Here's a look back on how the coronavirus outbreak began, and how it has unfolded in the U.S. so far.

It was four months ago Thursday that the Centers for Disease Control and Prevention announced the first confirmed coronavirus case in the U.S.

In the weeks since, health officials have confirmed hundreds of thousands of COVID-19 cases across the nation and tens of thousands of deaths. Millions more Americans have lost their jobs, and tens of millions are emerging from stay-at-home orders to confront a new normal.

As we continue to learn more about the virus and grapple with the effects of the pandemic, here's a look back on how the outbreak began, and how it has unfolded in the U.S. so far.

Before arriving in the US, the virus spread through China and abroad November: Various reports suggest that the first case arose in Wuhan, China, toward the end of 2019, though some reports point to cases in early December. Dec. 30: Li Wenliang, an ophthalmologist at Wuhan Central Hospital, alerted physicians about the emergence of a SARS-like illness. He was later detained by police on charges of spreading rumors.  Dec. 31:  The Wuhan Municipal Health Commission reported 27 cases of viral pneumonia.  Jan. 1: Wuhan officials closed down the Huanan seafood market, which is thought to be linked to the first group of cases. Jan. 7: Chinese President Xi Jinping recognized the viral pneumonia internally during a meeting of China's highest council. Jan. 11: China reported its first death. Jan. 13: Thailand confirmed the first known case of the coronavirus outside China. Jan. 14: Top Chinese officials determined they likely were facing a pandemic, according to internal documents obtained by The Associated Press. In the following days, Wuhan hosted a mass banquet for tens of thousands of people. Jan.17: Airport screenings

The CDC began implementing public health entry screening at San Francisco (SFO), New York (JFK) and Los Angeles (LAX) airports. The CDC would later add screening at two more airports Atlanta (ATL) and Chicago (ORD).

Jan. 21: First case confirmed in US

The CDC confirmed the first U.S. case of a new coronavirus that had killed six people so far in China. The Washington state man in his 30s returned from Wuhan a week earlier, on Jan. 15. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, called the news "concerning," particularly in light of reports that the virus has begun to spread from person to person.

Jan. 23: Wuhan locks down

Chinese authorities locked down at least three cities with a combined population of more than 18 million in an unprecedented effort to contain the virus during the busy Lunar New Year travel period. 

Meanwhile, the World Health Organization declined to categorize the coronavirus as a global health emergency, saying there was no evidence of human-to-human infection outside China.

Jan. 24: First cases in Europe

French health officials confirmed the first three cases in Europe.

In China, the Lunar New Year holiday began. Public transportation halted for roughly 36 million people in 13 cities in central China, including Wuhan. Authorities in Wuhan said they were constructing a 1,000-bed hospital like one built in Beijing during a SARS outbreak, a similar respiratory virus.

President Donald Trump thanked China on Twitter for its efforts to contain the disease. "China has been working very hard to contain the Coronavirus. The United States greatly appreciates their efforts and transparency. It will all work out well. In particular, on behalf of the American People, I want to thank President Xi!" he said in a post.

Meanwhile, Sen. Rick Scott, R-Fla., urged the Trump administration to declare a public health emergency and sent a letter to the CDC requesting information about the agency’s plan to combat the virus. "We have to get serious about the threat of coronavirus coming from China," Scott said in a press release.

Jan. 24: Americans told 'risk is low'

Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, comments on the risk to Americans. "We don't want the American public to be worried about this because their risk is low," Fauci said. "On the other hand, we are taking this very seriously and are dealing very closely with Chinese authorities."

Jan. 28: 'Monitoring' since December

Alex Azar, secretary of Health and Human Services and chairman of the coronavirus task force, told reporters during a press briefing that the U.S. has "been monitoring this virus and preparing a response since back in December."

Jan. 29: 195 Americans return from China

The first group of passengers returned to the U.S. from China. They were expected to remain under observation for up to three days as they were screened, a CDC official said. The American passengers flew into California from Wuhan, with a stopover in Anchorage, Alaska, where they had also been screened.

Jan. 30: WHO declares global health emergency

The World Health Organization declared the coronavirus outbreak to be a "public health emergency of international concern." Dr. Tedros Adhanom Ghebreyesus, director-general of the WHO, praised China for its quick response to the crisis, saying the emergency declaration "is not a vote of no confidence in China."

Jan. 30: US reports first case of person-to-person transmission

The CDC reported that the first case of person-to-person transmission in the U.S. is the husband of a Chicago woman who developed symptoms after visiting China. "We understand this may be concerning, but based on what we know now, our assessment remains that the immediate risk to the American public is low," said Robert Redfield, director of the CDC.

Jan. 31: US public health emergency

The Trump administration declared the coronavirus outbreak to be a public health emergency in the United States, setting quarantines of Americans who have recently been to certain parts of China. CDC officials said it was the first quarantine order issued by the federal government in over 50 years.

Azar also announced a temporary suspension of entry into the United States of foreign nationals who had been in China in the previous 14 days. The ban was effective Feb. 2.

Meanwhile, officials began funneling all flights from China to the U.S. to one of seven airports that were designated ports of entry: New York, San Francisco, Seattle, Honolulu, Los Angeles, Chicago and Atlanta.

The outbreak had infected nearly 12,000 people, most of them in China, and killed more than 250 people, all in China, according to the WHO at the time.

Feb. 2: First death outside China

A 44-year-old Chinese man hospitalized in the Philippines became the first known fatality outside China from the new virus that has killed more than 300 people.

Feb. 6: First death in US

Autopsies on the bodies of two people who died at home on Feb. 6 and Feb. 17 showed they were positive for the virus, a California county announced April 21.

Previously, the first U.S. death had been thought to occur Feb. 29 outside Seattle. The autopsy findings revealed that the virus may have been spreading in U.S. communities earlier than previously known. The two people died during a time when very limited testing was available only through the CDC, and the agency's testing criteria restricted testing to only individuals with a known travel history and who sought medical care for specific symptoms. 

Feb. 7: Whistleblower dies

The Chinese doctor who was reprimanded by security police for warning fellow doctors about the initial coronavirus outbreak died of the illness.

In the U.S., Secretary of State Mike Pompeo announced that his department facilitated the transportation of nearly 17.8 tons of donated medical supplies to the China, including "masks, gowns, gauze, respirators and other vital materials."

A USA TODAY analysis later finds that American companies sold more than $17.5 million worth of face masks, more than $13.6 million in surgical garments and more than $27.2 million in ventilators to China during the first two months of the year, far exceeding that of any other similar period in the past decade.

Feb. 11: COVID-19

The WHO announced a formal name for the coronavirus – COVID-19. Meanwhile, China reported its highest daily coronavirus death toll, the 103 additional fatalities pushing the total past 1,100. "With 99% of cases in China, this remains very much an emergency for that country, but one that holds a very grave threat for the rest of the world," WHO's Dr. Tedros Adhanom Ghebreyesus said. 

The CDC confirmed the 13th U.S. coronavirus case, and about 800 Americans evacuated from Wuhan remain under quarantine. At a rally in New Hampshire, Trump said that, "in theory" once the weather warms up, "the virus" will "miraculously" go away.

Feb. 12: First American dies

A 60-year-old U.S. citizen became what appears to be the first American fatality from the global virus outbreak. The American victim, who was not identified, died in China after being diagnosed with the coronavirus in Wuhan, according to the U.S. Embassy.

Feb. 21: Pandemic 'likely'

Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, told reporters that U.S. health officials were preparing for the coronavirus to become a pandemic. "We're not seeing community spread here in the United States, yet, but it’s very possible, even likely, that it may eventually happen," she said.

Feb. 23: Italy locks down

Schools, businesses and restaurants were closed in a dozen northern Italian towns following reports of two deaths tied to an outbreak of the coronavirus in the region. The virus would begin to spread rapidly through Europe and Iran.

Feb. 26: CDC reports community spread; Pence to lead task force

The CDC confirmed an infection in California that would represent the first U.S. person to contract the virus despite not visiting a foreign country recently or coming in contact with an infected patient. This brought the number of coronavirus cases detected in the U.S. to 15, with 12 of them related to travel and the other two to direct contact with a patient.

Meanwhile, Trump announced that Vice President Mike Pence would lead the administration's coronavirus response. "We're very, very ready for this," Trump said at a press conference. "The risk to the American people remains very low."

Feb. 28: Flawed test kits

Messonnier told reporters that the CDC has taken steps to address problems with flawed test kits mailed to state and local labs. The agency has also expanded criteria for coronavirus testing.

Feb. 29: FDA begins to open up testing

In an effort to increase testing, the Food and Drug Administration announced it would be opening up its emergency authorization process to allow new testing technologies at hospitals and health care facilities nationwide.

U.S. Surgeon General Jerome Adams echoed CDC guidance encouraging Americans not to buy face masks needed by medical professionals. "They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can’t get them to care for sick patients, it puts them and our communities at risk," he said on Twitter.

A man in Washington state died after contracting the coronavirus – what was initially thought to be the first death from the new disease in the U.S. Gov. Jay Inslee declared a state of emergency in Washington hours later, saying that the outbreak "could likely be a worldwide pandemic."

March 3: U.S. surpasses 100 cases March 6: 'Anybody' can get a test

While touring the CDC headquarters in Atlanta, Trump told reporters: "Anybody that wants a test can get a test. That’s what the bottom line is."

March 11: Travel ban on Europe; WHO declares pandemic

Trump addressed the nation on the coronavirus outbreak and outlined strict travel restrictions on passengers arriving in the United States from hard-hit portions of Europe. Three days later, he added the United Kingdom and Ireland to the ban.

The WHO declared that the spread of COVID-19 had become a pandemic, which the organization has defined as "the worldwide spread of a new disease." Infections outside China have increased 13-fold in two weeks, WHO's director general said. In that same time, the number of countries hit by the outbreak has tripled.

March 12: US testing rollout 'a failing'

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the testing logjam constitutes a "failing" of the nation's health care system. "The idea of anybody getting (a coronavirus test) easily, the way people in other countries are doing it – we're not set up for that," Fauci told Congress. "That is a failing."

March 13: Trump declares national emergency

Trump declared the coronavirus pandemic to be a national emergency. Trump said the move would free up nearly $50 billion in additional disaster funding and would allow HHS to waive regulations and laws to deliver coronavirus testing quicker.

March 16: 15 days to slow the spread

Trump issued guidelines that called for Americans to avoid social gatherings of more than 10 people for the next 15 days and to limit discretionary travel, among other guidelines. Trump said the country may be dealing with a number of restrictions through July or August as a result of the virus. He acknowledged the economy may be heading into a recession.

March 17: Trump invokes the Defense Production Act

Trump invoked the Defense Production Act, a wartime authority that allows him to direct industry to produce critical equipment.

March 17: Report shows virus stable on surfaces

A study published in the New England Journal of Medicine found that viable virus could be detected up to three hours later in the air, up to four hours on copper, up to 24 hours on cardboard, and up to two to three days on plastic and stainless steel.

March 18: CDC report shows that all ages are at risk

A CDC report found that among the roughly 12% of COVID-19 cases in the U.S. known to need hospitalizations, about 1 in 5 were among people ages 20 to 44.

China reported no new domestic cases on the mainland – only cases in people returning from abroad.

March 19: U.S. surpasses 10,000 cases March 24: Tokyo Olympics postponed

The International Olympic Committee and Japanese government agreed to postpone the 2020 Summer Olympics "to a date beyond 2020 but not later than summer 2021" due to the ongoing coronavirus pandemic. It is the first time in modern Olympic history that a global health issue has disrupted the Games.

March 26: US has most cases

The U.S. surged past China and Italy to become the planet's most infected nation. More than 1,296 people had died in the U.S., according to a count maintained by Johns Hopkins University at the time.

March 27: Trump signs $2T stimulus package

President Donald Trump signed the largest stimulus package in U.S. history. The stimulus package was expected to provide $1,200 checks to many Americans – and more for families – while making available hundreds of billions of dollars for companies to maintain payroll through the crisis.

Trump also ordered his administration to use its authority under the Defense Production Act to force General Motors to expedite government contracts to build ventilators.

March 28: CDC issues travel advisory to New York area

The CDC issued a request asking residents of New York, New Jersey and Connecticut to curtail nonessential travel for 14 days.

Meanwhile, an infant younger than one year – who tested positive for the virus in Chicago – died.

March 29: White House extends social distancing guidelines

Trump announced that the White House would be extending its social distancing guidelines through April 30. "The peak in death rate is likely to hit in two weeks," Trump said. "Nothing would be worse than declaring victory before the victory is won." Trump said that he expects that, by June 1, "we will be well on our way to recovery."

April 1: The U.S. surpasses 200,000 cases

The U.S. surpassed 200,000 confirmed cases and topped 1,000 deaths in a single day for the first time, according to a count maintained by Johns Hopkins University at the time. The daily death toll was more than double that of two of America's most deadly illnesses – lung cancer and the flu.

April 2: More than 1M confirmed cases worldwide

The world registered more than 1 million confirmed cases in less than five months, according to a count maintained by Johns Hopkins University at the time. In reality, that mark was crossed much earlier because many more people have the virus but were not tested.

In the U.S., a record 6.65 million Americans filed first-time jobless claims the previous week, the Labor Department said. That number would later be revised up by 219,000 to an all-time high of 6.86 million.

April 3: CDC recommends use of face masks

The Trump administration advised people to start wearing face masks in public to stop the spread of the coronavirus, a reversal on previous guidance that urged people not to wear masks.

April 7: Thousands die in single day

The U.S. reported more than 2,000 deaths in a single day for the first time, according to a count maintained by Johns Hopkins University at the time. The disease eclipsed heart disease, the nation's No. 1 killer with about 1,772 deaths per day, according to the CDC. 

April 8: Wuhan lifts lockdown

The city of Wuhan was lit up after midnight to celebrate the lifting of a 76-day lockdown.

April 11: US has most deaths

The United States passed Italy to become the country with the most coronavirus deaths, according to a count maintained by Johns Hopkins University at the time. However, as a proportion of the total population in the U.S., virus deaths remain at about one-sixth of those in hard-hit Italy or Spain. More than 19,700 people in the U.S. had died due to complications from the coronavirus. Worldwide, the death count surpassed 104,000.

April 14: All 50 states report deaths

All 50 states reported at least one death, and more than 23,000 Americans had died, according to a count maintained by Johns Hopkins University at the time. President Donald Trump said his administration would "halt" funding to the WHO as it conducted a review of the global organization's handling of the pandemic.

April 15: Protests erupt over stay-at-home orders

Demonstrators drove thousands of vehicles to Michigan's state Capitol, protesting the state's stay-at-home order. Protests also erupted in Kentucky, Oklahoma and North Carolina.

April 16: White House issues guidance to reopen

The White House issued guidelines to states aimed at easing social distancing restrictions and reopening parts of the country. About 14% of the U.S. workforce had filed for unemployment in the past month.

April 20: States announce plans to reopen

The governors of Tennessee, South Carolina and Georgia announced various measures aimed at easing restrictions on some businesses in their states. 

April 21: FDA approves home-testing kit

LabCorp, a global life sciences company based in North Carolina, received FDA authorization for kits that enable people to collect nasal swab samples at home and mail them to a laboratory for testing.

April 23: $320B for small businesses

The House approved $484 billion legislation that includes funding for hospitals that have been overwhelmed during the crisis and money for a coronavirus testing program. The bill would pump $320 billion into the Paycheck Protection Program, which is designed to keep small businesses from shuttering and their workers from going on unemployment during the coronavirus pandemic.

April 24: Georgia reopens some businesses

In Georgia, gyms, tattoo parlors, hair and nail salons, massage therapists, and other businesses were allowed to reopen. Some businesses filled up with clients, but other remained dark.

The WHO issued a statement saying there is still "no evidence" that people who have recovered from COVID-19 and have antibodies are protected from a second infection.

April 26: More coronavirus symptoms

The CDC cautioned that six new symptoms could be signs of the coronavirus: chills, repeated shaking with chills, muscle pain, headache, sore throat and a loss of taste or smell.

April 27: Warning of meat shortages

The chairman of Tyson Foods warned of "meat shortages" due to what he called a breakdown in the food supply chain stemming from coronavirus outbreaks in factories throughout the country.

April 28: 1M cases in the US

The United States topped 1 million confirmed cases – nearly a third of the world's cases. More than 57,000 people in the U.S. have died, according to a count maintained by Johns Hopkins University at the time.

April 29: Economy shrinks

The U.S. economy shrank 4.8% in the first quarter – its first drop in output since early 2014 and the steepest since late 2008 during the depths of the Great Recession.

April 30: Federal social distancing guidelines expire

President Trump's social distancing guidelines expired, leaving the nation with a wide array of changing regulations.

May 1: Virus not man-made

Trump's director of national intelligence issued a statement on behalf of the U.S. intelligence community stating there was broad agreement that the virus was not man-made or genetically modified.

Meanwhile, the FDA issued emergency authorization for the use of experimental drug remdesivir to treat hospitalized coronavirus patients.

May 4: Death projection doubles

The model from the University of Washington’s Institute for Health Metrics and Evaluation nearly doubled its national death projection, from 72,000-plus to 134,475 by Aug. 4.

More than 1.1 million people had tested positive for the virus in the U.S., and more than 71,000 died, according to a count maintained by Johns Hopkins University at the time. That's more than twice the lives claimed during the 2018-19 flu season, which killed 34,000 people, according to the data from the CDC.

May 6: White House shelves CDC reopening guidance

The Trump administration shelved a 17-page report from the CDC with step-by-step advice to local authorities on how and when to reopen, the Associated Press first reported. The CDC was told that the guidance "would never see the light of day," according to the Associated Press.

May 7: Experts advise against antibody tests

Medical experts advised Americans against getting coronavirus antibody test, which haven't been validated by government regulators and may give people "a false sense of security."

May 8: Unemployment at 14.7%

The U.S. unemployment rate hit its highest since the Great Depression. The economy lost 20.5 million jobs in April and the unemployment rate soared to 14.7%, both record highs.

May 9: An inflammatory disease in children

Three children died in New York from an inflammatory disease that might be linked to the coronavirus. More cases later cropped up in other states.

May 11: States loosening restrictions

More than 15 states were set to move forward with reopening procedures.

Shops and schools reopened across Germany and France Monday, while British Prime Minister Boris Johnson "actively encouraged" people who can't work from home to return to their jobs.

May 14: More than 10M tests conducted in US

The U.S. had conducted more than 10.2 million coronavirus tests, with about 15% of people testing positive, according to data from a new online CDC dashboard.

The CDC released six one-page checklists providing guidance to schools, businesses, restaurants and more on when and how to safely reopen.

May 15: More than 300,000 deaths worldwide

Global deaths passed 300,000, but no country approached even half of the more than 85,000 American lives lost, according to a count maintained by Johns Hopkins University at the time.

President Trump announced Operation Warp Speed, a government coordinating effort aimed at securing a coronavirus vaccine by the end of the year.

May 18: Widespread reopenings

The majority of states were moving forward with phased-in approaches that often varied by county and city.

May 19: CDC releases longer guidance

The CDC published a longer 60-page document providing guidance to businesses, restaurants, schools and other establishments on how to reopen while minimizing the risk of spreading the virus.

PHOTOS Getty Images, AP; GRAPHICS Karl Gelles, Jim Sergent, Mitchell Thorson and Veronica Bravo/USA TODAY