page_title: 2009 swine flu pandemic timeline
section_title: Timeline
hierarchical_section_title: 2009 swine flu pandemic timeline / Timeline
caption_attribution_description: English: A graph showing the number of confirmed (N = 97) and probable (N = 260)* cases of swine-origin influenza A (H1N1) virus (S-OIV) infection, by date of illness onset, in Mexico, during March 15 to April 26, 2009. (*) Probable cases for which dates of illness onset are known. From March 15 through April 17, the daily number of confirmed and probable cases combined did not exceed five cases. However, the start of a substantial increase is indicated on April 18. This increase peaks at approximately 55 cases on April 22 and 23, before declining to fewer than 10 cases on April 26. Enhanced national surveillance had been initiated on April 17.
context_page_description: Flag icons denote the first announcements of confirmed cases by the respective nation-states, their first deaths, and relevant sessions and announcements of the World Health Organization, the European Union,
  and the U.S. Centers for Disease Control.
  Unless otherwise noted, references to terms like S-OIV, H1N1 and such, all refer to this new A strain and not to sundry other strains of H1N1 which are endemic in humans, birds and pigs.
context_section_description: Take note that the date of the first confirmations of the disease or any event in a country may be before or after the date of the events in local time because of the International Dateline.
caption: Probable and confirmed Mexican cases by date of illness onset, March 15 – April 26. —CDC
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