Terminal Complement Deficiencies (C5-C9) - Patients have increased susceptibility to invasive infections with Neisseria species. Complement deficiencies are found more frequently in patients with recurrent Neisserial infections or infections with unusual serotypes.
Alternative Complement Defects (properidin or factor D deficiency) - Patients have increased susceptibility to invasive infections with Neisseria species.
Asplenia - Patients are at increased risk for invasive infections with encapsulated bacteria such as Neisseria. Asplenia may be congenital , acquired (surgery), or functional (sickle-cell disease).