IStock Photo 1833082 © Miles Sherrill

Few young baby boomers went tromping through the backyard without the parental warning, “Don’t step on a rusty nail. You’ll get lockjaw!” echoing behind them.

There was a certain urgency in the warnings that today’s children just don’t hear from their parents. Lockjaw, or tetanus, a brutal bacterial infection, is now entirely preventable, thanks to a routine vaccine that has been given since the late 1940s. The odds a person will be diagnosed with the disease in a year are 1 in 7,302,000. You’re more than twice as likely to die falling out of a tree (1 in 3,290,000).

The spore-producing bacteria Clostridium tetani, which under a microscope resemble swarms of long-handled tennis rackets, live in low-oxygen environments such as moist soils and animal feces and, of course, those rusty nails (rust removes oxygen). When these dirt-dwellers infiltrate torn flesh, the spores germinate and excrete tetanospasmin, one of the three most poisonous substances known to humans (the two others are botulism and diphtheria). The toxin migrates through the bloodstream, enters the nervous system, and disrupts electrical signals meant to control body muscles.

Symptoms begin 5 to 15 days after injury with stiffness and mild spasms in the jaw. Later, painful skeletal muscle contractions can cause bone and spine fractures (inspiring some dramatic nineteenth century artwork). Throat muscles can clench, leading to suffocation, coma, and death. With proper treatment, however, less than 10% of those infected die.

Even a bout of tetanus does not endow immunity, and so vaccination is the only way to prevent tetanus. Most people who contract the disease in the US are immigrants who arrived unvaccinated, elderly people who may not have received a tetanus shot in childhood or recent years, or people who decide against vaccination.

An epidemiological study conducted by the CDC in 2002 found that the great majority of tetanus cases in children during the past decade occurred in children whose parents had a philosophic or religious objection to vaccination. Some intravenous drug users are also at an elevated risk for tetanus because the quinine used to dilute heroin supports the growth of Clostridium tetani in contaminated supplies.

Diabetics are 3.2 times more likely to be diagnosed with tetanus than non-diabetics. For a diabetic with tetanus, it is likely a foot ulcer or gangrene that placed him or her at risk.

People most at risk of contracting tetanus live in parts of Sub-Saharan Africa and Southern and East Asia where there is inadequate access to vaccines and sanitary childbirth conditions. Many tetanus fatalities occur in homes and go unreported, but UNICEF reports that tetanus killed 128,000 newborns in 2004, and 15,000 to 30,000 mothers die from the infection each year. Unvaccinated mothers do not pass on antibodies to infants, and umbilical cords may be cut with instruments contaminated with spores of the ubiquitous Clostridium tetani.

These figures, however, represent huge improvements over the past few decades, thanks to the efforts of global vaccination programs. For example, in 1988, the World Health Organization reported 787,000 infant tetanus deaths.

Between 2000 and April, 2009, 14 countries eliminated maternal and neonatal tetanus. There are still 44 countries struggling with the problem.