A timeline of events in the swine flu outbreak:
— December 2005 to January 2009: The Centers for Disease Control and Prevention receives reports of 12 cases of human infection with swine flu. Five of these 12 cases occurred in patients who had direct exposure to pigs and six reported being near pigs. Exposure in one case is unknown.
— March 28: Believed to be the date of the earliest onset of the swine flu cases in the U.S., Dr. Nancy Cox of the CDC said in an April 23 press briefing.
— April 2: A 4-year-old boy contracted the virus before this date in Veracruz state, Mexican Health Secretary Jose Angel Cordova later said citing test results. A community in Veracruz has been protesting pollution from a large pig farm.
— April 6: Local health officials declare a health alert due to a respiratory disease outbreak in the Mexican town of La Gloria in Veracruz state. Health officials record 400 cases of people who sought medical treatment in the previous week in the town. About 60 percent of the town of 3,000 are affected.
— April 17: CDC determines that two children in adjacent counties in southern California had illnesses caused by infection with swine flu. Both children became sick in late March.
— April 22: CDC confirms three additional cases of swine flu in California and two in Texas, near San Antonio.
— April 22: The Oaxaca Health Department indicates that 16 employees at the Hospital Civil Aurelio Valdivieso have contracted respiratory disease.
— April 24: Mexico's Minister of Health confirms 20 deaths from swine flu, but 40 other fatalities were being probed and at least 943 nationwide were sick from the suspected flu. Mexico City shuts down schools, museums, libraries, and state-run theaters across the capital.
— April 26: The number of confirmed cases in the U.S. climbs to 20 in five states. Mexico reports suspect clinical cases have been reported in 19 of the country's 32 states. Canada confirms six cases.
— April 27: The World Health Organization raises its pandemic alert status to Phase 4, meaning there is sustained human-to-human transmission of the virus causing outbreaks in at least one country.
Cordova said 1,995 people have been hospitalized with serious cases of pneumonia since mid-April and about half of those have been released. The government does not yet know how many were swine flu. The CDC reports the suspected death toll in Mexico has climbed to 149.
The number of confirmed cases in the U.S. climbs to at least 42 in five states.
Spain reports its first confirmed swine flu case.
—April 28: The number of confirmed swine flu cases in the U.S. is up to 68 and more than a dozen suspected cases, including two probable cases in South Carolina and a confirmed case in Indiana.
There is a suspected case in Orlando, Fla., but the CDC has yet to confirm it.
The number of worldwide cases reportedly climbed to 93, including two confirmed cases in Israel and a second case in Spain.
Meanwhile, the WHO says U.S. swine flu patients may have transmitted the virus to others in the United States, indicating that the new strain is spreading beyond travelers returning from Mexico.
Mexico's capital orders restaurants to serve only take-out food in the widening swine flu shutdown.
World stock markets fall as investors worried that any swine flu pandemic could derail a global economic recovery.
Cuba suspends flights to and from Mexico for a 48-hour time period as a precautionary measure.
Carnival Cruise Lines announced it canceled Mexico stops for three ships scheduled to visit the country Tuesday. It hasn't yet announced a decision on future stops there.
Swine flu has been ruled out as the cause of one of two recent deaths being investigated by the Los Angeles County coroner's office. Coroner's Assistant Chief Ed Winter said Tuesday that swine flu was not found in a La Mirada man. Winter says lab testing is pending in the case of a Long Beach man but swine flu is now not suspected.
— April 29: A 23-month-old boy from Mexico died at a Houston, Texas hospital Monday night from a variant of H1N1 swine flu.
Probable swine flu cases are being reported in Illinois, Nebraska and Minnesota.
Germany, which confirmed three cases, is the latest country affected.
In Cairo, the Egyptian government says it will slaughter all pigs in the country because of swine flu.
A Massachusetts health official says two siblings in that state have tested positive for swine flu after traveling to Mexico.
There is a total of 91 confirmed swine flu cases in the U.S., inlcuding Michigan, Arizona, Nevada and Indiana.
South Carolina health officials have identified eight additional 'probable' cases of swine flu, bringing the total number to 10.
In California, 39 Marines were confined to their base in California after one came down with the disease.
— April 30: Mexico orders a halt to nonessential business and federal government activities.
Switzerland and the Netherlands are the latest countries to report swine flu infections.
In the Swiss case, a 19-year-old infected student was mistakenly released from a hospital before being hastily readmitted.
European Union health ministers are planning emergency talks in Luxembourg to coordinate national efforts in preventing the spread of swine flu in Europe.
In the U.S., fears over the flu have forced nearly 300 schools to close.
Vice President Joe Biden is arguing that there would be no practical benefit in shutting down the country's border with Mexico.
State officials confirmed cases in Minnesota, Georgia, New Jersey, Delaware, Utah, New Jersey and Colorado.
At least 130 cases are confirmed in 20 states.
The WHO reports that the number of confirmed swine flu cases worldwide has reached 236.
Biden says people should avoid planes, subways and trains.
Wisconsin Gov. Jim Doyle declares a public health emergency after two more probable cases of swine flu were identified.
A pediatrician in Washington state sees 22 patients with flu-like symptoms before she develops series symptoms and goes to the emergency room, according to reports.
A security aide helping with arrangements during President Barack Obama's recent trip to Mexico become sick with flu-like symptoms and three members of his family later contracted probable swine flu, the White House says.
The World Health Organization says it plans to no longer call the deadly flu "swine flu" to avoid confusion over the risk from pigs and eating pork.
— May 1: Confirmed U.S. cases reach 141.
Germany's top public health authority confirms the first case of swine flu transmission within the country.
U.S. authorities pledge to eventually produce enough swine flu vaccine for everyone but the shots won't begin until fall at the earliest.
— May 4: Mayor Michael Bloomberg says New York City has 73 confirmed and six probable cases of swine flu. That's 10 more confirmed cases than the city reported on Sunday.
Students in New York return to St. Francis Preparatory School, which had been closed after a swine flu outbreak.
Infections in the United States spread to 35 states.
Dr. Richard Besser of the Centers for Disease Control and Prevention, says it's too early to say the threat of a swine flu pandemic has leveled off, as Mexican officials have claimed.
New infections reported in Spain, Italy, France, Portugal, El Salvador and New Zealand.
Mexico will allow most businesses to reopen Wednesday nationwide, citing ebb in flu outbreak.
The heads of the United Nations and the World Health Organization say there are no imminent plans to raise its pandemic level to its highest alert.
There were now 1,003 confirmed cases of swine flu in 20 countries.
CDC confirms four cases of swine flu in the state of Maryland.
—May 5: U.S. swine flu tally jumps to 403 Cases in 38 states.
U.S. health officials are no longer recommending that schools close because of swine flu.
The government last week advised schools to shut down for about two weeks if there were suspected cases of swine flu. Hundreds of schools around the country have followed that guidance and closed schools.
Health and Human Services Secretary Kathleen Sebelius said Tuesday that the swine flu virus had turned out to be milder than initially feared. She says the government is changing its advice on closing schools.
Sebelius says parents should still make sure to keep sick children at home.
Mexico announces that swine flu will cost the country about $2.2 billion, much of which is due to reduced tourism. The country pledges a $1.3 billion stimulas package as well as tax breaks to help businesses offset revenue stemming from the outbreak.
— May 6: Haiti turns away a Mexican ship carrying desperately needed food aid because of swine flu fears.
Dozens of Mexican nationals quarantined in China despite having no swine flu symptoms arrive in Mexico City on a government-chartered jet.
U.S. Navy cancels the deployment of a San Diego-based ship and orders its crew of about 370 to be treated with antiviral drugs after a crew member's illness is confirmed as swine flu.
U.S. health officials say it took only two weeks to identify the genetic characteristics of the strain, and they are in good position to quickly produce a vaccine if the flu takes a turn for the worse. They say there are still elements of the virus they don't understand.
— May 7: Mexico's health secretary says tests have confirmed two more deaths from swine flu, bringing the toll to 44.
Diplomats and officials say the World Health Organization intends to shorten its annual meeting in Geneva later this month because health ministries around the world are busy working on the outbreak.
Mexico City lets all businesses reopen, including sports arenas, dance halls, movie theaters and restaurants, but they must screen for ill people and make surgical masks mandatory for employees and customers.
Swine flu survivors in Mexico complain they've been shunned and discriminated against.
— May 8: Asian countries, which have had few cases so far, pledge on Friday to increase stockpiles of flu medicine and cooperate in an emergency, taking no chances this time after the damage wrought by SARS and bird flu in recent years.
The CDC reports 896 confirmed cases in 41 states.
Mexico's confirmed death toll ticks up to 45 and the total number of people sickened is 1,319.
— May 9: The CDC says the U.S. now has 2,254 confirmed cases of the H1N1 swine flu in 44 different states.
— May 10: Washington state health officials confirm a man in his 30s has died from what appears to be complications from the H1N1 virus. In addition to the heart conditions, the man had viral pneumonia at the time of his death, but swine flu was considered a factor in his death.