The condition commonly called 'long COVID' may not be one syndrome but possibly up to four different syndromes, according to a new review.
The finding comes from a dynamic themed review of available scientific evidence published by the National Institute for Health Research (NIHR).
The paper, Living with COVID19 draws on the latest expert consensus and published evidence, as well as the experience of patients.
It formed the first output from the NIHR Centre for Engagement and Dissemination (NIHR CED) which is working towards a real-time knowledge base in what is an emerging field.
It is estimated that as many as 60,000 people in the UK may have long COVID.
Long COVID 'May Be a Catch All Term'
The review found clear consistencies for a wide range of recurring symptoms among people who had been hospitalised because of COVID-19, as well as those who had COVID-19 in the community.
Those who experienced ongoing COVID had problems with the respiratory system, the brain, cardiovascular system and heart, kidneys, the gut, the liver, and even skin.
The authors said that such a wide range of symptoms created diagnostic uncertainty.
"We believe that the term 'long COVID' is being used as a catch-all for more than one syndrome, possibly up to four," said Dr Elaine Maxwell, the review's author.
She told a briefing hosted by the Science Media Centre (SMC) that while some patients experience "classic post-critical illness symptoms", others reported "fatigue and brain fog in a way that's consistent with post-viral fatigue syndrome".
A third group experienced "permanent organ damage caused by the virus", while another significant group "describe a rollercoaster of symptoms that move around the body and do not steadily progress towards recovery".
"We believe that the lack of distinction between these syndromes may explain the challenges people are having in being believed, and accessing services," said Dr Maxwell.
Patients who were unable to have their symptoms addressed and treated in the absence of an agreed definition of ongoing COVID, particularly those who were not hospitalised and never formerly diagnosed, may in turn go on to encounter a psychological impact, the review said.
Another notable feature of ongoing COVID was a wide spectrum in how long patients reported feeling unwell.
"People asking for help and advice now are being told that they should recover within 2 to 3 weeks," said Dr Maxwell, "but we heard from people who are still unable to work, study, or care for dependents 7 months after their initial infection."
As part of the study, the NIHR CED held a focus group with 14 members of the Long COVID Facebook group, whose members include post-hospitalised and non-hospitalised people.
One of them, Joanna House, a climate change academic at the University of Bristol, developed COVID-19 in March after she and her partner, Ash, helped an elderly neighbour who had fallen in his home, and who was infected with the SARS-CoV-2 virus.
After 7 months, both Jo and Ash continue to experience ongoing COVID symptoms, including breathlessness, fatigue, tachycardia, and 'brain fog'.
They told the researchers that their experience of seeking help from health professionals had been mixed and at times frustrating because they had not been hospitalised and had not been tested at the time.
"Without formal recognition of long COVID, and the sort of support that would come with it, we feel in limbo," Jo told researchers.
Urgent Research Needed
The review authors said the challenge now was to design research that integrated the needs of those who have the condition with clinical models of care, and which recognise the social and psychological consequences of ongoing COVID.
Dr Philip Pearson, a respiratory consultant from Northampton, said the current lack of data about ongoing COVID needed to be addressed "swiftly".
He told the SMC briefing: "I have patients and colleagues with post-COVID symptoms. I need to know how to advise them, now.
"As a second wave begins, about the only things we can be sure of – there are going to be more admissions, there are going to be more ICU admissions, and there are going to be more people dealing with the longer-term effects of COVID infection."
Candace Imison, associate director of evidence and dissemination at the NIHR CED, said work was ongoing and additions to the website would be made as new evidence emerged, including a major update in January or February 2021.
She added: "I'm also pleased to say, as you'll probably be aware, that the importance of this topic is being picked up elsewhere – so NICE are currently developing a rapid guideline for this group of patients that should hopefully be available by the end of the year."