On Monday we learned of the first known imported case of H7N9 into North America (see PHAC Statement On Canada’s Imported H7N9 Case) when a woman, recently returned from China with her husband, developed flu-like symptoms and was tested by her doctor in Vancouver.
Her husband briefly developed flu-like symptoms as well, and also suspected as having been infected. Neither were sick enough to be hospitalized, self-isolated at home, and are now recovered.
Last night it was announced that the husband’s tests had come back positive for H7N9 infection. He developed symptoms about a day before his wife, suggesting they had a shared exposure, but the exact route of their infection remains unknown.
None of these patient’s close contacts have developed symptoms, and given H7N9’s incubation period, authorities believe it unlikely any additional cases will arise in Canada linked to this event.
This from Helen Branswell.
Couple believed to have contracted virus in recent trip to China
By Helen Branswell, The Canadian Press Posted: Jan 29, 2015 9:24 PM PT Last Updated: Jan 29, 2015 9:28 PM PT
A British Columbia man has been confirmed as Canada's second case of H7N9 bird flu.
The unidentified man and his wife are believed to have contracted the virus during a recent trip to China.
They are the first North Americans known to have been infected with this virus.
B.C.'s deputy provincial health officer says the positive test result was confirmed late Thursday by the National Microbiology Laboratory in Winnipeg.
It is remarkable that these cases were diagnosed at all, given their mild symptoms and their occurring during the midst of a very busy regular flu season.
While 30% of known H7N9 cases have died, this is essentially the mortality rate among those sick enough to be hospitalized and tested. Unknown is how many mild or moderate cases occur each winter in China, that are never picked up by surveillance.
That two travelers should return from China with mild symptoms suggests that mild or moderate cases are more common than we know .Something that the researchers at the University of Hong Kong have been saying for the past 18 months.
In Lancet: Clinical Severity Of Human H7N9 Infection) we saw a study that proposed, after roughly 130 cases were confirmed in the spring of 2013, that:
Our estimate that between 1500 and 27 000 symptomatic infections with avian influenza A H7N9 virus might have occurred as of May 28, 2013, is much larger than the number of laboratory-confirmed cases.
How accurate these estimates are is unknown, but it is highly likely that the official case counts under-represent the real burden of H7N9, perhaps by a sizable margin.
Somewhat more reassuring, we’ve seen a relatively low number of family clusters or contacts of known cases test positive for the virus, suggesting a low human-to-human transmission rate. For now, direct contact with infected birds is believed the primary route of infection.
That said, a study published earlier this week (see EID Journal: H7N9 Antibodies In Close Contacts Of Known Cases) looked at 225 close contacts of confirmed H7N9 cases in China, and found 22 (9.8%) with elevated HI H7N9 antibody titers (>1:40).
All of these seropositive contacts were asymptomatic.
All of which means we still have major gaps in our understanding of how fast and how far this virus is spreading in China. And given the amount of travel to and from Asia, we should not be surprised to see future introductions of H7N9, and other novel flu viruses, to North America.