Seventy per cent of the about 138,600 Canadians infected with hepatitis C based on blood tests did not know they had the virus, Statistics Canada says.
Wednesday's results from the Canadian Health Measures Survey come amid calls for baby boomers to be screened with a one-time test for hepatitis C infection (HCV), which liver specialists say can be eradicated if treated early.
"Accurate infection awareness is important for health-care seeking, receipt of treatment, vaccination uptake, and disease prevention, but more than half of respondents who tested positive for hepatitis B and hepatitis C did not know that they were infected," Michelle Rotermann of the agency's health analysis division and her co-authors concluded.
Hepatitis C is transmitted through blood, blood products, organs, tissues and cell transplants, infected needles and other sharp objects, and from mother to infant during pregnancy. Sexual transmission is less common, Statistics Canada said.
The prevalence of HCV infection from blood tests was 0.5 per cent, which represents an estimated 138,600 people.
The survey severely underestimates the true number of patients infected with hepatitis C, said Dr. Morris Sherman, chairman of the Canadian Liver Foundation.
"Since the hepatitis C test first became available in 1991 or '92, there have been about 300,000 people identified as having hepatitis C," said Sherman, a liver specialist at Toronto General Hospital.
Sherman noted the survey likely didn't include patients he sees from immigrant communities who don't speak English. First Nations people living on reserves, inmates, and the homeless were also excluded.
For present hepatitis B infections, the prevalence was 0.4 per cent, representing an estimated 111,800.
Among those who tested positive for HCV, 69.5 per cent said they were not aware of the infection. For those with hepatitis B, 54.5 per cent said they didn't know they had it.
Generally, 75 per cent to 80 per cent of people with hepatitis C develop chronic HCV infections, the authors say.
Hepatitis B and C infections are reported to provincial, territorial and national public health agencies, but accurate diagnosing and reporting is a challenge since many infections don't result in symptoms, the authors add.
They noted that many sexually transmitted and blood-borne infections are asymptomatic, which may explain why so many weren't aware of the infection.
Hepatitis B in childhood is more likely to become chronic, previous research suggests. In the early to mid-1990s, Canada rolled out universal hepatitis B vaccination programs for infants and school-aged children.
Statistics Canada said this is the first study to analyze the infections directly from a nationally representative sample of Canadian households.
The results from the 2007-09 and 2009-11 Canadian Health Measures Survey can be applied to the overall population aged 14 to 79.