Infections in the immunocompromised host

The prevention and treatment of opportunistic infections are relevant to paediatricians, everywhere, in view of the increasing prevalence of patients with immunocompromising conditions. The presence of an underlying immunodeficiency should be seriously considered when an unusual organism, or one of generally low pathogenicity in a normal child, causes a serious or life-threatening illness. The type of infections that occur in immunocompromised patients usually reflect the underlying immunodeficiency, and can help in identifying what part of the immune system may be compromised. Patients with cell-mediated immune dysfunction tend to be infected with a range of viral infections, including the Herpes group of viruses, intracellular bacteria, and fungi, including Pneumocystitis. This is in contrast to patients with primarily a defect in humoral immunity, where infections with encapsulated bacteria, including Staphylococcus aureus, and enteric organisms such Giardia lamblia and enteroviruses predominate. Patients with phagocytic defects are especially prone to infections with Gram-negative bacteria and fungi, whilst those with complement disorders are prone to recurrent infections with encapsulated bacteria, especially Neisseria, Pneumococcus, and Haemophilus. The most common opportunistic organisms seen in clinical practice include Pneumocystitis jiroveci, Aspergillus, Candida, and cytomegalovirus. Following targeted treatment of these infections, prophylaxis is often required for the duration of the period of immunodeficiency.