You’ve probably experienced it at some point during the Covid pandemic — you fall sick with all the symptoms of the virus but consistently test negative.
Then a week or so later, you take a turn for the worse and feel even more ill — and, perhaps miraculously, a test returns a positive result.
The phenomenon, dubbed ‘pre-Covid’, is taking hold again amid a fresh uptick in infections from the virus.
One theory is that the period of symptoms before the positive test is caused by someone catching a mild bug or other virus, leaving their immune system more vulnerable to a Covid infection.
Another is that it is simply the early stages of a Covid infection — known as the incubation period — and the amount of virus in the body is too low to detect via a test.
People may have Covid but not test positive for the virus, say scientists (stock image)
Dozens of people have shared their experiences with ‘pre-Covid’ on social media, another from Alaska wrote: ‘Pretty sure I have Covid, but I keep testing negative…’
They added: ‘The person I live with has it and I’m definitely sick, just testing negative. I don’t know if I should keep quarantining from her or not.’
A third person from Canada said: ‘I think I might be sick. Rapid tests are coming up negative though.
‘The most prevalent symptom is that my sinuses hurt, and my nose is going back and forth from stuffy to sniffy. I’m sneezing a lot and I feel extra foggy.’
Scientists say Covid cases are now ticking upwards, likely driven by new variant EG.5 or ‘Eris’ which is now behind one in five infections in the US.
Hospitalizations are also up 60 percent on the record low recorded last month — and up 14 percent in a week — but are still well below levels even in January this year.
People suffering flu-like symptoms who are testing negative for Covid could also have other diseases, however, such as the common cold.
Explaining the pre-Covid phenomenon, Dr Stuart Fischer, an emergency medicine expert in New York City, told DailyMail.com: ‘The symptoms that people relate might be their immune response to Covid [being triggered] from past exposure or vaccination.
‘When someone is vaccinated, this stimulates their immune response in a way that would become memory.
‘In other words, if the person was exposed again, the body would remember what to do and would release chemicals to fight the infection.’
Asked how long this phase might last before someone tests positive for Covid, he said it would not be beyond a couple of days.
Dr Fischer added that it was also possible for someone to have the symptoms, have Covid, but never actually test positive.
He said this was because the immune system would kick in and remove the virus before it had managed to gain a foothold.
Dr Thomas Moore, an infectious diseases expert at the University of Kansas, said: ‘It takes a while for the virus to be shed in enough quantities to be detectable.
‘If you have symptoms and test negative initially, you should test again 48 hours ltaer. The chance of a positive test increases significantly every other day.’
He added: ‘There are also cases where patients are convinced that they have Covid or are concerned that they have Covid and test repeatedly but get a negative result because they don’t have it.
‘But if they keep testing, they may eventually test positive because they have coincidentally picked up the virus along the way.’
Dr Moore also said people are likely to come forward to get a Covid test more rapidly than earlier in the pandemic because they are now more aware of the symptoms.
The above shows how EG.5 is growing in the US and has already become the most dominant variant of the virus behind nearly one in five infections
Covid hospitalizations are up 40 percent from their record lows recorded last month, but are still well-below levels from earlier in the pandemic
Covid deaths are continuing to fall, statistics from the Centers for Disease Control and Prevention show
It is also possible that the symptoms could be down to other infections, such as the common cold, which trigger similar symptoms to Covid.
Symptoms someone might suffer during the ‘pre-Covid’ stage include headaches, according to a 2020 study.
He added: ‘All illnesses exist in a subclinical form whether they are pneumonia, toothache, gout, hypertension, we all have a very mild version that is possibly really short-lived with symptoms that are just too weak to be recognized.
‘A person may recognize something is vaguely wrong but by the time they get to the doctors this has subsided.’
Lateral flow Covid tests are still sold in most pharmacies for people to check whether they have the virus, while PCRs can be ordered online.
The CDC says that people who have symptoms of Covid or who have been near someone who has tested positive for Covid should also get checked for the virus.
But there is no requirement to self-isolate if you test positive, with the CDC having relaxed these rules in August last year.
They said at the time that the conditions were ‘very different’ to those from the start of the pandemic.
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