The new coronavirus SARS-CoV-2 is as fast-spreading as it is enigmatic -- with those afflicted experiencing everything from no symptoms to a scratchy throat to life-threatening pneumonia. While it seems that most infections lead to only mild cases of Covid-19, a significant portion of the tens of millions of people who have “recovered” suffer from lingering and sometimes debilitating heart, lung and nervous-system impairments. As researchers try to measure the durability and depth of what’s being called “long Covid,” patient anecdotes and a burgeoning number of post–Covid clinics indicate recovery can be slow and painful, likely meaning the pandemic will sap health resources long after it ends.

1. What are the persistent ailments?

Surveys and preliminary research indicate the most commonly reported include fatigue, breathlessness, headache, insomnia, chest pain, joint pain, coughing, loss of taste and smell, intermittent fevers and skin rashes. Less frequently, hearing problems, “brain fog,” mental-health problems and hair loss have been reported, though these have yet to be confirmed by studies. Besides these general symptoms, specific organ dysfunction has been reported, involving primarily the heart, lungs, and brain -- even among those whose acute infection led to no discernible symptoms. But the science is still evolving and there’s no consensus yet on a clinical definition for long, or post-acute, Covid.

2. What’s the risk?

It probably increases with the severity of the initial bout of Covid-19. For instance, two-thirds of patients who had mild-to-moderate Covid-19 reported at least one persistent symptom 60 days after falling ill, according to a French study that followed 150 non-critical patients from March to June. A similarly sized study of older, more seriously ill hospital patients in Italy found 87% had at least one symptom, particularly fatigue and shortness of breath, an average of two months later. A survey in the U.S. found 35% of patients who weren’t hospitalized had not returned to normal health as long as three weeks after testing positive. Among 18-to-34-year-olds with no chronic medical conditions, the figure was 19%.

3. How big a problem is this?

We don’t know yet because Covid-19 is a new disease. Researchers haven’t studied enough patients over a long enough period of time to know what the full range of long-term effects, or sequelae, might be. Nor do they know what proportion of patients will suffer from them or for how long. The uncertainties have sometimes led to what so-called long haulers describe as medical gaslighting by health professionals who don’t take their complaints seriously, especially if the patient is a woman. Early findings and the demand for specialized post-Covid clinics to help survivors deal with scarred lungs, chronic heart damage, post-viral fatigue and other debilitating conditions indicate a significant prevalence. The social and economic impact would be magnified if people end up enduring years or decades of coronavirus-related disability. Some researchers say the pandemic may spur chronic fatigue syndrome, also called myalgic encephalomyelitis or ME, and neurodegenerative diseases like Parkinson’s.

4. Do other viruses cause prolonged illness?

Yes. Post-viral syndromes occur after many viral infections, including the common cold, influenza, HIV, infectious mononucleosis, measles and hepatitis B. Diabetes and other long-term consequences were observed in survivors of severe acute respiratory syndrome, which is caused by a related coronavirus. A Canadian study found 21 health-care workers from Toronto had post-viral symptoms for as long as three years after catching SARS in 2003, and were unable to return to their usual work. Some people who were hospitalized with SARS in Hong Kong still had impaired lung function two years later, a study of 55 patients published in 2010 found. Still, it’s not known yet whether the lessons of SARS are applicable to Covid-19. What’s novel about SARS-CoV-2 is the broad spectrum of symptoms that are being reported and the duration of months not weeks.

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©2020 Bloomberg L.P.