Five patients who were treated at the Tri-City Colonoscopy Clinic in Kitchener on Christmas Eve in 2013 were infected with hepatitis C, says Waterloo Region Public Health.

The patients were among 13 who received treatment at the clinic that day, said a report published Tuesday by the public health department.

"This is strong evidence of patient to patient transmission of hepatitis C due to a lapse in infection prevention and control practices at the clinic," the report said. 

Waterloo Region Public Health first started investigating in November 2014 while conducting a routine follow-up with a patient recently diagnosed with hepatitis C. The patient's medical records didn't show any risk factors, other than the fact they had been treated at the colonoscopy clinic on Sportsworld Crossing Road. 

Public health then launched an official investigation, and discovered a second case of the virus found in another patient treated at the same clinic on the same day. 

'It’s better it was discovered earlier than later'

After sending blood samples of both infected patients to the National Public Health Lab in Winnipeg, it was determined the genetic makeup of the virus was too similar to be coincidence. Officials decided to conduct further testing on all 13 patients who visited the Kitchener clinic on Christmas Eve in 2013.

The public health department received test results last week and found three more clients had been diagnosed with hepatitis C, bringing the total of infected clients to five. The remaining eight clients tested negative for the virus.

"All of the individuals have been referred to specialist care so they can get specific treatment related to managing hepatitis C and to give them to the best possible health going forward, in spite of hepatitis C diagnosis," said Dr. Liana Nolan, the medical officer of health for Waterloo Region.

"In this case it’s better it was discovered earlier than later,” Dr. Nolan said. 

Public Health has also conducted tests of all the clinic's staff and patients who were seen within a two-day window of Dec. 24, 2013. So far no other people have tested positive for hepatitis C. 

"At this point in time, Public Health has no evidence that there was a risk to clients seen on other days at Tri-City Colonoscopy Clinic," the report said.

Clinic cooperating with investigation

The Tri-City Colonoscopy Clinic, which is an outpatient outpatient endoscopy clinic that has performed colonoscopies and gastroscopies in Kitchener since Oct. 14, 2010, has been cooperating with Public Health's investigation.

The public health department has done an assessment of the infection prevention and control practices at the clinic and hasn't found anything that was likely to have caused the transmission of hepatitis C. Still, it has worked with the clinic to strengthen its current practices as the clinic remains open. 

"We’ve interviewed them, we’ve done inspections, we’ve reviewed their procedures and made some suggestions about how to make improvements and we didn’t find any current evidence of infection control lapses," said Dr. Nolan.

In a statement to CBC News, the Tri-City Colonoscopy Clinic said it "has been cooperating fully with Region of Waterloo Public Health Office and offers its sincerest apologies to the patients that may have been affected."

The College of Physicians and Surgeons of Ontario will also investigate the clinic, as the governing body for community colonoscopy clinics.

Hepatitis C a chronic virus

Hepatitis C is most commonly spread through infected needles, but can also be transmitted through blood, blood products, organs, tissues and cell transplants, and other sharp objects, and from mother to infant during pregnancy. 

Chronic infection can cause inflammation of the liver, scarring of the organ, cirrhosis and other complications, including liver cancer.

More than 300,000 Canadians live with chronic hepatitis C, according to the Canadian Liver Foundation. And because it can take up to two or three decades for the symptoms to progress, it's believed that number should be higher.