneumoniae | Legionnaire's disease | Chlamydophilia (Chlamydia) pneumoniae |
|---|---|---|---|
| Symptoms | |||
| Mental confusion | ±a | + | – |
| Prominent headache | – | ± | – |
| Meningismus | – | – | – |
| Myalgias | ± | ± | ± |
| Ear pain | ± | – | ± |
| Pleuritic pain | – | ± | – |
| Abdominal pain | – | + | – |
| Diarrhoea | + | + | – |
| Signs | |||
| Rash | ±b | – | – |
| Non-exudative pharyngitis | + | – | + |
| Haemoptysis | – | ± | – |
| Lobar consolidation | – | ± | – |
| Cardiac involvement | ±c | – | – |
| Splenomegaly | – | – | – |
| Relative bradycardia | – | + | – |
| Shock/hypotensiong | – | + | – |
| Chest X-ray | |||
| Infiltrates | Patchy | Rapidly progressive Asymmetrical ± consolidation | ‘Circumscribed’ lesions |
| Bilateral hilar adenopathy | – | – | – |
| Pleural effusion | ± (small) | ± | ± |
| Laboratory Abnormalities | |||
| WBC count | ↑/ N | ↑ | N |
| Hyponatraemia | – | + | – |
| Hypophosphataemia | – | + | – |
| Mild/early transient increased AST/ALT (SGOT/SGPT) | – | + | – |
| ↑ Cold agglutinins (≥ 1 : 64) | + | – | – |
| Microscopic haematuria | – | ± | – |
| Diagnostic Tests | |||
| Direct isolation (culture) | +d | +d | +d |
| Serology | CF | IFA | CF |
| Psittacosis CF litres | – | ↑ | ↑ |
| Legionella IFA litres | – | ↑↑↑ | – |
| Legionella DFA | – | +e | – |
| Legionella urinary antigen | – | +f | – |
ALT, alanine aminotransferase; AST, aspartate aminotransferase; CF, complement fixation; DFA/IFA, direct/indirect fluorescent antibody test; N, normal; WBC, white blood cell; +, usually present; ±, sometimes present; –, usually absent; ↑, increased; ↓, decreased; ↑↑↑, markedly increased
a
rarely, only with Mycoplasma mengoencephalitis (cold agglutinins > 1 : 512)
b
erythema multiforme
c
myocarditis, heart block, or pericarditis
d
requires special media
e
rapidly becomes negative with anti-Legionalla therapy
f
may be falsely negative early, useful only Legionella pneumophila (serotype 01)
g
without acute cardiac/pulmonary events.