McDonald's arches
A McDonald's sign is seen outside a restaurant in Boston on March 14, 2001. Darren McCollester/Newsmakers

A slight uptick in third-quarter sales at McDonald's U.S. restaurants in the U.S. could be derailed by the deadly E. coli outbreak tied to its Quarter Pounder hamburgers.

The fast food giant said Tuesday that same-store U.S. sales rose 0.3% from July through September, reversing a 0.7% decline during the second quarter.

McDonalds acknowledged during an earnings call that the recent E. coli outbreak hurt its sales momentum, without sharing numbers, according to the Associated Press.

But Placer.ai, which tracks retail traffic using cell phone data and other signals, said it saw a 9% year-over-year decrease in visits to U.S. McDonald's at the end of last week, AP said.

On Oct. 22, The Centers for Disease Control and Prevention announced that 49 people were sickened, one fatally, by E. coli infections that were likely caused by tainted onions on Quarter Pounders.

The total number of cases has since risen to at least 75 in 13 states, the CDC reported.

Chris Kempczinski, McDonald's chairman, president and CEO, apologized for the outbreak during Tuesday's conference call and said he "relieved that this situation appears to be contained."

Kempczinski said the company hoped to win back American customers because it acted swiftly to contain the outbreak, cooperated with authorities and was promoting offers that include $5 meals and limited-time Chicken Big Macs.

McDonald's will also take further actions if necessary, he said.

The company's stock price jumped 1.7% during the first five minutes of trading Monday but quickly fell and was up less than 0.1% around noon ET.

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