Hundreds of thousands of Americans have sought medical care for post-Covid health problems that they had not been diagnosed with before becoming infected, according to the largest study to date of long-term symptoms.

The study, tracking the health insurance records of nearly two million Americans who contracted Covid-19 last year, found that one month or more after their infection, almost one- quarter — 23% — of them sought treatment for new conditions. Those affected were all ages, including children.

Their most common new health problems were pain, including in nerves and muscles; breathing difficulties; high cholesterol; malaise and fatigue; and high blood pressure. Other issues included intestinal symptoms; migraines; skin problems; heart abnormalities; sleep disorders; and mental health conditions like anxiety and depression. Post-Covid problems were common even among people who had not gotten sick from the virus at all.

While nearly half of patients who were hospitalised for Covid-19 experienced subsequent medical issues, so did 27% of people who had mild or moderate symptoms and 19% of those who said they were asymptomatic, according to the study by non-profit FAIR Health. Robin Gelburd, president of the organisation, said the fact that asymptomatic people can have post-Covid symptoms is important to emphasise, so that patients can know to consider the possibility that some health issues may actually be after-effects of Covid. “There are some people who may not have even known they had Covid,” she said. More than half of the 1,959,982 Covid patients whose records were evaluated reported no symptoms. Forty percent had symptoms but didn’t require hospitalisation, including 1% whose only symptom was loss of taste or smell; only 5% were hospitalised.