The World Health Organization has said that Swine flu has swept the globe at "unprecedented speed," as a study warned the pandemic could tip the world into deflation and delay the economic recovery.
The WHO said it would stop giving figures on the numbers infected by the A(H1N1) virus to allow countries to channel resources into close monitoring of unexpected developments and patterns in the spread of the disease.
Argentina, meanwhile, issued a nationwide alert after pigs were confirmed to have the swine flu virus, health authorities said.
"We have detected clinical cases of the A(H1N1) influenza in a pig farm in Buenos Aires province, they have been confirmed by laboratory tests," the national farm and food standards agency said.
In Brazil, the number of deaths from swine flu nearly tripled to 11, including the first person shown to have caught the virus spontaneously within the country.
The increased tally given by Health Minister Jose Gomes late Thursday added seven to the four fatalities previously given.
The WHO said in an information note on its website the influenza pandemic had "spread internationally with unprecedented speed."
"In past pandemics, influenza viruses have needed more than six months to spread as widely as the new H1N1 virus has spread in less than six weeks."
The Geneva-based health agency said the counting of all individual cases was no longer essential to assess the risk from swine flu.
"WHO will continue to request that these countries report the first confirmed cases and, as far as feasible, provide weekly aggregated case numbers and descriptive epidemiology of the early cases," it added.
While it eased its overall reporting requirement, the WHO called on all countries to "closely monitor unusual events," such as possible clusters of severe or fatal infections, or unusual patterns that might be associated with worsening disease.
In Britain, a study by Oxford Economics, a forecasting consultancy whose clients include multinational corporations and government, said recovery could be delayed by a couple of years due to the swine flu pandemic.
"Although so far the social and economic impacts have been very small, if infection rates were to rise much further, significant costs could be expected," it said.
Comparing the outbreak to the 2003 SARS crisis, it said that outbreak had occurred at a time of strong economic growth. Both consumption and growth had returned as soon as the epidemic was considered under control.
"This time around, such a sharp rebound is unlikely," it said.
"There is a risk that swine flu tips the United Kingdom and the world economy into deflation. This is because the pandemic would hit at a time when businesses and banks are still reeling from the economic crisis."
On Thursday, England's chief medical officer Liam Donaldson said that in a worst case scenario, around one in three Britons could be infected and 65,000 could die.
The WHO policy shift was partly motivated by the "mildness of symptoms in the overwhelming majority of patients, who usually recover, even without medical treatment, within a week of the onset of symptoms."
In some countries, the investigation and laboratory testing of all cases had absorbed huge resources, leaving health systems with little capacity to monitor severe cases or exceptional events that might mark an increase in the virulence of swine flu.
In the last table released by the WHO on July 6, the health agency had recorded 94,512 laboratory-confirmed cases in 136 countries and territories since April, including 429 deaths.