More than 40 per cent patients, who suffered Covid-19 disease, are at an increased risk of developing autoimmune disease such as rheumatoid arthritis, according to a study led by German researchers.

Autoimmune disease happens when the body's natural defence system can't tell the difference between your own cells and foreign cells, causing the body to mistakenly attack normal cells. There are more than 80 types of autoimmune diseases that affect a wide range of body parts.

The study, published in the preprint site Medrxiv and not peer-reviewed yet, found a 42.63 per cent higher likelihood of newly acquiring autoimmunity for patients who had suffered from Covid, in about three to 15 months after SARS-CoV-2 infection.

Further, those with any pre-existing autoimmune disease and Covid had a 23 per cent higher likelihood of being diagnosed with another autoimmune disease.

The patients suffered risk from the commonly known autoimmune disorders such as Hashimoto thyroiditis, rheumatoid arthritis, or Sjoegren syndrome

"SARS-CoV-2 infection is associated with an increased risk of developing new-onset autoimmune diseases after the acute phase of infection," Falko Tesch from the University Hospital Carl Gustav Carus Dresden in Germany was quoted as saying in the paper.

The team included 641,704 patients with Covid-19.

Comparing the incidence rates in the Covid and matched control groups, the researchers found that patients with a more severe course of Covid were at a greater risk for incident autoimmune diseases.

The findings also showed that the incidence rates of any autoimmune disease were higher among women compared to men, among older compared to younger individuals and among those without pre-existing autoimmune disease.

In addition, a higher incidence rate for a new-onset autoimmune disease was observed in children and adolescents than in adults with/without Covid. However, differences between age groups did not reach statistical significance, the team noted.

The study warrants more epidemiologic, clinical and basic science to determine whether SARS-CoV-2 infection triggers the onset of autoimmune disease, as well as to identify the underlying mechanisms and persons at risk, and to investigate effective means of prevention or early treatment, the researchers said.