As people recover from Covid-19 amid the global pandemic, many continue to report a wide array of persistent symptoms, known as post-acute sequelae of SARS-CoV-2 (PASC) or “long Covid”. Now, a study looked at the prevalence of this phenomenon in the US, finding that about 30% of 1,000 patients analyzed developed the condition.

There’s no universally accepted definition of long Covid, but researchers increasingly feel like understanding why it happens and fighting it is key at this stage of the pandemic. The World Health Organization (WHO) defines “post Covid-19 condition” when people are still having symptoms three months after an initial bout of Covid, while the UK’s National Health Service suggests refers to symptoms that last more than four weeks as “post-Covid syndrome.”

Its prevalence has been difficult to estimate, mainly because of the lack of a single way to identify cases and other factors such as demographics and when the data was collected. Back in March, US lawmakers said that the Centers for Disease Control and Prevention (CDC) won’t have reliable data on long Covid for another two years.

However, researchers have been trying to estimate how significant the condition is even with imperfect information. A review from 2021 by University of Michigan researchers estimated the global prevalence to be 43%, based on data from 50 studies. Among patients who needed hospitalization, the prevalence increased to 57%. Women were more affected by men.

Now, a new study in the US has found that as many as 30% of people infected with Covid-19 developed long Covid. Researchers from the University of California, Los Angeles (UCLA) tracked the evolution of 1,038 patients between April 2020 and February 2021 and found that 309 of them registered symptoms of long Covid.

“This study illustrates the need to follow diverse patient populations longitudinally to understand the Long COVID disease trajectory and evaluate how individual factors such as pre-existing co-morbidities, sociodemographic factors, vaccination status and virus variant type affect type and persistence of Long COVID symptoms,” Sun Yoo, study lead, said in a statement.

Looking into long Covid

In April 2020, UCLA created a COVID Ambulatory Monitoring Program to clinically care for the diverse group of COVID-19 patients discharged from the hospital as well as high-risk COVID-19 patients cared for in the outpatient setting. Patients were eligible from all the UCLA Health system, which includes over 40 primary care clinics.

A questionnaire collected information on functional status prior to COVID-19 infection and post-COVID clinical symptoms. Follow-up monitoring continued at 30, 60, and 90 days. Of the 1,296 enrolled in the program, 1,038 patients completed the follow-up surveys and were included in the study. The mean age of the cohort was 60 years.

A person was considered to have long Covid if they reported persistent symptoms on questionnaires 60 or 90 days after infection or hospitalization. This was the case for 309 patients in the study, 29.8% of the total. The most persistent symptoms were fatigue and shortness of breath in hospitalized persons and loss of smell in outpatients.

People covered by Medicaid, as opposed to commercial health insurance were less likely to develop long Covid, while those with a track of hospitalization, diabetes, and higher body mass index had higher chances of developing the condition. Surprisingly, ethnicity, older age, and socioeconomic status weren’t associated with long Covid.

“Because persistent symptoms can be subjective in nature, we need better tools to accurately diagnose Long COVID and to differentiate it from exacerbations of other emerging or chronic conditions. Finally, we need to ensure equitable access to outpatient Long COVID care,” Sun Yoo said in a statement.

There’s still much we have to learn about this condition, but it seems to be a serious long-term problem — one that we’d be wise to consider when assessing our infection risk.

The report was published in the Journal of General Internal Medicine.