Microbiological investigations for VAP

The results of microbiological investigations for ventilator-associated pneumonia (VAP) can enable directed therapy or de-escalation of antibiotic treatment. Collect blood samples and, if possible, lower respiratory tract samples for Gram stain and culture, ideally before starting antibiotic therapy. Interpret Gram-stain results of respiratory tract samples with care¹.

Investigations for Legionella, Mycoplasma and Chlamydia species are not routinely required for patients with VAP. Consider performing investigations for these pathogens if the response to empirical antibiotic therapy is inadequate. Given increasing recognition of nosocomial transmission of respiratory viruses, consider testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other viruses such as influenza and respiratory syncytial virus (RSV).

For patients with immune compromise who have VAP, consider performing investigations for a broader range of pathogens (see Aetiology of VAP in patients with immune compromise).

In patients who are severely unwell or not improving, there may be an advantage in obtaining samples for culture with more invasive methods (eg bronchoalveolar lavage [BAL] or mini-BAL).

¹ Gram stain of poor-quality respiratory samples can give misleading results. Ensure a good quality sample (collected before starting antibiotics) is used for adjusting therapy. A good quality sample is indicated by presence of polymorphs, but few or no squamous epithelial cells on microscopy. The pathogen should be predominant in the Gram stain as well as the culture.Return