Q. Today, my daughter and I ate lunch in a place that could be called a “dive.” After she finished her mac & cheese, we found a dead cockroach in the bottom of the bowl!! Of course I complained loudly to the manager. They were very apologetic about it and didn’t charge us, but I want to know what are the chances that my daughter could get sick from eating cockroach-contaminated food?

A. There’s little doubt that cockroaches contribute to cases of gastroenteritis. Obviously the risk of illness is greatest when you combine large numbers of cockroaches with unsanitary conditions in food storage or preparation. When people eat food contaminated with Salmonella, Staphylococcus, and certain other bacteria, food poisoning can result. This happens most often when the contaminated foods are eaten uncooked (bread or cheese, for example).

While fleas, ticks, and mosquitoes transmit blood-borne diseases directly when they bite, cockroaches are “passive” or “mechanical vectors.” They pick up various bacteria and viruses on their legs and antennae and then transfer them to food, dishes, and other items that they walk across. They also eat contaminated food or feces and transfer disease organisms in their droppings or when they regurgitate. When the feces of cockroaches contaminated with Salmonella were spread on crackers, the bacteria survived for more than 4 years!

Some people say that we’re too hard on the cockroach; that it has never been directly implicated in the transmission of disease. Admittedly, cockroach transmission is a difficult thing to prove in the real world. In the laboratory, however, researchers can clearly show that cockroaches carry and transmit bacteria, viruses, and other pathogens, including those causing typhoid fever, hepatitis, polio, and dysentery.

In one study, German cockroaches were collected from 41 different sites in New York including restaurants, bakeries, hospitals, prisons, private homes, and apartments. Researchers found that almost 90% of the cockroaches collected carried at least three different disease bacteria that could cause food poisoning. Cockroaches carrying Staphylococcus were collected from a nursery school sink, supermarket food carts, and from cooking utensils and coffee machines in a hospital. Cockroaches carrying Escherichia coli (from human fecal material) were found in hospitals and in an ice cream establishment. Studies like these support the need for good sanitation and good pest control wherever foods are handled.

Chances are good that your daughter will be just fine. Look at the numbers of people in this country who live with cockroaches in their homes every day. There’s no way to know (without testing) whether that cockroach was carrying disease organisms, and there are lots of factors that have to come together just right in order for disease to be transmitted.