Community acquired pneumonia (CAP)

Last updated: Tuesday, June 20, 2017

These guidelines are based upon a range of information resources and may not represent your local policy. Check if your Trust has local CAP guidelines before reading on.

Case definition
Diagnosis is based upon symptoms and signs of an acute lower respiratory tract infection and can be confirmed radiologically. Click to learn more.
CAP presents as new or worsening shadowing on the chest X-ray or CT of a patient with clinical features which usually include cough, chest pain, fever (> 38.0⁰C) and difficulty breathing (although these clinical features may be absent such as in older patients).
Exclusions: septic shock, immunocompromised, hospital acquired pneumonia, bronchiectasis, pneumonia expected to be a terminal event.
Typical pathogen profile
Streptococcus pneumoniae is the most common pathogen but a range of atypicals and other bacteria and viruses may be responsible. Click to learn more.
Gram positive
Streptococcus pneumoniae (39%)
Staphylococcus aureus (1.9%)

Gram negative
Haemophilus influenzae (5.2%)
Moraxella catarrhalis (1.9%)
Gram negative bacilli (1.9%)

Consider in nursing home residents

Legionella spp. (3.6%)
Chlamydophila pneumoniae (13.1%)
Mycoplasma pneumoniae (10.8%)
Chlamydophila psittaci (2.6%)
Coxiella burnetii (1.2%)

Viruses including influenza 13%
Microbiology investigations 
Blood and sputum samples should be taken. Additional tests may be required. Click to learn more.
Consider combined nose and throat swab for influenza and other respiratory virus detection.
Consider pneumococcal and legionella urinary antigen tests 

Evidence of infection
Antibiotic treatment is guided by changes in the patient's vital signs and the presence of respiratory symptoms. Click to learn more.
If one respiratory complaint is present (including cough, chest pain or shortness of breath) AND there is at least one abnormality of the vital signs (temperature > 38.0⁰C, pulse > 100 beats per minute, respiratory rate > 20 breaths per minute, or pulse oximetry < 95% on room air), order X-ray and start antibiotics.
If vital signs are normal, order X-ray and withhold antibiotics. If X-ray result is normal do not start antibiotics and monitor patient.
Risk of antibiotic resistance
Resistance to commonly used antibiotics for CAP is a major consideration when choosing empirical therapy. There are a range of risk factors. Click to learn more.
Recent travel to Europe or USA linked to a risk of penicillin-resistant pneumococcus
Nursing home resident
Alcohol dependence/homelessness – risk of Gram negative enteric bacilli and Klebsiella
Bronchiectasis/interstitial lung disease/enteral tube feeding - risk of Pseudomonas
If recent hospital inpatient, review previous M,C&S to guide therapy
Severity assessment
There are several severity scoring systems available. Click to see an example.
  • Confusion/disorientation
  • Urea > 7mmol/L
  • Respiratory rate ≥ 30 breaths per minute
  • BP systolic < 90 mmHg
  • O2 sats on room air < 86%
  • Multilobar infiltrates

High severity:  ≥ 3 criteria consider referral to critical care
Moderate severity: 0-2 criteria treat on ward as moderate severity CAP
Choosing an antibiotic
Please consult your local antibiotics guidelines for the preferred choice of agents. Here is an example protocol from University Hospital Southampton, for you to look at, but it is not intended to replace your local guidelines
Follow up
There are a number of methods to assess the clinical stability of patients with pneumonia. One of these is ‘Halm’s stability criteria’ and progress is assessed according to how many of the criteria the patient meets. These may help to inform whether a patient can be switched from intravenous to oral antibiotics, for example. Click to learn more.
Halm's stability criteria are:
1. Temperature ≤ 37.8⁰C
2. Heart rate ≤ 100 beats per minute
3. Respiratory rate ≤ 24 breaths per minute
4. Systolic blood pressure ≥ 90 mmHg
5. O2 sats ≥ 90%
6. Normal mental status
7. Normal oral intake
Duration guide 
There is considerable variation between different sources so check your local guidelines. This is an example protocol:
Hospitalised, moderate severity: 5 days (if ≤ 37.8⁰C for 48 hours)
Hospitalised, high severity: 5-7 days (stop at 5 days if ≤ 37.8⁰C for 48 hours AND no more than one sign of instability (Halm's criteria 1-5) AND patient not immunosuppressed, not on intensive care, no chest drain required and no Legionella / Gram negative enteric bacilli /Pseudomonas /S.aureus from MC&S results).