Expansion
The context predicts the organism
Expansion
| Context | Organism |
|---|---|
| Any community pneumonia | Streptococcus pneumoniae, commonest overall |
| Following influenza | Staphylococcus aureus, cavitating |
| COPD | Haemophilus influenzae, Moraxella |
| Young adult, dry cough, erythema multiforme | Mycoplasma pneumoniae |
| Air conditioning, hyponatraemia, deranged LFTs | Legionella pneumophila |
| Birds | Chlamydia psittaci |
| Farm animals, abattoir | Coxiella burnetii (Q fever) |
| Alcohol dependence, “redcurrant jelly” sputum | Klebsiella, upper lobe cavitation |
| Aspiration | Anaerobes and oral flora |
| HIV with a low CD4 count | Pneumocystis jirovecii |
| Bronchiectasis, cystic fibrosis | Pseudomonas, Burkholderia |
| Hospital acquired, over 48 hours | Gram negatives, Pseudomonas, MRSA |
“Flu then staph, birds then chlamydia, alcohol then klebsiella” covers the three associations most often tested.
Aspiration goes to the right lung, because the right main bronchus is wider, shorter and more vertical: the lower lobe when upright, and the apical segment of the lower lobe or the posterior segment of the upper lobe when supine.
Pneumocystis characteristically has a normal or near normal chest radiograph early, with exertional desaturation and a raised LDH, which is why exercise oximetry is used.