Chipotle Mexican Grill Inc. is preparing to reopen its 43 restaurants in Washington and Oregon which had closed following E. Coli food poisoning cases.

Tech Times reported that health officials declared that the restaurant chain could reopen its restaurants as early as Wednesday, Nov. 11, after batch of tests revealed negative E. coli results of food samples.

The exact source of E. coli infection cases remains unresolved.

Chipotle was reported to be the cause of E. coli food poisoning cases in Washington and Oregon. There were more than 40 people infected by E. coli after they ate at Chipotle.

The company was forced to close 43 of its restaurants started from Oct. 31 after health officials linked some Chipotle outlets to the food poisoning cases.

Chipotle had ran steps in respond to the E. coli cases. The company hired food safety consulting firms and performed batch testing on fresh products, raw meat, and dairy products. The company also needs to sanitize all food items, throw out all food stocks and bring in new batches of supplies.

Chipotle also implemented additional safety procedures and audits in all of its approximately 2,000 restaurants.

The health officials conducted the investigation on samples collected from the patients and found the infective pathogen E. coli O26. The officials said that the cause may have been raw ingredients such as tomatoes, lettuce or cilantro.

However, the tests on samples taken from several Chipotle restaurants didn't reveal E. coli bacteria presence.

The officials tests cannot necessarily determine an exact source of the infection because the contaminated food might have been consumed before the food samples were obtained.

The E. Coli outbreak brings the challenge to Chipotle including slower sales after years of rapid growth. According to The Wall Street Journals, a survey conducted by financial services firm Blair & Co. showed that 51% of 800 respondents were aware of the E. Coli link to Chipotle.

Analysts said that the E. Coli outbreak could lead to short-term impact on the sales but they doubt that it would have a lasting impact.

Chipotle shares had fallen 5% through Monday since the company announced the closure of its restaurants.  The shares gained 2.4% at $623.96 on Tuesday, according to Reuters.

Chipotle had been linked to other food poisoning cases in recent months. In August and September, the restaurant chain linked to Salmonella infection cases in Minnesota with more than 60 people reporting illness.

It also linked to norovirus infection case in Southern California that sicken 80 customers and 13 employees.

The company declined the relation of its restaurants to the food poisoning cases as the cause of the infection wasn't resolved.