Here’s how health officials are investigating foodborne outbreaks like Quarter Pounders E. Coli

On October 22, the Centers for Disease Control and Prevention reported that dozens of E. coli infections were linked to McDonald’s Quarter Pounders. In response, McDonald’s temporarily removed Quarter Pounders from the menu in several states. At least 75 people have entered so far 13 states have been infected, with 22 hospitalized and one death due to illnesses that started in the last week of September. Preliminary data imply that chopped onions used on Quarter Pounders are a possible source, and are recent testing of the Colorado Department of Agriculture excludes beef patties, according to the company. Other fast food chains, including Taco Bell, Pizza Hut and KFC, also removed onions from their menus and onion supplier Taylor Farms issued a voluntary recall. The specific strain of E. coli is O157:H7, a known pathogen that produces a toxin that can cause fever, abdominal cramps, severe and even bloody diarrhea, and kidney failure.

Whether it’s E. coli from onions at McDonald’s or Listeria of Boar’s Head meats, foodborne illness is a common problem worldwide. In the United States alone, the CDC it is estimated that there are more than 47 million cases and more than 127,000 hospital admissions per year. Here’s how public health authorities use basic epidemiology to track the source of a foodborne outbreak for a specific food or supplier.

Every outbreak investigation starts with notifying health authorities, such as the local health department, CDC, the USDA or the FDA, that people are sick. A notification can be made via a telephone call, e-mail, text message or media report. The source of the report is often an astute doctor who recognizes an unusual disease pattern in his or her patients and then sounds the alarm. Other potential sources may include the patients themselves, laboratories that observe unusual numbers of positive laboratory samples, or pharmacies that observe large numbers of prescription and over-the-counter medications being purchased.

A report prompts public health authorities to seek more information to determine if there is indeed an outbreak. They then follow a series of steps and use epidemiological methods to track down the cause. They will first create a case definition to define the signs and symptoms of the disease and use that definition to look for additional cases. In an E. coli outbreak, the case definition may also include someone with fever, diarrhea, and a positive stool test for E. coli. As more information is collected, a timeline of dates of illness and possible sources of exposure can be included.

It is then important to ask the cases about possible exposures. This is usually done through a series of questions, such as where people ate during a certain time frame, what they ate, who else ate with them, and whether anyone else they know is sick is sick. This information can provide an early indication of a possible cause. In the case of the E. coli outbreak at McDonald’s, when McDonald’s was identified as a common place where patients ate before their illness, that could be the impetus to ask more specific questions about McDonald’s.

In order to conduct a so-called case-control study, the first thing would be to obtain a menu of all the possible food options at McDonald’s and then ask the patient what they ate and what they didn’t eat. help with the inclusion or exclusion of the different foods. It is also useful to interview other people as a control group who are not sick but who have also eaten at McDonald’s during the same time period as the cases. The goal is to identify a common source of infection. Mathematical calculations are then made to compare the likelihood of infection from eating different foods. This will help not only determine that the culprit was Quarter Pounders, but to more specifically determine whether the meat in the Quarter Pounders or something else on the Quarter Pounders, such as onions, is the likely cause.

At this point, epidemiologists will double-check whether their suspected source of the epidemic stands up to scrutiny. This includes a reassessment to ensure that their data is not missing anything important and that the foods involved make biological sense. In an E. coli situation, the organism is found in the intestines of animals and can contaminate meat or soil, so it is biologically plausible whether it is hamburgers or onions. Genetic testing of the E. coli can also be used to further compare a possible source found in implicated foods and from patient samples.

Public health authorities want to be reasonably sure they are right about the cause of the outbreak before issuing press releases. There are a number of reasons for this: this type of research is potentially politically charged and has enormous consequences for the companies that may be affected. As we have seen, McDonald’s stock price fell off a cliff on the date of the outbreak announcement. Affected businesses could lose money or go bankrupt as scared customers choose to dine elsewhere.

The goal is to quickly identify the source and mitigate the problem by alerting the public to cease further consumption of the affected foods. Ultimately, the real test is whether they have achieved the goal of reducing the number of cases. And if that happens, then: bon appétit.