The rind of a cantaloupe may be hard enough to knock on, but it’s not tough enough to keep out harmful pathogens, as an outbreak of Salmonella Panama reminded consumers this week. What is it that makes this melon one of the most common carriers of foodborne illness among fruits and vegetables?

Cantaloupe is particularly susceptible to contamination because it grows on the ground, where it can come into contact with bacteria from animal feces harbored in soil or rainwater runoff. However, like any fruit or vegetable, it can also pick up pathogens during harvest, handling or preparation.

Foodborne illness outbreaks from cantaloupe have been traced back to wash water, shipping ice and even contact with contaminated meat, according to a 2005 study in the International Journal of Food Microbiology.

Cantaloupe is also risky as a home for pathogens because of its unique skin. Bacteria sticks easily to the rough surface, and can even penetrate through the porous rind to the inside of the fruit.

“When it rains, [cantaloupe] could actually be sitting in water, and whatever’s in that water could actually enter inside the flesh,” says Doug Powell, professor and food safety expert at Kansas State University.

And there is one more aspect of this marbled melon that makes it more apt to cause an outbreak than other fruits: bacteria can grow on its surface after harvest. While bacteria normally cannot grow on fruits or vegetables after they are picked due to a lack of moisture and nutrients, E. coli has been shown to multiply on the surface of cantaloupe and watermelon, according to an FDA article on fresh produce safety.

If not washed off the melon, bacteria can travel from the exterior to the edible part in a number of ways. Aside from permeating the rind itself, bacteria can be transferred when a person handles a husk carrying germs and then touches the fruit. It can also travel on the knife as the fruit is cut, according to the 2005 study.

Even a small amount of bacteria can be dangerous if it reaches the inside of the cantaloupe, because once there it can increase. The FDA Food Code cites cut melon as a potentially hazardous food, since its low acidity and high water content make it capable of supporting bacteria growth.

Just how risky is it to eat cantaloupe? “Cantaloupe’s always in the top five of fresh fruits and vegetables for outbreaks,” says Powell.

Indeed there have been at least five outbreaks linked to cantaloupe in the past five years alone, according to

In 2001, out of a sample of 151 imported cantaloupes, the FDA isolated Salmonella from eight (5.3 percent), and Shigella from three (2 percent). Foreign cantaloupe has historically been responsible for the majority of foodborne illnesses associated with that fruit.

But outside the realm of fresh produce, cantaloupe remains relatively low on the list of overall foodborne risks. Overall, produce accounts for 13 percent of foodborne illness outbreaks, according to a report from the Center for Science in the Public Interest (CSPI).

And to reduce the risk of foodborne illness from cantaloupe even further, consumers can take precautionary steps when preparing and eating it. These include:

— cleaning knives and cutting boards after cutting cantaloupe open, before scooping out the flesh

— washing hands thoroughly after handling the exterior of the melon, before touching the edible part

— keeping cut cantaloupe refrigerated to prevent the growth of bacteria

Opinions are mixed as to whether washing cantaloupe helps reduce the risk of illness. According to the 2005 study, washing melon in running fresh water produced a significant reduction in bacteria, as did soaking the melon in chlorine. However, soaking melon in water made contamination worse, as it allowed bacteria to survive and even to travel from one melon to another.

If consumers choose to wash melon, they should be advised that bacteria can splash onto surrounding surfaces, and should be sure to clean these before next preparing food on them.