Normally, transmission is through a puncture wound that is contaminated by soil, dust, or animal excreta containing C. tetani, or by way of burns and minor wounds. After C. tetani enters the body, it causes local infection and tissue necrosis. It also produces toxins that then enter the bloodstream and lymphatics and eventually spread to central nervous system tissue.

Tetanus occurs worldwide, but it’s more prevalent in agricultural regions and developing countries that lack mass immunization programs. It’s one of the most common causes of neonatal deaths in developing countries, where neonates of unimmunized mothers are delivered under unsterile conditions. In such neonates, the unhealed umbilical cord is the portal of entry.

In America, about 75% of all cases occur between April and September.

The incubation period varies from 3 to 4 weeks in mild tetanus to less than 2 days in severe tetanus. When symptoms occur within 3 days after injury, death is more likely. If tetanus remains localized, signs of onset are spasm and increased muscle tone near the wound.