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Primary immune deficiencies represent a class of disorders in which there is an intrinsic defect in the immune system. In contrast, acquired or secondary immune deficiency states occur as a consequence of external agents such as infection or chemotherapy. Over 150 distinct primary immune deficiency syndromes have been recognized. The true prevalence of primary immune deficiencies is not known as routine screening for these defects is not performed at birth or at any time during life. One well-conducted telephone survey of 10,000 households found that the population rate for the diagnosis of primary immune deficiency was 0.0863%, which translates into approximately 250,000 persons (95% confidence interval: 151,769 to 361,408) with primary immune deficiency in the United States.46
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The diagnosis of a primary immune deficiency in a child is one of the more challenging diagnoses in medicine. It requires both an understanding of immune function and development and a clinical understanding of age-related infections and relevant genetic risks and environmental exposures. Children with primary immunodeficiency diseases most commonly present with recurrent infections. When evaluating a child with recurrent infections, it is important to remember the normal pattern of infections for different ages and situations. For example, a normal child living at home may have 6 to 12 infections per year if living only at home, and up to 18 infections per year when cared for at a day care center. Children with primary immunodeficiencies commonly have a positive family history. A thorough physical examination may reveal subtle scaring from previous infections, eczema, lymphadenopathy, or prior surgery.
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A history suggestive of childhood immunodeficiency usually contains one or more “red flags” (Table 59–1). Situations that warrant consideration of a primary immune deficiency include frequent chronic infections without any other explanation. Always consider immunodeficiency in children with recurrent infections and associated failure to thrive. Likewise, any severe or unusual infection, in particular, infections with opportunistic organisms warrants consideration of an immunodeficiency state.
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The components of the immune response are exceedingly complex and require the close cooperation ...