Pneumonia: Streptococcus and Mycoplasma are common causes.

Clinical bottom line (level 4)

  1. Common causes of pneumonia are Streptococcus pneumoniae and Mycoplasma pneumoniae.
  2. Patients with bloody sputum, a high white cell count or a lobar infiltrate on chest X-ray are more likely to have a pnuemococcal infection.
  3. A prolonged illness or age < 40 make a Mycoplasma pneumoniae infection more likely.
Farr et al: Thorax 1989; 44: 1031-1035
Expires March 2003

The study

Setting: 25 acute hospitals, UK

441 patients (aged 15 to 74, ?% male) admitted with a community-acquired pneumonia

Independent ?blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
Reference standard:
  • microbial aetiology defined by culture and Gram stain of sputum; blood culture; complement fixation tests for psittacosis, Q fever, influenza A and B, respiratory syncytial virus and parainfluenza; serology for Mycoplasma pneumonia and Legionella pneumophilia
Diagnostic test: clinical features on admission
  • A multivariate regression analysis was performed to identify the features independently predictive of the aetiology.

The evidence


differential diagnosis number of patients prevalence
(95% CI)
unknown 148 34%
(29% to 38%)
Streptococcus pneumoniae 142 32%
(28% to 37%)
Mycoplasma pneumoniae 73 17%
(13% to 20%)
Influenza A 24 5.4%
(3.3% to 7.6%)
Haemophilus influenzae 18 4.1%
(2.2% to 5.9%)
Chlamydia psittaci 10 2.3%
(0.9% to 3.7%)
Legionella pneumophila 7 1.6%
(0.4% to 2.8%)
Coxiella burnetti 5 1.1%
(0.1% to 2.1%)
Staphylococcus aureus 4 0.9%
(0.02% to 1.8%)
other 16 3.6%
(1.9% to 5.4%)

  • Patients with pneumococcal pneumonia were more likely to have
    • bloody sputum
    • white cell count > 14.4
    • a lobar infiltrate
  • Patients with Mycoplasma pneumoniae were more likely to
    • be aged < 40
    • have been ill for 9 or more days

Citation

  1. Farr BM, Kaiser DL, Harrison BD, et al: prediction of microbial aetiology at admission to hospital for pneumonia from the presenting clinical features. Thorax 1989; 44: 1031-1035
Search Terms: ?
Contributor: Chris Ball and Clare Wotton, December 1999
Reviewer: Dirk Stengel

Clinical Question.
Patient pneumonia
Intervention or Exposure clinical features at presentation
Outcome infecting organism