Pneumonia is an infection of the lung tissue, causing inflammation in the alveolar space. Pneumonia can be seen as a consolidation on a chest x-ray.
Acute bronchitis refers to infection and inflammation in the bronchi and bronchioles. Both pneumonia and acute bronchitis are classed as lower respiratory tract infections. Upper respiratory tract infections (e.g., a common cold) are usually viral. As a general rule, the lower down the respiratory tract, the higher the probability of bacterial infection, as opposed to viral.
Classification
Pneumonia can be classified based on where the infection was acquired:
- Community-acquired pneumonia (CAP) develops in the community
- Hospital-acquired pneumonia (HAP) develops after more than 48 hours in a hospital
- Ventilator-acquired pneumonia (VAP) develops in intubated patients in the intensive care unit
Aspiration pneumonia is when the infection develops due to the aspiration of food or fluids, usually in patients with impaired swallowing (e.g., following a stroke or advanced dementia). Aspiration pneumonia is associated with anaerobic bacteria.
Presentation
Presenting symptoms of pneumonia are:
- Cough
- Sputum production
- Shortness of breath
- Fever
- Feeling generally unwell
- Haemoptysis (coughing up blood)
- Pleuritic chest pain (sharp chest pain, worse on inspiration)
- Delirium (acute confusion)
Characteristic chest signs of pneumonia include:
- Bronchial breath sounds (harsh inspiratory and expiratory breath sounds) due to consolidation around the airways
- Focal coarse crackles caused by air passing through sputum in the airways
- Dullness to percussion due to lung tissue filled with sputum or collapsed
There may be a derangement in basic observations. These can indicate sepsis secondary to pneumonia:
- Tachypnoea (raised respiratory rate)
- Tachycardia (raised heart rate)
- Hypoxia (low oxygen)
- Hypotension (shock)
- Fever
- Confusion
Severity Assessment
The NICE guidelines on pneumonia (updated 2022) recommend using the CRB-65 scoring system out of hospital and CURB-65 in hospital. They suggest considering hospital assessment when the CRB-65 score is more than 0.
- C – Confusion (new disorientation in person, place or time)
- U – Urea > 7 mmol/L
- R – Respiratory rate ≥ 30
- B – Blood pressure < 90 systolic or ≤ 60 diastolic.]
- 65 – Age ≥ 65
The CURB-65 score predicts mortality. NICE state 0/1 is low risk (under 3%), 2 is intermediate risk (3-15%), and 3-5 is high risk (above 15%):
- Score 0/1: Consider treatment at home
- Score ≥ 2: Consider hospital admission
- Score ≥ 3: Consider intensive care
Causes
The top causes of typical bacterial pneumonia are:
- Streptococcus pneumoniae (most common)
- Haemophilus influenzae
Other causes include:
- Moraxella catarrhalis in immunocompromised patients or those with chronic pulmonary disease
- Pseudomonas aeruginosa in patients with cystic fibrosis or bronchiectasis
- Staphylococcus aureus in patients with cystic fibrosis
- Methicillin-resistant Staphylococcus aureus (MRSA) in hospital-acquired infections
Atypical Pneumonia
Atypical pneumonia is caused by organisms that cannot be cultured in the normal way or detected using a gram stain. Treatment with penicillin is ineffective. They are treated with macrolides (e.g., clarithromycin), fluoroquinolones (e.g., levofloxacin) and tetracyclines (e.g., doxycycline).
Legionella pneumophila (Legionnaires’ disease) is typically caused by inhaling infected water from infected water systems, such as air conditioning units. It can cause a syndrome of inappropriate ADH (SIADH), resulting in hyponatraemia (low sodium). The typical exam patient has recently had a cheap hotel holiday and presents with pneumonia symptoms and hyponatraemia. A urine antigen test can be used as an initial screening test.
Mycoplasma pneumoniae causes milder pneumonia and a rash called erythema multiforme, characterised by varying-sized “target lesions” formed by pink rings with pale centres. It can cause neurological symptoms in young patients.
Chlamydophila pneumoniae causes mild to moderate chronic pneumonia and wheezing in school-age children. Be cautious, as this presentation is common without chlamydophila pneumoniae infection.
Coxiella burnetii, or Q fever, is linked to exposure to the bodily fluids of animals. The typical exam patient is a farmer with a flu-like illness.
Chlamydia psittaci is typically contracted from contact with infected birds. The typical exam patient is a parrot owner.
TOM TIP: You can remember the 5 causes of atypical pneumonia with the mnemonic: “Legions of psittaci MCQs”:
- Legions – Legionella pneumophila
- Psittaci – Chlamydia psittaci
- M – Mycoplasma pneumoniae
- C – Chlamydophila pneumoniae
- Qs – Q fever (coxiella burnetii)
Other Causes
Pneumocystis jirovecii pneumonia (PCP), a fungal pneumonia, occurs in immunocompromised patients. Patients with poorly controlled HIV and a low CD4 count are particularly at risk. It usually presents subtly with dry cough (without sputum), shortness of breath on exertion and night sweats. Co-trimoxazole (trimethoprim/sulfamethoxazole) treats PCP (brand name Septrin). Patients with a low CD4 count are prescribed prophylactic co-trimoxazole to protect against PCP.
The covid-19 virus (SARS-CoV-2) can cause pneumonia. The symptoms vary enormously. Anosmia (loss of smell) is a clue to the diagnosis. Patients may not feel particularly short of breath despite having low oxygen saturations (“silent hypoxia”). Vaccination has dramatically reduced the number of severe infections. Covid-19 pneumonia is treated with respiratory support (e.g., oxygen), dexamethasone and monoclonal antibodies.
Investigations
Patients in the community with CRB 0 or 1 pneumonia do not necessarily need investigations.
A point-of-care test for the CRP level can be used in primary care to help guide diagnosis and the use of antibiotics.
Investigations for patients admitted to hospital include:
- Chest x-ray
- Full blood count (raised white cell count)
- Renal profile (urea level for the CURB-65 score and acute kidney injury)
- C-reactive protein (raised in inflammation and infection)
Patients with moderate or severe infection will also have:
- Sputum cultures
- Blood cultures
- Pneumococcal and Legionella urinary antigen tests
White blood cells and CRP are raised roughly in proportion to the severity of the infection. The trend can help monitor the progress of the patient towards recovery. CRP starts rising 6 hours behind the onset of inflammation and peaks after 24-48 hours. It may initially be low before becoming very high a day or two later.
Antibiotics
Always follow your local area guidelines. These are developed by looking at the antibiotic resistance of the bacteria in the local area and are specific to the local population.
Mild community-acquired pneumonia is typically treated with 5 days of oral antibiotics, for example:
- Amoxicillin
- Doxycycline
- Clarithromycin
Moderate or severe pneumonia is usually treated initially with intravenous antibiotics and stepped down to oral antibiotics as the condition improves. Respiratory support (e.g., oxygen or intubation and ventilation) is also used.
Complications
Complications of pneumonia include:
- Sepsis
- Acute respiratory distress syndrome
- Pleural effusion
- Empyema
- Lung abscess
- Death
Last updated May 2023
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