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People who tested positive for SARS-CoV-2, the virus that causes COVID-19, had greater use of the health care system, including more time in hospital, in the months after infection, compared with their peers who tested negative, according to a study of more than half a million Ontarians.

The study, published in the CMAJ on Monday, found, on average, the number of days in hospital, outpatient visits and home care visits among Ontarians who had tested positive for the virus were modestly higher than those who had tested negative.

But the difference was stark when it came to the top 1 per cent of people who used the health care system the most. Among this 1 per cent, those who were infected spent about seven additional days in hospital a year compared to those of the same age, sex, socioeconomic scores, vaccination status, and other characteristics who tested negative, said lead author Candace McNaughton, an emergency physician at Toronto’s Sunnybrook Research Institute.

Moreover, based on estimates that nearly half of all Canadians were infected by the first few months of 2022, she calculated a family doctor who had 20 clinic visits a day before the pandemic would now need to find time and resources for 100 more clinic visits a year.

While these are relatively small individual increases, the effect is large on a cumulative scale, she said. This rise in health care use could lead to heart attack or stroke patients having to wait in emergency department hallways for an available hospital bed, or even longer wait times to see family physicians, Dr. McNaughton said.

“Our health care system is already experiencing extraordinary challenges, with nursing shortages, surgical backlogs, emergency department closures, challenges accessing primary care, et cetera,” she said, noting she is concerned that it will not be able to handle an increased demand.

The study looked at data from ICES (formerly the Institute for Clinical Evaluative Sciences) for 531 ,702 adults in Ontario who had a PCR test between January, 2020, and March, 2021.

The researchers did not examine why patients used the health care system more after infection. But from what she has observed clinically, Dr. McNaughton said it appears certain patients become quite frail after infection, including some as young as in their 20s.

Patients come to the emergency department with conditions that aren’t immediately easy to tie to their original infection, such as heart palpitations, lung or kidney problems and brain fog, she said. “It sort of runs the gamut because the virus can affect sort of so many different organs.”

Most people with lingering symptoms after COVID-19 do get better, however, said Manali Mukherjee, an assistant professor of the department of medicine at Hamilton’s McMaster University, who was not involved in the CMAJ study.

In her own research, Dr. Mukherjee followed more than 100 people who had tested positive on a PCR test. Many had symptoms, such as extreme fatigue and coughing, at three and six months after infection, and inflammatory markers in their blood. But about 75 per cent were better at 12 months.

So while health care utilization may increase in the first few months after infection, she suggested most people will recover.

However, the remaining subset of about 25 per cent of participants she studied had persistent symptoms at 12 months, as well as inflammatory markers and certain autoantibodies, which are antibodies that target one’s own tissues and organs. Autoantibodies are associated with systemic disease, like autoimmune diseases which develop over time, Dr. Mukherjee said.

That doesn’t mean these people have an autoimmune disease, she said. “But there is always this fear that they might develop an autoimmune disease which will lead to massive health care usage.”

She suggested those who still are not well by 12 months should see a rheumatologist to assess the need for early intervention.