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Chronic and Hidden Infections: The Fatigue Cause Doctors Often Miss
A dormant virus you caught years ago (most often Epstein-Barr, the cause of mono), a bacterial infection that technically "cleared" after treatment (like Lyme disease), or a low-grade, easy-to-miss bacterial source (a recurrent bladder infection, a lingering sinus or dental infection) can each keep your immune system quietly activated long after you feel fine — and that ongoing activation is a well-documented, independent cause of persistent fatigue.
Why an Infection You "Already Got Over" Can Still Be Draining You
- Some infections never fully leave. Certain viruses go dormant inside your cells rather than being cleared, and certain bacterial infections can trigger a lingering immune response even after the bacteria themselves are gone.
- This is different from the tiredness of a cold or flu, which resolves in days. Hidden infection fatigue can persist for months or years, often without any of the dramatic symptoms — high fever, severe pain — that would normally send someone to a doctor.
- Roughly 95% of adults carry the Epstein-Barr virus in a dormant state, and it's the most well-studied example of a "silent" infection capable of reactivating and driving fatigue directly through inflammatory signaling.
- This article walks through exactly how a dormant or "cleared" infection can still generate fatigue, why post-treatment Lyme disease is a recognized syndrome even after the bacteria are gone, how a low-grade urinary or dental infection can produce tiredness with almost no other symptoms, and precisely what to test for and ask about next.
- Viral Latency: How a Virus You Beat Years Ago Can Still Be Active
- Epstein-Barr Virus Reactivation: The Best-Studied Hidden Fatigue Trigger
- Post-Treatment Lyme Disease Syndrome: Fatigue After the Bacteria Are Gone
- Low-Grade Bacterial Sources: Recurrent UTIs, Sinus, and Dental Infections
- Why This Fatigue Rarely Comes With Dramatic Symptoms
- Fatigue Type Comparison at a Glance
- How This Differs From Other Fatigue Causes You May Have Already Considered
- Who Should Be Especially Alert to a Hidden Infection Source
- Proper Testing: What a Doctor Actually Checks
- A Nuanced View: Where the "Chronic Infection" Theory Gets Overused
- Home Tracking: Building a Symptom Timeline That Helps Your Doctor
- Interactions and Complications Worth Knowing About
- Red Flags: When This Becomes a Medical Emergency
- What Actually Helps, Beyond "Just Rest More"
- The 2026–2027 Outlook: Post-Infectious Fatigue Research
- Real-World Scenarios: Where Do You Fit?
- Decision Guide — Your Situation, Your Next Step
- Frequently Asked Questions
- Summary and Next Steps
1. Viral Latency: How a Virus You Beat Years Ago Can Still Be Active
Not every infection your immune system fights is fully eliminated. A specific family of viruses, the herpesviruses, has evolved a different survival strategy entirely: rather than being cleared, they retreat into a dormant, or latent, state inside certain cells and simply wait. Epstein-Barr virus, the virus responsible for infectious mononucleosis, is the most common and best-studied example, but the same basic strategy is shared by other herpesviruses, including human herpesvirus 6.
Periodically, often triggered by physical stress, emotional stress, another illness, or simply immune system fluctuation, these dormant viruses can reactivate — beginning to replicate again at a low level. The immune system responds to this renewed activity the same way it would respond to a fresh infection, releasing inflammatory cytokines such as interleukin-6, interleukin-8, and tumor necrosis factor-alpha. These are the same class of signaling molecules discussed in the context of autoimmune disease fatigue, though here the trigger is an outside pathogen reactivating rather than the immune system attacking the body's own tissue.
Critically, reactivation doesn't need to become a second bout of full-blown mononucleosis to cause symptoms. Subclinical reactivation — active enough to provoke an inflammatory response, but not active enough to produce a sore throat or swollen glands — appears to be common, and is exactly the kind of hidden process that can leave someone feeling drained without an obvious explanation.
2. Epstein-Barr Virus Reactivation: The Best-Studied Hidden Fatigue Trigger
Because EBV infects such a large share of the population, it's also the pathogen researchers have studied most closely as a fatigue trigger, and the data here is more specific than for almost any other hidden infection source.
Following an initial bout of infectious mononucleosis, a meaningful share of people go on to develop a persistent, debilitating fatigue that meets the clinical criteria discussed in the site's ME/CFS vs. normal fatigue comparison. Multiple prospective studies following people after confirmed EBV-driven mononucleosis have found that around 10% still meet fatigue-syndrome criteria six months later, with a smaller share remaining affected at one year. Some studies looking specifically at younger populations have found even higher short-term rates before gradual improvement.
Separately from that acute-to-chronic pathway, ongoing EBV reactivation independent of a recent mononucleosis episode has been studied as a contributor in several chronic illness populations, with reactivation markers showing up more often in people with persistent fatigue than in healthy comparison groups. The mechanism appears to run through the same inflammatory cytokine pathway, alongside effects on mitochondrial energy production and natural killer cell function — the immune cells that normally help keep latent viruses in check.
Because roughly 19 out of 20 adults carry EBV in a dormant state, a positive antibody test on its own doesn't prove much — it's expected in almost everyone. What matters clinically is the pattern of specific antibody types that indicate recent or ongoing reactivation, which is why Section 9 covers the specific tests worth requesting rather than a single generic EBV test.
3. Post-Treatment Lyme Disease Syndrome: Fatigue After the Bacteria Are Gone
Lyme disease, caused by Borrelia bacteria transmitted through tick bites, is typically cured by a standard course of antibiotics. But a documented minority of people who complete treatment successfully — meaning the infection itself has cleared — go on to develop lingering fatigue, joint pain, and cognitive difficulties that persist for six months or longer. The CDC refers to this specifically as Post-Treatment Lyme Disease Syndrome (PTLDS), and deliberately avoids the term "chronic Lyme disease," since that phrase implies an ongoing bacterial infection that current evidence doesn't support.
Estimates across multiple cohort studies put the prevalence of PTLDS at roughly 10 to 20% of people treated for confirmed Lyme disease, with fatigue consistently reported as the most common lingering symptom. What's still genuinely unresolved is the underlying mechanism — leading theories include a lingering, dysregulated immune response triggered by the original infection, residual tissue damage, or an overlap with the same post-infectious processes seen in long COVID fatigue and EBV-driven ME/CFS, rather than bacteria that simply weren't fully killed by antibiotics.
Randomized, placebo-controlled trials have consistently found that extended or repeated courses of antibiotics don't reliably improve PTLDS symptoms and carry real risks of their own. This is a source of genuine tension in the patient community, covered more fully in Section 10, but it's an important, evidence-based point to know before pursuing extended antibiotic treatment for lingering post-Lyme fatigue.
4. Low-Grade Bacterial Sources: Recurrent UTIs, Sinus, and Dental Infections
Not every hidden infection source is viral or tick-borne. A quietly recurring or low-grade bacterial infection can produce fatigue with surprisingly few of the symptoms people associate with infection.
Recurrent or Subclinical Urinary Tract Infections
In some people, especially older adults, a urinary tract infection can produce far more subtle symptoms than the classic burning or urgency — sometimes presenting mainly as fatigue, mild confusion, or simply feeling "off," without a dramatic fever. Because the urinary symptoms are muted, the infection can go unaddressed for longer than it otherwise would, sustaining a low-grade immune response and the fatigue that comes with it.
Chronic Sinus Infections
A sinus infection that lingers for weeks, sometimes without severe congestion or facial pain, keeps a local inflammatory process active that can contribute to systemic fatigue through the same cytokine signaling described in Section 1, even when the person doesn't feel obviously "sick."
Untreated Dental Infections
An abscessed tooth or chronic gum infection can act as a persistent, low-level source of bacterial and inflammatory load. Dental infections are a frequently overlooked fatigue source precisely because people don't associate tooth or gum problems with whole-body tiredness, and mild dental infections can smolder for a long time before becoming painful enough to prompt a dental visit.
If fatigue has been persistent and no clear cause has turned up on standard bloodwork, a basic urinalysis, a look at recent sinus symptoms, and a dental check-up are inexpensive, low-effort steps that are easy to overlook precisely because they don't feel like "fatigue tests."
5. Why This Fatigue Rarely Comes With Dramatic Symptoms
A theme runs through every mechanism in this article: the fatigue-producing process is often too low-grade to trigger the obvious warning signs — high fever, severe pain, visible swelling — that would normally prompt someone to seek care quickly. EBV reactivation without a fresh case of mononucleosis, PTLDS after bacteria have already cleared, and low-grade UTIs or dental infections all share this quality of being immunologically active enough to drain energy, but not active enough to look dramatic.
This is part of why hidden infection fatigue is so often initially mistaken for burnout, poor sleep, or ordinary overwork. Unlike the acute, unmistakable exhaustion of a bad flu, this kind of fatigue tends to be described as a persistent, unshakeable heaviness that doesn't clearly trace back to any single event — very similar in character, though different in cause, to the fatigue described in the site's burnout and fatigue guide.
6. Fatigue Type Comparison at a Glance
| Hidden Source | What It Feels Like | Typical Trigger | Speed of Onset |
|---|---|---|---|
| EBV reactivation | Flu-like heaviness, sometimes with mild sore throat or swollen glands | Stress, illness, or immune fluctuation reawakening a dormant virus | Gradual to sudden |
| Post-EBV ME/CFS-level fatigue | Severe, disabling exhaustion with post-exertional crashes | Persisting for 6+ months after an initial mononucleosis episode | Chronic, following acute illness |
| Post-Treatment Lyme Disease Syndrome | Persistent fatigue, joint pain, and cognitive fog after "cured" infection | Occurs in a minority of people after otherwise successful Lyme treatment | Chronic, following treatment |
| Recurrent/subclinical UTI | Vague tiredness or mild confusion, often without classic urinary symptoms | Low-grade or recurring bladder infection, more common in older adults | Gradual |
| Chronic sinus or dental infection | Persistent dull fatigue without feeling acutely "sick" | Smoldering local infection with ongoing low-grade inflammatory signaling | Very gradual |
7. How This Differs From Other Fatigue Causes You May Have Already Considered
| Condition | Key Distinguishing Feature | Where to Read More |
|---|---|---|
| Long COVID fatigue | Scoped specifically to SARS-CoV-2 infection, with its own distinct symptom cluster and timeline | Long COVID Fatigue |
| Autoimmune disease fatigue | Driven by the immune system attacking the body's own tissue, not a reactivating or lingering outside pathogen | Autoimmune Disease Fatigue |
| ME/CFS (general) | A diagnosis defined by its own specific criteria, including post-exertional malaise, regardless of which trigger (if any) is identified | ME/CFS vs Normal Fatigue |
| Iron-deficiency fatigue | Corrects with iron repletion, unrelated to immune activation from a pathogen | Iron Deficiency Fatigue |
| Thyroid fatigue | Driven by hormone output, with cold intolerance and weight change as hallmarks rather than infection markers | Thyroid Fatigue Guide |
| Chronic stress / cortisol dysregulation | Fatigue tracks with life stressors rather than infection or inflammatory markers | Cortisol and Fatigue |
These causes can genuinely overlap. A confirmed EBV reactivation doesn't rule out a concurrent thyroid problem or iron deficiency — which is exactly why Section 9 covers a broader panel rather than a single infection-specific test.
8. Who Should Be Especially Alert to a Hidden Infection Source
Anyone With Fatigue That Began Shortly After a Known Infection
Fatigue that started within weeks of a confirmed mononucleosis diagnosis, a tick bite, or a treated urinary tract infection and never fully resolved is a meaningful pattern worth raising specifically, rather than assuming enough time has simply passed for it to be unrelated.
Older Adults With New Confusion or Fatigue Without Classic Infection Signs
Because urinary tract infections in older adults can present atypically, unexplained new fatigue or mental fogginess in this group is worth a urinalysis even without burning or urgency.
People With a History of Tick Exposure in Endemic Areas
Anyone who has spent time in regions where Lyme disease is common and later developed unexplained, persistent fatigue and joint pain should mention the possibility even without recalling a specific tick bite, since the classic bullseye rash is not always noticed or present.
People With Frequent, Recurring Minor Illnesses
Someone who seems to catch every cold that goes around, alongside baseline fatigue, may be dealing with an immune system that's already partially occupied managing a reactivating latent virus, making it worth mentioning both patterns together.
9. Proper Testing: What a Doctor Actually Checks
| Test | What It Measures | Why It's Used |
|---|---|---|
| EBV antibody panel (VCA IgM/IgG, EBNA, EA) | Distinguishes recent, past, and reactivating EBV infection | A single positive EBV IgG means almost nothing on its own; the specific pattern across all four markers is what indicates active reactivation, per Section 2 |
| Lyme disease two-tier serology | Antibodies against Borrelia burgdorferi | Confirms past or current infection; used alongside a symptom timeline to evaluate possible PTLDS, per Section 3 |
| Urinalysis and urine culture | Signs of bacterial infection in the urinary tract | Identifies recurrent or subclinical UTIs, especially relevant in older adults per Section 8 |
| CRP and ESR | General systemic inflammation | Can flag ongoing low-grade inflammatory activity, though results can be unremarkable even with a genuine hidden source |
| Complete blood count | White blood cell patterns, anemia screening | Certain patterns can suggest ongoing immune activation or overlap with anemia of chronic disease |
| Dental and sinus evaluation | Structural or visible infection sources | Rules in or out the low-grade bacterial sources described in Section 4, which routine bloodwork won't reliably catch |
If fatigue began around a known illness or tick exposure and has never fully resolved, ask specifically for the full EBV antibody panel or Lyme two-tier serology by name, rather than a general "infection check" — the specific pattern of markers, not just a single positive result, is what your doctor needs to interpret this correctly.
10. A Nuanced View: Where the "Chronic Infection" Theory Gets Overused
It's worth being direct about a real tension in this space. "Chronic infection" has become a popular explanation across wellness media for fatigue of almost any kind, and that popularity has outpaced the actual evidence in several respects.
The CDC and most infectious disease specialists specifically discourage the term "chronic Lyme disease" because rigorous, placebo-controlled trials have not shown that prolonged bacteria persist in most people with lingering post-treatment symptoms, and extended antibiotic courses carry real risks — including serious adverse events — without reliable benefit. Similarly, while EBV reactivation markers do appear more often in some chronic fatigue populations than in healthy people, the association is not so strong or consistent that a positive EBV antibody test alone should be treated as a definitive explanation for someone's fatigue, especially given how nearly universal past EBV exposure is.
None of this means hidden infections are irrelevant — the data in Sections 2 and 3 is genuinely solid for meaningful subsets of patients. It means the evidence supports a more measured position: hidden or reactivated infection is a real, worth-investigating possibility, not an automatic explanation that should be assumed without a specific, consistent testing pattern and a plausible timeline.
Hidden infection is worth ruling in or out with specific testing, described in Section 9 — but it's one possible piece of a larger picture, not a shortcut that replaces a broader fatigue workup covering thyroid function, iron status, sleep, and mood.
11. Home Tracking: Building a Symptom Timeline That Helps Your Doctor
Mark the date fatigue started, as precisely as you can
A timeline anchored to a specific illness, tick bite, or infection treatment date is far more useful to a doctor than "I've been tired for a while."
Note any mild, easy-to-dismiss symptoms alongside fatigue
A sore throat that comes and goes, mild swollen glands, or occasional low-grade fevers can be meaningful clues toward EBV reactivation described in Section 2, even if none of them alone seemed worth mentioning.
Record any outdoor exposure history
Time spent in wooded or grassy areas in regions where ticks are common is relevant even without a remembered bite or rash, given how easily both can be missed.
Track how fatigue responds to rest specifically
Fatigue that persists despite adequate rest, similar to the pattern described for autoimmune disease, is a useful detail that points away from a simple sleep-debt explanation.
12. Interactions and Complications Worth Knowing About
| Situation | Why It Matters |
|---|---|
| Repeated or long-term antibiotic courses for suspected "chronic Lyme" | Extended antibiotics carry real risks, including gut microbiome disruption and, with IV regimens, catheter-related infection, without reliable symptom benefit per Section 10. |
| Immunosuppressive medication + EBV reactivation risk | People on immunosuppressants for another condition, including several treatments discussed in the autoimmune fatigue guide, may have a higher baseline risk of viral reactivation and are worth monitoring accordingly. |
| Untreated dental infection + certain heart conditions | Some dental infections carry a small risk of spreading bacteria into the bloodstream, which is a distinct concern from fatigue alone in people with specific heart valve conditions — worth flagging to both a dentist and physician. |
| Recurrent UTIs + diabetes | Diabetes increases susceptibility to urinary tract infections, compounding the fatigue mechanisms already described in the site's diabetes fatigue guide. |
13. Red Flags: When This Becomes a Medical Emergency
Most hidden infection fatigue develops gradually and isn't itself an emergency, but certain accompanying symptoms need prompt evaluation:
- High fever with confusion, especially in an older adult, which can indicate a urinary or other infection progressing toward sepsis.
- Severe headache with neck stiffness and light sensitivity, which can indicate meningitis and needs immediate evaluation.
- New facial drooping, numbness, or muscle weakness, which can occur with untreated Lyme disease affecting the nervous system.
- Chest pain, palpitations, or fainting alongside a known or suspected tick-borne illness, which can indicate Lyme carditis, a rare but serious complication.
- Facial swelling or spreading redness alongside a dental infection, which can indicate a spreading abscess requiring urgent dental or medical care.
14. What Actually Helps, Beyond "Just Rest More"
Get the specific test, not a generic one
A single EBV or Lyme test result is easy to misinterpret. Requesting the full antibody panel described in Section 9 gives your doctor the pattern needed to distinguish past exposure from active reactivation.
Address low-grade bacterial sources directly
A urinalysis, sinus evaluation, or dental check-up are simple, low-cost steps that resolve a genuinely fixable fatigue source when one is present.
Pace activity rather than pushing through crashes
For post-viral and post-Lyme fatigue that includes post-exertional worsening, graded, careful pacing tends to produce steadier energy than alternating between overexertion and full collapse.
Treat this as one piece of a broader workup
Checking thyroid function, iron status, and sleep quality alongside infection markers, rather than instead of them, gives a far more complete picture than assuming one hidden infection explains everything.
15. The 2026–2027 Outlook: Post-Infectious Fatigue Research
The surge of research into long COVID has had a notable side effect: it's brought new scientific attention and funding to post-infectious fatigue syndromes more broadly, including post-EBV and post-Lyme fatigue, which researchers increasingly view as related conditions worth studying together rather than in isolation. Several current research programs are specifically comparing immune and metabolic signatures across long COVID, post-mononucleosis ME/CFS, and PTLDS, looking for shared biological markers that could eventually support more precise diagnosis.
There's also growing interest in antiviral and immune-modulating approaches specifically targeted at herpesvirus reactivation, rather than the broad-spectrum antibiotic approaches that evidence has not supported for post-Lyme fatigue. None of this represents an imminent cure, but it does reflect a meaningful shift away from treating "I still feel tired after that infection" as an unexplainable complaint, and toward treating it as a biological phenomenon worth its own dedicated research track.
16. Real-World Scenarios: Where Do You Fit?
"I had mono in college, felt awful for a month, and never quite got back to full energy, even years later."
This matches the post-mononucleosis fatigue pattern in Section 2. A full EBV antibody panel, alongside a general fatigue workup, is a reasonable starting point even years after the original illness.
"I was treated for Lyme disease six months ago, and my doctor says the infection is gone, but I still feel exhausted and foggy."
This fits Post-Treatment Lyme Disease Syndrome from Section 3. Extended antibiotics aren't well-supported for this pattern per Section 10; a broader fatigue workup and pacing strategies from Section 14 are the better-evidenced next step.
"I'm in my seventies, and I've been more tired and a little foggy lately, without any burning or urgency when I urinate."
This matches the atypical urinary tract infection presentation in older adults described in Section 4 and 8. A simple urinalysis is a reasonable, low-effort first step.
"My fatigue started around the same time as a tooth infection I never fully got treated."
This fits the low-grade dental infection pattern in Section 4. A dental evaluation, alongside standard fatigue bloodwork, is worth prioritizing.
17. Decision Guide — Your Situation, Your Next Step
| Your Situation | Most Likely Explanation | First Action This Week |
|---|---|---|
| Fatigue since a past mononucleosis episode, never fully resolved | Post-EBV fatigue (Section 2) | Request a full EBV antibody panel by name, not a single generic test. |
| Persistent fatigue and joint pain after "successful" Lyme treatment | Post-Treatment Lyme Disease Syndrome (Section 3) | Discuss a broader fatigue workup with your doctor; avoid extended antibiotics without strong evidence of ongoing infection. |
| New fatigue or mild confusion in an older adult, no classic urinary symptoms | Subclinical urinary tract infection (Section 4) | Request a urinalysis this week. |
| Long-lingering sinus symptoms or an untreated dental issue alongside fatigue | Low-grade bacterial source (Section 4) | Schedule a sinus or dental evaluation. |
| High fever with confusion, neck stiffness, facial drooping, or chest pain | Possible medical emergency (Section 13) | Seek emergency care immediately; do not wait for a scheduled appointment. |
18. Frequently Asked Questions
If my EBV antibody test is positive, does that prove it's causing my fatigue?
Not on its own. Since roughly 95% of adults carry EBV in a dormant state, a single positive antibody result is expected in nearly everyone. What matters is the specific pattern across the full antibody panel described in Section 9, interpreted alongside your symptom timeline, not one isolated positive result.
Is "chronic Lyme disease" a real, ongoing infection?
Current evidence doesn't support that framing for most people with lingering post-treatment symptoms, which is why the CDC uses the term Post-Treatment Lyme Disease Syndrome instead, as covered in Section 3. The symptoms themselves are real and often disabling; the mechanism appears to be a lingering immune response rather than persistent bacteria in most documented cases.
Should I ask for a long-term antibiotic course if I suspect a hidden infection is causing my fatigue?
For post-treatment Lyme disease symptoms specifically, randomized controlled trials have found extended antibiotics don't reliably help and carry real risks, as discussed in Section 10. A more targeted approach — confirming an active, treatable infection first, such as a UTI or dental abscess — is better supported than open-ended antibiotic use.
Can a hidden infection cause fatigue without any other symptoms at all?
Yes, and this is one of the more important points in this article. Low-grade urinary, sinus, and dental infections in particular can produce fatigue as close to the only noticeable symptom, especially in older adults, which is exactly why Section 4 recommends checking these sources even without classic infection symptoms present.
How is this different from Long COVID or ME/CFS?
Long COVID is scoped specifically to SARS-CoV-2 infection. ME/CFS is a diagnosis defined by its own clinical criteria, regardless of which trigger is identified, if any. This article instead focuses on the specific mechanisms behind several other named, well-studied pathogen sources — EBV reactivation, post-treatment Lyme disease, and low-grade bacterial infections — that can also lead to persistent fatigue, sometimes meeting ME/CFS criteria and sometimes not.
19. Summary and Next Steps
Hidden infection fatigue isn't a single condition — it's a family of related mechanisms, some viral and some bacterial, that share a common thread: an immune system quietly staying activated long after the obvious symptoms of infection have faded.
What the evidence actually supports is more precise, and considerably more actionable:
- Certain viruses, especially Epstein-Barr, go dormant rather than disappearing, and periodic reactivation can drive fatigue through the same inflammatory signaling seen in other immune-related fatigue causes.
- A meaningful minority of people develop persistent, disabling fatigue after mononucleosis, sometimes meeting formal ME/CFS criteria for months or years afterward.
- Post-Treatment Lyme Disease Syndrome is real and well-documented, but current evidence points toward a lingering immune response rather than ongoing bacterial infection, which is why extended antibiotics aren't well-supported as a fix.
- Low-grade urinary, sinus, and dental infections can cause fatigue with very few other symptoms, especially in older adults, and are worth checking specifically rather than assumed away.
- The "chronic infection" explanation is genuinely useful but also genuinely overused, and deserves specific, pattern-based testing rather than being treated as an automatic answer for unexplained fatigue.
- A broader workup — thyroid, iron, sleep, and mood — alongside infection-specific testing gives a far more complete picture than focusing on any single hidden infection alone.
Scientific References
- CDC — Chronic Symptoms and Lyme Disease. cdc.gov — Chronic Symptoms and Lyme Disease
- CDC — About Epstein-Barr Virus and Infectious Mononucleosis. cdc.gov — Epstein-Barr Virus
- Mayo Clinic — Chronic Fatigue Syndrome: Symptoms and Causes. mayoclinic.org — Chronic Fatigue Syndrome
- Johns Hopkins Lyme Disease Research Center — Post-Treatment Lyme Disease Research. hopkinslyme.org — Lyme Disease Research Center
- Cleveland Clinic — Urinary Tract Infections in Older Adults. clevelandclinic.org — Urinary Tract Infections
- National Institutes of Health / PMC — Epstein-Barr Virus and the Origin of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. pmc.ncbi.nlm.nih.gov — PMC8634673
