Community Acquired Pneumonia

Pneumonia is a lower respiratory tract infection which often leads to inflammation of the lung tissue, most commonly due to a bacterial or viral infection. Community acquired pneumonia is a pneumonia which is acquired outside of the hospital setting.

Causes

Community acquired pneumonia is typically spread by respiratory droplets which are inhaled and subsequently enter the lower respiratory tract.

Typical Bacteria

• Streptococcus pneumoniae (pneumococcus) is the most common cause
• Haemophilus influenzae
• Moraxella catarrhalis

Atypical Bacteria

• Mycoplasma pneumoniae
• Staphylococcus aureus
• Legionella pneumophila: Tends to occur from air conditioners/infected water sources.
• Chlamydia pneumoniae

Viruses

• Influenza
• Cytomegalovirus
• Adenovirus

Risk Factors

• Smoking
• Old age
• Use of PPI
• Alcohol
• Immunosuppression
• Recent influenza

Clinical Features

• Fevers
• Rigors
• Chills
• Dyspnoea
• Cough (can be both non-productive or productive)
• Pleuritic chest pain
• Loss of appetite
• Upper abdominal pain may be present, particularly in patients with lower lobe pneumonia.
• Haemoptysis

On examination, bronchial breathing and coarse crackles may be auscultated alongside dull percussion notes and increased tactile vocal fremitus which suggests the presence of a consolidation. A pleural rub may also be heard.

Investigations

Bedside

• Sputum Culture: Confirms bacterial growth from the lungs and allows tailoring of antibiotics based on sensitivities.
• Blood Culture: If suspecting sepsis or patients with moderate or high-risk pneumonia
• Pneumococcal and legionella urinary antigen tests: If patient has moderate or high-risk pneumonia
• Atypical Pneumonia Screen: Includes testing for chlamydia pneumoniae, legionella pneumophila, and mycoplasma pneumonia

Bloods

• FBC: Looking for raised white cell count
• U&E: For baseline as well as severity scoring
• CRP: Usually raised in infection
• LFT: If patient is complaining of right upper quadrant pain to rule out an abdominal cause
• Arterial blood gas: Check for respiratory failure

Imaging

• Chest x-ray: A plain chest x-ray is the main diagnostic method for pneumonia. A positive chest x-ray will show an area of consolidation. Normally, the airways appear ‘black’ on a chest x-ray (low opacity) as they are patent airways. If there is a process in the lungs causing alveoli to become fluid filled e.g. infection, this will appear as a ‘white’ (high opacity) area on the x-ray.

Mikael Häggström, M.D. - Author info - Reusing imagesWritten informed consent was obtained from the individual, including online publication., CC0, via Wikimedia Commons

Consolidation in Right Lower Zone