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Listeria Outbreaks Confirm the Need for Care in Food Preparation

This is a tale of two cantaloupes, one that killed and one that cured.

This is a tale of two cantaloupes, one that killed and one that cured.

Herb Stevens was a spry 86-year-old who suddenly developed tremors and chills and became so weak that he was unable to get up from the toilet. And so began a downward spiral of complications that would eventually lead to his demise. Tests revealed that Stevens had been infected with Listeria monocytogenes, a soil bacterium commonly found in animal feces. Two weeks earlier, the retired hydrologist had eaten half a cantaloupe purchased at local Colorado supermarket, a purchase that would turn out to have lethal consequences.

Stevens was not the only victim; before the 2011 Listeria epidemic subsided, 147 people would be hospitalized and 33 would lose their lives. All had eaten cantaloupes that were eventually traced to a Colorado farm owned by brothers Eric and Ryan Jensen, who now face the possibility of jail after being charged with introducing adulterated food into interstate commerce.

The charge does not imply that they knew, or should have known, about the contamination. But as owners of the farm, they were accountable for maintaining sanitary conditions. Prosecutors decided on the heavy-handed approach to send a strong message to the food industry about its responsibility to reduce food-borne illness. It is indeed a critical responsibility, given that bacteria and viruses lurk everywhere in our food supply.

It is difficult to estimate the extent of illness caused by microbes because the vast majority of cases resolve after a brief tussle with cramps, nausea and diarrhea — and never get reported. The so-called “24-hour flu” is a misnomer. Influenza is not a one-day phenomenon, but symptoms associated with food poisoning can sometimes pass in 24 hours. If you’re unlucky, contaminated food can kill. The Centers for Disease Control in Atlanta estimates that in the U.S. there are about 50 million food-related illnesses a year, with 130,000 hospitalizations and 3,000 deaths. Most of the victims are children, the elderly and people whose immune system is compromised. Pregnant women are especially at risk, but healthy people generally are not seriously affected.

Virtually any food can be contaminated by bacteria, but cantaloupes are particularly prone because of their continued contact with the soil during growth. Furthermore, their rough skin can trap and hold bacteria, some of which can even penetrate to the inside of the melon. Just slicing a melon can transfer bacteria from the outside to the inside, which is why washing the fruit before cutting is wise. Growers are expected to minimize risk by maximizing precautions, but there are many points during processing that allow for the possibility of contamination. Investigation showed that Jensen Farms was lax in the maintenance of proper sanitary conditions.

Although the exact source of the bacteria was never pinpointed, numerous samples taken around the farm revealed the presence of Listeria. Contact with a potato-washing machine was a possibility. Cattle mature was found on transport-truck tires. The packing house had pools of water on the floor. And the melons were not properly cooled after coming off the fields.

Listeria is not the only bacterium that can contaminate cantaloupes. In 2012, a Salmonella outbreak that made 261 people sick and caused three deaths was traced to Chamberlain Farms in Indiana. The victims were located in 24 states, a sobering reminder of how our current food-distribution system can cause widespread problems. A cattle pasture next to the growing field may have been the origin of the bacteria, but once again the major problem was a bevy of inadequate practices in the packing house that ranged from lack of monitoring of wash-water disinfectant levels to droppings from birds roosting in the rafters above food-contact surfaces. These outbreaks, although tragic, serve to highlight the need for vigilance in food production, and the lessons learned should reduce the risk of future problems. At home, people should wash produce with running water, even if it is going to be peeled. Fruits or vegetables with uneven surfaces, such as a cantaloupe, can be scrubbed with a produce brush to remove microbes that are otherwise difficult to dislodge. Care should be taken not to spray water during the washing, because bacteria and viruses can live on surfaces for a long time. For extra safety, surroundings can be wiped with a sanitizing solution made by adding a teaspoon of bleach to a litre of water. Wipe surfaces and wait 10 minutes before rinsing with clean water. This discussion certainly is not intended to scare anyone away from eating cantaloupe, a fruit that is a good source of the antioxidants beta carotene and vitamin C. Rather, the goal is to highlight the need for awareness of microbial contamination, the biggest concern when it comes to the safety of our food supply. One bite of contaminated food can have deadly consequences. Obviously a cantaloupe can kill, but cure? A case can be made for one particular cantaloupe, purchased in 1941 by Mary Hunt, a bacteriologist working at the Agricultural Research Lab in Peoria, Illinois. Thirteen years earlier, Alexander Fleming had discovered the antibiotic properties of a mould that had accidentally drifted into one of his bacterial cultures, and within 10 years Florey and Chain had identified penicillin as the bactericidal ingredient. The search was now on to find a mould that would produce a higher yield of the substance. Researchers throughout the world were asked to send samples of mouldy fruit, grains and vegetables to Peoria for testing. Mary Hunt also took up the challenge, and on her usual shopping trips scoured produce for mould. One day she found a mouldy Texas cantaloupe that aroused her interest and she brought it to the lab. After cutting out the mould, she and fellow workers enjoyed the sweet taste of the historic fruit. When the mould that had contaminated the melon was steeped in a vat of corn liquor, it yielded 20 times more penicillin than any other mould tested.

Within a year, enough penicillin was produced to treat a vast number of battlefield infections, saving thousands of lives. “Moldy Mary,” as she came to be known, had chanced upon the most celebrated cantaloupe ever grown.

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