Adult-Onset Recurrent Bacterial Meningitis: Immunological Red Herrings

To the Editor—In their recent article, Lopez et al report the identification of specific polysaccharide antibody deficiencies (SPADs) in adults presenting with invasive infection caused by encapsulated bacteria [1]. The identification of SPAD is important as it may permit intervention with strategies to mitigate the risk of subsequent infection, for example, protein-conjugate vaccination, antibiotic prophylaxis, and immunoglobulin replacement. Not all patients, however, with SPAD will require intervention. Up to 11% of healthy individuals meet the immunological criteria for SPAD [2]. More importantly, the identification of an immunological abnormality, which may be incidental to a patient's infection susceptibility, has the potential to distract from consideration of other causes of infection susceptibility. To illustrate this, we present a case of adult-onset, recurrent bacterial meningitis, in which identification of an immunoglobulin G2 (IgG2) subclass deficiency, with associated SPAD, was incidental to his infection susceptibility.