Ottawa Public Health has sent a letter to parents with children at Gisèle-Lalonde High School in Orleans warning them of possible exposure last year to two people who had tuberculosis.

"It's a little bit uncommon to have two in the same school, which is why additional precautions are being taken to see if any other student may have been exposed," said Dr. Rosamund Lewis, an associate medical officer of health at OPH.

The city's public health agency sent out letters on Friday saying anyone who attended the French public school between Sept. 15, 2013 and Dec. 24, 2013 may have been exposed.

The persons with TB did not know they had it at the time they attended school, but may have spread the tuberculosis bacteria.

There are generally about 50 cases of active TB in Ottawa each year.

TB bacteria are spread through the air when the person with TB coughs, but it takes prolonged, close contact to breathe in the TB bacteria.

It can take up to eight weeks for the body to show it has breathed in the bacteria, which can lie dormant in the body without any symptoms for weeks, months, and even decades, wrote Brenda MacLean, a program manager with the healthy agency's outbreak management unit.

"It is strongly recommended that you have a TB skin test now to show if you breathed in the TB bacteria," wrote MacLean.

The health agency will be offering TB skin tests on Oct. 6 to 8 from 9 a.m. to 4 p.m. at the school.

"We're at a prevention stage right now and it's pretty low risk," said Stephane Vachon, a wellness superintendent with the French public board. "The first step is to find out and inform parents and then from there on offer follow ups."

People who may have been exposed who have been coughing for several days and are experiencing fever and weight loss should contact Ottawa Public Health immediately at 613-580-6744, ext. 24224.