( CNN ) -- As the swine flu outbreak escalates across the globe , U.S. travelers returning from Mexico are wondering what to do when they come home . Travelers leaving a Mexican airport fill out questionnaires about their health . On Wednesday , Christine Kovar of San Francisco , California , returned from a vacation to Nuevo Vallarta , Mexico . She said she was n't sure whether she should attend work or stay home . `` I feel fine , '' said Kovar . `` It will be the discretion of my boss whether I go back to work . '' The Centers for Disease Control and Prevention in Atlanta , Georgia , is advising U.S. travelers back from Mexico with at least two of the swine flu symptoms to stay at home and avoid public places upon return . Symptoms of swine flu , also known as 2009 N1H1 , can include a fever , sore throat , cough , chills , headaches and runny nose . People with symptoms should report to a health care provider or local health department and provide itinerary details and symptoms , according to the CDC . If infected , the swine flu is contagious for up to seven days . People who are n't sick should continue to work and use normal precautions like washing hands , according to the CDC . They should monitor their health for seven days . `` As long as they are n't presenting any flu-like symptoms , there is no reason why they ca n't continue to do things that they normally would , '' said Llelwyn Grant , a spokesman for the CDC . Meanwhile , the death toll from swine flu continues to climb . On Thursday , the World Health Organization reported 236 cases of swine flu worldwide . In the United States , the CDC said it confirmed 109 cases of swine flu , or 2009 H1N1 , in 11 states , an increase of 18 from its previous total . On Wednesday , the WHO raised the pandemic threat level to 5 on a six-step scale . These numbers are causing alarm among the public , as schools and businesses try to contain the disease and protect the health of others . Some companies are erring on the side of safety , telling employees who returned from Mexico to stay at home for a few days . One university in Pennsylvania barred nearly two dozen students back from Mexico from attending graduation . More than 100 schools across the country have shut down . Greenville County School District in South Carolina shut down on Thursday to clean the buildings and busses when 18 students reported flu-like symptoms after a band trip to Disney World in Florida . School officials are awaiting the test results of the children . `` We are being proactive and trying to take [ the ] right precautions , '' said Oby Lyles , spokesman for the Greenville County School District . Several state health departments such as the New York , where there are 50 confirmed cases , and Kansas , where there are two confirmed cases , said they have n't made state-level advisories yet on whether travelers from Mexico who feel healthy should attend work or not . If travelers are feeling sick , the state departments said travelers should follow CDC guidelines and stay at home . `` If you are n't sick , make sure you are practicing the common sense precautions , '' said a spokesman at the New York State Department of Health . `` Wash your hands . Cover your mouth when you sneeze . '' In addition to advising ill U.S. travelers returning from Mexico to stay confined , government officials are turning to the travel industry for help , particularly air travel . The CDC is advising airline crew members who have arrived from domestic and international areas affected by the swine flu to be on the lookout for ill passengers . Airlines have been advised to stock the planes with gloves and face masks in case of an emergency . The CDC said airline crew members need to ask passengers who appear sick to be quarantined at one of the CDC 's 20 locations across the country . It 's been smooth sailing at U.S. airports , several passengers say . There have been no nationwide questionnaires being issued at the airports , according to a spokeswoman at U.S. Customs and Border Protection yet . In contrast , at some Mexican airports , travelers are asked to fill out forms asking about his or her health , passengers interviewed say . Still , travelers will find warnings about swine flu all over the airport . At O'Hare International Airport in Chicago , Illinois , travel warnings about the flu are being distributed . Signs informing passengers about swine flu , particularly in the international terminal , are posted . As of Friday , the CDC was recommending U.S. travelers avoid all nonessential travel to Mexico .
Travelers with flu-like symptoms coming back from Mexico should stay at home . Comment: There are more than 230 confirmed cases of swine flu worldwide , according to WHO . Companies and schools are erring on the side of safety asking people not to come .