Post-acute sequelae of COVID-19: understanding and addressing the burden of multisystem manifestations

Long-term cardiovascular disease outcomes in non-hospitalized medicare beneficiaries diagnosed with COVID-19: Population-based matched cohort study

BACKGROUND

SARS-CoV2, the virus that causes coronavirus disease 2019 (COVID-19), can affect multiple human organs structurally and functionally, including the cardiovascular system and brain. Many studies focused on the acute effects of COVID-19 on risk of cardiovascular disease (CVD) and stroke especially among hospitalized patients with limited follow-up time. This study examined long-term mortality, hospitalization, CVD and stroke outcomes after non-hospitalized COVID-19 among Medicare fee-for-service (FFS) beneficiaries in the United States.

METHODS

This retrospective matched cohort study included 944,371 FFS beneficiaries aged ≥66 years diagnosed with non-hospitalized COVID-19 from April 1, 2020, to April 30, 2021, and followed-up to May 31, 2022, and 944,371 propensity score matched FFS beneficiaries without COVID-19. Primary outcomes were all-cause mortality, hospitalization, and incidence of 15 CVD and stroke. Because most outcomes violated the proportional hazards assumption, we used restricted cubic splines to model non-proportional hazards in Cox models and presented time-varying hazard ratios (HRs) and Bonferroni corrected 95% confidence intervals (CI).

RESULTS

The mean age was 75.3 years; 58.0% women and 82.6% non-Hispanic White. The median follow-up was 18.5 months (interquartile range 16.5 to 20.5). COVID-19 showed initial stronger effects on all-cause mortality, hospitalization and 12 incident CVD outcomes with adjusted HRs in 0-3 months ranging from 1.05 (95% CI 1.01-1.09) for mortality to 2.55 (2.26-2.87) for pulmonary embolism. The effects of COVID-19 on outcomes reduced significantly after 3-month follow-up. Risk of mortality, acute myocardial infarction, cardiomyopathy, deep vein thrombosis, and pulmonary embolism returned to baseline after 6-month follow-up. Patterns of initial stronger effects of COVID-19 were largely consistent across age groups, sex, and race/ethnicity.

CONCLUSIONS

Our results showed a consistent time-varying effects of COVID-19 on mortality, hospitalization, and incident CVD among non-hospitalized COVID-19 survivors.

Assessment of the Impact of RNase in Patients With Severe Fatigue Related to Post-Acute Sequelae of SARS-CoV-2 Infection (PASC): A Randomized Phase 2 Trial of RSLV-132

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA and RNA debris persist in viral reservoirs for weeks to months following infection, potentially triggering interferon production and chronic inflammation. RSLV-132 is a biologic drug composed of catalytically active human RNase1 fused to human IgG1 Fc and is designed to remain in circulation and digest extracellular RNA. We hypothesized that removal of SARS-CoV-2 viral RNA from latent reservoirs may improve inflammation, neuroinflammation, and fatigue associated with post-acute sequelae of SARS-CoV-2 infection (PASC).

METHODS

This was a phase 2, double-blind, placebo-controlled randomized clinical trial in participants with a 24-week history of PASC and severe fatigue. The primary endpoint of the trial assessed the impact of 6 intravenous doses of RSLV-132 on the mean change from baseline at day 71 in the Patient-Reported Outcomes Measurement Information System Fatigue Short Form 7a (PROMIS Fatigue SF 7a).

RESULTS

A statistically significant difference on day 71 was not observed with respect to the primary or secondary endpoints. This was likely due to a placebo response that increased during the trial. Statistically significant improvement in fatigue as measured by the PROMIS Fatigue SF 7a, Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue), and Physicians Global Assessment (PGA) instruments were observed earlier in the trial, with women demonstrating greater responses to RSLV-132 than men.

CONCLUSION

While fatigue was not statistically significantly improved at Day 71, earlier timepoints revealed statistically significant improvement in fatigue and physician global assessment. The data suggest eliminating latent viral RNA by increasing serum RNase activity may improve fatigue in PASC patients. Women may respond better to this approach than men. Future studies will aim to confirm these findings.

Neutrophil ALDH2 is a new therapeutic target for the effective treatment of sepsis-induced ARDS

Acetaldehyde dehydrogenase 2 (ALDH2) mutations are commonly found in a subgroup of the Asian population. However, the role of ALDH2 in septic acute respiratory distress syndrome (ARDS) remains unknown. Here, we showed that human subjects carrying the ALDH2rs671 mutation were highly susceptible to developing septic ARDS. Intriguingly, ALDH2rs671-ARDS patients showed higher levels of blood cell-free DNA (cfDNA) and myeloperoxidase (MPO)-DNA than ALDH2WT-ARDS patients. To investigate the mechanisms underlying ALDH2 deficiency in the development of septic ARDS, we utilized Aldh2 gene knockout mice and Aldh2rs671 gene knock-in mice. In clinically relevant mouse sepsis models, Aldh2-/- mice and Aldh2rs671 mice exhibited pulmonary and circulating NETosis, a specific process that releases neutrophil extracellular traps (NETs) from neutrophils. Furthermore, we discovered that NETosis strongly promoted endothelial destruction, accelerated vascular leakage, and exacerbated septic ARDS. At the molecular level, ALDH2 increased K48-linked polyubiquitination and degradation of peptidylarginine deiminase 4 (PAD4) to inhibit NETosis, which was achieved by promoting PAD4 binding to the E3 ubiquitin ligase CHIP. Pharmacological administration of the ALDH2-specific activator Alda-1 substantially alleviated septic ARDS by inhibiting NETosis. Together, our data reveal a novel ALDH2-based protective mechanism against septic ARDS, and the activation of ALDH2 may be an effective treatment strategy for sepsis.

Post-COVID-19 respiratory sequelae two years after hospitalization: an ambidirectional study

Background

COVID-19 lung sequelae can impact the course of patient lives. We investigated the evolution of pulmonary abnormalities in post-COVID-19 patients 18-24 months after hospital discharge.

Methods

A cohort of COVID-19 patients admitted to the Hospital das Clínicas da Faculdade de Medicina da USP in São Paulo, Brazil, between March and August of 2020, were followed-up 6-12 months after hospital discharge. A subset of patients with pulmonary involvement and chest computed tomography (CT) scans were eligible to participate in this second follow-up (18-24 months). Data was analyzed in an ambidirectional manner, including retrospective data from the hospitalization, and from the first follow-up (6-12 months after discharge), and compared with the prospective data collected in this new follow-up.

Findings

From 348 patients eligible, 237 (68%) participated in this follow-up. Among participants, 139 (58%) patients presented ground-glass opacities and reticulations, and 80 (33%) presented fibrotic-like lesions (traction bronchiectasis and architectural distortion). Five (2%) patients improved compared to the 6-12-month assessment, but 20 (25%) of 80 presented worsening of lung abnormalities. For those with relevant assessments on both occasions, comparing the CT findings between this follow-up with the previous assessment, there was an increase in patients with architectural distortion (43 [21%] of 204 vs 57 [28%] of 204, p = 0.0093), as well as in traction bronchiectasis (55 [27%] of 204 vs 69 [34%] of 204, p = 0.0043). Patients presented a persistent functional impairment with demonstrated restrictive pattern in both follow-ups (87 [42%] of 207 vs 91 [44%] of 207, p = 0.76), as well as for the reduced diffusion capacity (88 [42%] of 208 vs 87 [42%] of 208, p = 1.0). Length of hospitalization (OR 1.04 [1.01-1.07], p = 0.0040), invasive mechanical ventilation (OR 3.11 [1.3-7.5] p = 0.011), patient's age (OR 1.03 [1.01-1.06] p = 0.0074 were consistent predictors for development of fibrotic-like lung lesions in post-COVID-19 patients.

Interpretation

Post-COVID-19 lung sequelae can persist and progress after hospital discharge, suggesting airways involvement and formation of new fibrotic-like lesions, mainly in patients who were in intensive care unit (ICU).

Funding

São Paulo Research Foundation (22/01769-5) and Instituto Todos pela Saúde (C1721).

Special Issue "Molecular and Genetic Aspects of SARS-CoV-2 Infection and COVID-19 Disease"

We are pleased to present the first and second editions of this Special Issue, titled "Molecular and Genetic Aspects of SARS-CoV-2 Infection and COVID-19 Disease", of the International Journal of Molecular Sciences [...].

Distinct Type 1 Immune Networks Underlie the Severity of Restrictive Lung Disease after COVID-19

The variable etiology of persistent breathlessness after COVID-19 have confounded efforts to decipher the immunopathology of lung sequelae. Here, we analyzed hundreds of cellular and molecular features in the context of discrete pulmonary phenotypes to define the systemic immune landscape of post-COVID lung disease. Cluster analysis of lung physiology measures highlighted two phenotypes of restrictive lung disease that differed by their impaired diffusion and severity of fibrosis. Machine learning revealed marked CCR5+CD95+ CD8+ T-cell perturbations in mild-to-moderate lung disease, but attenuated T-cell responses hallmarked by elevated CXCL13 in more severe disease. Distinct sets of cells, mediators, and autoantibodies distinguished each restrictive phenotype, and differed from those of patients without significant lung involvement. These differences were reflected in divergent T-cell-based type 1 networks according to severity of lung disease. Our findings, which provide an immunological basis for active lung injury versus advanced disease after COVID-19, might offer new targets for treatment.

Cardiorespiratory abnormalities in ICU survivors of COVID-19 with postacute sequelae of SARS-CoV-2 infection are unrelated to invasive mechanical ventilation

Postacute sequelae of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (PASC) often leads to exertional intolerance and reduced exercise capacity, particularly in individuals previously admitted to an intensive care unit (ICU). However, the impact of invasive mechanical ventilation (IMV) on PASC-associated cardiorespiratory abnormalities during exercise remains poorly understood. This single-center, cross-sectional study aimed to gather knowledge on this topic. Fifty-two patients with PASC recruited ∼6 mo after ICU discharge were clustered based on their need for IMV (PASC + IMV, n = 27) or noninvasive support therapy (PASC + NIS, n = 25). Patients underwent pulmonary function and cardiopulmonary exercise testing (CPX) and were compared with a reference group (CONTROL, n = 19) comprising individuals of both sexes with similar age, comorbidities, and physical activity levels but without a history of COVID-19 illness. Individuals with PASC, irrespective of support therapy, presented with higher rates of cardiorespiratory abnormalities than CONTROL, especially dysfunctional breathing patterns, dynamic hyperinflation, reduced oxygen uptake and oxygen pulse, and blunted heart rate recovery (all P < 0.05). Only the rate of abnormal oxygen pulse was greater among PASC + IMV group than PASC + NIS group (P = 0.05). Mean estimates for all CPX variables were comparable between PASC + IMV and PASC + NIS groups (all P > 0.05). These findings indicate significant involvement of both central and peripheral factors, leading to exertional intolerance in individuals with PASC previously admitted to the ICU, regardless of their need for IMV.NEW & NOTEWORTHY We found cardiorespiratory abnormalities in ICU survivors of severe-to-critical COVID-19 with PASC to be independent of IMV need. Overall, both group of patients experienced dysfunctional breathing patterns, dynamic hyperinflation, lower oxygen uptake and oxygen pulse, and blunted heart rate responses to CPX. PASC seems to impact exertional tolerance and exercise capacity due to ventilatory inefficiency, impaired aerobic metabolism, and potential systolic and autonomic dysfunction, all of these irrespective of support therapy during ICU stay.

Seroprevalence of SARS-CoV-2 IgG in people with cystic fibrosis

Background

When the first known US case of COVID-19 (Coronavirus Disease 2019) was reported in early 2020, little was known about the impact of this novel virus on the cystic fibrosis community. As the majority of individuals with CF have chronic lung disease, this population was initially considered to be at high risk for severe disease as infection with a multitude of viruses has proven to cause pulmonary exacerbation. SARS-CoV-2 virus has proven challenging to study given the multiple disease manifestations, range of severity, and wave-like phenomenon that varies geographically. People with CF who become infected with COVID-19 can be asymptomatic or have symptoms ranging from mild cough and congestion to full respiratory failure, similar to the manifestations seen in non-CF individuals. By studying the seroprevalence, clinical course, and antibody durability due to COVID-19 and vaccinations, we will be better equipped to provide appropriate and informed care to people with CF.

Methods

Between July 2020 and April 2021 we enrolled 123 people with CF (pwCF) who receive care at the MN CF Center. We monitored their serology every 6 months for SARS-CoV-2 immunoglobulins (nucleocapsid and spike IgG) for evidence of natural and induced immunity. Medication use, pulmonary function, exacerbation history, and hospitalizations were extracted via electronic medical record (EMR).

Results

84% (101/120) of enrolled participants were vaccinated against SARS-CoV-2 during the study. Eighty three percent of the cohort showed evidence of either natural or induced "immunity." The average duration of antibody from induced immunity in participants was 6.1 months and from natural immunity was 7.4 months with an overall average duration of antibody of 6.8 months. Earliest antibody detected was 12 days after a single dose of the BNT162b2 vaccine and antibody was detectable across a span of 13 months. Eleven percent of vaccinated individuals did not have measurable IgG. 36% of non-responders (NRs) were solid organ transplant patients on chronic immunosuppressive therapy. Only 3 people within this cohort were hospitalized due to COVID pneumonia and all three survived.

Conclusion

To our knowledge, this is the first report on the seroprevalence and longevity of SARS-CoV-2 IgG to 1 year in adults with CF after the widespread availability of SARS-CoV-2 vaccinations. These data show that pwCF respond to the COVID vaccination and produce long-lasting antibodies similar to the general population.

Type I interferon signaling, cognition and neurodegeneration following COVID-19: update on a mechanistic pathogenetic model with implications for Alzheimer's disease

COVID-19's effects on the human brain reveal a multifactorial impact on cognition and the potential to inflict lasting neuronal damage. Type I interferon signaling, a pathway that represents our defense against pathogens, is primarily affected by COVID-19. Type I interferon signaling, however, is known to mediate cognitive dysfunction upon its dysregulation following synaptopathy, microgliosis and neuronal damage. In previous studies, we proposed a model of outside-in dysregulation of tonic IFN-I signaling in the brain following a COVID-19. This disruption would be mediated by the crosstalk between central and peripheral immunity, and could potentially establish feed-forward IFN-I dysregulation leading to neuroinflammation and potentially, neurodegeneration. We proposed that for the CNS, the second-order mediators would be intrinsic disease-associated molecular patterns (DAMPs) such as proteopathic seeds, without the requirement of neuroinvasion to sustain inflammation. Selective vulnerability of neurogenesis sites to IFN-I dysregulation would then lead to clinical manifestations such as anosmia and cognitive impairment. Since the inception of our model at the beginning of the pandemic, a growing body of studies has provided further evidence for the effects of SARS-CoV-2 infection on the human CNS and cognition. Several preclinical and clinical studies have displayed IFN-I dysregulation and tauopathy in gene expression and neuropathological data in new cases, correspondingly. Furthermore, neurodegeneration identified with a predilection for the extended olfactory network furthermore supports the neuroanatomical concept of our model, and its independence from fulminant neuroinvasion and encephalitis as a cause of CNS damage. In this perspective, we summarize the data on IFN-I as a plausible mechanism of cognitive impairment in this setting, and its potential contribution to Alzheimer's disease and its interplay with COVID-19.

Autoantibody profiles assessment in individuals with persistent olfactory impairment following SARS-CoV-2 infection

BACKGROUND

Olfactory impairment, particularly hyposmia and anosmia, has emerged as a distinctive early symptom of SARS-CoV-2. Drawing on the historical association of autoimmune diseases with olfactory function, this study delves into the connections between COVID-19, autoimmunity, and persistent olfactory dysfunctions, focusing on individuals experiencing long-lasting smell disorders (3-18 months post-SARS-CoV-2 infection).

METHODS

The study comprised 36 Long Covid patients with persistent olfactory dysfunctions, alongside two control groups. Olfactory functionality was assessed using the Sniffin' Sticks extended test. Non-invasive olfactory mucosa brushing and nasal secretions were processed for nasal samples, while serum samples were obtained through peripheral venous sampling. A panel of autoantibodies, including Immunocirculating Complexes, ANA, ENA, and AECA, was investigated in serum and brush supernatant samples.

RESULTS

Contrary to expectations, the absence of traditional autoantibodies challenges the proposed autoimmune etiology of Long Covid-associated olfactory dysfunction. However, the presence and potential pathogenic role of AECA suggest viral cytopathic and inflammatory involvement in specific anatomical districts. One hypothesis explores the impact of inflammation and cytokine release induced by the viral infection, altering neuronal signaling and contributing to persistent hyposmia.

CONCLUSION

This research contributes to our understanding of the complex relationships between autoimmunity, olfactory impairment, and COVID-19. The absence of classical autoantibodies challenges prevailing theories, while the prominence of AECA hints at unique viral-induced pathogenic mechanisms. By unraveling these complexities, this study enhances our comprehension of post-acute sequelae, offering valuable perspectives on immune-mediated responses in the aftermath of the pandemic.

Use of a Virtual Multi-Disciplinary Clinic for the Treatment of Post-COVID-19 Patients

Post-COVID-19 has been recognized as possibly affecting millions of people worldwide. In order to optimize care and ensure equality, we established a multidisciplinary virtual Post-COVID-19 clinic (VPCC) within Maccabi Healthcare Services, the second largest HMO in Israel. This study aims to describe the structure, process and patient satisfaction with this clinic. The multidisciplinary team consisted of physicians, physiotherapists, social workers, occupational therapists and dieticians. Patient entry was to be at least four weeks after COVID-19 infection. A patient satisfaction survey was carried out 7-8 months after the clinic was closed. Demographic data were collected and compared to the general Maccabi COVID-19 population. The clinic treated 1614 patients, aged 16-91, over a period of 18 months. In total, 679 family physicians referred patients. In comparison to the general COVID-19 population, a higher percentage of the VPCC patients lived in the periphery of Israel, South (14.9% compared to 17.8%) and North (17.1% compared to 18.2%). In total, 249 patients answered the survey, and of them, 75% were highly satisfied with the medical care of the physician in the VPCC. A total of 54% of respondents would have preferred a face-to-face consultation, but 50% felt that communication was good in the virtual mode. In conclusion, the VPCC provided a dedicated service for patients, and the virtual format made it equally accessible to all parts of the country.

SARS-CoV-2 and its Multifaceted Impact on Bone Health: Mechanisms and Clinical Evidence

PURPOSE OF REVIEW

SARS-CoV-2 infection, the culprit of the COVID-19 pandemic, has been associated with significant long-term effects on various organ systems, including bone health. This review explores the current understanding of the impacts of SARS-CoV-2 infection on bone health and its potential long-term consequences.

RECENT FINDINGS

As part of the post-acute sequelae of SARS-CoV-2 infection, bone health changes are affected by COVID-19 both directly and indirectly, with multiple potential mechanisms and risk factors involved. In vitro and preclinical studies suggest that SARS-CoV-2 may directly infect bone marrow cells, leading to alterations in bone structure and osteoclast numbers. The virus can also trigger a robust inflammatory response, often referred to as a "cytokine storm", which can stimulate osteoclast activity and contribute to bone loss. Clinical evidence suggests that SARS-CoV-2 may lead to hypocalcemia, altered bone turnover markers, and a high prevalence of vertebral fractures. Furthermore, disease severity has been correlated with a decrease in bone mineral density. Indirect effects of SARS-CoV-2 on bone health, mediated through muscle weakness, mechanical unloading, nutritional deficiencies, and corticosteroid use, also contribute to the long-term consequences. The interplay of concurrent conditions such as diabetes, obesity, and kidney dysfunction with SARS-CoV-2 infection further complicates the disease's impact on bone health. SARS-CoV-2 infection directly and indirectly affects bone health, leading to potential long-term consequences. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

COVID-19 and Bone Loss: A Review of Risk Factors, Mechanisms, and Future Directions

PURPOSE OF REVIEW

SARS-CoV-2 drove the catastrophic global phenomenon of the COVID-19 pandemic resulting in a multitude of systemic health issues, including bone loss. The purpose of this review is to summarize recent findings related to bone loss and potential mechanisms.

RECENT FINDINGS

The early clinical evidence indicates an increase in vertebral fractures, hypocalcemia, vitamin D deficiencies, and a loss in BMD among COVID-19 patients. Additionally, lower BMD is associated with more severe SARS-CoV-2 infection. Preclinical models have shown bone loss and increased osteoclastogenesis. The bone loss associated with SARS-CoV-2 infection could be the result of many factors that directly affect the bone such as higher inflammation, activation of the NLRP3 inflammasome, recruitment of Th17 cells, the hypoxic environment, and changes in RANKL/OPG signaling. Additionally, SARS-CoV-2 infection can exert indirect effects on the skeleton, as mechanical unloading may occur with severe disease (e.g., bed rest) or with BMI loss and muscle wasting that has also been shown to occur with SARS-CoV-2 infection. Muscle wasting can also cause systemic issues that may influence the bone. Medications used to treat SARS-CoV-2 infection also have a negative effect on the bone. Lastly, SARS-CoV-2 infection may also worsen conditions such as diabetes and negatively affect kidney function, all of which could contribute to bone loss and increased fracture risk. SARS-CoV-2 can negatively affect the bone through multiple direct and indirect mechanisms. Future work will be needed to determine what patient populations are at risk of COVID-19-related increases in fracture risk, the mechanisms behind bone loss, and therapeutic options. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

The injured monocyte: The link to chronic critical illness and mortality following injury

BACKGROUND

This study aimed to understand the altered innate immune response in severely injured patients leading to chronic critical illness (CCI). Specifically, it focused on characterizing the monocyte populations and their correlation with CCI development and long-term complications.

METHODS

Over a 3-year period, we monitored patients with severe injuries for up to 1-year postinjury. Chronic critical illness was defined as an ICU stay exceeding 14 days with persistent organ failure. Blood samples were collected on Days 1 and 5 for monocyte phenotypic expression analysis using cytometry by time flight. The monocyte subpopulations studied were classical (CL), intermediate (INT), and nonclassical (NC), along with cell surface receptor expression and activation.

RESULTS

Out of 80 enrolled patients, 26 (32.5%) developed CCI. Patients with CCI had more severe injuries (Injury Severity Score, 32.4 + 5.2 vs. 29.6 + 4.1, p = 0.01) and received a higher number of red blood cells (8.9 + 4.1 vs. 4.7 + 3.8 units, p < 0.01) compared with those without CCI. In patients with CCI, the NC monocytes were significantly reduced by over twofold early, and significantly increased later, compared with those without CCI. Moreover, significant changes in intracellular cytokine expression and cell receptors were observed within each monocyte subpopulation in patients with CCI, indicating an increased proinflammatory phenotype but decreased phagocytic capacity and antigen presentation. The development of CCI and the presence of this unique monocyte phenotype were associated with a significantly increased risk of infection, discharge to a long-term care facility, and 1-year mortality of 27%.

CONCLUSION

Development of CCI following severe injury is associated with significant long-term morbidity and unacceptably high mortality. The altered NC phenotype with reduced phagocytic capacity and antigen presentation in patients developing CCI after severe injury is appears partially responsible. Early identification of this unique phenotype may help predict and treat patients at risk for CCI, leading to improved outcomes.

LEVEL OF EVIDENCE

Prognostic and Epidemiological; Level III.

A review of post COVID syndrome pathophysiology, clinical presentation and management in children and young people

Post Covid Syndrome (PCS) is a complex multi-system disorder with a spectrum of presentations. Severity ranges from mild to very severe with variable duration of illness and recovery. This paper discusses the difficulties defining and describing PCS. We review the current understanding of PCS, epidemiology, and predisposing factors. We consider potential mechanisms including viral persistence, clotting dysfunction and immunity. We review presentation and diagnosis and finally consider management strategies including addressing symptom burden, rehabilitation, and novel therapies.

High Plasma Osteopontin Levels Are Associated with Serious Post-Acute-COVID-19-Related Dyspnea

COVID-19 survivors commonly report persistent symptoms. In this observational study, we investigated the link between osteopontin (OPN) and post-acute COVID-19 symptoms and lung functional/imaging abnormalities. We recorded symptoms and lung imaging/functional data from previously hospitalized COVID-19 patients, who were followed for 4-84 weeks (122 patients/181 visits) post-symptom onset at our outpatient clinic. Circulating OPN was determined using ELISA. Plasma OPN levels were higher in symptomatic patients (compared with the asymptomatic ones); those with dyspnea (compared with those without dyspnea);those with a combination of serious symptoms, i.e., the presence of at least one of the following: dyspnea, fatigue and muscular weakness (compared with those with none of these symptoms); and those with dyspnea and m-MRC > 1 (compared with those with m-MRC = 0-1). Plasma OPN levels were inversely correlated with EQ-VAS (visual analog scale of the EQ-5D-5L health-related quality-of-life questionnaire) values. High-resolution CT or diffusion lung capacity (DLCO) findings were not related to circulating OPN. In the multiple logistic regression, the presence of symptoms, dyspnea, or the combination of serious symptoms were linked to female gender, increased BMI and pre-existing dyspnea (before the acute disease), while increased plasma OPN levels, female gender and pre-existing dyspnea with m-MRC > 1 were independently associated with severe post-COVID-19 dyspnea (m-MRC > 1). Using a correlation matrix to investigate multiple correlations between EQ-VAS, OPN and epidemiological data, we observed an inverse correlation between the OPN and EQ-VAS values. Increased circulating OPN was linked to the persistence of severe exertional dyspnea and impaired quality of life in previously hospitalized COVID-19 patients.

What Role Does Microthrombosis Play in Long COVID?

Soon after the outbreak of coronavirus disease 2019 (COVID-19), unexplained sustained fatigue, cognitive disturbance, and muscle ache/weakness were reported in patients who had recovered from acute COVID-19 infection. This abnormal condition has been recognized as "long COVID (postacute sequelae of COVID-19 [PASC])" with a prevalence estimated to be from 10 to 20% of convalescent patients. Although the pathophysiology of PASC has been studied, the exact mechanism remains obscure. Microclots in circulation can represent one of the possible causes of PASC. Although hypercoagulability and thrombosis are critical mechanisms of acute COVID-19, recent studies have reported that thromboinflammation continues in some patients, even after the virus has cleared. Viral spike proteins and RNA can be detected months after patients have recovered, findings that may be responsible for persistent thromboinflammation and the development of microclots. Despite this theory, long-term results of anticoagulation, antiplatelet therapy, and vascular endothelial protection are inconsistent, and could not always show beneficial treatment effects. In summary, PASC reflects a heterogeneous condition, and microclots cannot explain all the presenting symptoms. After clarification of the pathomechanisms of each symptom, a symptom- or biomarker-based stratified approach should be considered for future studies.