Pneumonia

Pneumonia is characterised by acute inflammation with an intense infiltration of neutrophils in and around the alveoli and the terminal bronchioles. The affected bronchopulmonary segment or the entire lobe may be consolidated by the resulting inflammation and oedema.

The annual incidence of community-acquired pneumonia is 5-11 per 1000 adult population. The illness results in about 83,000 hospital admissions each year and is the fifth leading cause of death in the UK. Most episodes occur during the autumn or winter.

Risk factors

• Age: especially infants, young children and the elderly
• Lifestyle: smoking, alcohol
• Preceding viral infections, e.g. influenza predisposing to Streptococcus pneumoniae infection
• Respiratory: asthma, COPD, malignancy, bronchiectasis, cystic fibrosis
• Immunosuppression, AIDS, cytotoxic therapy - increased risk of infection with Staphylococcus, tuberculosis, Gram negative bacilli and Pneumocystis carinii
• Intravenous drug abuse, often associated with Staphylococcus aureus infection
• Hospitalisation - often involving Gram negative organisms
• Aspiration pneumonia: patients with impaired consciousness, neurological disease such as cerebrovascular or Parkinson's disease, or patients with oesophageal obstruction are at risk of aspiration pneumonia which usually affects the right lung and is caused by anaerobes from the oropharynx
• Underlying predisposing disease: diabetes mellitus, cardiovascular disease

Community acquired pneumonia^1,2

Causes include:

• Bacteria: Streptococcus pneumoniae (30-50% of cases). Haemophilus influenzae (5-15%), Staphylococcus aureus, Klebsiella pneumoniae, Enterobacteria (e.g. E. coli), anaerobes. Moraxella catarrhalis and Pseudomonas are more common in COPD patients.
• 'Atypical' pathogens: Mycoplasma pneumoniae, Legionella pneumophilia, Chlamydia pneumoniae, Chlamydia psittaci, Coxiella burnetii.
• Viruses: Influenza A, RSV.

Hospital acquired pneumonia

This is defined as a new infection of lung parenchyma appearing more than 48 hours after admission to the hospital.

• It occurs mostly in patients who are severely debilitated, immunocompromised or mechanically ventilated.
• Infection occurring during the first four days of the hospital stay is usually caused by Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis.
• Onset more than four days after admission is more often caused by Gram-negative enterobacteria, Staphylococcus aureus or Legionella pneumophilia.
• Hospital acquired pneumonia is often caused by multiple organisms.

Symptoms

• Pneumonia usually develops over several days with cough and sputum production (possibly with haemoptysis), dyspnoea, pleuritic chest pain, weakness, malaise and often myalgia.
• More severe pneumonia may lead to confusion, respiratory distress and cyanosis.
• Presentation may be more sudden with a dramatic rigor as the first symptom and this is more common in healthy young adults.
• In older patients, the presentation may be more insidious, with minimal cough and no fever. This age group often present with confusion and hypothermia.
• Occasionally, a lower lobe infection irritates the diaphragm to cause upper abdominal pain, which is referred to the shoulder.

Signs

• Fever, breathless at rest.
• Chest expansion is reduced on the affected side.
• Percussion is dull over the diseased lobe or lobes.
• Auscultation may reveal crackles, bronchial breathing or pleural friction rub, depending on the degree of consolidation.
• Occasionally, there is evidence of an effusion with stony dullness on the affected side.
• Septicaemia should be suspected if the patient is cold, clammy and hypotensive.
• Immunocompromised patients may present with just fever, tachypnoea and agitation or altered mental function.

• Different organism responsible
• Pulmonary oedema
• Pleural effusion
• Pneumothorax
• Pulmonary embolus
• Asthma
• Chronic obstructive pulmonary disease
• Bronchiectasis
• Fibrosing alveolitis
• Neoplasm
• Sarcoidosis
• Pneumonia complication, e.g. empyema, lung abscess

• Full blood count with differential white cell count
• Renal function and electrolytes
• Blood cultures
• Chest x-ray
• Sputum examination and culture
• Cold agglutinins to detect Mycoplasma pneumoniae
• Immunoelectrophoresis: pneumococcal antigen from sputum or blood
• Pulse oximetry or blood gases
• Acute and convalescent serology to detect antibodies to viruses, Mycoplasma, Chlamydia, Legionella and Coxiella burnetii
• Aspiration of pleural fluid (for biochemistry and culture)

• The decision to admit is based on a variety of factors including severity of illness, age, underlying health problems and social circumstances.
• The British Thoracic Society guidelines for community acquired pneumonia in adults recommend use of the CURB-65 score. A 6-point score, one point for each of Confusion, Urea >7 mmol/l, Respiratory rate 30/min or more, systolic Blood pressure below 90mmHg (or diastolic below 60mmHg), Age 65 years or older.
  • Patients who have a CRB-65 score of 0 are at low risk of death and do not normally require hospitalisation for clinical reasons.
  • Patients who have a CRB-65 score of 1 or 2 are at increased risk of death and hospital referral and assessment should be considered, particularly with a score of 2.
  • Patients who have a CRB-65 score of 3 or more are at high risk of death and require urgent hospital admission.

Start blind therapy immediately and adjust as the underlying organism becomes more certain. The choice of antibiotic regime will be governed by updated local guidelines but the following is a guide.
A recent study found that initial discordant (inactive in vitro as opposed to concordant, i.e. active in vitro) treatment with beta-lactam antibiotics is not associated with a statistically significant Increase in mortality or clinical or bacteriological failure of therapy for pneumococcal pneumonia.⁴

• Uncomplicated community-acquired pneumonia:
  • Amoxicillin (erythromycin if penicillin-allergic)
  • Add flucloxacillin if staphylococci suspected, e.g. in influenza or measles; treat for 7 days (14-21 days for infections caused by staphylococci); pneumococci with decreased penicillin sensitivity has been isolated but not yet common in the UK; add erythromycin if atypical pathogens suspected
• Severe community-acquired pneumonia of unknown aetiology:
  • Cefuroxime (or cefotaxime) plus erythromycin
  • Add flucloxacillin if staphylococci suspected; treat for 10 days (14-21 days if staphylococci, legionella, or Gram-negative enteric bacilli is suspected)
• Pneumonia possibly caused by atypical pathogens:
  • Erythromycin
  • Severe Legionella infections may require addition of rifampicin; tetracycline is an alternative for chlamydial and mycoplasma infections; treat for at least 14 days(14-21 days for legionella)
• Hospital-acquired pneumonia:
  • A broad-spectrum cephalosporin (e.g. cefotaxime or ceftazidime) or an antipseudomonal penicillin or another antipseudomonal beta-lactam
  • An aminoglycoside may be added in severe illness
• Management other than antibiotics:
  • Oxygen for hypoxia; ventilation if severe hypoxia
  • Fluids for dehydration
  • Analgesics: NSAIDs and paracetamol - for mild pleuritic pain; more severe pain may require opiate analgesia but care is needed not to aggravate CO₂ retention.
  • Nebulised saline may help expectoration.
  • Chest physiotherapy has doubtful benefit. Physiotherapy may be more important in helping to mobilise the patient.

The Royal College of Radiologists recommends a follow-up chest X-ray 6 weeks after recovery from pneumonia for all adults who have persistent symptoms or signs, or who are at higher risk of underlying malignancy (smokers and those aged over 50 years). Follow-up chest X-ray in children is recommended only if there are persisting clinical symptoms or signs.

• Pleural effusion - usually sterile
• Empyema: a reactive effusion can occur but is trivial. Empyema is potentially more serious and presents as the persistence of fever and leukocytosis after 4-5 days of appropriate antibiotic therapy.
• Lung abscess: can occur in disease due to S. pneumoniae and is classically seen in patients with staphylococcal or klebsiella pneumonia.
• Pneumatocoele
• Pneumothorax
• Pyopneumothorax - eg. following rupture of a staphylococcal lung abscess in the pleural cavity
• Deep vein thrombosis
• Septicaemia, pericarditis, endocarditis, osteomyelitis, septic arthritis, cerebral abscess, meningitis (particularly in pneumococcal pneumonia)
• Postinfective bronchiectasis
• Acute renal failure

Mortality from community-acquired pneumonia is about 1%, but for patients in hospital, mortality is approximately 13-15% and it ranges from 22 to 54% in patients requiring intensive care.

• Early appropriate antibiotic therapy reduces mortality and morbidity
• Influenza and pneumococcal vaccination
• Targeted risk reduction, such as smoking cessation