Nearly a third of hospital patients with Covid-19 end up being readmitted within a month of being home.
Hospital patients with Covid-19 have "increased rates of multiorgan dysfunction" compared with the general population, researchers found.
The study also found that within 140 days more than one in ten patients had died.
They said that people who have post-Covid syndrome need to get "integrated rather than organ or disease specific" care.
The study, published in The BMJ, examined data on almost 48,000 patients who had been admitted to hospital with Covid-19 and were sent home before August 31 last year.
They also examined information on the same number of people - or so-called "matched controls" - who had not been admitted to hospital.
How did the study work?
Experts, led by researchers from the University of Leicester, examined whether people needed to be readmitted, death rates and diagnoses of respiratory, cardiovascular, metabolic, kidney and liver diseases.
After an average follow-up period of 140 days, nearly a third - or 14,060 of 47,780 - were readmitted.
And during the follow-up period more than one in 10 (5,875) died after discharge.
Rates of respiratory disease, diabetes and cardiovascular disease were also significantly raised in Covid-19 patients, the authors said.
The rate of multiorgan dysfunction after discharge was greater among patients under the age of 70 compared with those over 70, they found, and the rate was higher in ethnic minority groups than in the white population.
The authors called for more research to be done to "establish risk factors".
‘Urgent research is needed’
"Individuals discharged from hospital after acute Covid-19 had an increased risk of mortality, readmission, and multiorgan dysfunction compared with similar individuals in the general population," they wrote.
"And the relative increase in risk was not confined to the elderly and was not uniform across ethnic groups.
"Urgent research is needed to understand the risk factors for post-Covid syndrome so that treatment can be targeted better to demographically and clinically at risk populations."