Uncertainty over asymptomatic or mild cases means true number of those who have, or have had, COVID-19, likely to be much higher.
Amid the uniquely unsettling novelty the coronavirus epidemic has brought, one thing is more uncertain than any other: how many of us have, or have had, the virus? Harry de Quetteville writes in the Telegraph that on Tuesday, for example, Italy’s civil protection chief, Dr. Angelo Borrelli, briefed reporters with the latest statistics: cases up 3,612 to 54,030. The problem was that, earlier in the day, he had suggested there might be as many as 600,000. Asked to account for the difference, he said his earlier answer had taken into account asymptomatic cases. So what is it? 54,000 or 600,000?
Italy is not alone. Earlier this week, the Self-Defense Forces Central Hospital in Tokyo published a report into the Diamond Princess cruise ship, which was quarantined in February with more than 800 of the 3,711 people on board eventually diagnosed with COVID-19. 
According to the report, cited by the Japan Times, four-fifths of those infected showed no symptoms or just mild symptoms. Scans showed their lungs had suffered some physical consequences from the virus, but the patients had not been led by their symptoms to believe they were infected. Quite the reverse.
“One way or another, it is clear that far more of us have, or have had, Covid-19, than the official figures tell us. But how many more? Only mass testing will give us a real picture of what is happening,” de Quetteville writes.