By Nathaniel Meyersohn, CNN

New York (CNN) — Americans around the country avoided McDonald’s last week after an E. coli outbreak left dozens of people sick.

On Wednesday, the day after the E. coli outbreak was announced, customer visits to McDonald’s dropped 6.4% across the country and 24% in Colorado, where the outbreak was most prevalent, according to Placer.ai, which tracks foot traffic to restaurants and retailers.

More customers stayed away from McDonald’s in the following days. By Thursday, visits to McDonald’s dropped 9% nationwide and 31% in Colorado.

The following day, visits declined 10% around the country and 33% in Colorado.

McDonald’s declined to comment on the Placer.ai data. The company is expected to discuss the outbreak on a conference call with investors following the release of its quarterly financial results this morning.

McDonald’s will resume selling Quarter Pounders in all of its restaurants this week after the Colorado Department of Agriculture said the company’s beef patties used for the Quarter Pounder tested negative for E. coli. The customers who got sick ordered that particular burger.

“The issue appears to be contained to a particular ingredient and geography, and we remain very confident that any contaminated product related to this outbreak has been removed from our supply chain and is out of all McDonald’s restaurants,” McDonald’s said Sunday.

US health officials said Friday that the number of illnesses linked to McDonald’s Quarter Pounders had risen to 75 — up from the initial report of 49 — including one death. Those numbers could go up again, as it can take weeks for officials to determine whether an illness is part of an outbreak.

Food safety concerns can impact restaurants for an extended period. But RJ Hottovy, an analyst at Placer.ai, expects McDonald’s to recover quickly because the company was able to identify the source of the outbreak, communicate it to health officials and the public, and implement preventative measures.

The E. coli outbreak has overshadowed McDonald’s business and came as the chain was struggling to win back customers put off by higher prices. The average price of McDonald’s menu items is up around 40% over the past five years.

McDonald’s announced Tuesday that sales at restaurants open for at least one year ticked up 0.3% in the United States during its latest quarter, but fell 1.5% globally. The quarter ended on September 30 and did not include sales following the announcement of the E. coli outbreak.

The results were an improvement from McDonald’s previous quarter, when sales dropped 0.7% in the United States. The bounceback at American restaurants was driven in part by McDonald’s $5 value meal promotion. McDonald’s also had some hugely successful limited-time specials, including a Crocs partnership and a series of nostalgia-heavy collector’s cups.