Patients with complement deficiency are at risk of infections with encapsulated organisms. There are several types of complement deficiency, two of note are C3 and C5,6,7,8,9. A C3 deficiency allows for infection by encapsulated organisms such as; Neisseria, Group B Strep, Klebsiella, Salmonella, HIB and Pneumococci. A C5,6,7,8,9 (the MAC, membrane attack complex, or terminal complement proteins) deficiency lead to unopposed Neisserial infections.