Passengers in Mexico City's subway wear masks to guard against infection April 24, 2009. Health experts advise regular hand washing as another precaution.
A new strain of never-before-seen influenza that has surfaced in Mexico and in parts of the U.S. has international health authorities on guard and sparked fears of a worldwide flu pandemic.
Health officials yesterday confirmed the severe respiratory illness that has killed more than 60 people in Mexico appears, in some cases, to be genetically similar to the eight cases of swine flu reported in parts of Texas and Southern California.
The new strain of swine influenza is likely already in Ontario, said Dr. Michael Gardam, one of Ontario's top infectious disease specialists, because about 60,000 people return to the province from Mexico every month.
"We have to assume that it is circulating in Ontario," he said. "You just have to look at air travel patterns to realize that what goes on in Mexico has to come to Canada."
With the spectre of SARS still looming over the Toronto area, local infectious disease experts are emphasizing the new strain of swine flu should not be compared to the severe acute respiratory syndrome that swept the city in 2003 and killed 44 people.
"It is a different virus from what we've seen before," said Gardam, who is director of infectious diseases prevention and control at the Ontario Agency for Health Protection and Promotion. "But that is not a comment on how easily it is spread and how sick it would make you."
Scientists around the world are moving quickly to uncover more details of the novel swine flu, a combination of human, swine and avian viruses not previously detected in pigs or humans and which can be spread from human to human. Health officials stress public health alerts and recommendations will change as new facts emerge.
"Our concern has grown since yesterday in light of what we have learned since then," Dr. Richard Besser, acting director of U.S. Centers for Disease Control, said at a news teleconference yesterday.
No cases of swine flu have been reported in Canada, and officials said only a "handful" of cases are under investigation here.
The Mexican government has reported more than 900 cases of severe respiratory illness, or SRI, and 62 related deaths, according to a release from the World Health Organization. As of Thursday, there were 854 cases of SRI and 59 deaths in Mexico City, 24 cases and three deaths in San Luis Potosi, in central Mexico, and four cases in Mexicali, near the U.S. border.
Canadian scientists at the National Microbiology Laboratory in Winnipeg confirmed 16 of the Mexican cases are Swine Influenza A/H1N1 viruses. The lab received 51 samples from Mexico on Wednesday.
Besser said the CDC found 12 cases are genetically identical to the A/H1N1 viruses from California, where six cases were confirmed in two counties next to the Mexican border. Two more cases have turned up in San Antonio, Tex., and nine cases are under investigation.
The majority of infected individuals in the U.S. had mild symptoms – only one person was kept in hospital – and all have since recovered.
The strain of swine flu is sensitive to antiviral drugs, including the anti-flu drug Tamiflu. Scientists are working to decode the entire DNA of the virus, and the CDC is developing a vaccine.
Canadian and U.S. health officials have not issued travel advisories to California, Texas or Mexico. Public health experts are asking potential travellers to protect themselves from influenza as they would anywhere else at home and abroad by using precautionary measures, such as regular hand washing.
Infectious disease specialists worldwide are worried the new strain of swine flu could lead to an influenza pandemic. Right now, officials say the most concerning factors are the human-to-human spread of an animal influenza virus, that clusters of cases are geographically separated, and that otherwise healthy young adults seem to be most affected by the virus.
Besser said the WHO is convening a group of experts to determine whether the pandemic threat level should be changed. Currently, the world is at level 3 out of a possible six levels, with the sixth level indicating a pandemic.
Mexico's government cancelled classes for millions of children and university students in Mexico City and the surrounding area yesterday. Large concert venues, libraries and museums were also closed.
Dr. Alison McGeer, director of infection control at Mount Sinai Hospital, said it is too early to judge whether the swine flu will turn into a pandemic.
"The critical question of whether it's going to be a pandemic is whether it's going to spread to other countries and how much it's already spread in Mexico," she said. "We simply don't know that today."