世界衛生組織（World Health Organization，WHO）4月29日表示，A型豬流感H1N1病毒正快速散播中。秘書長陳馮富珍（Margaret Chan）已將該種流感大流行的警戒等級從6個等級中的第四級提高為第五級。陳博士表示，她是以所有可獲得的資料進行評估，以及諮詢衛生專家之後決定的。
豬流感病例的實驗室驗證是由位於亞特蘭大（Atlanta）的美國疾病管制中心（U.S. Centers for Disease Control and Prevention）完成的，醫師們相信那位男童在進入美國之前就感染了豬流感。
墨西哥的衛生局長（Health Secretary）蔻德瓦（Jose Angel Cordova）4月28日向記者透露，在159名可能與流感有關且因嚴重非典型肺炎（atypical pneumonia）或嚴重呼吸功能不足（respiratory insufficiency）而死亡的病例中，有7名已經確認是豬流感病例。
Swine influenza A/H1N1 is spreading rapidly, the World Health Organization announced today. Director-General Margaret Chan raised the level of influenza pandemic alert from phase 4 to phase 5, out of six possible levels. Dr. Chan said her decision was based on assessment of all available information and consultations with health experts.
"All countries should immediately activate their pandemic preparedness plans," said Chan, advising countries to remain on high alert for unusual outbreaks of influenza-like illness and severe pneumonia.
Phase 5 is characterized by human-to-human spread of the virus into at least two countries in one WHO region. While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.
"This change to a higher phase of alert is a signal to governments, to ministries of health and other ministries, to the pharmaceutical industry and the business community that certain actions should now be undertaken with increased urgency, and at an accelerated pace," Chan advised.
Nine countries have officially reported 148 cases of the swine flu A/H1N1 infection. A total of eight people are confirmed to have died of the disease. Mexico has reported 26 confirmed human cases of infection including seven deaths. The U.S. government has reported 91 laboratory confirmed human cases, with one death.
The first confirmed swine flu death in the United States happened in Houston. A 22-month-old boy from Mexico City who was hospitalized earlier this month in Brownsville, died Monday night in a Houston hospital.
A preliminary investigation indicates that on April 4 the boy had traveled with his family on a commercial flight from Mexico City to Matamoros, Mexico, for a visit with relatives in Brownsville, just across the Mexico-Texas border.
Swine flu was confirmed in laboratory testing done by the U.S. Centers for Disease Control and Prevention in Atlanta. Doctors believe the boy contracted the swine flu before coming to the United States.
Though an investigation continues, state health officials said the boy would not have been infectious on the Mexico-to-Matamoros flight and that none of the boy's known close contacts have subsequently become ill with influenza-like symptoms.
Mexico's Health Secretary Jose Angel Cordova told reporters Tuesday that of the 159 deaths from serious atypical pneumonia or serious respiratory insufficiency possibly associated with flu, seven have been confirmed as swine flu.
Seven other countries have reported laboratory confirmed cases with no deaths - Austria (1), Canada (13), Germany (3), Israel (2), New Zealand (3), Spain (4) and the United Kingdom (5).
At this stage, says the World Health Organization, effective and essential measures include heightened surveillance, early detection and treatment of cases, and infection control in all health facilities.