Pregnant women and people with leukemia and several other types of cancer are as much as 1,000 times more susceptible to Listeria infections, French researchers report.

Doctors at the French Institute for Public Health Surveillance (Institut de Veille Sanitaire) summarized the results of a major study of French listeriosis patients, concluding that pregnant women and cancer patients are far more at risk than the population at large.

Based on their review of  nearly 2,000 listeria cases, leukemia patients were 1,000 times more likely to contract the disease, researchers said.

As a result, researchers concluded that, to prevent Listeria outbreaks, health officials should target their efforts on populations at higher risk – especially pregnant women and cancer patients. In particular, at-risk people should avoid foods that are susceptible to Listeria.

The study incorporated 1,959 listeria cases in France from 2001 to 2008.  In addition to the leukemia patients, it  identified higher risks for people living with liver cancer, multiple myeloma, and cancers of the esophagus, stomach, pancreas, lung and brain.  Pregnant women and people who had undergone organ transplants also faced risks ranging from 100 to 1,000 times greater than the population at large.

In the United States, the Centers for Disease Control and Prevention recommends that people at higher risk for Listeria avoid the following foods:

— Hot dogs, luncheon meats, cold cuts, other deli meats (such as bologna), or fermented or dry sausages unless they are first heated to an internal temperature of 165°F or until steaming hot just before serving. Also avoid refrigerated pâté or meat spreads.

— Soft cheese such as feta, queso blanco, queso fresco, brie, Camembert, blue-veined, or panela (queso panela) unless it is labeled as made with pasteurized milk.

— Refrigerated smoked seafood such as salmon, trout, whitefish, cod, tuna, and mackerel (often labeled as nova-style, lox, kippered, smoked, or jerky) unless it is contained in a cooked dish, such as a casserole, or unless it is a canned or shelf-stable product.

Until this year, Listeria had not been detected in cantaloupes — then Listeria-contaminated melons sickened 146, killing 30 and causing at least one miscarriage. The FDA recommends washing one’s hands with warm water and soap for at least 20 seconds before and after handling any whole melon, such as cantaloupe, watermelon, or honeydew. Scrub the surface of melons with a clean produce brush under running water and dry them with a clean cloth or paper towel before cutting. Be sure that your scrub brush is sanitized after each use, to avoid transferring bacteria between melons.

Promptly consume cut melon or refrigerate promptly. Keep cut melon refrigerated at, or less than 40 degrees F (32-34 degrees F is best), for no more than 7 days. Discard cut melons left at room temperature for more than 4 hours.