As the result of the recent Listeria outbreak associated with the consumption of cantaloupe that has sickened residents of Colorado, Nebraska, and Texas, and has caused one death, we are again reminded of the risks associated with cantaloupes and other melons.

Roy Costa, a contributing author for Food Safety News, reported a few months ago on why cantaloupes in particular stand out as a food safety problem. According to his article:

Investigators have known about the melon’s food safety problem since at least the early 90s, when numerous nationwide outbreaks of Salmonella occurred with melons; tens of thousands of cases were reported in these outbreaks. Cantaloupes (musk melons) are most the most frequently identified melons in outbreaks, although watermelon and honeydew (rarely) have also caused outbreaks. 

The reason why melons like cantaloupe can present such a food safety issue, is that there are countless places along the supply chain where they may become contaminated. As Costa explains, “hazardous points [begin] with growing and harvesting and continuing through packing, storage, transport, distribution, processing and final consumption.” He adds:

Cantaloupe can be contaminated any time the crop is in the ground, but the contamination problem is likely to start when the fruit is ripe and ready to be picked. Animals such as deer, coyotes, raccoons, rodents, feral pigs, and birds are attracted to the crop at this stage. Animal vectors in the growing environment may also include amphibians, reptiles and domestic animals.

Animals can affect the crop directly or through contamination of the water supply used for irrigation and crop protection. Manure may contain animal wastes, and fertilizers pose their own unique threat.

Infected humans are also a risk anywhere in this chain. Fecal matter, especially human waste in the growing or harvesting area, is a very significant risk factor and farmers must strictly control this potential.

Although, it seems hard to believe that contamination in the growing field could remain on the cantaloupes even after traveling thousands of miles to the grocery store, Costa reports that “once contaminated, a cantaloupe will likely remain contaminated until reaching the consumer.” He says:

Cantaloupes are not typically washed before packing. If they are packed in a packinghouse, they go through a grading process to remove damaged and diseased fruit; they are then loaded either in bins for further distribution or in retail size boxes. Netted bags bay be used, and packers may also individually wrap melons. Like cantaloupes, watermelon and honey dew may also be packed without a wash step, or even packed for final shipment directly to retailers from the field.

Unfortunately, the thick and rough rind of cantaloupes provides little protection to potential bacterial contamination. Scientists once thoughts that bacteria could only grow on the outer surfaces of cantaloupes; however, new research has shown that it is possible for some bacteria to, as Costa explains, “actually penetrate the exterior of the melon, even when no bruising occurs.”