Federal officials have updated the number of patients in an outbreak of E. coli O157:H7 infections traced to slivered onions on McDonald’s Quarter Pounder hamburgers. The patient count now stands at 104.

The Food and Drug Administration and the Centers for Disease Control and Prevention are continuing to investigate the outbreak. Of 98 patients interviewed, 34 have been hospitalized. One person has died. Four patients have developed hemolytic uremic syndrome, which can cause kidney failure. The sick people are spread across 14 states. McDonald’s locations in all 14 states received slivered onions from a Taylor Farms facility in Colorado.

There are likely many more sick people that are on the confirmed patient list. The CDC reports that for every confirmed patient infected with E. Coli O157:H7 there are 26 who are not confirmed. This is because some people do not seek medical attention and others are not specifically tested for E. coli.

Of  81 people interviewed about the food that ate before becoming ill, 80 reported eating at McDonald’s. Of 75 people who could remember what menu item they ate at McDonald’s, 63 reported a menu item containing fresh slivered onions.

Investigators with the FDA have focused on the Taylor Farms facility in Colorado and an onion grower in Washington state. The agency reports that its investigation into the two locations has been completed but has not reported much in the way of details. The FDA has not reported what onion grower was investigated.

Thus far, FDA testing has shown E. coli in a sample of onions taken from the Taylor Farms facility, but the sample is not the same as the outbreak strain. However, additional test results are still pending. No E. Coli was found in hamburger that was tested and the FDA has ruled out hamburger as the source of the pathogen in the outbreak.

Early in the outbreak McDonald’s stopped using slivered onions in some states where outbreak patients were reported. Taylor Farms later recalled its slivered and whole yellow onions that were distributed in almost 20 states. Food service customers were notified by Taylor Farms that they should not sell or serve recalled yellow onions.

McDonald’s has reintroduced slivered onions from a different onion supplier into their full menu. At this time, there does not appear to be a continued food safety concern related to this outbreak at McDonald’s restaurants, according to the FDA.

About E. coli infections
Anyone who ate at McDonald’s from mid-September through late October and developed symptoms of E. coli infection should seek medical attention and tell their doctor about their possible exposure to the bacteria. Specific tests are required to diagnose the infections, which can mimic other illnesses.

The symptoms of E. coli infections vary for each person but often include severe stomach cramps and diarrhea, which is often bloody. Some patients may also have a fever. Most patients recover within five to seven days. Others can develop severe or life-threatening symptoms and complications, according to the Centers for Disease Control and Prevention (CDC).

About 5 to 10 percent of those diagnosed with E. coli infections develop a potentially life-threatening kidney failure complication, known as a hemolytic uremic syndrome (HUS). Symptoms of HUS include fever, abdominal pain, feeling very tired, decreased frequency of urination, small unexplained bruises or bleeding, and pallor.

Many people with HUS recover within a few weeks, but some suffer permanent injuries or death. This condition can occur among people of any age but is most common in children younger than five years old because of their immature immune systems, older adults because of deteriorating immune systems, and people with compromised immune systems such as cancer patients.

People who experience HUS symptoms should immediately seek emergency medical care. People with HUS will likely be hospitalized because the condition can cause other serious and ongoing problems such as hypertension, chronic kidney disease, brain damage, and neurologic problems.