Authorities in Mexico said the death toll had risen to 85, and infected cases rose to 4,721 with scientists advancing through a backlog of samples.
New cases were reported across the globe, as A(H1N1) cases worldwide soared to nearly 13,000.
The virus has caused 92 deaths and infected 12,954 people in 46 countries since it was first uncovered last month, according to the WHO's latest figures.
With the continued spread of the disease, the WHO enlisted scientists to help clear up the criteria needed for declaring a pandemic, amid concern the response of the Geneva headquartered body may have caused undue fear and disruption.
"We are trying to see what kind of adjustments must be made to make sure that the definitions really meet the situation," said World Health Organization interim Assistant Director General Keiji Fukuda.
The move follows appeals by several countries for more caution before moving up a step from the current phase five alert to declaring a pandemic for the new A(H1