Infection in immunocompromised patients


The term 'immunocompromised' refers to individuals whose resistance to infection has been reduced by disease (congenital or acquired) or by therapeutic measures such as the treatment of malignant disease or organ transplantation. Increased susceptibility to infection may result from a defect in the immune system and/or neutropenia.

The infection may be endogenous, Le arising from within the patient, or exogenous. Endogenous infection may be due to invasion of tissues or organs by bacteria, e.g. E coli, by fungi such as Candida albicans which are present in health in the patient's gastrointestinal tract, or by reactivation of organisms which have remained dormant since primary infection earlier in life. Examples of latent organisms which can cause infection in immunocompromised patients include the herpesviruses (varicella zoster. Herpes simplex. Epstein-Barr virus and cytomegalovirus), mycobacteria. Toxoplasma gondii and leishmania.

Infection is a common cause of death in immunocompromised patients, in whom it may have a fulminating onset or be refractory to therapy. Diagnosis can be difficult as the infections may present atypically, sometimes with very few signs and symptoms until well advanced. Due to

Microorganisms causing infections in immunocompromised patients
Defect in host response Microorganism Infections (examples)
Phagocytic abnormalities (Polymorphs, macrophages)
  • Staph. aureus
  • Strep. pneumoniae
  • Legionella pneumophila
  • Strep. pyogenes
  • H. influenzae
  • Gram-negative bacilli
  • Candida albicans
  • Skin, soft tissue
  • Pneumonia
  • Pneumonia
  • Septicaemia
  • Meningitis
  • Septicaemia
  • Fungaemia
Cell-mediated defects (T cells)
  • Herpesviruses
  • Parvovirus
  • Candida albicans
  • Cryptococcus
  • Mycobacteria
  • Listeria monocytogenes
  • Pneumocystis carinii
  • Toxoplasma gondii
  • Leishmania
  • Shingles
  • Bone marrow infection
  • Pneumonia
  • CNS infections
  • Tuberculosis
  • Meningitis
  • Pneumonia
  • Encephalitis
  • Leishmaniasis
  • Enteritis
Humoral defects (immunoglobulins)
  • Cryptosporidium
  • Strep. pneumoniae
  • Strep. pyogenes
  • Pseudomonas aeruginosa
  • Neisseria meningitidis
  • H. influenzae
  • Mycoplasma spp.
  • Pneumonia
  • Septicaemia
  • Septicaemia
  • Meningitis
  • Pneumonia
  • Arthritis

the body's reduced defences against infection, treatment should be started on clinical suspicion, modified according to the results of investigations.

Table lists the important organisms causing infections in immunocompromised patients.

Concepts of infection
Major manifestations of infection
Principles of management of infection
Diseases due to viruses
DNA viruses
Diseases due to chlamydiae
Diseases due to rickettsiae
Diseases due to bacteria
  • Streptococcal infections
  • Staphylococcal infections
  • Corynebacterial infections
  • Bacillus infections
  • Bordetella infections
  • Salmonella infections
  • Food poisoning
  • Dysentery
  • Other true bacterial infections
  • Mycobacterial infections
Diseases due to spirochaetes
  • Leptospira infections
  • Borrelia infections
  • Treponema infections
Diseases due to fungi (mycoses)
  • Cutaneous fungal infections
  • Subcutaneous fungal infections
  • Systemic fungal infections
Diseases due to protozoa
Diseases due to helminths
  • Trematode (fluke) infections
  • Cestode (tapeworm) infections
  • Nematode (roundworm) infections
  • Zoonotic helminth infections
Diseases due to arthropods
Sexually transmitted diseases
  • Sexually transmitted bacterial diseases
  • Sexually transmitted viral diseases
  • Miscellaneous conditions