The United States' leading public health organisation says it is investigating a "fast-moving outbreak" of the bacterial infection E. coli linked to hamburgers sold at McDonald's stores, which has already caused the death of one person.
The Centers for Disease Control and Prevention (CDC) says 49 cases of the infection have already been reported to federal authorities across 10 states, with at least 10 people hospitalised due to illness.
An older adult has died in Colorado after developing a serious health condition known as hemolytic-uremic syndrome, which can lead to kidney failure.
[Ecoli map link]E. coli are bacterial germs that can make people sick if they have consumed contaminated food or water or come in to contact with infected animals and environments.
People who contract E. coli typically experience severe stomach cramps, diarrhoea and vomiting within four days of infection and recover within a week.
The CDC says most of the cases already identified from the latest outbreak "are reporting eating the Quarter Pounder hamburger at McDonald's before coming sick", but the specific food ingredient causing the illnesses remains unknown.
A health advisory released by the CDC shows that the ages of people impacted in the outbreak range from 13 to 88 years, and are mostly male.
"McDonald's is collaborating with investigation partners to determine what food ingredient in Quarter Pounders is making people sick," the CDC advisory said.
"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.
"In addition, 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."
Joe Erlinger, the president of McDonald's USA, said the business was actively communicating with its customers "because food safety is so important to me and everyone at McDonald's".
"It's important to note that the majority of states and the majority of menu items are not affected. Other beef products including the Cheeseburger, Hamburger, Big Mac, McDouble and the Double Cheeseburger are not impacted," he said.
"We are working quickly to return our full menu in these states as soon as possible.
"I hope these steps demonstrate McDonald's commitemnt to food safety."
The first case of E. coli reported by the CDC was on September 27, but between September 29 and October 8 another 45 infections were identified.
The CDC says the outbreak appears to be contained to the mountain states in the west and mid-west of the US. Colorado is the worst-affected with 26 cases uncovered, while the neighbouring states of Utah, Wyoming and Nebraska have each recorded four infections.
Authorities have also said that Quarter Pounder hamburgers will temporarily be made unavailable at McDonald's stores in some states while the investigation is underway.
A spokesperson for McDonald's Australia has told the ABC there is currently no concern about food safety standards across its 1,044 stores.
