Case 7.6 – Community Acquired Pneumonia

Duration of symptoms

Other systemic symptoms: Fever, rigors, shivering, nausea and vomiting, anorexia

Other respiratory symptoms: Cough, appearance of sputum, pain history

Past history: Intercurrent systemic illness, past history of pneumonia, past or current history of smoking, alcohol use

Examination of the respiratory system including vital signs: BP, pulse, temperature, respiratory rate, pulse oximetry

Chest X-ray:

• An x-ray is not essential but confident diagnosis necessitates chest radiography
• In lobar pneumonia, a homogeneous opacity localised to the affected lobe or segment usually appears within 12-18 hours from the onset of the illness
• Radiological examination is also helpful if a complication such as parapneumonic effusion, intrapulmonary abscess formation, or empyema is suspected

Microbial investigations:

Tests ordered should be based on the severity of presenting symptoms.

Very unwell patients require more extensive investigations, both to identify the correct organism and therefore facilitate treatment. There may also be public health implications such as Legionnaires Disease. Microbiological investigations include:

• Sputum
• Blood cultures
• Serology
• Cold agglutinins

Assessment of gas exchange:

• Pulse oximetry provides a simple non-invasive method of measuring arterial oxygen saturation (SaO₂), and assists in monitoring response to oxygen therapy
• An arterial blood gas should be sampled in those with SaO₂ < 92% or with features of severe pneumonia to assess whether the patient has evidence of ventilatory failure or acidosis

General blood tests:

• The white cell count is often only marginally raised or may even be normal in patients with pneumonia caused by atypical organisms, whereas a neutrophil leucocytosis of more than 15 × 10⁹/l favours a bacterial aetiology
• A very high (> 20 × 10⁹/l) or low (< 4 × 10⁹/l) white cell count may be seen in severe pneumonia
• The urea and electrolytes and liver function tests should also be checked
• The C-reactive protein (CRP) is typically elevated

Pneumonia typically presents as an acute illness in which systemic features such as fever, rigors, shivering and vomiting often predominate.

The appetite is usually lost and headache frequently reported.

Pulmonary symptoms include cough, which at first is characteristically short, painful and dry, but later accompanied by the expectoration of mucopurulent sputum. Rust-coloured sputum may be seen in patients with Streptococcus pneumoniae, and the occasional patient may report haemoptysis. Pleuritic chest pain may be a presenting feature and on occasion may be referred to the shoulder or anterior abdominal wall.

Upper abdominal tenderness is sometimes apparent in patients with lower lobe pneumonia or if there is associated hepatitis.

Less typical presentations may be seen in the very young and the elderly.

• Pulmonary infarction
• Pulmonary/pleural TB
• Pulmonary oedema (can be unilateral)
• Pulmonary eosinophilia
• Malignancy: bronchoalveolar cell carcinoma
• Rare disorders: cryptogenic organising pneumonia/bronchiolitis obliterans organising pneumonia (COP/BOOP)

Organism	Clinical features
Streptococcus pneumoniae	Most common in winter. All age groups but particularly young to middle-aged. Rapid onset, high fever, pleuritic chest pain, herpes labialis, 'rusty' sputum. Bacteraemia is more common in women and patients with diabetes and COPD
Chlamydia pneumoniae	Young to middle-aged, large-scale epidemics, or sporadic, often mild, self-limiting disease. Headaches and a longer duration of symptoms before hospital admission. Usually diagnosed on serology
Mycoplasma pneumoniae	Children and young adults. Common in autumn. Epidemics occur every 3-4 years. Rare complications include haemolytic anaemia, Stevens-Johnson syndrome
Legionella pneumophila	Middle to old age, recent foreign travel, local epidemics around point source, e.g. cooling tower. A variety of features are said to be more common such as headache, confusion, malaise, myalgia, high fever and diarrhoea. Laboratory results include hyponatraemia, elevated liver enzymes, hypoalbuminaemia and elevated creatine kinase. Chest X-ray appearances may be slow to resolve.

All patients:

• Sputum: Direct smear by Gram and Ziehl-Neelsen stains. Culture and antimicrobial sensitivity testing
• Blood culture: Frequently positive in pneumococcal pneumonia
• Serology: Acute and convalescent titres to diagnose Mycoplasma, Chlamydia, Legionella and viral infections. Pneumococcal antigen detection in serum

Severe community acquired pneumonia:

The above tests plus consider:

• Tracheal aspirate, induced sputum, bronchoalveolar lavage, protected brush specimen or percutaneous needle aspiration. Direct fluorescent antibody stain for Legionella and viruses
• Serology: Legionella antigen in urine. Pneumococcal antigen in sputum and blood. Immediate IgM for Mycoplasma
• Cold agglutinins: Positive in 50% of patients with Mycoplasma

Selected patients:

• Throat/nasopharyngeal swabs: Helpful in children or during influenza epidemic
• Pleural fluid: Should always be sampled when present in more than trivial amounts, preferably with ultrasound guidance