Chipotle, the popular fast food chain, voluntarily shut down 43 of their stores in Washington and Oregon. Health authorities began investigating an E. coli outbreak last weekend. Eight people have been admitted to the hospital but no deaths have occurred.

The E. coli bacteria commonly reside in the intestines of people and animals, but some strains are capable of inducing illness and, in extreme cases, death.

Infections occur when people swallow small amounts of human or animal feces. Typically this happens while swimming in lakes, petting animals or, in this case, eating food prepared by people that did not adequately wash their hands after restroom use.

Illness can cause vomiting, watery or bloody diarrhea and cramps within one to 10 days. Treatments of hydration are common and many cases resolve themselves within a week. Many possible victims who don’t even consider the connection can easily recover without treatment.

Health authorities are investigating 19 known cases in Washington and three in Oregon. Chris Arnold, communication director for Chipotle released this statement:

“There have been links made to six restaurants in the Seattle and Portland areas. We have closed 43 restaurants in those markets out of an abundance of caution.”

Oregon health authorities said in a statement the infection affected people who ate at the restaurant during Oct. 14-23. Reported symptoms were from customers in Clackamas and Washington counties in Oregon and Clark, King, Skagit and Cowlitz counties in Washington State. They also noted that “Many people affected with Shiga toxin E. coli may not seek health care, so the number of people made ill by this outbreak is likely more than identified.”

“We believe that a food item is probably the cause of these infections but we don’t know at this time what food item that is,” said Marisa D’Angeli, medical epidemiologist with the Washington State Department of Health.

Chipotle received praise for their omission of GMO’s from all their food in April, but despite that triumph, the road has been rocky for the restaurant chain.

Last August, Minnesota health and agriculture officials reported a salmonella epidemic among customers from 17 different Chipotle locations, primarily in the Twin Cities metro area. Tomatoes were cited as the main cause for the infection, affecting 64 customers; nine of those sickened customers were hospitalized.

Also in August, a Chipotle restaurant in Simi Valley, California, temporarily shuttered after 80 customers and 18 employees reported symptoms of norovirus.

Chipotle was also under fire when their main pork supplier, Niman Ranch, was purchased by poultry titan Perdue Farms. Niman Ranch has been credited with being a pioneer in animal treatment and higher standards for raising pig and cattle, while Perdue has received an onslaught of lawsuits for their alleged mistreatment.

Chipotle was recently the target of a class action lawsuit claiming that they aren’t truly GMO free. The lawsuit was filed on behalf of all California customers who purchased Chipotle after April 27, 2015. The lawsuit argues that the soda brands served at Chipotle have corn syrup, an ingredient that is almost always made with GMO corn.

The fast food chain’s stock fell 1.7 percent to 629.29 in morning trading Monday. The stock was already down 6.5 percent for the year at the end of last week when investors became concerned about slowing growth. Company officials have described sales in October as “very, very choppy.”

Reporting by Daniel Anderson