Later that week, on February 28, a study of nearly 1100 Chinese patients suggested a lower death rate, of 1.4 per cent. Four days later, on March 3, the World Health Organisation said the global mortality rate was 3.4 per cent. Loading Replay Replay video Play video Play video How could it have changed so much in such a short period of time? "It's hard to say what the case-fatality rates are until the dust settles," said Dr George Rutherford, an epidemiologist and infectious disease expert at UC San Francisco.

"It's not a statistic to be looking at kind of on an ongoing basis, even though I do it just as much as everybody else does," he admitted. Loading That includes members of Congress. On Wednesday, they asked Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, what was going on. He urged them not to get so fixated on the fatality rate, emphasising that scientists still have a lot to learn about it. The biggest uncertainty surrounds the number of people who have been infected with the coronavirus. The official count has surpassed 100,000, but the true number is probably much higher. Scientists suspected that many patients who experienced only mild illnesses never saw a doctor and therefore never got an official lab test to see if they were infected. As a result, they weren't factored into the case-fatality rate.

Neither were people who wanted to be tested but weren't because of a lack of resources. In a situation where test kits are limited, it's better to save them for 80-year-olds with poor lung function and skip the healthier 40-year-olds with mild illness. Counting problems aside, the case-fatality rate can change over the course of an outbreak. Loading Replay Replay video Play video Play video For instance, the authors of the study of nearly 45,000 Chinese patients noted that the case-fatality rate in Hubei, the province at the centre of the outbreak, was 2.9 per cent. Elsewhere in China, it was 0.4 per cent. It's possible that as China catches up on counting deaths, the fatality rate outside of Hubei will rise.

But it's also possible that the difference is real because public health authorities outside of Hubei had a chance to get ready for the coronavirus, "so people aren't dying at the same rates as they did before," Rutherford said. Loading At UCSF, for instance, doctors are prepared to treat the coronavirus in a containment facility set up in the parking lot for the emergency room, he said. Other countries are reporting different case-fatality rates. With 6767 confirmed cases as of late Friday, South Korea has more coronavirus patients than any country besides China. That high number may in part be a function of the country's sweeping testing program that involved tens of thousands of people. When balanced against the country's 44 deaths, the case-fatality ratio is less than 0.7 per cent.

That figure may offer a better sense of COVID-19's true fatality rate, said Dr. Jeremy Faust, an emergency physician at Brigham and Women's Hospital in Boston and an instructor at Harvard Medical School. "By testing so many people, they were actually able to find more cases," Faust said. "It means they noticed the disease was everywhere, and it doesn't kill that many people. "The more testing you do, the more accurate your numbers become," he added. Rutherford predicted that by the time the dust settles, the overall case-fatality rate for COVID-19 will fall to somewhere between 1 per cent to 2 per cent. Fauci agreed that the death rate could end up being as low as 1 per cent. But even if that's the case, he said, it would still be 10 times worse than the average death rate for the seasonal flu.

The symptoms of coronavirus include fever, cough, sore throat, headache, shortness of breath and breathing difficulties. If you suspect you or a family member has coronavirus you should call (not visit) your GP or ring the national Coronavirus Health Information Hotline on 1800 020 080. Los Angeles Times