Diagnosis of HAP

There are no universally accepted diagnostic criteria for hospital-acquired pneumonia (HAP). The isolation of bacteria from culture of sputum or a lower respiratory tract sample often represents colonisation; it is not sufficient to diagnose HAP.

Note: Isolation of bacteria from a respiratory tract sample is not sufficient to diagnose HAP.

A diagnosis of HAP is suggested in patients who have a new, progressive, or persistent infiltrate on chest X-ray (not explained by other causes), plus at least one of the following featuresAmerican Thoracic, 2005Kalil, 2016US Food and Drug Administration (FDA), 2020Weiss, 2017:

  • temperature above 38°C or below 35°C
  • total white cell count above or below the normal range
  • presence, or increased amount, of purulent sputum or lower respiratory tract secretions
  • worsening gas exchange (eg desaturation, increased oxygen requirement) or tachypnoea.

If clinical signs and symptoms suggest pneumonia, perform a chest X-ray to confirm the diagnosis. For adults, the initial chest X-ray provides a comparison for follow-up imaging, if this is required. The signs of pneumonia are often more subtle in older patients and patients with comorbid lung disease or immune compromise. If the chest X-ray is performed very early in the illness (eg in the first 24 hours), the infiltrate may not be evident. If pneumonia is suspected clinically but consolidation is not obvious on the chest X-ray, consider repeating the X-ray in a few days’ time.

Many postoperative patients with shadowing on chest X-ray do not have pneumonia. Postoperative atelectasis is common and usually noninfective, but can predispose the patient to pneumonia. Management of postoperative atelectasis with chest physiotherapy is recommended.

Tailor further investigations such as ultrasound and computed tomography (CT) as indicated to consider other differential diagnoses (eg pulmonary embolism, pleural effusion).

Consider alternative diagnoses to pneumonia in patients with immune compromise and pulmonary infiltrates on X-ray, given the broad differential. This may include noninfectious pathologies such as:

  • acute respiratory distress syndrome
  • drug-related pneumonitis
  • progression of underlying disease such as malignancy
  • connective tissue disease.

Symptoms of pneumonia overlap with symptoms of an exacerbation of chronic obstructive pulmonary disease (COPD) or bronchiectasis. An accurate diagnosis is important as treatment of exacerbations differs from treatment of pneumonia. Consider a diagnosis of pneumonia if the patient is more unwell than with previous exacerbations. Signs suggestive of pneumonia in patients with COPD or bronchiectasis include tachypnoea at rest, tachycardia, rigors, and crepitations (crackles) on auscultation that do not clear with coughing. A chest X-ray is usually required. For antibiotic management of an exacerbation of these conditions, see:

For patients with cystic fibrosis and symptoms of pneumonia, treatment must be directed by a specialist cystic fibrosis centre – see Airway infection and antibiotic therapy in cystic fibrosis.