Influenza Severity Scoring Systems
The CRB-65 (or CURB-65 in hospital settings) score is the recommended severity assessment tool for influenza-related pneumonia, though no scoring system has been specifically validated for influenza itself. 1
CRB-65 Score Components
The CRB-65 score assigns 1 point for each of the following criteria present 1:
- Confusion (Mental Test Score ≤8, or new disorientation in person, place, or time)
- Respiratory rate ≥30/min
- Blood pressure (Systolic BP <90 mmHg or Diastolic BP ≤60 mmHg)
- Age ≥65 years
Note: The CURB-65 score adds Urea >7 mmol/L as an additional criterion when laboratory testing is available in hospital settings. 1
Clinical Application and Management Algorithm
Score Interpretation for Hospital Referral 1
- CRB-65 = 0: Likely suitable for home treatment
- CRB-65 = 1 or 2: Consider hospital referral (particularly with score of 2)
- CRB-65 = 3 or 4: Urgent hospital admission required
Critical Override Criteria
Patients with bilateral chest signs (crackles) on examination should be referred to hospital for further assessment regardless of CRB-65 score due to the rapid and fulminant course of primary viral pneumonia. 1
Additional Severity Indicators Beyond CRB-65
Unstable Clinical Factors for Admission 2, 3
Consider hospital admission if ≥2 of the following are present:
- Temperature >37.8°C
- Heart rate >100/min
- Respiratory rate >24/min
- Systolic blood pressure <90 mmHg
- Oxygen saturation <90%
- Inability to maintain oral intake
- Abnormal mental status
Pediatric Severity Indicators 1
Children should be referred for assessment if they exhibit 1:
- Respiratory distress with raised PaCO₂ (>6.5 kPa)
- Failure to maintain SaO₂ >92% in FiO₂ >0.6
- Shock
- Recurrent apnea or slow irregular breathing
- Evidence of encephalopathy
- Severe dehydration
- Altered conscious level
Important Caveats
The CRB-65 score does not replace clinical judgment. 1 A patient's social circumstances must always be taken into account when making management decisions. 1
There is no validated severity assessment tool developed specifically for influenza-related pneumonia. 1 The CRB-65 score was originally developed for community-acquired pneumonia and is adapted for use in influenza-related pneumonia. 1
Common Pitfalls to Avoid
- Do not rely solely on CRB-65 score when bilateral chest signs are present—these patients require hospital referral regardless of score 1
- Do not delay assessment in patients with rapid deterioration or worsening dyspnea, even if initial CRB-65 score was low 1
- Remember that elderly or immunocompromised patients may not mount a fever response, which can falsely lower perceived severity 2