It's not just tests. All symptoms disappear - we had health workers coming back to hospital and days later symptoms reappeared

EDIT: to clarify: in my hospital there were colleagues who tested positive, isolated, had no symptoms, went back to work, still no symptoms. After a few days symptoms are back and they tested positive again

It's flu season, it's quite possible they have had both flu and Coronavirus. My wife had the flu in Feb & early March and the symptoms are identical to the Coronavirus.

They're working in a hospital so they'll catch everything.

Stupid question does being infected with some virus helps if a second pathogen infects you ? As in 'immune system globally more active' or not at all ?

Not a stupid question, but pretty much not at all. In fact, you are slightly immune compromised by the first pathogen against the second pathogen because your adaptive immune system is highly active against the first pathogen. The body has two systems, an innate immune system that has mechanisms to innately attack bacterial and viral pathogens in general and an adaptive immune system that adapts to each specific pathogen. The innate system is a first line of defense but is like a form of combined suicide bomber and cannon fodder throwing cell after cell to overwhelm the pathogen with death and there is significant collateral damage. The adaptive immune system takes time to ramp up to each new pathogen and if it's working on one pathogen doesn't really switch to working on the other. Rather older cells are/have adapted to the first pathogen and newly born cells begin to work on adapting a defense to the new pathogen. This takes time and there are, at the beginning, very few cells adapting to the new pathogen.

Could it be that the first test was false positive then and the first symptoms where actually not corona virus?

Not if they were tested with PCR. PCR can have false negative, but false positive is extremely unlikely.

As someone also said, one of the biggest enemies of PCR is contamination, or perhaps the samples had conservation / handling problems which meant the RNA ended up degraded.

Given the (currently) very low numbers of these "apparently relapsed" cases versus the total recovered cases, I think it is most likely.

What about the symptoms?

I can think of two ideas on top of my head:

- Similar sympthoms but different disease (flu?)

- False negatives, and so people were still actually sick

In addition, I wonder if those patients had distinct clinical features compared to others. In absence of more data (and these cases are very uncommon) it is hard to tell.

Probably a good idea would be to do a study with periodical follow up of a large cohort of discharged patients. This would probably give better indication.

It’s the other way around. It’s very easy to get a false positive due to DNA contamination.

Globally we are running 100-thousands of tests per week, we must expect to see some false positives under these circumstances.

There is a video of the head of a hospital in Korea talking about reactivation occurring.

I feel that the “false positive” answer is often quickly given, without considering that it is likely that some people that get the virus have it flair up again. Perhaps it is caused by wishful thinking: reactivation is scary so let’s find a less scary reason?

Correction as per video at 8 minutes: https://youtu.be/gAk7aX5hksU

What is the false positive rate for these tests?