What Are the Causes of Foodborne Illness?

Article excerpt

If food that was going to leave you with gut-wrenching cramps--or more--tasted sickening, few people would indulge. The problem, of course, is that sickening food can taste quite scrumptious.

Indeed, when the hour of reckoning arrives, many of us don't suspect what hit us--mistaking our discomfort for a stress headache, bout of flu, or jittery stomach triggered by nerves. Doctors, too, can misread the symptoms. Indeed, the surest way to diagnose food poisoning is to test for telltale germs in the stool of patients who report suspicious symptoms--a procedure that physicians don't routinely employ.

While all of this makes tallying the incidence of food poisoning quite challenging, it hasn't stopped Uncle Sam from trying. This past fall, Paul S. Mead and his colleagues at the federal Centers for Disease Control and Prevention (CDC) offered up their latest estimate in a 19-page report. Published in the September-October issue of Emerging Infectious Diseases, it concludes that some 76 million U.S. residents develop foodborne illness each year.

That incidence rate would indicate that on average more than one in four people eat sickening food each year. The data also indicate that an estimated 325,000 require hospitalization-and almost 5,200 die-because of foodborne illness.

Where did Mead's team come up with these numbers? They extracted confirmed cases of food poisoning from nine data bases, such as the Foodborne Diseases Active Surveillance Network (FoodNet) and the National Hospital Discharge Survey. In addition, they read studies that described investigations into particular outbreaks and the degree to which poisoning events appear to have been underreported. Then, they multiplied the number of known cases by the likely underreporting figure, taking into account the different types of disease-causing agents, and summed the totals.

For instance, they cite unpublished data indicating that about 38 times as many cases of Salmonella poisoning occur as are reported. Because the bacterium responsible for this illness causes nonbloody diarrhea, Mead's team multiplied the number of cases of Salmonella poisoning and other nonbloody diarrheal incidents by 38. Because the underreporting rate for E. colt 0157:H7--which causes a bloody stool--is only about half as large, the epidemiologists upped the known incidence of bloody diarrheal disease 20-fold.

That gave them the gross, upper estimate of incidence for diseases caused by these germs. However, because these germs can be transmitted by means other than food--such as water contamination--they had to scale down their tally, in some cases by around two-thirds.

What They Know ... Among all illnesses linked to food, the scientists estimated that 67% trace to contamination with viruses such as Rotavirus, Norwalk-like viruses, or Hepatitis A; 30% are caused by bacteria, such as Salmonella, E. coli, and Campylobacter; and less than 3% are caused by parasites such as Cryptosporidium or Trichinella.

As their data show (excerpted in table, next page), the most common causes of food poisoning--viruses--are least likely to lead to fatalities. Even among the other classes of disease-causing agents, only a few stand out as being particularly deadly. Toxoplasmosis, for instance, caused by a parasite most commonly associated with sheep and cat feces, was linked to 20% of food-poisoning deaths, while accounting for less than 1% of all foodborne illness.

And Listeria--a bacterium that can multiply prolifically even in refrigerated foods--caused nearly 30% of food-poisoning deaths, while hardly registering as a major source of illness. Indeed, these new data indicate that nearly every Listeria victim requires hospitalization, and one in five of Listeria poisonings proves fatal.

Though most people know and fear botulism, only about 60 people in the United States contract this disease annually. That's just 2. …