Throughout the coronavirus pandemic, the two main symptoms of the virus that members of the public have been told by the NHS to look out for have been a fever and a new, persistent cough.
However, people around the world have reported experiencing various other symptoms, including loss of smell and taste, "Covid toe" and rashes on other parts of their bodies.
Epidemiologists, ophthalmologists and dermatologists have also warned about other symptoms that could be indicative of a patient who is positive of the coronavirus.
Here are several lesser-known symptoms that are currently being investigated for possible links to Covid-19.
In a new study published in The Lancet on Monday 18 May, it claims that delirium and confusion could be rife among seriously ill coronavirus patients.
The team of researchers conducted an investigation on a small number of Covid-19-positive patients.
In more than 60 per cent of the cases of intensive care patients, they discovered evidence of confusion and agitation.
The scientists, from the UK and Italy, concluded that patients who have to stay in intensive care for long periods of time and who are in need of ventilation treatment may be at greater risk of experiencing delirium and confusion.
The research, which assessed patients with Sars (severe acute respiratory syndrome), Mers (Middle-East respiratory syndrome) and Covid-19, also found that people who exhibit mild symptoms are less likely to experience as significant an impact on their mental health.
Professor Gitte Moos Knudsen, chair of the Department of Neurology and Neurobiology Research Unit at Copenhagen University Hospital, explained that "any condition associated with hospitalisation, fever, depletion of sensory inputs - particularly in the elderly - carries an increased risk for delirium".
"In Covid-19 patients that have been artificially ventilated, a PTSD condition may arise; but we do not have evidence that the frequency is higher in Covid-19 patients than in any other disorder," Professor Knudsen added.
Dr Michael Bloomfield, consultant psychiatrist and head of Translational Psychiatry Research Group University College London, said that the study is "important and well-conducted research".
"This study provides further evidence that the harm caused by Covid-19 extends beyond the widely reported effects on the lungs. This study tells us that Covid can have profound effects on mental health," he stated.
"Of particular cause for alarm is the finding that a third of patients from previous epidemics experienced post-traumatic stress disorder and it seems reasonable to anticipate similar rates of PTSD in people who have had life-threatening Covid."
Tom Dening, professor of Dementia Research at the University of Nottingham, pointed out that scientists "know much less about the prevalence of mild or asymptomatic Covid-19", adding that patients who experience milder cases of the virus are less likely to experience mental health issues, "especially delirium, which is generally a marker for severe physical illness".
"The authors draw attention to how delirium is an important and common feature in people admitted to hospital with coronaviruses. In some situations, probably more so in older people, delirium may even be the presenting feature of a severe Covid-19 infection, so it's important that health professionals and care home staff are aware of this possibility," the professor said.
2. Covid toe and other rashes
Over the past few weeks, the term "Covid toe" has been increasingly discussed as a possible symptom of the coronavirus.
The condition, which involves chilblain-like lesions appearing on the feet, is one of several skin conditions currently being investigated as potential signs of Covid-19.
On 29 April, researchers from Spain published a study concerning the "cutaneous manifestations of Covid-19 disease", cutaneous meaning "relating to the skin".
The scientists came across five different forms of rashes affecting 375 Covid-19 patients.
These included itchy or painful chilblain-like lesions on the hands and feet, including Covid toe; small blisters on the torso; small, flat and raised red bumps; blotchy red or blue-looking skin; and pink or white raised areas of the skin that looked similar to nettle rash.
In a statement sent to The Independent, Dr Ruth Murphy, president of the British Association of Dermatologists, stressed that rashes are "extremely common and in the vast majority of cases have no link to Covid-19".
Nonetheless, the dermatologist added that the study "contributes to our overall knowledge of the disease".
Dr John Ingram, editor-in-chief of the British Journal of Dermatology, added that the investigation is "the most definitive piece of research on the skin features associated with Covid-19 to date".
"There has been speculation for some time that the virus is responsible for a number of skin signs, but until now these had largely been individual or small scale case reports. This study represents a much more systematic and thorough categorisation of the features," he stated.
"The main beneficiaries of this research will be medical professionals and researchers. It will be useful in diagnosing people with Covid-19, particularly those with relatively few symptoms. It will also provide a firm foundation for future research into COVID-19 and the skin."
The American Academy of Dermatology has created a dedicated task force to study Covid toe.
Several reports have been circulating as of late regarding the possibility that the coronavirus could cause conjunctivitis, an eye condition that develops as a result of infection or allergies.
In April, the American Academy of Ophthalmology released an alert for ophthalmologists highlighting two studies that indicated the potential link between the virus and conjunctivitis.
In a study of 30 patients hospitalised for the virus in China, one had conjunctivitis. "That patient - and not the other 29 - had SARS-CoV-2 in their ocular secretions. This suggests that SARS-CoV-2 can infect the conjunctiva and cause conjunctivitis, and virus particles are present in ocular secretions," the American Academy of Ophthalmology said.
In a larger study published in the New England Journal of Medicine, which assessed 1,099 hospitalised coronavirus-positive patients in China, nine had "conjunctival congestion".
In a statement sent to The Independent, Moorfields Eye Hospital in London emphasised that "of the many people infected worldwide with Covid-19, there are only a few reports of patients presenting with conjunctivitis." The hospital added that there is "therefore a possibility, but it is incredibly rare".
The hospital has not noticed an increase in patients being admitted for conjunctivitis during the pandemic, adding that the "there is no evidence that the conjunctivitis in Covid-19 is more severe than any other type of viral conjunctivitis".
Moorfields outlined that if the virus were to cause a patient to develop conjunctivitis, this would likely occur either through "direct exposure of the surface of the eye to Covid-19" (such as by rubbing the eyes) or "indirect exposure where the virus tracks up the duct that connects the surface of the eye to the nose and throat".
The Royal College of Ophthalmologists (RCO) and the College of Optometrists explained that if a person presents conjunctivitis after contracting coronavirus, it is unlikely they would do so without also showing other, more recognisable symptoms of the virus.
"Recent reports have suggested that Covid-19 may cause conjunctivitis, and it is known that viral particles can be found in tears, which has caused some concern amongst eye health professionals," the organisations stated.
"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."
The RCO and the College of Optometrists stated that as viral conjunctivitis is not listed as an official symptom of Covid-19, medical practitioners should treat patients with the condition "as they would usually treat any presentation of viral conjunctivitis", as long as they are not also showing signs of the coronavirus.
They stressed that during the pandemic, "scrupulous infection control and hand hygiene measures" should be carried out when treating all patients, while any "close examinations" should be "kept to a minimum safe level".
4. Inflammation among children
Earlier this month, it was reported that up to 100 children in the UK had been affected by a rare disease linked to the coronavirus.
The syndrome appears to bear similarities with Kawasaki disease, causing an inflammatory response in children ranging from infants to older teenagers.
Russell Viner, president of the Royal College of Paediatrics and Child Health (RCPCH), stated that while symptoms are fairly mild for the majority of children affected, "a small proportion have become much more severely ill".
Professor Rosalind Smyth, director and professor of Child Health at the UCL Great Ormond St Institute of Child Health added that "it remains the case that the great majority of children with COVID-19 have mild symptoms only".
In a report on the cases admitted to London Children's Hospital, it said that symptoms include "unrelenting fever", "variable rash", conjunctivitis, swelling, pain and "significant gastrointestinal symptoms", such as diarrhoea and vomiting.
NHS England released an alert about the condition in late April, stating that the cases of children in intensive care with a "multi-system inflammatory state" have "overlapping features" of two health conditions - toxic shock syndrome and "atypical" (or incomplete) Kawasaki disease.
The health service added that the children have also had "blood parameters consistent with severe Covid-19 in children".
Dr Julia Kenny, consultant in paediatric infectious diseases and immunology at Evelina London Children's Hospital explained that much more research is needed on the subject before it can be more thoroughly understood.
"As this new syndrome has only been identified in the past four weeks, it will be vital to learn more about its presentation and treatment, and to establish how the disease mechanism is linked to Covid-19 which has pre-dominantly affected adult patients to date," Dr Kenny said.
Professor Smyth added that at the moment, "it seems that this condition is very rare".
"One of the purposes of the current alerts and guidance is to increase awareness, so that all possible cases can be identified. This will help to identify the true incidence," the professor outlined. "We know very little about the cause and mechanisms. Indeed, our understanding of the mechanisms of the condition which it may resemble, Kawasaki's syndrome, is incomplete.
"Working out a possible relationship to Covid-19 will depend on testing for the virus, repeatedly during the course of the illness, and for the antibody, following recovery, to work out if there is a temporal relationship with SARS-CoV-2, in some, or all, cases."