Dozens of patients and staff in several London hospitals may have been exposed to tuberculosis from a health care provider who had gone undiagnosed in months, health officials said on Tuesday.

The health care provider had worked in out-patient clinics at both St. Joseph's Health Center and London Health Sciences Center, and he is now being treated. Officials from Middlesex London Health Unit (MLHU) are currently tracking down the potential spread of TB in these hospitals.

Dr. Robin Walker, who is the integrated vice president of Medical Affairs at both hospitals, said it is not unusual to find cases of TB, but it is rare to discover the disease in a health care provider in a hospital.

"It is very unusual, indeed," said Walker. "It's been many years."

About 38 patients at London Health Sciences Center and another 29 at St. Joseph's could have been exposed to TB, Walker said. The number might also increase.

"We're still in the process of full contact testing," said Walker.

Walker and his colleagues are optimistic that majority of the people exposed to the disease will not contract it.

According to health officials, the risk of infection is very low, as well as the risk of spread within the hospitals.

Medical Health Officer Dr. Chris Mackie of MLHU said about 10 percent of people exposed to the disease would go on to develop an active infection that has an ammonia component and could possible spread to others. They are confident that there will be no secondary cases.

Walker said the safety and well-being of patients and staff at both hospitals is their main priority.

"We will continue to work together with the MLHU to ensure that all individuals at potential risk are identified and assessed as quickly as possible," said Walker.

TB is caused by bacteria that affect the lungs. The symptoms include fever, cough, loss of weight and night sweats. The disease is usually spread through frequent and prolonged exposure with a person who has the disease.

Most people who are exposed to the disease are not infected because their bodies fight it off, Mackie said.

It will take weeks before the exposed individuals are ruled out for TB. It usually takes eight weeks for the bacteria to turn into an infection, officials said. If any of the exposed individuals test positive, anyone who came into contact with them will be tested as well.

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