Half of all patients requiring hospital treatment for Covid-19 go on to experience long Covid, a major US study of nearly two million patients found.
Almost one in five people whose infection was classified as symptomatic also had lingering effects from the virus.
Long Covid is a term used to describe ill-effects that continue for weeks or even months after contracting coronavirus.
Based on healthcare insurance claims, the study by Fair Health found that pain was the most common long Covid symptom, with breathing difficulties and high blood pressure also often seen.
In its white paper report, A Detailed Study of Patients with Long-Haul Covid, Fair Health said “post-Covid” symptoms were more common in individuals whose initial symptoms were more severe.
Of patients admitted to hospital with Covid-19, the proportion with "a post-Covid condition was 50 per cent; of patients who were symptomatic but not hospitalised, 27.5 per cent; and of patients who were asymptomatic, 19 per cent," the report stated.
Fair Health classified cases as asymptomatic when there was no insurance claim made over symptoms, meaning that no medical care was sought. However, it said that in some of these cases, the patient may actually have experienced symptoms.
The study looked at the presence of 38 long Covid symptoms 30 days after initial diagnosis in 1,959,982 Covid-19 patients – said to be the largest number of individuals analysed together for long Covid – who received a diagnosis between February and December last year.
Patients battle pain, fatigue and breathing troubles
Among all Covid-19 patients included in the study, Fair Health – a non-profit organisation that helps consumers understand healthcare costs and cover – said 23.2 per cent had at least one long Covid symptom.
The most common was pain, affecting 5.1 per cent of all Covid-19 patients, followed by breathing difficulties, hyperlipidaemia (elevated levels of fats in the blood), malaise and fatigue, and hypertension or high blood pressure.
While doctors’ understanding of long Covid is still developing, the condition is known to affect people for as long as nine months after the initial diagnosis, previous research has found.
Fair Health cited other findings indicating that between 10 per cent and 30 per cent of Covid-19 patients experience the condition in some form, with a wide variety of symptoms reported.
These include ongoing neurological problems that may affect a person’s ability to concentrate, muscle pain, kidney problems and joint pain.
Dr Andrew Freedman, an infectious diseases specialist at Cardiff University in the UK, said the numbers of people with long-Covid appeared to be higher than with some other respiratory infections, such as influenza.
It remained poorly understood, however, and he said it was likely to represent the effects of multiple conditions.
“Long-Covid is very heterogeneous,” he said. “Some of it is just post-viral fatigue. Some patients will have been sicker – they may have organ damage [such as] lung damage, heart damage. It’s organic illness that may take a long time to recover or may never recover. Post ITU syndrome – people seriously unwell – it may take months or years to recover from that.”
The mental toll of long Covid
The new study reported that issues ranging from skin problems to tinnitus, heart problems and anaemia were linked to long Covid.
Patients’ mental health is sometimes affected, and Fair Health reported that, of the long Covid mental health conditions it looked at, anxiety was the most common, followed by depression.
Several possible causes of long Covid are being suggested, including reduced effectiveness of the immune system, a reinfection of the virus and ongoing inflammation.
Post-traumatic stress and the lingering effects of inactivity or being confined to bed are other potential factors.
Of all the types of pre-existing conditions considered, intellectual disabilities were most heavily linked to an increased risk of death 30 days after diagnosis.
Young people at risk of heart problems
A notable finding of the report was the relatively high prevalence of heart inflammation as a long Covid symptom in younger people, with 25.4 per cent of those reporting this being between 19 and 29 years old.
“This was disproportionate to that age group’s share of the population of Covid-19 patients overall, 20.9 per cent,” the report stated.
“Myocardial conditions such as cardiac inflammation are usually associated with older age.”
Overall, 55 per cent of infections were classed as asymptomatic, with 39 per cent symptomatic, 5 per cent involving hospital admission and the remaining per cent involving only the loss of the sense of taste or smell.
The over-70s were the only group in which symptomatic infections outnumbered asymptomatic, and they also had the highest rates of hospital admissions, at more than 15 per cent.
Another finding of the report was that more than two thirds of long Covid symptoms looked at were found more commonly in females than in males.
The report also said that Covid-19 patients admitted to hospital and discharged were 46 times as likely to die 30 or more days after diagnosis than patients who had not been admitted to hospital.