Two or More COVID Infections Linked To Fivefold Higher Odds of Respiratory Diagnosis, Canadian Study Finds

Adults who reported having COVID-19 two or more times had about five times the odds of being diagnosed with a new respiratory condition compared with those who reported no infections, according to a Canadian government study. The research adds to evidence that repeated SARS-CoV-2 infections are associated with newly diagnosed health conditions.

The study, published this week in the Canada Communicable Disease Report, was carried out by researchers from the Public Health Agency of Canada and Statistics Canada. It analysed data from 8,809 adults who took part in the Canadian COVID-19 Antibody and Health Survey and its follow-up questionnaire between April 2022 and June 2023.

What the Study Found

Participants were asked how many confirmed or suspected COVID-19 infections they had experienced. They were also asked whether a healthcare professional had diagnosed them with any of 21 conditions, including respiratory, cardiovascular, neurological and musculoskeletal disorders, since their first infection.

Around 47 per cent reported one infection, while roughly 20 per cent reported two or more. Those with repeat infections had 76 per cent higher odds of receiving a new diagnosis of any kind than people who reported no infections.

The researchers stressed that the findings show an association and do not establish that reinfection directly caused the conditions.

Back Problems and Lingering Symptoms Also Flagged

Repeat infections were associated with nearly four times the odds of a new back-problem diagnosis. The researchers noted that the confidence intervals around this figure were wide, meaning there is more uncertainty about the precise scale of the association.

People whose first infection caused symptoms severe enough to disrupt daily life had 63 per cent higher odds of being diagnosed with a new condition. Those still experiencing symptoms three months or more after infection had more than triple the odds of a fresh diagnosis.

The researchers cautioned that these findings may partly reflect greater healthcare use and opportunities for diagnosis.

Researchers Urge Caution Over Limitations

The study's authors were careful to stress that their findings show an association, not proof that reinfection directly causes new illness. The infection and health data were self-reported, leaving room for inaccurate recall, misclassification and other potential biases.

Participants were asked to include both infections confirmed by testing and infections they suspected were COVID-19 because of symptoms or contact with a case.

Some participants who reported no infections may in fact have had undiagnosed or symptomless COVID-19.

The authors also pointed out that people with severe or ongoing symptoms may have visited doctors more often, which could itself increase the chance of an unrelated condition being picked up and diagnosed.

Despite the caveats, the researchers said the results contribute to evidence that can inform future public-health practice, clinical decision-making and research.

They called for further investigation into repeated infections and the factors that might explain the pattern, including how infection characteristics and longer-term symptoms relate to new diagnoses. The findings come as the NHS continues to provide guidance and treatment for people experiencing long COVID.

For readers, the study adds to evidence that repeated SARS-CoV-2 infections may be associated with newly diagnosed health conditions.

Given the wide confidence intervals around some findings and the study's observational design, however, the precise scale of individual associations remains uncertain, and the results should not be interpreted as proof that repeated COVID-19 infections directly cause new health conditions.