Spasmodic contractions may be so powerful that they tear the muscles or cause compression fractures of the vertebrae. During these episodes, fractures and muscle tears can occur. The incubation period is 5 days to 15 weeks, with 8 to 12 days as the average. About 100 cases of tetanus occur every year in the U.S., all in unimmunized individuals or those whose last immunization was no longer current. In developing countries, tetanus frequently causes death in newborn infants when the umbilical stump becomes infected.
Immunization is considered to provide protection for ten years.
Studies in the army suggest that good protection persists up to 12 years after the last immunization. Older teenagers and adults who have been injured, especially puncture type injuries, should receive booster immunizations for tetanus if their last immunization was more than 10 years previously. Diagnostic studies generally are of little value. Cultures of the wound site are negative for clostridia two-thirds of the time. When the culture is positive it is diagnostic.