Professor Philip Nolan:

No, I have no concern that they were false positives because the setting they are in is a high-prevalence setting. The disease was clearly there and that gives one confidence that the positives were true positives. It is only when one is screening large numbers of people who are very unlikely to have the disease that there is a concern about false positives. The proportion of asymptomatic people, which was 59%, mirrors the experience internationally. When one goes in and tests everybody in a large workplace setting, one finds that at least half of the cases are asymptomatic. That was the case in the recent set of outbreaks in meat factories, with 41% symptomatic and 59% asymptomatic.