Chipotle has 1,900 locations nationwide with room to grow and more than $4 billion in revenues. (iStockPhoto)

Chipotle Mexican Grill (ticker: CMG) can't seem to escape headlines that would shake any food company.

From October to November, more than 50 people fell ill with E. coli poisoning, which the Centers for Disease Control and Prevention linked to the fast-casual chain. Then, in early December, more than 140 students at Boston College, including members of the men's basketball team, were diagnosed with a norovirus after eating at a Boston-area Chipotle.

For a company founded on fresh ingredients and locally sourced food, it was a nightmare that seemed to have no end. Neither did the stock's fall, which dropped 24 percent in two months.

But Chipotle has been one of the best and brightest growth stories in food over the past decade. It redefined the fast-food industry, creating an new experience for diners looking for a healthy, grab-and-go meal. Could this spell an end for its growth prospects? Has Chipotle's feel-good tale turned into a horror story?

Here's what you should know about investing in CMG stock.

Chipotle announces major changes. The CDC has yet to discover the cause of the E. coli breakout, which limited Chipotle's brass in its response to the current issues. But in December, founder and co-CEO Steve Ells announced major changes that Chipotle would take to prevent a similar outbreak in the future.

Instead of dicing tomatoes, lettuce and cilantro in the restaurants, Chipotle will cut produce at a centralized location and sanitize it before placing the products in bags to ship to restaurants. This will remove some of the prep work from the local kitchens. It's also implementing a DNA-based test for all produce before restaurants receive the ingredients.

"Basically, every product will be tested from farm to distribution," says Bernstein Research analyst Sara Senatore. "Their goal is to be the safest place to eat, but they can't guarantee that nothing will happen."

Senatore says the company is 10 to 20 years ahead of competitors in food testing. But if people continue to get sick, that message will get lost.

Fresh food is still important. Chipotle's growth story has been remarkable, rising 1,160 percent since its initial public offering in 2006. Its growth has been predicated on fresh food.

"It redefined consumers' approach and how they think about quick-service food," says Sharon Zackfia, a partner in William Blair and Co. in Chicago.

But that use of fresh ingredients is also why the company faces illness issues. Since it doesn't fry its food or use many preservatives, it leaves the company more susceptible to foodborne illnesses..

"Chipotle's greatest strength can create these issues," Senatore says. "It's very much a function of the quality of the food and freshness."

In response, Chipotle will reduce the number of locally sourced products, which the Wall Street Journal reports is about 10 percent of the overall produce bought in a year. That speaks to what Chipotle's shifting to: centrally controlled food production.

It's still the top name in fast casual. Despite the recent food issues, Chipotle remains the No. 1 player in fast-casual restaurant chains. And it has plenty of room to grow.

Chipotle has 1,900 locations nationwide, and Zackfia says it could "double or triple" that without saturating its brand. That doesn't even include international growth, which is a potential driver in the future for the Mexican food chain. With only 1 percent of stores operating outside the U.S., it has begun to try new markets, including Canada, London and Paris.

Comparing Chipotle to its other competitors in the fast-casual Mexican food vertical is no contest. It has more than $4 billion in revenues, while Qdoba, owned by Jack in the Box (JACK), has $338 million. In terms of size, Chipotle's greater competitors may be fast-food chains such as McDonald's Corp. (MCD) and Taco Bell, which is owned by Yum! Brands (YUM).

But within the fast-casual line, CMG stock offers a rare opportunity of size and growth potential. BTIG managing director Peter Saleh says that a new Chipotle restaurant returns 60 to 70 percent of investment within the first year. "You're lucky to get 20 to 30 percent" from other restaurant openings, he says.

It might be time to buy CMG stock. Following the fallout of the E. coli scare, Chipotle had to revise its yearly expectations. It announced that it expected same-store sales to fall between 8 and 11 percent this year since people stayed away the past few weeks. And the CDC hasn't yet cleared the restaurant of what issue brought on the illnesses, which means the outbreak may not be over.

But this has also created a unique time to buy, if you're comfortable with some of the near-term volatility. "Prior to the E coli outbreak, everything seemed fundamentally moving in the right direction," says Zackfia, who has Chipotle among her best investing picks of 2016.

Chipotle has had a five-year average price-to-earnings ratio of 44.7, according to Morningstar. It's now at 33.1. "One year's earnings doesn't change the value of the company dramatically," says Senatore, whose target price of $730 for CMG stock is a 32 percent premium over its current price.