Hospital-acquired pneumonia

• Pneumonia that occurs >48 hours after admission to hospital.
• Ventilator-associated pneumonia (VAP) is a subset, that occurs >48 hours after intubation.
• Is heavily over-diagnosed in the hospital. Hospitalised patients commonly have transient chest x-ray infiltrates (e.g. atelectasis, cardiac failure) that are not HAP.
• Unlike community-acquired pneumonia (CAP), Gram negative organisms become more important in HAP.
• Patients living in rest homes, including ‘hospital-level care’, should generally be managed as CAP, rather than hospital-acquired pneumonia.

• Microbiology has very little role to play in the diagnosis of HAP or VAP.
• HAP and VAP are clinical and radiological diagnoses.
• A positive sputum culture in a hospitalised patient with sputum production is not diagnostic of HAP or VAP, and is not an indication for antibiotics in itself.
• Determining the causative organism for HAP is usually not possible with any degree of certainty. This is because many of the organisms that can cause HAP colonise the upper respiratory tract of hospitalised patients, so tend to grow in sputum samples regardless.

Patients with mild-moderate HAP do not require any microbiological testing, other than COVID-19 if appropriate.

• Exception: patients with significant immunocompromise should have sputum sent for Gram stain and culture.

For patients with severe HAP, VAP, or HAP occurring in ICU, these tests are recommended:

• 2 sets of blood cultures before antibiotics
• Sputum (or other deep respiratory sample) for Gram stain and culture

A positive sputum culture in a patient without clinical or radiological features of pneumonia is usually meaningless, and not an indication for antibiotics.

Because sputum culture is so inaccurate for determining the causative organism for HAP or VAP, we recommend using sputum culture as a screen for resistant organisms to the antibiotics they are on, rather than to determine the microbiological cause of infection.

Possible scenarios and responses:

• Patient responding to antibiotics + no resistant organisms grown
  • Continue same antibiotics or rationalise to narrower spectrum
• Patient responding to antibiotics + resistant organism grown
  • Continue same antibiotics and monitor response
• Patient not responding to antibiotics + resistant organism grown
  • Confirm diagnosis of HAP/VAP is correct
  • Adjust antibiotics to cover resistant organism

Sputum Gram stain and culture:

• Avoid sending this in patients with productive cough in hospital outside the recommendations above. The culture will often be positive, and commonly leads to unnecessary antibiotic use.