Lessons Learned From Cantaloupe-Listeria Outbreak
CDC report confirms potential for fresh produce to cause severe foodborne illness

By Steven Reinberg
HealthDay Reporter

THURSDAY, Sept. 5 (HealthDay News) — Of all the dangerous bacteria lurking in foods, perhaps the most deadly is listeria, and the lesson from a 2011 outbreak is to always handle food safely, U.S. health officials say.

In the summer and fall of 2011, cantaloupes contaminated with listeria sickened 147 people in 28 states, killing 33 of them. That listeria outbreak — the deadliest in a decade — was unusual because listeria is rarely associated with fresh produce, according to a new report from the U.S. Centers for Disease Control and Prevention (CDC).

Although rare, listeria is an important public-health issue because of its severity, said report co-author Benjamin Silk, a CDC epidemiologist in the division of foodborne, waterborne and environmental diseases. “Nearly all people who have listeria infections diagnosed are hospitalized, and about one in five die,” Silk said.

The new report, published Sept. 5 in the New England Journal of Medicine, highlights lessons learned from an investigation into the 2011 outbreak.

The authors found that for the 145 people for whom complete records were available, all but two were hospitalized and nearly one-quarter died.

Most of those sickened were in their 60s or older and suffered from other illnesses. But there also were seven pregnancy-associated infections among four women and three infants. One of the four women miscarried because of the infection.

Overall, this is typical of the general consequences of a listeria outbreak, one expert said.

“Listeria is only a problem for immuno-compromised folks and pregnant women, but in those cases people can and do get quite ill and almost all are hospitalized,” said Dr. Marc Siegel, an associate professor of medicine at the NYU Langone Medical Center in New York City.

“In this case, pregnant women were a small percentage, though they are usually more,” he said. “Outbreaks are limited as healthy people don’t generally get ill.”

The contaminated cantaloupes were traced to a Colorado grower, and while the exact cause of the contamination isn’t known, unsanitary conditions were likely the culprit, according to the report.

“The problem is that listeria bacteria grows on produce — in this case cantaloupes — and occurs especially when proper precautions aren’t taken at the farm or processing facility,” Siegel said.

One possible contributor to the outbreak is inadequate facility and equipment design, which hampered thorough cleaning of surfaces the melons could touch, according to the report. Another possible route to contamination is a truck kept next to the processing line that went to and from a cattle operation.

In addition, the Colorado farm did not cool its cantaloupes before placing them in cold storage, which may have caused condensation that promoted the growth of listeria.

“This outbreak confirms the viability of raw produce, including cantaloupe, as a vehicle for listeriosis and highlights the importance of preventing produce contamination within farm and processing environments,” the report noted.

Listeria is associated with about 1,600 infections in the United States annually, Silk said. A partnership between the CDC and state health departments, known as the Listeria Initiative, enabled the agency quickly to identify the source of the 2011 outbreak, he said.

The CDC continues to monitor and follow up on all listeria cases, Silk said. In addition, the FDA has stepped up inspections of cantaloupe farms and has issued guidelines to cantaloupe growers.

The best way to avoid listeria is to follow common-sense food-safety procedures, Silk said.

To help prevent infection, the CDC recommends you do the following:

• Rinse fruits and vegetables thoroughly under running water before eating, cutting or cooking them.
• Scrub farm produce, such as melons and cucumbers, with a clean produce brush.
• Dry produce with a clean cloth or paper towel.
• Separate uncooked meats and poultry from vegetables, cooked foods and ready-to-eat foods.
• Wash hands, knives, countertops and cutting boards after handling and preparing uncooked foods.
• Because listeria can grow in foods in the refrigerator, keep the temperature of your refrigerator at 40 degrees or lower and the freezer at 0 degrees or lower.
• Clean up all spills in the refrigerator, especially juices from hot dogs, lunch meat, raw meat and raw poultry.
• Clean the inside walls and shelves of the refrigerator with hot water and liquid soap, and then rinse.
• Thoroughly cook beef, pork or poultry.

More information

For more information on listeria, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Benjamin Silk, Ph.D., M.P.H., epidemiologist, division of foodborne, waterborne, and environmental diseases, U.S. Centers for Disease Control and Prevention; Marc Siegel, M.D., associate professor, medicine, NYU Langone Medical Center, New York City; Sept. 5, 2013, New England Journal of Medicine

Last Updated: Sept. 05, 2013