Last reviewed: 8 Jan 2023
Last updated: 31 Jan 2023



History and exam

Key diagnostic factors

  • cough with increasing sputum production
  • dyspnoea
  • pleuritic chest pain
  • rigors or night sweats
  • fever
  • abnormal auscultatory findings
  • confusion
  • presence of risk factors

Other diagnostic factors

  • myalgia
  • malaise
  • anorexia
  • lethargy
  • worsening of pre-existing conditions
  • sore throat
  • headache
  • nausea
  • abdominal pain
  • diarrhoea

Risk factors

  • age >65 years
  • residence in a healthcare setting
  • COPD
  • exposure to cigarette smoke
  • alcohol abuse
  • poor oral hygiene
  • use of acid-reducing drugs
  • contact with children
  • diabetes mellitus
  • chronic renal disease
  • chronic liver disease
  • use of opioids

Diagnostic investigations

1st investigations to order

  • chest x-ray
  • pulse oximetry
  • arterial blood gas (ABG)
  • urea and electrolytes
  • full blood count
  • C-reactive protein (CRP)
  • liver function tests

Investigations to consider

  • blood culture
  • sputum culture (± Gram stain)
  • urinary antigen testing for legionella and pneumococcus
  • polymerase chain reaction (PCR) and/or serological tests
  • CT scan of chest
  • chest ultrasound
  • thoracocentesis and pleural fluid culture
  • computer tomographic pulmonary angiography (CTPA)
  • bronchoscopy
  • serum procalcitonin
  • point-of-care CRP

Treatment algorithm


Expert advisers

Jonathan Bennett, MD

Honorary Professor of Respiratory Sciences

University of Leicester

Respiratory Consultant

Glenfield Hospital




JB is deputy medical director RCP Invited service Reviews, and speaker at National Society (e.g., BTS), Primary Care respiratory Society, and Society Cardiothoracic Surgeons meetings.


JB declares that he has no competing interests.


BMJ Best Practice would like to gratefully acknowledge the previous team of expert contributors, whose work has been retained in parts of the content:

Catia Cilloniz MSc, PhD

Post-doctoral Research

Pneumology Department

Hospital Clinic of Barcelona





Antoni Torres MD, PhD

Professor of Medicine


Pulmonary Intensive Care Unit

Respiratory Institute

Hospital Clinic of Barcelona




CC and AT are each authors of a number of references cited in this topic.

Peer reviewers

Wei Shen Lim

Consultant Respiratory Physician and Honorary Professor of Medicine

Nottingham University Hospitals NHS Trust




WSL was chairman of the British Thoracic Society community-acquired pneumonia guidelines committee and a member of the guideline development group for the National Institute for Health and Care Excellence pneumonia guidelines. His institution has received unrestricted investigator-initiated research funding from Pfizer for a multicentre study of pneumococcal pneumonia in which he was the chief investigator, and research funding from the National Institute for Health Research for studies in pneumonia in which he was the principal investigator. He is also an author of at least one reference cited in the topic.


Helena Delgado-Cohen

Section Editor, BMJ Best Practice


HDC declares that she has no competing interests.

Rachel Wheeler

Lead Section Editor, BMJ Best Practice


RW declares that she has no competing interests.

Julie Costello

Comorbidities Editor, BMJ Best Practice


JC declares that she has no competing interests.

Adam Mitchell

Drug Editor, BMJ Best Practice


AM declares that he has no competing interests.

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