This patient most likely has a late complement component deficiency. He has a history of meningococcal meningitis, and the current episode suggests recurrent meningococcal meningitis with bacteremia. Patients with late (terminal) complement component deficiencies (C5, C6, C7, C8, C9) may present with recurrent, invasive meningococcal or gonococcal infections. Complement deficiency can be acquired or inherited. The likelihood of complement deficiency is increased to greater than 30% among persons who have had more than one episode of meningococcal infection or who have a family history of meningococcal infection; for those with inherited late complement component deficiencies, the mode of inheritance is autosomal codominant. C5 deficiency confers impaired chemotaxis and absent serum bactericidal activity. C6, C7, and C8 deficiencies result in absent serum bactericidal activity, and C9 deficiency results in impaired serum bactericidal activity. The susceptibility to systemic neisserial infections, especially meningococcal disease, is greatest for those deficient in C5, C6, C7, or C8 compared with those deficient of C9. Meningococcal disease is the most common infection in those with complement deficiency. Up to 60% of those with a deficiency of a late complement component or of the circulating complement-potentiating protein properdin will experience at least one episode of infection during their lifetime. Meningococcal disease in patients with complement deficiencies also tends to be caused by uncommon serogroups, especially groups Y, W-135, and X relative to nondeficient patients with meningococcal meningitis. Recurrent meningococcal disease occurs in approximately 45% of those deficient in C5, C6, C7, or C8.

Common variable immunodeficiency (CVID) involves B- and T-cell abnormalities, and the usual manifestation is hypogammaglobulinemia. Bacterial infections, often of the sinus tract and lungs, are common, and the immune dysregulation seen in CVID is associated with autoimmunity and malignant disease. However, CVID is not associated with recurrent meningococcal infection.

Selective IgA deficiency is a common B-cell immunodeficiency. Most patients are asymptomatic or have sinopulmonary infections or gastrointestinal involvement with inflammatory bowel disease, sprue-like illness, or celiac disease. Giardiasis may also be seen. It is not associated with recurrent meningococcal infection.

Classical complement pathway (C1, C4, C2) deficiencies are often associated with a rheumatologic disorder, such as systemic lupus erythematosus, vasculitis, dermatomyositis, or scleroderma. Frequency of infection is relatively low in those with C1, C4, or C2 deficiency compared with deficiencies of other complement components. When they do occur, common infections are caused by encapsulated bacteria, especially Streptococcus pneumoniae.