One in three people who have Covid-19 have no symptoms.

At the start of the pandemic in the UK in March last year, experts said the virus could have been circulating across the country as early as January.

This has left many people wondering whether they might have actually already had coronavirus.

The NHS states that the three main symptoms of Covid-19 are a new persistent cough, a high temperature or a loss of taste and smell (anosmia).

Here are some of the signs that may indicate you already had coronavirus...

1. Stomach ache

Some Covid-19 patients have reported experiencing tummy ache just before developing the other known symptoms.

A study, published in the American Journal of Gastroenterology, suggests people might experience digestive issues, such as diarrhoea, when they are infected with coronavirus.

The Centre for Disease Control (CDC) in the US already lists diarrhoea as a symptom of Covid-19.

Researchers analysed data from 204 patients with Covid-19 in China’s Hubei province and they discovered that 48.5 per cent of these patients arrived at the hospital with digestive symptoms such as diarrhoea, vomiting or abdominal pain.

2. Shortness of breath

Shortness of breath can be a very serious manifestation of Covid-19, and it can occur on its own, without a cough.

If your chest becomes tight or you begin to feel as if you cannot breathe deeply enough to get a good breath, that's a sign to act, experts say.

Patients who are usually older or have a pre-existing health condition are normally the people who experience difficulty breathing – known as dyspnea.

Signs that a person is experiencing dyspnea include shortness of breath, feeling smothered or suffocated, tightness in the chest, rapid, shallow breathing, heart palpitations and wheezing.

3. Memory loss 

Many sufferers have reported having trouble thinking clearly for months after getting over the first part of disease.

4. Covid tongue

According to Professor Tim Spector more and more people are heading to doctors complaining of issues with their tongue.

The King's College London epidemiologist, who heads the Covid Symptom Study App, said that the disease seems to cause tongue changes including pain, discolouration, swelling or a strange texture.

"Seeing increasing numbers of Covid tongues and strange mouth ulcers," Professor Spector tweeted.

"If you have a strange symptom or even just headache and fatigue stay at home."

5. Eye infections

Recent reports have suggested that Covid-19 may cause eye infections such as conjunctivitis.

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 it has occurred."

6. A dry cough

A dry persistent cough is a ‘classic’ symptom of coronavirus, according to Dr Sarah Jarvis, GP and Clinical Director of Patientaccess.com.

She says a dry persistent cough is normally new for you (or different from your normal cough if, for instance, you have a ‘smoker’s cough’).

It's also persistent – not just because you’re clearing your throat or because you have something caught in your throat - and it needs to last for at least half a day.

A dry (rather than ‘fruity’ cough) is more likely to be due to coronavirus, but you need to self-isolate regardless of whether your cough is dry or productive.

The NHS describes a "dry cough" as a cough where no phlegm or mucus is produced, which is also irritating and usually associated with a tickly throat.

7. A high temperature

A fever is a key symptom of coronavirus, experts say.

The NHS says it's really not a fever until your temperature reaches at least 100 degrees Fahrenheit (37.7 degrees Celsius) for children and adults.

They say you can tell if you have a fever when you feel hot to touch on your chest or back.

Lancaster And Morecambe Citizen: A high temperature could be a sign of CovidA high temperature could be a sign of Covid

8. Dizziness

Some research has linked vertigo to COVID-19.

In fact, a review of research published in the Ear, Nose & Throat Journal called dizziness “one of the main clinical manifestation of COVID-19.”

9. Loss of taste and smell

If you previously lost your sense of taste and smell you could have already had coronavirus.

The British Association of Otorhinolaryngology (ENT UK) says patients who do not have a fever or a cough could show a loss of smell or taste after contracting the deadly bug.

In May a loss of taste and smell was added to the official NHS symptoms list.

10. Hearing loss 

Hearing loss and other auditory problems may be strongly linked to coronavirus, new research suggests.

Scientists estimate 7.6 per cent of people infected with COVID-19 experience hearing loss, while 14.8 per cent suffer tinnitus.

They also found the prevalence of vertigo was 7.2 per cent.

How to find out if you had coronavirus

An antibody test can tell you whether or not you have had Covid-19.

But the NHS says they don't work for everyone and not everyone who has had the virus will have antibodies in their system.

These tests are not yet widely available and are currently only available for certain people who work in primary care, social care or education.

The NHS says: "These tests are to help the NHS and scientists learn more about who has already had the virus and how it has spread in the UK".

The test is done by taking blood from a finger prick.

When a person gets infected by the virus, the body starts making specially designed proteins called antibodies to fight the infection.

Users or pharmacists will have to prick a finger and place a drop of blood on a stick, which looks like a home pregnancy test.

Some will give an immediate result and others must be returned to a lab. Results will be recorded on medical records.