Fatigue, ill-health and breathlessness are all common following Covid-19, but these symptoms appear to be unrelated to the severity of initial infection, according to a new study.

Published online in the Annals of the American Thoracic Society, the study examined the recovery of lung function and overall wellness in individuals who had varying degrees of Covid-19 severity.

Researchers looked at a number of measures of recovery for 153 patients who were followed in an outpatient clinic a median of 75 days after their Covid-19 diagnoses.

Patients' initial infection severity was graded as: (1) not requiring admission; (2) requiring hospital admission, or (3) requiring ICU care. Nearly half (74) of these patients required hospital admission during acute infection.

The researchers also examined the association between the patients' initial illness and abnormal chest x-ray, six-minute walk test distance and perception of maximal exertion during their follow-up appointments. Patients were also asked about whether they felt fatigued and whether they thought they had returned to full health. Their responses were graded using validated scales.

Not possible to predict who will have ongoing symptoms

Chest x-rays were examined in order to detect persistent infection or significant scarring (fibrosis) and performed CT imaging for patients with abnormal chest x-rays. Bloodwork was done to measure such indicators of disease as C-reactive protein, which increases when there is inflammation in the body. Statistical analyses were performed.

Dr Liam Townsend of the Department of Infectious Diseases, St James's Hospital and Department of Clinical Medicine, Trinity Translational Medicine Institute, Trinity College, Dublin, Ireland, said: "We were surprised by our findings. We expected a greater number of abnormal chest x-rays. We also expected the measures of ongoing ill-health and abnormal findings to be related to severity of initial infection, which was not the case."

The authors' findings suggest that Covid-19 does not cause significant fibrosis, with lung scarring seen on CT scans of only 4% of study participants, following x-ray detection of earlier abnormalities in a larger group. 62% felt they had not returned to full health, while 47% were classified as having fatigue.

Patients who felt they had to exert themselves during moderate exercise also reported they felt fatigued and in poor health. Patients' length of inpatient hospital stays and frailty were associated with covering less distance in the walk test.

Dr Townsend added: "These findings have implications for clinical care, in that they demonstrate the importance of following up all patients who were diagnosed with Covid-19, irrespective of severity of initial infection. It is not possible to predict who will have ongoing symptoms."