A systematic review of current research related to long COVID, published in the Journal of the Royal Society of Medicine, found that having five symptoms in the first week of infection was 'significantly associated with the development of long COVID irrespective of age or gender'.
However, the researchers also highlighted that a significant number of patients will develop long COVID, which is officially known as post-COVID-19 syndrome in patients where symptoms last for longer than 12 weeks, regardless of the severity of their initial infection.
The review, which summarises current evidence on symptoms, complications and management of long COVID, found that the 10 most common symptoms of long COVID were fatigue, shortness of breath, muscle pain, cough, headache, joint pain, chest pain, altered smell, diarrhoea and altered taste.
It also identified two main 'symptom clusters' of long COVID - those involving fatigue, headache and upper respiratory complaints exclusively and those with multi-system complaints, which included ongoing fever and gastroenterological symptoms.
The review was led by the University of Birmingham Therapies for Long COVID (TLC) Study Group, which is one a number of government-funded studies researching long COVID. It also found that both hospitalised and non-hospitalised patients might require rehabilitation to recover.
For non-hospitalised patients this would be particularly important for those with cardiopulmonary symptoms, who may need significant rehabilitation, the researchers said. However, they warned that it might be difficult to identify this cohort of patients due to 'under-recognition and under-investigation of symptoms'.
'There is also a risk that non-hospitalised patients with long COVID with mild-to-moderate symptoms, who are likely to represent a significant proportion of long COVID sufferers, may not be prioritised for follow-up care,' the researchers added.
The findings come as the authors of another study into long COVID called for a national screening programme for the condition to help prevent people from 'suffering in silence'.
That study, which was led by scientists at UCL alongside a patient research collaborative, identified over 200 symptoms associated with long COVID by using results from a web based survey that gained responses from 3,762 eligible participants in 56 countries.
The research, published in the Lancet’s EClinicalMedicine, found a total of 203 symptoms spanning 10 organ systems were present in long COVID, and a third of the symptoms continued to affect patients after six months.
The researchers said that participants also experienced 'symptoms that are not commonly mentioned in public discussion of long COVID', including anaphylaxis and new allergies, seizures, changes in sensitivity to medication, vision loss, hearing loss, and facial paralysis.
A total of 85% of respondents experienced persistent memory and cognitive dysfunction. Meanwhile headaches, insomnia, vertigo, neuralgia, neuropsychiatric changes, tremors, sensitivity to noise and light, hallucinations, tinnitus, and other sensorimotor symptoms were also all common, which the researchers said may point to larger neurological issues involving both the central and peripheral nervous system.
The researchers said that clinical guidelines, which currently advise cardiovascular and respiratory function tests for suspected long COVID, should be widened to include neuropsychiatric, neurological, and activity intolerance symptoms.
Senior author of the UCL study, Dr Athena Akrami, neuroscientist at the Sainsbury Wellcome Centre at UCL, said: 'For the first time this study shines a light on the vast spectrum of symptoms, particularly neurological, prevalent and persistent in patients with long COVID.
'Along with the well-documented respiratory and cardiovascular symptoms, there is now a clear need to widen medical guidelines to assess a far wider range of symptoms when diagnosing long COVID.
'Furthermore, there are likely to be tens of thousands of long COVID patients suffering in silence, unsure that their symptoms are connected to COVID-19. Building on the network of long COVID clinics, which take GP referrals, we now believe a national programme could be rolled out into communities able to screen, diagnose and treat all those suspected of have long COVID symptoms.'
Quality of life
Lead author of the Birmingham study, Dr Olalekan Lee Aiyegbusi, deputy director at the University of Birmingham’s Centre for Patient Reported Outcomes Research, said: 'There is evidence that the impact of acute COVID-19 on patients, regardless of severity, extends beyond hospitalisation in the most severe cases, to ongoing impaired quality of life, mental health and employment issues.
'People living with long COVID generally feel abandoned and dismissed by healthcare providers and receive limited or conflicting advice. More than one-third of the patients in one of the studies included in the review reported they still felt ill or in a worse clinical condition at eight weeks than at the onset of COVID-19.'
This month NHS England launched a new enhanced service for long COVID, which practices can choose to sign up to. The enhanced service is backed by £30m of funding and practices will be required ensure staff are trained on how to identify, assess and manage long COVID, develop support for self management, understand local clinical pathways and correctly coded patient data.