(CNN)  -- The World Health Organization cautioned that the swine flu outbreak could gain momentum in the months ahead, despite claims by the health secretary of Mexico -- the epicenter of the outbreak -- that the virus "is in its declining phase." The number of confimed cases of the H1N1 virus continue to multiply. As of early Monday, Mexican health officials reported 568 cases and 22 fatalities linked to the flu. WHO says it has confirmed 506 cases and 19 deaths in Mexico. The world has 985 confirmed cases of the virus, known to scientists H1N1 virus, in a total of 20 countries, WHO said Monday.
@highlight
WHO has confirmed 985 cases of H1N1 virus worldwide
@highlight
Mexico says illness declining there; WHO warns it could return
@highlight
Mexico has largest number of confirmed cases, followed by U.S., WHO says
@highlight
Canadian officials claim pigs at farm have been affected by virus
The U.S. cases include one death -- a @placeholder toddler visiting relatives in the United States.