Tetanus injections are given as intramuscular injections in the upper arm or the buttock. Tetanus vaccines include tetanus antitoxin, which requires a skin test. Patients with a positive skin test must either undergo desensitization therapy or avoid using it, and can switch to tetanus immunoglobulin, which doesn't require a skin test but is more expensive than tetanus antitoxin. The purpose of the tetanus shot is to prevent infection by Clostridium tetani, an anaerobic bacterium. It is particularly important for patients with deep wounds or heavily contaminated wounds; or wounds contaminated with rust or soil to receive tetanus treatment to prevent Clostridium tetani from colonizing the body through wound mucosa and producing neurotoxins that affect breathing.