Association between Severe Pandemic 2009 Influenza A (H1N1) Virus Infection and Immunoglobulin G2 Subclass Deficiency

Severe H1N1 infection appears to be associated with immunoglobulin G2 subclass deficiency in both nonpregnant and pregnant patients. Healthy pregnant women were mildly deficient in immunoglobulin G2, but pregnant women with severe H1N1 infection had lower levels. Immunoglobulin G2 deficiency persisted after recovery in the majority (73%) of cases. Background. Severe pandemic 2009 influenza A virus (H1N1) infection is associated with risk factors that include pregnancy, obesity, and immunosuppression. After identification of immunoglobulin G2 (IgG2) deficiency in 1 severe case, we assessed IgG subclass levels in a cohort of patients with H1N1 infection. Methods. Patient features, including levels of serum IgG and IgG subclasses, were assessed in patients with acute severe H1N1 infection (defined as infection requiring respiratory support in an intensive care unit), patients with moderate H1N1 infection (defined as inpatients not hospitalized in an intensive care unit), and a random sample of healthy pregnant women. Results. Among the 39 patients with H1N1 infection (19 with severe infection, 7 of whom were pregnant; 20 with moderate infection, 2 of whom were pregnant), hypoabuminemia (P