TORONTO - The number of countries reporting findings of Tamiflu-resistant human influenza viruses has risen to 14, the World Health Organization said Thursday as European and Canadian laboratories released new figures on how many of the viruses have been found.
Ten European countries, Canada, the United States, Australia and Hong Kong have reported finding H1N1 flu viruses resistant to oseltamivir (Tamiflu), the drug on which many national pandemic stockpiles are built.
Nearly seven per cent of the H1N1 viruses tested so far this season by Canada's National Microbiology Laboratory in Winnipeg are Tamiflu resistant, Dr. Frank Plummer, scientific director of the lab, said in an interview Thursday.
Of 173 H1N1 viruses tested, 12 were not susceptible to the drug. The bulk of those viruses - nine - were recovered from flu patients in Ontario, but individual cases have been seen in British Columbia, Newfoundland and Labrador, and Manitoba. The British Columbia case, an infant, is believed to have been infected outside the country.
The latest tally from European countries was released Thursday by the European Centre for Disease Prevention and Control in Stockholm.
Resistant viruses have been found in Denmark (10 per cent), Finland (27 per cent), France (39 per cent), Germany (seven per cent), Greece (11 per cent), the Netherlands (six per cent), Norway (64 per cent), Portugal (33 per cent), Sweden (eight per cent) and the United Kingdom (seven per cent).
A total of 19 European countries have submitted viruses for testing; 152 of 761, or 20 per cent, were resistant.
But while key influenza laboratories have been working flat out to do this testing, the number of viruses checked to date is still relatively low, particularly in some countries. Flu season is really only now getting underway in parts of Europe and North America.
And listing resistant viruses as a percentage of the total tested can paint a misleading picture. Portugal's 33 per cent, for instance, looks less ominous when described another way: two of six H1N1 viruses tested there that carry the mutation renders them resistant to Tamiflu.
On the other hand, numbers from France and Norway continue to surprise. France has tested 208 H1N1 viruses, finding 81 of them to be Tamiflu resistant. And in Norway, where the problem first came to light, 42 of 66 viruses are resistant.
An article in this week's online journal Eurosurveillance warns against reading too much into shifts in numbers at this point.
"Week-on-week changes need to be interpreted cautiously, as they are more a reflection of having more testing than any changes in the underlying epidemiology," said the article, written by staff of the European disease centre.
"For example, virologists in France and Germany have worked especially hard in the last week to test many more specimens. As a result, there are quite substantial changes in the overall prevalence of the resistant viruses in European countries."
"However, since data are available for many countries and the observed prevalence ranges from zero to over 60 per cent, a 'European average' should probably not be considered a useful statistic."
New figures from the United States will be published Friday. But according to the latest figures from the WHO, 15 of 179 viruses there, or 8.4 per cent, have been found to be resistant to the drug.
Australia reported finding two resistant H1N1 viruses in October, towards the end of their flu season, Dr. Frederick Hayden, a flu expert with the World Health Organization, said in an e-mail.
As well, Hong Kong reported that seven per cent of H1N1 viruses checked there were resistant to the drug. But to date no resistant viruses have been reported from Japan, the country with the highest per capita use of Tamiflu.
