Public health officials on both sides of the border are still trying to determine the source of an E. coli outbreak linked to romaine lettuce.

Many restaurants have stopped serving ceaser salads and stores have taken lettuce off shelves, leaving some consumers looking for alternatives.

Under artificial light, more than 20-thousand heads of greenleaf and butterhead lettuce grows in Landmark, Man., at Neva Farms

In less than eight weeks, owner Denny Black watches them grow from tiny plants into full grown greens.

“I think people are looking for an alternative to field grown crops,” said Black, who has been following the latest E. coli outbreak.

“Whereas other lettuce may be grown in a field and exposed to the elements, animals, or birds, ours is indoors under a roof,” he said.

Black said his lettuce is never watered from the top down, which helps prevent it from getting into the crevasses of leaves.

Instead of using soil and manure, he uses a mix of nutrients like a calcium and nitrogen combined with water.

To ensure his lettuce is grown as safely as possible, Black said all employees must change footwear. The farm also tracks the production date of its lettuce so buyers know when it was seeded.

Because he sells his greens to local stores and restaurants, Black believes his product travels shorter distances and spends less time in shortage.

He said romaine lettuce doesn't do well under these conditions, but he is looking at growing a similar variety called ‘Crunchita’ to possibly fill a gap in demand.

Food safety expert Claudia Narvaez said growing lettuce in a more controlled environment like a hydroponic farm can be moderately safer compared to soil, depending on the source of the water, and if people follow proper safety procedures.

Narvaez warns hydroponic foods are not immune from E. coli, salmonella and listeria.

"If the seeds for that lettuce is contaminated with a food borne pathogen, you can't, you won't get rid of it even in a hydroponic production system," Narvaez said from the University of Manitoba, where she is an associate professor in the food science department.

As of Friday Nov. 23, 22 cases of the potentially dangerous bacteria have been confirmed in Ontario, Quebec and New Brunswick. No cases have been confirmed in Manitoba.

The Public Health Agency of Canada says online the current strain is more likely to cause severe illness.

It said leafy greens can be contaminated in the field by soil, water, animals or improperly composted manure.

It can also happen after the lettuce has been harvested when it’s being handled, stored or transported.

Contamination is also possible at the grocery store, in the refrigerator or on a cutting board.