A new analysis of long COVID patients has identified five distinct subtypes that researchers say will help doctors diagnose the condition.
The new five-type index, developed by federal researchers with the National Institutes of Health’s RECOVER COVID Initiative, identified the most common symptoms in 14,000 people with long COVID, with data from an additional 4000 people added to the updated 2024 index.
By using the index, physicians and researchers can better understand the condition, which is difficult to treat and diagnose because no standard definitions or therapies have been developed. Doctors can use the index to offer more targeted care and help patients manage their symptoms more effectively.
The index may also help researchers find more treatments for long COVID. Because long COVID can affect so many different parts of the body, it will take time to fully understand how to treat it, but studies like this are making progress in the right direction, experts said.
This new index uses an updated point system, where points are allotted to each symptom in a list of the 44 most reported symptoms in people with likely long COVID based on how often they occur. Among people in the study with prior COVID infection, 2213 (18%) met the threshold for long COVID.
The 44 most common symptoms were then distributed among five subtypes, with each representing a difference in impact on quality of life and overall health. The most common symptoms were fatigue (85.8%), postexertional malaise (87.4%), and postexertional soreness (75.0%) — where persistent fatigue and discomfort occur after physical or mental exertion — dizziness (65.8%), brain fog (63.8%), gastrointestinal symptoms (59.3%), and palpitations (58%).
For those with prior COVID infection, symptoms were more prevalent in all cases.
Subtype 1
Those grouped into subtype 1 did not report a high incidence of impact on quality of life, physical health, or daily function. Only 21% of people in subtype 1 reported a “poor or fair quality of life.”
A change in smell or taste — usually a symptom that’s bothersome but doesn’t seriously impact overall health — was most present in subtype 1, with 100% of people in subtype 1 reporting it.
The only other symptoms in over 50% of people with subtype 1— which were 490 of the 2213 with prior COVID infection — were fatigue (66%), postexertional malaise (53%), and postexertional soreness (55%).
Though these two symptoms can certainly impact quality of life, they became much more prevalent in other subtypes.
Subtype 2
The prevalence of possibly debilitating symptoms like postexertional malaise (94%), fatigue (81%), and chronic cough (100%) rose dramatically in people grouped into subtype 2.
Plus, 25% of people in subtype 2 reported a “poor or fair quality of life. Postexertional malaise, I think, is probably one of the most debilitating of the symptoms. When somebody comes in and tells me that they’re tired and I think they might have long COVID, the first thing I try to do is see if it is postexertional malaise vs just postinfectious fatigue,” said Lisa Sanders, MD, medical director of Yale’s Long Covid Multidisciplinary Care Center in New Haven, Connecticut.
Postinfectious fatigue usually resolves much more quickly than postexertional malaise. The latter accounts for several symptoms as also associated with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). ME/CFS is a chronic illness that causes severe fatigue and makes it difficult for sufferers to perform routine, daily activities.
“Postexertional malaise is an additive symptom of ME/CFS, and that can take a long time to resolve,” Sanders added.
The similarity between these two symptoms highlights the importance that physicians must place in scrutinizing symptoms to a high degree when they suspect a patient of having long COVID, experts said. By doing so, clinicians can unveil the mask of overlapping symptoms between long COVID symptoms and symptoms of other illnesses.
Subtype 3
About 37% of people grouped in subtype 3 reported a poor or fair quality of life, a significant rise from subtypes 1 and 2.
Fatigue symptoms were reported by 92%, whereas 82% reported postexertional soreness, and 70% reported dizziness. Additionally, 100% of people in subtype 3 reported brain fog as a symptom.
Sanders said these symptoms are also common in people with postural orthostatic tachycardia syndrome. This condition results from a reduced volume of blood returning to the heart after standing up, which leads to an abnormally fast heart rate. Palpitations and fainting can then occur.
Brain fog can be especially debilitating in people who are used to multitasking. With brain fog, people accustomed to easily alternating between tasks or doing multiple tasks at once can only do one thing at a time. This can cause stress and an overload of thoughts, even precipitating a change in careers if severe enough.
Though brain fog tends to resolve within 6-9 months after infection, it can last up to 18 months or more. Experts say doctors should always be on the lookout if a patient complains they have trouble concentrating or multitasking in the months after a COVID infection. A neurological exam and cognitive testing can identify abnormalities in brain function.
Subtype 4
About 40% of people in the study grouped into subtype 4 reported a poor or fair quality of life, a modest increase from those with subtype 3. About 65% reported symptoms of brain fog and 92% reported palpitations.
Dizziness was also prevalent at 71%, whereas 60% reported gastrointestinal issues, and 36% said they experienced fever, sweats, and chills.
Nearly 700 of the 2213 people fell into this subtype group, by far the highest number.
Subtype 5
A whopping 66% of people in subtype 5 reported a poor to fair quality of life. These people usually reported multisystem symptoms.
In terms of prevalence rises across the spectrum of 44 common long COVID symptoms, 99% reported shortness of breath; 98%, postexertional soreness; 94%, dizziness; 92%, postexertional malaise; 80%, GI problems; 78%, weakness; and 69%, chest pain.
A higher proportion of Hispanic and multiracial participants were classified as having subtype 5. Also, according to the study, “higher proportions of unvaccinated participants and those with SARS-CoV-2 infection before circulation of the Omicron variant were in subtype 5.”
This suggests the severity of the Delta variant of COVID-19 be linked to some of the worst long COVID symptoms, but further study would have to be done to conclusively determine may be just a correlation.
When Do Symptoms Resolve?
According to Sanders, around 17 million Americans are thought to have long COVID. Although 90%-100% of people typically recover within 3 years, that still leaves possibly around 5% of those who don’t recover.
“What people usually say is, ‘I got COVID, and I never quite recovered,” Sanders said.
“Five percent of 17 million turns out to be a lot. It’s a lot of suffering,” she added. “I would say that the most common symptoms are fatigue, brain fog, anosmia or dysgeusia, and sleep disorders,” as evidenced by the high percentage of people in certain subtypes of the study reporting a poor quality of life.