People with prior illness more likely to report longer symptoms after COVID-19 infection, research finds

A study from King's College London, which is published on the pre-print server MedRxiv and has not been peer-reviewed, shows that while two thirds of individuals with post-COVID illness were healthy before infection, individuals with long illness duration were significantly more likely to have similar symptoms one to two months before developing COVID-19.

Most people with COVID-19 recover completely within a few days or weeks. However, some report ongoing symptoms including fatigue, "brain fog," sneezing, a runny nose and headache long after infection. For some individuals, this may manifest as long COVID.

In this study, researchers first analyzed data from over 23,000 ZOE Symptom Study app users, who reported their health (whether healthy or unhealthy) at least once weekly, both before and after they had COVID-19. They found that individuals who had symptoms before they caught SARS-CoV-2 infection were significantly more likely to have a longer illness duration.

The researchers then assessed 1,350 adults who reported long-term symptoms after COVID-19 (at least eight weeks, with nearly a thousand having symptoms for more than 12 weeks), matched with 1,350 individuals whose symptoms had resolved within four weeks.

They found that two-thirds of participants with long illness duration had been well before they experienced COVID-19. However, one third had similar symptoms beforehand, twice as likely as individuals with short illness (32.5% vs. 18.0%).

Consistent with this, individuals with long illness duration were also significantly more likely to have prior physical and mental health comorbidities. This suggests that at least for some individuals, their long symptoms after COVID-19 might be due to other underlying serious illnesses, such as asthma or lung disease, rather than due to SARS-CoV-2 infection itself.

"Individuals with long symptom duration after SARS-CoV-2 need careful and holistic assessment. For many, their symptoms are new, and represent an ongoing legacy after their COVID-19 illness. But for others, their symptoms may be ongoing manifestations of a prior non-COVID illness, such as asthma or depression. It is important that that these other conditions are not missed, as they have well-established and effective treatments," says author Professor Emma Duncan, School of Life Course & Population Sciences

She added, "If all long duration symptoms after COVID-19 are blamed automatically on SARS-CoV-2 infection, then we will miss the opportunity to treat other illnesses appropriately, and to help patients recover as expeditiously as possible."