A chronology of the outbreak of H1N1 swine flu, which on Thursday was declared a global pandemic - the first since 1968 - by the World Health Organization:
March 18 - Mexican government starts tracking an increase in cases of severe respiratory illness in Mexico.
March 31 - A clinical trial designed to assess the efficacy of a new rapid diagnostic test for influenza finds an untypeable flu virus in a sample from a person from the San Diego area. Public health is alerted and the virus is sent for testing in Wisconsin and later to the U.S. Centers for Disease Control.
April 17 - The CDC informs the World Health Organization it has found a case where an H1N1 swine flu virus infected a person in California. The virus is similar to the triple reassortant but with two swapped genes. Human infection with animal flu viruses signals a pandemic threat and WHO alerts member states.
April 17 - The head of Mexico's national microbiology lab emails Dr. Frank Plummer, head of Canada's national lab in Winnipeg, asking for help figuring out what is behind outbreaks of severe respiratory disease in parts of Mexico. Plummer offers assistance.
April 20 - The Public Health Agency of Canada warns quarantine services to be on the lookout for sick travellers returning from Mexico.
April 21 - The CDC issues an advisory revealing it has found two human swine flu cases in California. The WHO says it is watching.
April 22 - Specimens from Mexico arrive at the Winnipeg lab shortly before lunch. Within 24 hours researchers there realize at least some of the Mexican cases are human infections with the H1N1 swine flu virus.
April 23 - The CDC says they've found seven swine flu infections, in California and Texas.
April 24 - Mexico informs the WHO the Winnipeg lab has confirmed H1N1 swine flu is causing disease in Mexico. Health Minister Leona Aglukkaq and Canada's chief public health officer, Dr. David Butler-Jones, hold first media briefing on swine flu.
April 26 - Canadian officials confirm Canada's first cases: four in Nova Scotia and two in B.C. U.S. Centers for Disease Control and Prevention confirm 20 cases in the United States.
April 27 - The WHO raises the pandemic alert level to Phase 4 for the first time since the scale was created. Five countries have cases.
April 28 - Ontario confirms its first cases of swine flu in the province with four mild cases, all in the Toronto area. Alberta announces two mild cases. All involve people who travelled to Mexico.
April 29 - The WHO raises the pandemic alert level to Phase 5, one away from a pandemic. It says the virus is spreading from person to person in both Mexico and the United States. Officials announce first confirmed death in the U.S., a 23-month-old Mexican child who died in Houston.
April 30 - B.C. health officials close an elementary school in Vernon after a student is diagnosed with swine flu. WHO says it will stop using the term 'swine flu'; virus now referred to by its scientific name H1N1.
May 1 - Asia's first confirmed case is detected in Hong Kong. New Brunswick confirms its first case. The number of cases in Canada is 51.
May 2 - Federal officials say pigs in Alberta contracted swine flu from farm worker following recent visit to Mexico. The number of Canada's confirmed cases is 85.
May 3 - China stops imports of Alberta pork in response to flu strain detected in some pigs at an Alberta farm. The number of confirmed human cases in Canada rises to 101.
May 4 - Young Alberta girl is Canada's first severe case; case numbers continue to rise nationwide. Minister of international trade calls Chinese ban on Alberta pork "disappointing and unwarranted."
May 5 - Mexico cancels Cinco de Mayo celebrations but plans to allow most businesses and universities to reopen before week's end. Texas health officials confirm the first death of a U.S. resident with swine flu.
May 6 - Canada's agriculture minister says pork remains safe to eat. China lifts quarantine two days early for a group of Canadian students after Ottawa and the WHO ask Beijing to explain such measures.
May 7 - Saskatchewan reports its first two cases, bringing national total to 214.
May 8 - Health officials confirm swine flu contributed to the death of a woman in northern Alberta who had pre-existing medical conditions.
May 9 - Alberta officials cull 500 pigs from flu quarantined herd because of overcrowding concerns and not because of the flu infection. The number of confirmed human cases in Canada now stands at 281.
May 10 - A Chinese man returning from studying at a U.S. university becomes the first case of swine flu in mainland China.
May 11 - Millions of Mexican children return to disinfected classrooms. Chinese health authorities scramble to quarantine hundreds of passengers who flew with the mainland's first confirmed case.
May 12 - The WHO and leading influenza research groups are investigating unpublished claims that the new H1N1 swine flu virus may have evolved in a laboratory, not in nature.
May 13 - Chinese authorities expand search for travellers who might have been in contact with a 19-year-old student recently returned from Canada who was confirmed as the mainland's second case of swine flu.
May 18 - Canada lifts an advisory against non-essential travel to Mexico as cases of swine flu there start to wane.
May 21 - Mexico City lowers its swine flu alert level from yellow to green. There have been no new infections there for a week.
June 1 - Third Canadian dies of swine flu. Ontario's health minister confirms a person hospitalized with swine flu infection died May 31.
June 8 - Quebec reports its first swine flu death, a woman over age 65 from Quebec City.
June 11 - World Health Organization declares global H1N1 swine flu pandemic.