With more cases being reported, the US Centers for Disease Control and Prevention (CDC) has confirmed that at least 75 people in the country have been sickened by the E. coli outbreak linked to McDonald’s Quarter Pounder hamburgers.

The latest tally, up from 49, including one death, earlier this week, has been reported in 13 states, Xinhua news agency reported.

The most recent illness started on October 10, according to the CDC on Friday.

Of 61 people with information available, 22 have been hospitalised, and two people developed hemolytic uremic syndrome, a serious condition that can cause kidney failure.

The CDC said in an update that McDonald’s is collaborating with investigation partners to determine what food ingredient in Quarter Pounders is making people sick.

McDonald’s stopped using fresh slivered onions and quarter-pound beef patties in several states while the investigation is ongoing to identify the ingredient causing illness.

“The true number of sick people in this outbreak is likely much higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because many people recover without medical care and are not tested for E. coli,” warned the CDC, adding that “recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak”.

Taylor Farms, the supplier of slivered onions to the affected McDonald’s locations, has initiated a voluntary recall and has asked customers to stop using some onions while this investigation is ongoing, said the CDC in its update, adding that food service customers were contacted directly and told to remove onions.

The company is a California-based producer of fresh-cut fruits and vegetables.

Quarter Pounder hamburgers will not be available temporarily in some states while McDonald’s makes some supply changes.

The fast-food giant’s stores in Colorado, Kansas, Utah, Wyoming, and portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma have temporarily stopped using their current supply of Quarter Pounder slivered onions and beef patties.

Some fast food chains, including KFC, Pizza Hut, Taco Bell, and Burger King, are reportedly removing onions from some of their locations in the country amid the E. coli outbreak.

E. coli is a group of bacteria that can cause infections in one’s gut (GI tract), urinary tract, and other parts of the body.

Most of the time, it can live in one’s gut without hurting him. But some strains can make one sick with watery diarrhoea, vomiting, and a fever.