Microbiological investigations for HAP

The results of microbiological investigations for hospital-acquired pneumonia (HAP) can enable directed therapy or de-escalation of antibiotic treatment. Collect the following samples for Gram stain and culture:

• blood samples
• sputum samples (if available)
• in intubated patients, lower respiratory tract samples (if possible).

Samples for culture should ideally be collected before starting antibiotic therapy.

At the onset of HAP, many patients do not produce sputum. If a sputum sample can be collected before starting antibiotic therapy, a good quality sample (presence of polymorphs, but few or no squamous epithelial cells on microscopy) can assist in detection of the pathogen.

Testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other respiratory viruses (eg influenza, respiratory syncytial virus [RSV]) should be performed for patients with HAP, given the possibility of nosocomial spread.

Investigations for Legionella species, Chlamydophila (Chlamydia) pneumoniae and Mycoplasma pneumoniae are not routinely required because these are rare causes of HAPHagel, 2019. Consider performing investigations for these pathogens if the response to empirical antibiotic therapy is inadequate.

For patients with immune compromise who have high-severity HAP or significant immunosuppression (eg recent solid organ or haematopoietic stem cell transplant), consider performing investigations for a broader range of pathogens (see Aetiology of HAP in patients with immune compromise). Discuss with a respiratory physician the need for bronchoscopy for patients with immune compromise who have HAP if either:

• response to empirical antibiotic therapy is inadequate
• there are concerns for opportunistic pathogens (eg Pneumocystis jirovecii or other fungal pathogens) that may not be diagnosed by non-invasive sampling.