( 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 . The United States has reported 226 confirmed cases in 30 states . The U.S. cases include one death -- a Mexican toddler visiting relatives in the United States . According to WHO , Canada has 85 confirmed cases ; Spain has 40 ; the United Kingdom has 15 ; Germany has 8 ; New Zealand has 4 ; Israel has 3 ; El Salvador has 2 ; France has 2 ; and Austria , China , Colombia , Costa Rica , Denmark , Ireland , Netherlands , Italy , South Korea and Switzerland each have one . The outbreak is only about 10 days old , and even if the illness is declining , it could return , said Gregory Hartl , the WHO spokesman for epidemic and pandemic diseases , at a briefing Sunday . `` I ... would like to remind people that in 1918 the Spanish flu showed a surge in the spring , and then disappeared in the summer months , only to return in the autumn of 1918 with a vengeance , '' Hartl said . `` And we know that that eventually killed 40 million to 50 million people . '' Mexican authorities believe the most active period of the virus in Mexico was between April 23 and April 28 , and Mexican Health Secretary Jose Cordova described the outbreak as being in decline in his country . In China , officials have quarantined 68 people , including 13 crew members , who were passengers of a Mexico City to Shanghai flight , which carried a passenger who tested positive for the virus , China 's state-run Xinhua news agency reported Sunday . None of the other passengers has exhibited any flu-like symptoms , one health official said . About another 110 people who were on the Aeromexico plane went on to other destinations , and may face quarantines elsewhere , the news agency said . Fifteen have been quarantined at a Beijing hotel . Shanghai 's airport is now barring other Aeromexico planes from landing there , a representative of the airline told CNN . Aeromexico is suspending flights to Shanghai until May 15 , the representative said . The airline does not fly to Hong Kong or Beijing . In the United States , New York has the most confirmed cases , with 63 , according to the Centers for Disease Control and Prevention . Texas has 40 ; California has 26 ; Arizona 18 ; South Carolina 15 ; Delaware 10 ; Massachusetts and New Jersey each have seven ; Colorado has four ; Florida , Illinois , Indiana , Ohio , Virginia , Wisconsin each have three ; Connecticut , Kansas and Michigan each have two ; Alabama , Iowa , Kentucky , Minnesota , Missouri , Nebraska , Nevada , New Hampshire , New Mexico , Rhode Island , Tennessee and Utah each have one . California officials suspended visitation and other `` nonessential activities '' at Centinela State Prison in Imperial County after an inmate was suspected of having swine flu . The case has yet to be confirmed with lab testing . On Sunday , health officials in North Carolina and Pennsylvania announced the first confirmed cases in those states , and Louisiana 's governor said his state had seven confirmed cases . The cases from those three states were not immediately included in the CDC tally . In Washington , U.S. Secretary of Health Kathleen Sebelius , appearing on CNN 's `` State of the Union , '' warned that even if the flu outbreak wanes , `` it could come back with greater force in the winter and fall , when we get into flu season . '' `` So , this is no time for complacency , '' she said . `` We want to stay out ahead of this . '' Dr. Anne Schuchat , the CDC 's interim deputy director for public health , told reporters Sunday that she was `` heartened '' by Mexican authorities ' reports but still is `` very cautious . '' `` I know that influenza can be surprising , and the time course here in the United States is later . We believe we 're just on the upswing here , and in several parts of Mexico , cases began quite a while ago , '' Schuchat said . `` From what I know about influenza , I do expect more cases , more severe cases and I do expect more deaths , '' she added . `` And I 'm particularly concerned about what will happen in the fall . '' Acting CDC Director Richard Besser , also speaking on `` State of the Union , '' said U.S. health officials are examining whether people who received flu shots for the swine flu in 1976 may have some level of protection from the current swine flu . `` That 's going to play in very , very big as we move forward with our plans around vaccines , because that may help guide some of the issues around who is most at risk at getting this in the future , '' Besser said . Offering a general picture of the state of U.S. efforts to combat the virus , Besser said `` there are encouraging signs . '' `` We 're not out of the woods yet , '' he said . `` But what we 've learned about the virus itself -- it does n't contain the factors that we know are seen in much more severe flu strains . '' While the new virus strain in the recent outbreak has affected humans , Canadian officials said it has shown up at a pig farm in Alberta , Canada . Officials said the pigs may have been infected by a Canadian farmer who recently returned from a trip to Mexico , the epicenter of the outbreak . The pigs have since been quarantined . `` We have determined that the virus H1N1 , found in these pigs , is the virus which is being tracked in the human population , '' said Dr. Brian Evans of the Canadian Food Inspection Agency . iReport.com : How should H1N1 be handled ? Evans and other officials said it is not uncommon for flu viruses to jump from humans to animals , and that it does not pose a risk for consuming pork . The number of pigs infected was not disclosed . The infected farmer had flu-like symptoms , but he is recovering , Evans said . Learn about the virus » .
WHO has confirmed 985 cases of H1N1 virus worldwide . Mexico says illness declining there ; WHO warns it could return . Score: 6 Canadian officials claim pigs at farm have been affected by virus .