Just jules. The problem is I think that if everyone else tested negative that doesnt mean they havent had it at some point. But we don't know that without decent antibody testing and even then we arent far enough into this to know for sure what protection antibodies give and for how long.
CLKD mentioned the incubation period further back which I think is an interesting point.
From the BBC. The link below about a couple who returned to Singapore from China in January. The day of their return they went to church. Both felt well and had no symptoms. 2 days later they both fell ill and so did various members of the congregation. It was one of the very first cases there and the authorities were on to it quickly. From track and Trace they came to the conclusion that the couple were able to spread the virus 2 days before their symptoms. This couple didnt have tests until they became unwell and I think it would be interesting to know if they wouldve tested pos 2 days before symptoms. That's hard to do in most cases obvs as its retrospective. . The article also talks of asymptomatic spreaders. These things are what makes this virus so effective at spreading quickly and silently.
There is also the question of for how long a person stays contagious once infected and whether those who continue to test pos after several weeks are still able to pass it on. My family member tested positive when admitted to hospital with covid symptoms and 4 weeks later was still testing positive. Docs were unable to say with any certainty if at this point she was still contagious. They told us they just dont know for sure yet. And hers isnt an isolated case.
Btw She is 78 and diabetic and touch wood is recovering very well indeed. . She feels back to normal now 8 weeks later. They said they saw the "ground glass effect" in her lung scan but she didnt have significant breathing problems at any point . She has now been called back for a further lung scan. I expect they will learn from people like her. She was treated with hydroxychloroquine.
https://www-bbc-co-uk.cdn.ampproject.org/v/s/www.bbc.co.uk/news/amp/uk-52840763?amp_js_v=a3&_gsa=1&usqp=mq331AQFKAGwASA%3D#aoh=15917774915332&referrer=https%3A%2F%2Fwww.google.com&_tf=From%20%251%24sStay safe ladies xxxx
