TORONTO – It turns out that an American man who was treated in an Edmonton hospital may not have had H7 flu after all.
Last week the Public Health Agency of Canada revealed that an American whose plane diverted to Edmonton because he was ill had tested positive for antibodies to an H7 flu virus.
The antibody test could not determine which H7 flu virus he’d been infected with, but given that he’d recently travelled in China the suspicion was he’d been infected with the new H7N9 bird flu.
It appears, though, that the test may have been mistaken.
Public Health Agency officials say confirmatory testing done at the U.S. Centers for Disease Control did not find evidence of H7N9 antibodies.
Dr. Gregory Taylor, Canada’s acting chief public health officer, says the results are now deemed inconclusive.
Dr. Judith Bosse, assistant deputy minister for the infectious diseases prevention and control branch, says blood tests designed to detect antibodies to new viruses can be difficult to operate in the early days, when they haven’t been validated.
“Probably the initial reaction was what we call a false positive, which is the sad part about serology tests,” Bosse said in an interview. “And that’s why we have to run multiple (ones), is false positives do exist.”
She says in order to make sure a new blood test works well, a laboratory needs to test it against multiple blood samples taken from people who haven’t been exposed to the virus and people who were known to have been infected and have recovered. Those latter blood samples are called convalescent sera.
Only by running that kind of validation process can a lab be certain their blood test is catching true positive cases and not cross-reacting with antibodies to other viruses. If a test cross-reacts, it could generate a false positive result.
Bosse says the National Microbiology Laboratory in Winnipeg is still trying to get access to convalescent sera from China to use to validate its blood test. Other countries are in the same boat, she says.
But the U.S. CDC, which has also developed a blood test for H7 antibodies, also uses another type of test, known as micro-neutralization. It is considered “fairly specific,” says Bosse.
“That’s why we’re actually ruling out that this is not a conclusive sample,” she says, adding the Winnipeg laboratory doesn’t use this type of test.
Taylor says the Winnipeg lab is re-examining its H7N9 blood test as a result of the event.
The unidentified man had been travelling extensively in May and June. After visiting China in late May, he journeyed to India. While there, he became severely ill and spent time in an intensive care unit in a hospital.
After his release, the man travelled to the United Arab Emirates, where he boarded a flight bound for San Francisco. While that flight was in the air, the man became ill and lost consciousness. The plane was diverted to Edmonton, where doctors ordered tests for flu based on his travel history.
Taylor says he doesn’t know if the man has left Canada. As he is considered not to pose a public health risk, the agency is not following up further on his case.