Immunodeficiency Syndromes

Immunodeficiency means that one or more immune functions cannot prevent, contain, or clear infection effectively. Primary immunodeficiency (PID) comprises more than 230 genetically defined disorders involving humoral immunity, cellular immunity, phagocytes, complement, or combinations of these systems. Secondary immunodeficiency may arise from HIV, immunosuppressive medication, chemotherapy, malnutrition, diabetes, chronic kidney or liver disease, malignancy, or loss of splenic function. The experienced clinician does not count infections alone. Pattern matters. Repeated bacterial pneumonia, unusually severe disease, opportunistic organisms, persistent oral candidiasis, chronic diarrhoea, poor growth, deep abscesses, or an infection in an unusual site should prompt a search for the affected immune compartment. A family history of early unexplained death or severe infection increases concern. An 8-month-old with several episodes of otitis and pneumonia caused by Streptococcus pneumoniae and Haemophilus influenzae has a different clinical pattern from an infant with persistent thrush, chronic diarrhoea, and failure to thrive. Maternal IgG has waned by approximately 6 months, so recurrent encapsulated bacterial infection after that point can expose an antibody-production defect. The second infant may have profound T-cell dysfunction and requires a much...