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How E. Coli Spreads -- and What to Do About It

E. coli infections have been confirmed in more than 100 people and health officials suspect fresh spinach from California is the source. About 74 percent of the nation's supply of raw spinach comes from California, according to the California Farm Bureau Federation, and the outbreak raises questions about how E. coli gets into the food supply and what to do about the spinach problem.

The Organism: E. coli is a bacterium that lives in the intestines of animals -- including humans. Most strains are harmless, but E. coli O157:H7 produces a powerful toxin that can be harmful to people, with diarrhea the most common symptom. E. coli can multiply very quickly; it's been estimated that as few as 10 bacteria have set off previous outbreaks.

Current Outbreak: Since Sept. 18, 2006, 109 cases of illness due to E. coli infection have been reported to the Centers for Disease Control and Prevention, including one fatality. Nineteen states have reported cases. Epidemiological evidence suggests the source is tainted spinach grown in California's Salinas Valley; most people infected say they had recently bought fresh spinach grown and packaged there. But lab tests have yet to confirm the source of the outbreak.

Cases Each Year: An estimated 73,000 infections and 61 deaths occur in the United States.

Outbreaks Caused by Leafy Greens: Since 1995, there have been 19 E. coli outbreaks with leafy greens suspected as the cause. But most E. coli infections occur from eating undercooked ground beef. Meat can be tainted with animal waste during slaughtering. And in some cases, raw milk has become contaminated by bacteria on cow udders or equipment.

How it Happens: Spinach and lettuce can be contaminated in several ways. E. coli is transmitted by feces. Flood and irrigation waters contaminated by animal waste could be a source; water used in a processing plant to rinse vegetables may be tainted. Also, organic farms use manure instead of chemical fertilizers. If manure is not composted at a high enough temperature, E. coli could survive.

Symptoms: The toxins produced by E. coli O157:H7 cause diarrhea and bleeding in the intestines. More severe infections can lead to kidney failure, and, in 2 percent of cases, death.

What Health Officials are Doing: As health officials continue to look for the source, about two dozen brands of raw spinach have been recalled.

What You Should Do: Until the cause is identified, the FDA advises consumers not to eat any fresh spinach or salad blends containing spinach. This includes loose spinach on display at your supermarket -- any raw spinach shipped from California is under investigation.

Washing spinach, or any leafy greens for that matter, won't work for E. coli; the bacteria is too entrenched in the plant tissue. But cooking spinach at 160 degrees Fahrenheit for 15 seconds will kill the bacteria.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

Vikki Valentine
Vikki Valentine is a senior supervising editor on NPR's science desk. She oversees the network's health coverage across broadcast and digital platforms. Previously, Valentine was the network's climate change, energy, and environment editor and in this role was a recipient of a 2012 DuPont Award for coverage of natural gas drilling in Pennsylvania.