Tough US import controls on biological materials, introduced after the September 11 2001 attacks, hindered the rapid identification of the H1N1 virus because samples from infected Mexican patients had to be sent to Canada for analysis instead of the US.
Health officials said the detour highlighted how bureaucratic attempts to protect the US from terrorist attacks had backfired.
Confirmation of the decision, which delayed the international response to the outbreak, added to reports of hurdles to cross-border co-operation in the fight against the latest infectious disease, health officials said.
In order to get a result as quickly as possible, Mexico initially sent as many as 200 samples to the Canadian government laboratory in Winnipeg in mid-April. It then forwarded some samples to Centers for Disease Control and Prevention in Atlanta in the US, less than half the distance away.
The US centres had already analysed several cases of H1N1 in the US without realising it was the same virus.
Jose Angel Cordova, Mexico's health minister, told the FT: "There are always administrative procedures that can take time. And, given the urgency of needing a quicker response, we called Winnipeg, where they told us that they could do it in a day."
Mexican and Canadian public health specialists have long-established professional connections and personal relationships, which eased the rapidity of the analysis and informed Mr Cordova's decision.
The information adds to concerns that the US may have been too focused, in early April, on analysing domestic cases of H1N1 to look across the border and make comparisons with reported cases in Mexico.
There have also been suggestions that the World Health Organisation was slow to respond to media reports of outbreaks in Mexico in early April.
But Michael Ryan, director of global alert and response at the WHO, said his team had contacted Mexico on April 10 and April 17 regarding separate incidents, and were assured they had been investigated and found to be isolated cases.
The WHO then informed Mexico on April 19 of the US cases, and began talks that triggered an alert on April 22 of severe pneumonia associated with influenza.
Mr Ryan stressed that he had no criticism of the Mexican authorities. "They have been dealing with a complex situation and a difficult epidemic, and have been exceptionally responsive to requests for information."
As well as additional import controls after 9/11, the US imposed tough immigration restrictions, which squeezed the number of foreign visitors, including students attending universities.
At least 23 countries have confirmed more than 2,000 cases of the H1N1 flu virus. The US has reported two deaths and Mexico 42.
Copyright: The Financial Times Limited 2009
