Acute chest infection 2 Laboratory diagnosis

The following samples are required for laboratory diagnosis:

• Sputum (e.g. cough specimen, endotracheal tube aspirate, protected brush specimen, bronchoalveolar lavage specimen)

• Blood cultures

• Serology (in community acquired pneumonia)

• Urine for antigen tests (if Legionella, Candida or pneumococcus suspected)

In severe pneumonia, blind antibiotic therapy should not be withheld while awaiting results. Specimens should, however, be taken before starting antibiotics.

Microbiological yield is usually very low, especially if antibiotic therapy has started before sampling.

Where cultures are positive there is often multiple growth. Separating pathogenic organisms from colonising organisms may be difficult.

In hospital acquired pneumonia, known nosocomial pathogens are the likely source, e.g local Gram negative flora, MRSA.

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