What is Long Covid?

What is Long COVID?

Long COVID refers to persistent symptoms lasting longer than a month after recovering from acute infection by SARS-CoV-2. It is classified as a post-infectious syndrome with different subtypes. Fatigue is the most common symptom of Long COVID.


What is Long COVID?

Do You Have Long COVID?

Receiving a diagnosis of post-acute sequelae of SARS-CoV-2 (PASC), referred to as “Long COVID,” is a serious concern. You can feel unwell for months or years, leading to a sense of despair of ever returning to normal. The ICD-10-CM code for Long COVID is U09.9. The code for the sequelae of any infectious disease is B94.8. The World Health Organization (WHO) established the International Classification of Diseases (ICD) coding system to provide healthcare professionals, including doctors, with a universal system for organizing complex medical terms, procedures, and diagnoses using alphanumeric codes. Your doctor may record one or both codes in your medical chart.

Medical coding occurs during doctor office visits and hospital visits. The latest version, ICD-11, took effect on January 1, 2022. However, most clinics still use ICD-10 codes. In addition, your doctor will identify and assign diagnostic codes to additional symptoms you have. For example, Long COVID is labeled as “U09.9,” and you may experience ongoing fatigue (780.71), headaches (R51.9), and muscle pain referred to as myalgia (M79.10) by your doctor.

What Is Long COVID, and What Does It Mean?

Long COVID is the term patients give any group of symptoms following infection by SARS-CoV-2 that persists beyond the acute stage and lasts for an extended time. But this definition is too generalized. Can we be more specific? Are there similar conditions? How long must symptoms persist to establish a diagnosis, and can we rule out other conditions?

Are There Similar Conditions?

While Long COVID is a well-known post-acute viral illness, it’s not the only one. There are several others. Here are a few with similar symptoms to Long COVID:

Mononucleosis (Mono): Called the “kissing disease,” mononucleosis is common, especially among young adolescents who become infected through kissing, often when they begin dating the opposite sex. It’s caused by the human herpes virus 4 (HHV-4), associated with Epstein-Barr Virus (EBV). Mononucleosis is widespread, with 90% of adults testing positive for previous exposure. However, not everyone who is exposed gets sick. Some have no symptoms or mild ones. Common symptoms include a fever, sore throat, swollen lymph nodes, and severe fatigue. Acute EBV lasts two to four weeks. Most cases resolve without complications. Though, some experience a prolonged recovery requiring rest because of fatigue and weakness lasting 3 to 6 months. EBV can also trigger autoimmunity and is suspected of causing MS and playing a role in ME/CFS. Reactivation of dormant EBV is a possible cause of Long COVID.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): ME/CFS shares similar symptoms with Long COVID. However, not all Long COVID sufferers were previously diagnosed with ME/CFS, and not all had documented EBV. Symptoms can worsen even with light activity, such as folding clothes or standing upright. Many ME/CFS patients are bedbound, unable to perform even light household chores, much like those with Long COVID.

ME/CFS Symptoms

Non-restorative sleep
Brain fog/cognitive impairment
Joint pain
Inflamed lymph nodes
Neurological abnormalities
Reduced organ function
Sensitivity to light, sound, odors, chemicals, foods, and medications
Muscle pain
Sore throat

Postural Orthostatic Tachycardia Syndrome (POTS): This is a dysfunction of the autonomic nervous system, and the most common dysautonomia condition. Common symptoms of POTS include a rapid heart rate, spikes in blood pressure, dizziness, and fainting. Even light activities, such as house cleaning, can be exhausting for POTS patients. Viral infections like EBV and SARS-CoV-2 can cause POTS, and it’s also linked to Lyme disease. In addition to infections, POTS symptoms can occur in conditions like diabetes, heavy metal toxicity, and certain autoimmune disorders like Sjogren’s syndrome. POTS shares many symptoms with Long COVID.

Post-Intensive Care Syndrome (PICS): This condition, characterized by lingering health problems following a critical illness in a hospital ICU, can result in symptoms persisting for weeks, months, or even several years, like Long COVID. It’s worth noting that Long COVID shares similar symptoms, but not all Long COVID sufferers were ICU patients. Only 25% of Long COVID patients who received the U09.9 diagnosis were hospitalized with acute infection.

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Post-Acute Infection Syndrome (PAIS): The unexplained post-acute infection syndrome (PAIS) list is not limited to mono, POTS, and ME/CFS. Other PAISs include lingering symptoms after Dengue, Polio, Chikungunya, Ebola, H1N1 Influenza, and the original SARS. Though unrelenting fatigue is their central symptom, other shared clinical features include unrefreshed sleep, exercise intolerance, flu-like malaise, and musculoskeletal pain.

PAIS Symptoms

· Exertion intolerance
· Persistent fatigue, even with rest
· Flu-like symptoms and ‘sickness behavior’: subjective fever, muscle pain, feeling sick, malaise, sweating, and irritability.
· Neurological and neurocognitive symptoms: brain fog, impaired concentration or memory, trouble finding words.
· Rheumatologic symptoms: chronic or recurrent joint pain
· Condition-specific symptoms: eye problems post-Ebola, IBS post-Giardia, anosmia and ageusia post-COVID-19, motor disturbances post-polio and post-West Nile virus

Symptoms Unique to Long COVID

Is Long COVID considered another PAIS? Though similar, clinical differences set these conditions apart. In particular, the persistent loss of taste and smell distinguishes Long COVID from other PASCs. Altered taste and smell can cause severe psychological disruption and reduced well-being.

About half of acute COVID patients experience some loss of smell and taste, but most recover within weeks. However, around 10% have persistent problems with anosmia (loss of smell), hyposmia (reduced smell), or dysgeusia (distortion of basic tastes) that lasts for months.

Though little is medically known about the impact of the lack of taste and smell among Long COVID patients, online support sites like Fifthsense and the AbScent Facebook group help individuals make sense of their altered sensory experience. 

Is Long COVID a Disease, a Condition, or a Syndrome?

COVID molecule

A syndrome is a recognizable complex of symptoms and clinical findings associated with a particular disease or disorder, including examination findings and laboratory test results. Long COVID is classified as a post-COVID syndrome with four major subtypes, each having symptoms and universal findings.

SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is the communicable infectious disease responsible for the COVID-19 pandemic. The research remains unsure of what causes Long COVID. Is it from lingering SARS-CoV-2 viruses, reactivation of EBV, or an immunological disruption that doesn’t return to normal after infection?

What Are the Four Subtypes of Long COVID?

While there are no specific subtypes, researchers gathered information from over 20,000 COVID patients and analyzed them using a computer-based program for common diagnoses. They narrowed down over 200 Long COVID symptoms into four common categories: neurological, cardiopulmonary, respiratory, and gastrointestinal.

4 Types of Long COVID

Type 1: Heart, Kidney, and circulatory problems

Type 2: Lung conditions, sleep disorders, and anxiety

Type 3: Muscle pain, connective tissue disorders, and nervous system disorders

Type 4: Digestive and respiratory problems

A study published in Nature Medicine used machine learning to categorize PASC into patterns and grouped them into four clusters. The study aimed to define these four groups to help healthcare providers better serve patients during the early and mid-stages of illness.

Cluster 1 – Heart and Kidney: These patients primarily exhibited cardiac and renal-related symptoms, such as renal failure, anemia, and electrolyte imbalances. This group had an average age of 65, with a majority being men and experiencing more severe illness. They also took more prescription medications than the other groups.

Cluster 2 – Respiratory, Sleep, and Anxiety: This group primarily experienced respiratory symptoms, including acute upper respiratory symptoms and chronic lung disease. The average age was 51, and they were primarily women. They took anti-allergy medications, steroid inhalers, and anti-inflammatory drugs. Cluster 3 – Musculoskeletal and Nervous: The main symptoms in this group included musculoskeletal pain, headaches, and sleep disturbances. They were predominantly female, with an average age was 57, and had a higher usage of pain relievers compared to other groups.

Cluster 4 – Digestive and Respiratory: With an average age was 54, this cluster primarily consisted of women. Despite having the highest rate of emergency room visits, they had the lowest rate for ventilation usage and critical care. They had less underlying medical conditions and took more prescription drugs for the digestive system. Overall, they had the mildest acute symptoms.

Clusters of Symptoms Differ by Age

Another group of researchers organized symptoms into age-stratified clusters: a neurological cluster, a cardiopulmonary cluster, a respiratory cluster, a gastrointestinal cluster, and a comorbidity cluster.  

  • Patients under 21 years of age: neurological cluster, respiratory cluster, cardiopulmonary cluster, and gastrointestinal cluster
  • Patients 21-45 years of age: neurological cluster, cardiopulmonary cluster, and a comorbidity cluster
  • Patients 48-65 years of age: cardiopulmonary, comorbidity, and neurological clusters
  • Patients 66 years of age and older: a larger comorbidity cluster, plus cardiopulmonary and neurological clusters

Younger patients had fewer comorbidities, a condition when more than one disease occurs at the same time. The number and severity of comorbidities increased with age.

Main Symptoms of Long COVID

Long COVID symptoms are well-documented, with over 200 listed by the American Medical Association (AMA). The question is, which of these symptoms are the most important?

Persistent Fatigue Is Central to Long COVID

Fatigue is the most common and central symptom of Long COVID. Patients experience persistent exhaustion, impaired fitness, and post-exertional malaise, feeling tired without having done anything. If they do something, they tire easily and find recovery difficult. Even normal housework can be exhausting, taking several days to recover from. They may feel sleepy even during the daytime but don’t wake refreshed or feel better after a nap.

Impaired Fitness and Post-Exertional Malaise

Though not all Long COVID patients experience debilitating fatigue, impaired fitness is the most common symptom for those without severe fatigue. Many also suffer from post-exertional malaise after doing housework or mild exercise, leaving them bedridden for the rest of the day after just twenty minutes of mild activity around the house.

Brain Fog: Long COVID sufferers have “brain fog,” the sense of feeling mentally sluggish with fuzzy thinking. A Scientific American article calls for more attention to brain fog, a condition that includes mental confusion, concentration difficulty, forgetfulness, anxiety, and dull headaches.

Venous Insufficiency: Chronic venous insufficiency occurs when the veins in your legs are damaged or compromised. Leg symptoms are often worse when standing and are better when lying down. They feel heavy and may tingle, itch, and have rashes or discoloration.

Unexplained Achiness and Soreness: Chronic infection, including with SARS-CoV-2, is associated with the activation of inflammatory genes and the persistence of proinflammatory cytokines like cytotoxic CD8+ T-lymphocytes.

Changes in Heart Rate: 14% of Long COVID patients have elevated heart rates for months after initial infection.

Episodic and Relapsing: You start to get better. One day, you wake up feeling like your former self. You want to go for a run or hit the gym. You prepare a full breakfast and organize your closet. For the moment, you feel like your old self again. You get your gym bag ready, but as you head for the door, it feels as if it’s a hundred miles away. When you reach for the door handle, you’re so weak you can barely turn it. This is known as an exacerbation due to activity, and it’s not uncommon in ME/CFS and Long COVID. Patients often develop an aversion to trying anything new; some can’t even do normal housework because of exacerbating symptoms.

Do I Have Long COVID or Something Else?

Since there is no definitive laboratory test and so many symptoms, a diagnosis is made based on a confirmed history of SARS-CoV-2 infection, your general presentation, test results at a clinic or private physician’s office, and a specific set of symptoms.

You don’t want to be labeled as having Long COVID just because you experience exasperating symptoms. Here are some questions to ask yourself:

  • Have you had the same symptoms before the pandemic?
  • Were you diagnosed with a chronic condition like multiple sclerosis, rheumatoid arthritis, or ME/CFS before the pandemic?
  • Did you have symptoms of acute COVID during the pandemic?
  • Did you have a positive rapid antigen test?
  • Did you get another laboratory test?
  • Do you have the symptom profile, especially the cardinal ones like lack of taste and smell?
  • Have your symptoms persisted for more than four weeks? More than six months?

12 Hallmark Symptoms Doctors Use to Diagnose Long COVID 

The JAMA study identified twelve symptoms in Long COVID patients six months after initial infection. Think of these as hallmarks of Long COVID. You don’t have to have them all, but if you have at least six, you likely have Long COVID.

  1. Persistent fatigue
  2. Post-exertional malaise (fatigue exacerbated by even minor physical activity)
  3. Disruption of smell and taste
  4. Chronic cough
  5. Brain fog
  6. Thirst
  7. Palpitations
  8. Chest pain
  9. Diminished or absence of sexual desire
  10. Dizziness/light-headedness
  11. Gastrointestinal symptoms, including abdominal pain and diarrhea
  12. Abnormal movements, including tremors

If you answer yes to these questions, you likely have Long COVID. Otherwise, you could have a different condition with symptoms that overlap or mimic Long COVID, like an autoimmune disorder. Not everyone fits into easily identifiable groups. Long COVID has a wide range of symptoms and many individual variations that span multiple organ systems. It’s best not to try to diagnose yourself. Seek a doctor knowledgeable in chronic viral infections, autonomic nervous system disorders, or experience in treating COVID for a diagnosis.


Close to one billion people worldwide have been infected with SARS-CoV-2. It’s expected that some will have PAIS symptoms for weeks or a few months after infection. SARS-CoV-2 infection may cause serious complications that significantly influence a patient’s future health. 

Some individuals will not recover entirely but experience chronic, ongoing symptoms. Some will have relapsing episodes because, in Long COVID, there’s no steady reduction of symptoms over time, resulting in a complete return to normal. It’s a progression to a “new normal.”

Selected References

Burges Watson, D. L., Campbell, M., Hopkins, C., Smith, B., Kelly, C., & Deary, V. (2021). Altered smell and taste: Anosmia, parosmia and the impact of long COVID-19. PLOS ONE, 16(9), e0256998. https://doi.org/10.1371/journal.pone.0256998 [NZ1] 

Choutka, J., Jansari, V., Hornig, M. et al. Unexplained post-acute infection syndromes. Nat Med 28, 911–923 (2022). https://doi.org/10.1038/s41591-022-01810-6

Dunmire SK, Hogquist KA, Balfour HH. Infectious Mononucleosis. Curr Top Microbiol Immunol. 2015;390(Pt 1):211-40. doi:10.1007/978-3-319-22822-8_9. PMID: 26424648; PMCID: PMC4670567.

Gross M, Lansang NM, Gopaul U, Ogawa EF, Heyn PC, Santos FH, Sood P, Zanwar PP, Schwertfeger J, Faieta J. What Do I Need to Know About Long-COVID-related Fatigue, Brain Fog, and Mental Health Changes? Arch Phys Med Rehabil. 2023 Jun;104(6):996-1002. doi:10.1016/j.apmr.2022.11.021. Epub 2023 Mar 21. PMID: 36948378; PMCID: PMC10028338.

Iftekhar, Nafi et al. The Lancet, Volume 402, Issue 10401, e9

K. Pankiewicz, E. Chotkowska, B. Nowakowska, M. Gos & T. Issat (2023) COVID-19-related premature ovarian insufficiency: case report and literature review, Climacteric, DOI:10.1080/13697137.2023.2246878

Newman M. Chronic fatigue syndrome and long COVID: moving beyond the controversy. BMJ 2021; 373:n1559 doi:10.1136/bmj.n1559

Pfaff ER, Madlock-Brown C, Baratta JM, Bhatia A, Davis H, Girvin A, Hill E, Kelly L, Kostka K, Loomba J, McMurry JA, Wong R, Bennett TD, Moffitt R, Chute CG, Haendel M; N3C Consortium; RECOVER Consortium. Coding Long COVID: Characterizing a new disease through an ICD-10 lens. medRxiv [Preprint]. 2022 Sep 2:2022.04.18.22273968. doi:10.1101/2022.04.18.22273968. Update in: BMC Med. 2023 Feb 16;21(1):58. PMID: 36093345; PMCID: PMC9460974.

Sudre, C.H., Murray, B., Varsavsky, T. et al. Attributes and predictors of long COVID. Nat Med 27, 626–631 (2021). https://doi.org/10.1038/s41591-021-01292-y

Thaweethai T, Jolley SE, Karlson EW, et al. Development of a Definition of Postacute Sequelae of SARS-CoV-2 Infection. JAMA. 2023;329(22):1934–1946. doi:10.1001/jama.2023.8823

Wong TL, Weitzer DJ. Long COVID and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)-A Systemic Review and Comparison of Clinical Presentation and Symptomatology. Medicina (Kaunas). 2021 Apr 26;57(5):418. https://doi:10.3390/medicina57050418. PMID: 33925784; PMCID: PMC8145228.

Zhang, H., Zang, C., Xu, Z., Zhang, Y., Xu, J., Bian, J., Morozyuk, D., Khullar, D., Zhang, Y., Nordvig, A. S., Schenck, E. J., Shenkman, E. A., Rothman, R. L., Block, J. P., Lyman, K., Weiner, M. G., Carton, T. W., Wang, F., & Kaushal, R. (2023). Data-driven identification of post-acute SARS-CoV-2 infection subphenotypes. Nature Medicine, 29(1), 226-235. https://doi.org/10.1038/s41591-022-02116-3

About J. E. Williams, OMD, FAAIM

Dr. Williams is a highly respected integrative medicine clinician who treats and revitalizes patients with even the most severe stages of illness. His mission is to bridge complementary and alternative therapies with evidence-based clinical science. His integrative practice offers proven natural therapies, including acupuncture, regenerative therapies, advanced intravenous ozone, blood irradiation, personalized natural therapies, and nutritional supplements. Dr. Williams is the author of Viral Immunity and Beating the Flu.

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