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As of Tuesday, there were almost 850,000 reported cases of coronavirus worldwide. But the official statistics must come with a major caveat – they are almost certainly too low by an order of magnitude.

Coronavirus tests are still not widely available. As of Monday, Cayman had received 480 PCR (polymerase chain reaction) tests, bringing the total on island to 520. More tests are expected to arrive this week from the UK.

Even larger countries do not have enough tests to determine the precise number of cases. Germany now carries out about 200,000 tests each week, after it increased its capacity from 12,000 tests per day. This is more than most countries. Current figures show that, with about 5,000 new daily cases and roughly one in nine tests coming back as positive, even that number of tests is not large enough to quantify the true number of people infected with the coronavirus.

While the examples of South Korea and isolated cities in northern Italy suggest that testing the entire population repeatedly is key to controlling the spread of COVID-19 early and effectively, most countries do not yet have this option.

They therefore resort to testing only people with advanced symptoms and travel history to any of the world’s hotspots. The result of less testing is fewer reported positive cases.

In the UK, typically only people admitted to hospital and some healthcare staff are tested.

As of Tuesday morning, 31 March, the UK had only tested 143,186 people since the beginning of the coronavirus outbreak. Of those, 25,150 tested positive. At the same time, the US has done 964,865 tests, of which 163,536 were positive.

The lack of widespread testing in countries like the UK manipulates, whether deliberately or not, the way the crisis is perceived and hides the true extent of the problem.

The fact that even UK Prime Minister Boris Johnson and Health Secretary Matt Hancock have been infected with the virus indicates that the true scale of COVID-19 infections is significantly larger than official figures reported in the media.

Another reason for the underreporting is that in about a quarter to one-third of cases the virus is believed not to cause any symptoms at all. And in up to 80% of cases the symptoms will only be mild.

Mortality rates

One indication that case numbers are much higher than reported in the UK is that 1,789 people have died already from COVID-19. If the mortality rate related to COVID-19 is, as frequently estimated, around 1%, the already existing number of deaths would translate into almost 200,000 cases.

Professor Neil Ferguson, from University College London, a key epidemiologist whose modelling of the crisis is used to advise the British government, estimated on BBC Radio 4 that 3-5% of people in central London could have been infected and nationwide about 2-3% of the UK population may have contracted the virus at some point. This would be between 1.2 million and 1.8 million cases in the UK alone, rather than the reported 22,141.

The same statistical problems exist at a global level.

As of Tuesday afternoon, there were 837,104 reported cases worldwide. Of those, 41,249 people have died while 176,058 have recovered from the virus. This equates to a mortality rate of 18.98% among the cases that had an outcome. Even if all the remaining people who tested positive recovered from the disease and none died, the mortality rate among the reported cases would be 4.9%.

In reality, the mortality rate of the already-reported cases is going to be somewhere between 4.9% and 18.98%.

This means if the true mortality rate across all cases, including the ones that do not show up in any official statistics, is close to the estimated 1%, the true number of cases would be between 4.9 and 19 times the officially reported figures.

In Germany, however, even among the reported cases the mortality rate is below 0.9%. This indicates that the true number of cases worldwide could be higher still.

With that said, the number of reported cases highlights specific trends, if either the testing is consistent or fluctuations in testing are taken into account.

They can, for example, show when active case numbers or deaths are declining.

For now, they keep rising, albeit more slowly, in all countries except China and South  Korea.

The way forward

To get a hold on the crisis, all countries are ramping up testing.

Most countries are also pinning their hopes on so-called antibody tests, which are expected to be rolled out in the UK and Germany in the next weeks.

These tests will confirm who already had the virus and provide valuable information on the part of the population that may have developed some immunity to COVID-19.

This type of data is also necessary to inform decisionmakers when lockdown restrictions can be eased.

Full coverage: Coronavirus

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