Millions of people could already have contracted the new coronavirus Covid-19 and have no idea they had it, according to researchers at Oxford University's Evolutionary Ecology of Infectious Disease group.
The scientists say the disease may have been in the UK since the middle of January, meaning many of us caught it without knowing what it was -either experiencing no symptoms or just mild symptoms that we didn't recognise.
The study, which has yet to be peer-reviewed, says the disease could have been spreading for weeks before the alert went out at the end of February,
The key symptoms of Covid-19 are a new, dry, persistent cough and a fever - feeling hot on your head, chest or back or registering over 37.7C on a thermometer.
If you have these symptoms you should check your countries website for help.
Everyone should now be in lockdown, not leaving the house for anything for essential reasons, and anyone who has the cough, fever or other flu-like symptoms should self-isolate, not leaving their home at all.
In the weeks ahead, tests will be available to determine who has had the disease.
There are eight symptoms that could reveal that you have already had Covid-19.
It is important to note that you may have had one or several of these symptoms but have not had Covid-19.
1. Eye infections
New research has indicated that eye infection such as conjunctivitis may be a symptom of Covid-19.
The College of Optometrists said: "It is recognised that any upper respiratory tract infection may result in viral conjunctivitis as a secondary complication, and this is also the case with Covid-19.
"However, it is unlikely that a person would present with viral conjunctivitis secondary to Covid-19 without other symptoms of fever or a continuous cough as conjunctivitis seems to be a late feature where is has occurred."
2. A dry cough
Perhaps the most recognisable of the Covid-19 symptoms, given how different it can sound compared to a typical cough.
The cough is generally new for you - or different if you generally have a smoker's cough -and persistant.
More often than not it will last for at least half a day.
3. Mental fatigue
Although this has not been officially chalked up as a symptom, Covid-19 sufferers have reported experiencing mental fatigue.
Thea Jourdan told The Daily Mail that she first thought she may have been infected when she got a tickle in her throat and a headache.
The mum-of-three then began to experience brain fog.
"Initially I felt exhausted, as if I was dragging myself through treacle and had no choice but to go to my bed. I had no meaningful cough and I wasn’t running a fever," the Hampshire woman told the publication.
"But I had a peculiar sensation of something settling deep within my lungs, almost like breathing in talcum powder."
4. A high temperature
Although numbers vary for different people, a rise in body temperature generally counts as a fever once it reaches 37.7C (100F).
You can tell you have a fever if you feel hot to the touch on your chest or back.
5. It's difficult to catch your breath
If your chest starts to feel tight or you cannot breath, you may have caught the coronavirus.
Most young people or those without pre-existing health conditions are unlikely to experience this symptom.
Dyspnea - the term for when someone has difficulty breathing - may be coupled with a tightness in the chest, rapid breathing and heart palpitations.
6. Loss of sense of smell and taste
Over the weekend the British Association of Otorhinolaryngology warned that losing your sense of smell and taste may mean you have Covid-19.
The ear, nose and throat specialist recommended anyone with such symptoms self-isolate immediately.
It has been suggested that the phenomena may be caused by the coronavirus killing cells in the nose and throat.
"Evidence from other countries that the entry point for the coronavirus is often in the eyes, nose and throat areas," the Association said in a statement.
"We have also identified a new symptom (loss of sense of smell and taste) that may mean that people without other symptoms but with just the loss of this sense may have to self-isolate - again to reduce the spread of the virus."
7. Tummy ache
As with a loss of appetite, enduring a tummy ache may easily be passed off as a sign of something more innocuous.
However, a newly published study by the American Journal of Gastroenterology links tummy problems to Covid-19.
They found that 48.5% of 204 people who have been infected by the coronavirus in China's Hubei province had digestive symptoms such as diarrhoea.
8. Physical fatigue
Another common symptom of Covid-19, as well as cold, flu and many viruses in general, is feeling tired or fatigued.
Being told to rest is common when you’re ill, but feeling tired and not being able to sleep due to coughs and difficulty breathing, can make things all the more difficult.
Jaimuay Sae-ung, 73, was the first Thai national to contract coronavirus in December last year.
Despite having underlying health conditions, including a heart problem, Jaimuay survived the illness after doctors isolated her at a hospital in Thailand for treatment.
"I only knew (I had coronavirus) after I came to the hospital," the mother of seven told Sky News.
"I felt a bit sad, a bit shocked, tired and fatigued and I couldn't eat."