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Chest infections

Severe acute respiratory syndrome

Tuberculosis

Pneumonia in the immunocompromised

Parapneumonic effusions

Empyema

Further reading

Pneumonia

Management is based on four premises:

• pneumonia is associated with a wide range of largely non-specific clinical features
• it can be caused by >100 different organisms
• the relationship between specific clinical features and causative organism is too weak to allow a clinical diagnosis of the causative organism
• early administration of appropriate antibiotics is important

As a result antibiotic therapy should be started before the causative organism is known. The differential diagnosis can be narrowed using epidemiological clues. The most important are whether the pneumonia is community acquired or hospital acquired and whether the patient is immunocompromised.

Note that the flora and antibiotic resistance patterns vary from country to country, hospital to hospital and even between ICUs within a hospital and this must be taken into account

Pneumonia in the immunocompromised

• lungs are amongst the most frequent target organs for infectious complications in immunocompromised.
• incidence highest amongst patients with haematological malignancies, bone marrow transplant (BMT) recipients and patients with AIDS.

Aetiology

• speed of progression of pneumonia may suggest the aetiology eg bacterial pneumonias progress rapidly (1-2 days) while fungal and protozoal pneumonias are less fulminant (several days to a week or more). Viral pneumonias are usually not fulminant but on occasions may develop quite rapidly.

Causes of focal infiltrates

• Gram -ve rods.
• Staph aureus.
• Aspergillus.
• Malignancy.
• Non-specific interstitial pneumonitis.
• Cryptococcus.
• Nocardia.
• Mucor.
• Pneumocystis carinii (uncommon).
• Tuberculosis
• Legionella or legionella-like organisms.
• Radiation pneumonitis.

Causes of diffuse infiltrates

• CMV and other herpes viruses.
• Pneumocystis carinii.
• Drug reaction.
• Non-specific interstitial pneumonitis.
• Bacteria (uncommon).
• Aspergillus (advanced).
• Cryptococcus (uncommon).
• Radiation pneumonitis (uncommon).
• Malignancy.
• Leucoagglutinin reaction.

Non-infectious causes of fever and pulmonary infiltrates in immunocompromised patients

• Tumour.
• Radiation pneumonitis.
• Pulmonary haemorrhage.
• Pulmonary infarction.
• Leucoagglutinin reaction.
• Non-specific interstitial pneumonitis.
• Drug reaction:

• bleomycin
• cyclophosphamide
• busulphan (after very long periods of treatment)
• bis-chloroethylnitrosurea (BCNU)
• cyclohexylnitrosurea (CCNU)
• mitamycin
• chlorambucil
• melphalan
• procarbazine

Treatment

Empiric treatment

Pneumocystis carinii pneumonia (PCP)

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Bacterial pneumonia

• most common cause of acute respiratory failure in HIV positive patients.
• more common in HIV infected patients than in the general population and tends to be more severe
• Strep pneumoniae, Haemophilus influenza, Pseudomonas aeruginosa and S. aureus are the commonest organisms. Nocardia and gram negatives should also be considered.
• Atypical pathogens (eg Legionella, Mycoplasma pneumoniae) are rare
• Response to appropriate antibiotics is usually good but may require protracted courses of antibiotics because of high tendency to relapse.
• Severely immunocompromised patients (CD4⁺ count <100/ml) and one of the following should receive antibiotics that cover Pseudomonas aeruginosa and other Gram -ves:
  • history of Pseudomonas infection
  • bronchiectasis
  • relative or absolute neutropaenia

Tuberculosis

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CMV pneumonitis

• Important opportunistic infection
• Risk of infection is highest following allogeneic stem cell transplantation, followed by lung transplantation, pancreas transplantation and then liver, heart and renal transplantation and advanced AIDS.
  • If both the recipient and the donor are seronegative then the risk of both infection and disease are negligible.
  • If the recipient is seropositive the risk of infection is approximately 70% but the risk of disease is only 20%, regardless of the serostatus of the donor. 
  • If the recipient is seronegative and the donor is seropositive the risk of disease is 70%.
  • If steroid pulses and antilymphocyte globulin are given for treatment of acute rejection the risk of developing disease is markedly increased.
• Infection may be the result of primary infection or reactivation of latent infection. 
• Important, but often difficult, to distinguish between CMV infection and CMV disease and a definitive diagnosis can only be made histologically.
  • Detection of CMV-pp65 antigen in peripheral white blood cells (WBC) and detection of CMV DNA or RNA in the blood by quantitative polymerase chain reaction are the most useful tests for demonstrating CMV disease. Varying thresholds (10/50 000-100/200 000 positive circulating peripheral WBC) are used for CMV-ppp65.
• Treatment consists of intravenous ganciclovir for at least 14 days.
  • Foscarnet can be used if ganciclovir fails.

Parapneumonic effusions

Types

• Uncomplicated (majority). Resolve with antibiotic therapy aimed at pneumonia
• Complicated
  • Characteristics: increasing pleural fluid volume, continued fever, low fluid pH (<7.3), large nos. of WBCs ± organisms on Gram stain or culture
  • Require drainage for resolution of fever. Natural history is to progress to single loculus or multiple loculi and then to empyema.

Pathophysiology

Pathogenesis of parapneumonic effusion

• If pneumonia remains untreated parapneumonic effusions become bigger and bacteria multiply in lung and invade pleural space
• Bacteria rapidly cleared by lymphatics and therefore a positive gram stain and culture implies a high degree of invasion/multiplication in pleural space
• Large bacterial load results in a fall in glucose and pH (due to end-products of glucose metabolism).

Management

Empyema of the lung

Definition

Collection of pus in the pleural space

Aetiology

• Follows infection of the structures surrounding the pleural space, including subdiaphragamatic structures
• Chest trauma
• Malignancy
• Microbiology - commonest organisms are anaerobes:
  • streptococci
  • Gram negative rods

Diagnosis

• usually simple
• patient is usually "toxic"
• ± productive cough and chest pain
• chest X-ray may show features suggestive of a pleural effusion and underlying consolidation but may also show an abscess cavity with a fluid level in which case CT scanning will be required to distinguish between an abscess and an empyema

• ultrasound to confirm presence of fluid in pleural space

• confirmation of the diagnosis can be obtained by aspirating pus.

Treatment

• mainstay is drainage either by intercostal drain or by surgical intervention
• simple drainage usually sufficient for patients who present before pus is loculated and a fibrinous peel has formed on the lung. The addition of intrapleural fibrinolytics may reduce the need for subsequent surgery
• decortication
  • indication: empyema is more advanced or failure of simple drainage
  • major procedure and many patients with cardiac or chronic respiratory disease will not tolerate it. Alternatives for these patients are instillation of thrombolytics into the pleural space or thoracostomy
• antibiotics have only an adjunctive role. Broad spectrum antibiotic regimes with anaerobic cover should be used until the results of microbiological analysis of the aspirated pus are available

Further reading

Hamm, H. and Light, R. W. (1997). Parapneumonic effusion and empyema. Eur. Respir. J. 10, 1150-1156.

©Charles Gomersall, June, 2013 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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