Coronavirus has spread to every continent except Antarctica, and U.S. health officials have warned that it's likely to turn into a global pandemic.

Globally, the majority of about 81,000 cases of COVID-19, the disease caused by coronavirus, have been reported in China, where the outbreak began. But it has spread to at least 37 other countries, including Canada, according to the World Health Organization.

There have been clusters of new cases appearing in Italy, Iran, South Korea and Japan over the past week, and officials fear the virus could spread undetected in other countries that lack the capacity to monitor people for signs of infection.

The outbreak has taken about 3,000 lives, mostly in China, and its spread has rattled global financial markets. At least 13 cases have been reported in Canada.

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A Japanese patient tested positive for coronavirus a second time, but an infectious disease expert cautions that the virus can be detected long after a patient has recovered. 1:30

"As the coronavirus changes and travels across the globe, it's getting more and more difficult to isolate countries that are more specifically affected," Health Minister Patty Hajdu said Wednesday, encouraging Canadians to stockpile food and medication in their homes in case they have to be quarantined.

These graphics aim to put the outbreak into perspective and are current as of Feb. 26, 2020.

The vast majority of coronavirus cases initially occurred near Wuhan, China, and surrounding cities. But the outbreak has spread rapidly.

The WHO said Wednesday the number of new cases of the novel coronavirus reported outside China has exceeded the number of new cases developing in China.

The virus was first reported to World Health Organization officials in China on Dec. 31, 2019.

Most people who have caught COVID-19 have experienced symptoms similar to the flu and don't require emergency medical attention.

Doctors and World Health Organization officials are racing to develop a vaccine or antiviral medicine to prevent or treat the virus, but to date nothing exists.

Ebola and influenza are not in the same family of infections as SARS (Severe Acute Respiratory Syndrome), MERS (Middle East Respiratory Syndrome) or the 2019 coronavirus (2019-nCoV) — a temporary name for the new virus that was first detected in 2019. The other viruses are used here to put the severity of coronaviruses into perspective through comparison.

Lab-confirmed flu and pneumonia-related deaths in 2018 in Canada alone are higher than those of all three coronaviruses combined.

The lab-confirmed flu and pneumonia totals (shown above in grey) are not definitive. Many Canadians who become infected during any given year do not seek medical help and therefore never get tested .

Coronaviruses are a large family of viruses that includes SARS, which affected 26 countries and resulted in more than 8,000 cases in 2003.

While the 2019 and SARS coronavirus seem to be closely related genetically , less is known about how transmissible and deadly the former is.

"In essence, it's a version of SARS that spreads more easily, but causes less damage. The virus also uses the same receptor, the door used to get into human cells, which explains transmission and why it causes pneumonia," Ian Jones, a professor of virology at the University of Reading, wrote in an online comment.

To estimate how bad an outbreak could get, experts look at the case fatality rate — the proportion of deaths a disease causes within a group of people.

The problem with estimating the case fatality rate early in an outbreak is that the sickest people tend to go to the hospital or a doctor's office. Those who don't show or have mild symptoms may never seek medical care and won't be counted as cases.

A Civil Defence member wearing a protective suit sprays disinfectant as a precaution against the coronavirus in the closed shops, and hotels used by Iranian citizens in Najaf, Iraq, on Feb, 26. (Anmar Khalil/The Associated Press)

Symptoms from the virus can include: fever, cough and shortness of breath, according to the U.S. Centers for Disease Control and Prevention.

Complications can include serious conditions such as pneumonia or kidney failure .