ORIGINAL RESEARCH article

Front. Immunol., 03 September 2021

Sec. Viral Immunology

Volume 12 - 2021 | https://doi.org/10.3389/fimmu.2021.711741

Complication and Sequelae of COVID-19: What Should We Pay Attention to in the Post-Epidemic Era

  • 1. Department of Orthopedics, First Hospital of China Medical University, Shenyang, China

  • 2. Department of Pediatrics, Shengjing Hospital of China Medical University, Shenyang, China

  • 3. The First Department of Clinical Medicine, China Medical University, Shenyang, China

Abstract

COVID-19 is widespread worldwide and seriously affects the daily life and health of humans. Countries around the world are taking necessary measures to curb the spread. However, COVID-19 patients often have at least one organ complication and sequelae in addition to respiratory symptoms. Controlling the epidemic is only a phased victory, and the complication and sequelae of COVID-19 will need more attention in the post-epidemic era. We collected general information from over 1000 articles published in 2020 after the COVID-19 outbreak and systematically analyzed the complication and sequelae associated with eight major systems in COVID-19 patients caused by ACE2 intervention in the RAS regulatory axis. The autoimmune response induced by 2019-nCoV attacks and damages the normal tissues and organs of the body. Our research will help medical workers worldwide address COVID-19 complication and sequelae.

Introduction

COVID-19 was one of the most concerning issues in 2020. Coronavirus threatens the life and health of humans (). In addition, no country around the world has been completely spared. At present, humans have not truly controlled the spread of 2019-nCoV, and due to the alteration in climate, a second epidemic has appeared. According to the data of the World Health Organization (WHO), the global number of COVID-19 cases has reached to over 130 million, with no sign of weakening. Our previous studies indicated that 2019-nCoV and SARS share a very similar viral gene sequence, origin, and intracellular receptor, ACE2 (). People infected with 2019-nCoV will have symptoms of varying degrees ranging from a fever or a slight cough to pneumonia and even death (). Most patients are asymptomatic or have mild cases, and even patients with more severe symptoms can recover with the help of medical treatment.

A prominent problem in the post-epidemic era is the complication and sequelae of COVID-19. All systems of the human body are at risk of being attacked by COVID-19 (). A number of studies have demonstrated that patients with 2019-nCoV have at least one organ complication and sequelae in addition to respiratory symptoms even if the symptoms are mild (, ). More than three-quarters of COVID-19 patients reported having at least one sequelae six months after the onset of the disease (). Although COVID-19 is an infectious disease characterized by pneumonia, complication affecting the cardiovascular system are the most serious and fatal. In clinical testing of COVID-19 patients, it was found that the level of angiotensin converting enzyme (ACE) was extremely low (). A decline in ACE increases the risk of hypertension, myocarditis, and even heart failure (–). Meanwhile, the impact of 2019-nCoV on the nervous system is also very serious. A study indicated that nearly 40% of COVID-19 patients showed neurological symptoms (). Severe encephalitis causes cerebral parenchymal disease and induces brain death (). In addition, there is a certain impact of 2019-nCoV on the digestive, urinary and endocrine systems (–). Comparative genomics of different strains of 2019-nCoV around the world have been fully analyzed (–). As more and more people in various countries are vaccinated, it is believed that the epidemic will be brought under control soon. The prevention of and interventions for patients’ complication and sequelae will be the focus in the post-epidemic era.

Bibliometric analysis is an interdisciplinary science which could obtain the objective and quantifiable data of certain field (). It could provide research hotspots and directions in a specific field by analyzing various parameters of published works and foster collaborative transdisciplinary research (, ). Therefore, this study aimed to explore the research status and to predict future trends of COVID-19 complication and sequelae by using original research bibliometric analysis. We believe our study will attract the attention of medical workers and researchers worldwide and enrich the process of COVID-19 prevention and management.

Materials and Methods

Search Strategy and Inclusion Criteria

The relevant articles were retrieved from the Web of Science core collection database according to the indexes COVID-19 and complication or sequelae on December 30, 2020. The time range of retrieval covered all years, that is, from the year that the database was created to the search date. There were a total of 1169 publications, and their types included reviews, articles, early access, editorial materials, and letters. Then, we established the inclusion criteria and screened the articles against the inclusion criteria: (a) published in English, (b)involved COVID-19 research, and (c) focused on a discussion of complication and sequelae (Supplementary Figure 1).

Data Extraction

The above operations were performed by two reviewers independently, and a third reviewer helped them build a consensus when disagreements occurred. The general information of these articles was listed, including the title, publication date, name of the first author and corresponding author, geographic origin, publication journal, publication institution, research theme, and journal impact factor.

Bibliometric Analysis

The extracted information of these articles was imported into the Online Analysis Platform of Literature Metrology (http://bibliometric.com/) and integrated according to their characteristics. CiteSpace V5.5.R1 SE, 64 bit (Drexel University, Philadelphia, PA, USA) and VOSviewer (Leiden University, Leiden, the Netherlands) were used to visualize the network of this information, such as authors and counties, institutions, and journals (, ). We also identified research trends and predicted evolutionary directions in terms of high-frequency keywords on CiteSpace. The approach is described in detail in our previous study on COVID-19 and the SARS and MERS coronaviruses ().

Results

Most Active Countries and Institutions

The top ten most active countries according to the number of publications each year are shown in Figure 1. These ten countries all have highly developed economies and dense population flows, resulting in wide and rapid spread of the epidemic. Unsurprisingly, America and European countries (especially the UK) were the predominant countries. China also contributed a large number of articles due to the early detection of the coronavirus. International cooperation was dominated by the United States, Italy, and China, which was consistent with the ranking by the number of publishing articles (Figure 2). Based on the number of articles, we listed the top 10 institutions (Figure 3). Two universities from Wuhan, China, ranked in the top two. Huazhong University of Science and Technology ranked first with 78 articles, and Wuhan University ranked second with 45 articles. Columbia University, the Mayo Clinic and the University of Paris ranked third, fourth and fifth, with 37, 32 and 27 articles, respectively. Besides, Harvard Medical School, the National and Kapodistrian University of Athens, the University of Toronto, the University of Milan, and the Icahn School of Medicine at Mount Sinai each published over 20 articles.

Figure 1

Figure 2

Figure 3

Most Active Authors and Journals

We counted the authors who were the first or corresponding authors of these articles and ranked them in descending order by the published article count for the top ten authors (Table 1). Seven of these authors were from China. Zhang, Y published the most articles (n=8), one as the first author. Liu, H ranked second with five articles. Each of the remaining eight authors published 4 articles each: Wang, L, Connors, JM, Thachil, J, Khan, S, Liu, W, Li, XY, Yang, F and Chen, T. The top ten co-cited authors are listed in Figure 4 in descending order of article count. CiteSpace was used to reveal the network of these co-cited authors (Figure 5). All of these authors participated in over 100 articles and in over 200 articles of the top five authors. They were Huang CL (n=366), Zhou F (n=298), Wang DW (n=289), Guan W (n=265) and Chen NS (n=214).

Table 1

RankAuthorArticle countsFirst author countsCorresponding author counts
1Zhang, Y810
2Liu, H510
3Wang, L411
4Connors, JM411
5Thachill, J421
6Khan, S410
7Liu, W411
8Li, XY420
9Yang, F420
10Chen, T410

The top ten authors contributed to the research about COVID-19 complication and sequelae sorted by total number of articles.

Figure 4

Figure 5

The top ten journals are listed in descending order by the number of published articles (Table 2). The Journal of Medical Virology (IF: 2.327) published 14 articles, which was the highest number and accounted for 14.4% of the total 97 articles published by the ten journals. The second ranked journal was Journal of Clinical Medicine (IF: 4.241), which published 12 articles. Ten articles were published in each of the next four journals. They were Journal of Thrombosis and Haemostasis (IF: 5.824), Journal of Stroke and Cerebrovascular Disease (IF: 2.136), Frontiers in Neurology (IF: 4.003) and Diabetes Research and Clinical Care (IF: 5.602). The total citation count of Journal of Thrombosis and Haemostasis (IF: 5.824) was 85, belonging to Q1 according to the quartile in category which represents the credibility and recognition of the journal. In addition, of all these journals, Critical Care has the highest impact factors (IF: 9.097), while Frontiers in Immunology ranks the second (IF: 7.561).

Table 2

RankJournalArticle countsTotal counts of citationImpact factorQuartile in Category
1Journal of Medical Virology14322.327Q3
2Journal of Clinical Medicine1214.241Q1
3Journal of Thrombosis and Haemostasis10855.824Q1
4Journal of Stroke and Cerebrovascular Diseases1052.136Q2
5Frontiers in Neurology1014.003Q3
6Diabetes Research and Clinical Practice1015.602Q1
7Critical Care959.097Q1
8Frontiers in Immunology817.561Q2
9Clinical Medicine742.659Q1
10European Review for Medical and Pharmacological Sciences703.507Q2

The top 10 journals that published articles in COVID-19 complication and sequelae research sorted by article counts.

Research Hotspots

A total of 82 keywords were extracted and are listed in Table 3. The number of occurrences of keywords ranged from 69 to 3972 times. Through VOSviewer analysis, these items were classified into 5 clusters, which are shown in Figures 6A, B. Each cluster had a common theme: cluster 1 (23 items, in red, treatment), cluster 2 (19 items, in green, clinical manifestation), cluster 3 (16 items, in blue, risk factors), cluster 4 (12 items, in yellow, morbidity), and cluster 5 (12 items, in purple, diagnosis). The top five keywords of each cluster are listed as follows, and the number of occurrences is indicated:

  • Cluster 1: COVID (3972), Complication (1196), SARS cov (1028), Infection (970), Disease (761)

  • Cluster 2: Patient (3249), Study (685), Level (280), Time (231), Admission (227).

  • Cluster 3: Outcome (417), Mortality (363), Death (237), Age (226), Person (190).

  • Cluster 4: Pandemic (619), Risk (490), Management (314), Care (281), Surgery (234).

  • Cluster 5: Case (555), Symptom (352), Data (294), Pneumonia (216), Report (193).

Table 3

KeywordsclusterLinksTotal link strengthOccurrencesAverage publishing yearsAverage citations
Ace217729508220.30492.1854
Acute Respiratory Distress Syndrome181506712726.0632.8052
Addition1813290893.75280.4039
Admission2811150922710.61231.1422
Age3811172422617.25221.8612
April58160731216.34710.6831
Ards177406010212.52941.3486
Article18143031224.40160.4738
Association38150559330.54843.288
Care48194072815.06410.5468
Case5812145155512.66491.364
Child58149321514.04640.4355
China281765017225.4072.7346
Clinical Characteristic28140767732.61043.5099
Comorbidity381844917819.75842.1349
Complication1814344711969.87121.0629
Coronavirus181797223215.35781.6551
Coronavirus Disease1811963249818.9982.0448
Country4814056108101.0763
Covid181136572397210.18031.0958
Cytokine Storm1782548815.90120.6352
Data5811437329415.02721.6174
Day2811090421517.83261.9193
Death3811183823716.86081.8148
December28132548121.6792.3333
Diabete38178911736.9480.7478
Diabetes3795083896.14610.6615
Diagnosis58164941578.98730.9673
Disease1812923876111.29431.2156
Drug18154271448.07640.8693
Effect18187922229.43241.0152
Evidence181898624111.14521.1996
Fever581456110818.37961.9782
Group2811132522211.82881.2732
Higher Risk38132367317.83561.9197
Hospital280960418016.00561.7254
Hospitalization28147629524.37892.6239
Hypertension381596011121.87392.3543
Icu27934096911.21741.2073
Impact481625216410.79881.1683
Incidence281519610210.39221.1185
Individual3813734976.57730.713
Infection1813667797010.52991.1339
Intensive Care Unit281504210910.73391.1598
Level2811144928028.30363.0464
Management481118733146.98410.7548
March28070261428.08450.8701
Mortality3811837336318.14881.9547
Need48142831267.56350.8141
Number48172991708.62940.9317
Obesity3804120894.3820.4716
Outbreak481750816220.16052.1699
Outcome3812099841716.85851.8157
Pandemic481217006195.27630.5687
Patient281125336324916.94711.8251
Person38179361905.56320.5988
Pneumonia581877821613.37041.4391
Pregnancy580543011419.50882.0998
Pregnant Woman579458110213.43141.4456
Recommendation48040121167.92240.8527
Report581744819314.3991.5523
Review181129823277.22630.7778
Risk481188524909.42241.0182
Risk Factor38175511529.07240.9765
Role18153831713.64330.3921
Sars Cov1813606310289.20910.9926
Severe Acute Respiratory Syndrome Coronavirus181830423213.4311.4477
Severe Covid18140921036.04850.651
Severity381653413911.05041.1894
Study2813203368512.83071.381
Surgery478105412347.63250.8215
Symptom5811385335212.0541.2974
Time281954923113.87011.4971
Total28038527716.68831.7962
Treatment181194425218.31290.8985
Type38155129610.04171.0808
Use18159591549.32471.0068
Virus18181902349.37611.0092
Week57937377426.86492.8915
World4812941846.60710.717
Wuhan281483010534.27623.6892
Year2811029520024.0452.588
Ace217729508220.30492.1854
Acute Respiratory Distress Syndrome181506712726.0632.8052
Addition1813290893.75280.4039
Admission2811150922710.61231.1422
Age3811172422617.25221.8612
April58160731216.34710.6831
Ards177406010212.52941.3486
Article18143031224.40160.4738
Association38150559330.54843.288
Care48194072815.06410.5468
Case5812145155512.66491.364
Child58149321514.04640.4355
China281765017225.4072.7346
Clinical Characteristic28140767732.61043.5099
Comorbidity381844917819.75842.1349
Complication1814344711969.87121.0629
Coronavirus181797223215.35781.6551
Coronavirus Disease1811963249818.9982.0448
Country4814056108101.0763
Covid181136572397210.18031.0958
Cytokine Storm1782548815.90120.6352
Data5811437329415.02721.6174
Day2811090421517.83261.9193
Death3811183823716.86081.8148
December28132548121.6792.3333
Diabete38178911736.9480.7478
Diabetes3795083896.14610.6615
Diagnosis58164941578.98730.9673
Disease1812923876111.29431.2156
Drug18154271448.07640.8693
Effect18187922229.43241.0152
Evidence181898624111.14521.1996
Fever581456110818.37961.9782
Group2811132522211.82881.2732
Higher Risk38132367317.83561.9197
Hospital280960418016.00561.7254
Hospitalization28147629524.37892.6239
Hypertension381596011121.87392.3543
Icu27934096911.21741.2073
Impact481625216410.79881.1683
Incidence281519610210.39221.1185
Individual3813734976.57730.713
Infection1813667797010.52991.1339
Intensive Care Unit281504210910.73391.1598
Level2811144928028.30363.0464
Management481118733146.98410.7548
March28070261428.08450.8701
Mortality3811837336318.14881.9547
Need48142831267.56350.8141
Number48172991708.62940.9317
Obesity3804120894.3820.4716
Outbreak481750816220.16052.1699
Outcome3812099841716.85851.8157
Pandemic481217006195.27630.5687
Patient281125336324916.94711.8251
Person38179361905.56320.5988
Pneumonia581877821613.37041.4391
Pregnancy580543011419.50882.0998
Pregnant Woman579458110213.43141.4456
Recommendation48040121167.92240.8527
Report581744819314.3991.5523
Review181129823277.22630.7778
Risk481188524909.42241.0182
Risk Factor38175511529.07240.9765
Role18153831713.64330.3921
Sars Cov1813606310289.20910.9926
Severe Acute Respiratory Syndrome Coronavirus181830423213.4311.4477
Severe Covid18140921036.04850.651
Severity381653413911.05041.1894
Study2813203368512.83071.381
Surgery478105412347.63250.8215
Symptom5811385335212.0541.2974
Time281954923113.87011.4971
Total28038527716.68831.7962
Treatment181194425218.31290.8985
Type38155129610.04171.0808
Use18159591549.32471.0068
Virus18181902349.37611.0092
Week57937377426.86492.8915
World4812941846.60710.717
Wuhan281483010534.27623.6892
Year2811029520024.0452.588
Ace217729508220.30492.1854
Acute Respiratory Distress Syndrome181506712726.0632.8052
Addition1813290893.75280.4039
Admission2811150922710.61231.1422
Age3811172422617.25221.8612
April58160731216.34710.6831
Ards177406010212.52941.3486
Article18143031224.40160.4738
Association38150559330.54843.288
Care48194072815.06410.5468
Case5812145155512.66491.364
Child58149321514.04640.4355
China281765017225.4072.7346
Clinical Characteristic28140767732.61043.5099
Comorbidity381844917819.75842.1349
Complication1814344711969.87121.0629
Coronavirus181797223215.35781.6551
Coronavirus Disease1811963249818.9982.0448
Country4814056108101.0763
Covid181136572397210.18031.0958
Cytokine Storm1782548815.90120.6352
Data5811437329415.02721.6174
Day2811090421517.83261.9193
Death3811183823716.86081.8148
December28132548121.6792.3333
Diabete38178911736.9480.7478
Diabetes3795083896.14610.6615
Diagnosis58164941578.98730.9673
Disease1812923876111.29431.2156
Drug18154271448.07640.8693
Effect18187922229.43241.0152
Evidence181898624111.14521.1996
Fever581456110818.37961.9782
Group2811132522211.82881.2732
Higher Risk38132367317.83561.9197
Hospital280960418016.00561.7254
Hospitalization28147629524.37892.6239
Hypertension381596011121.87392.3543
Icu27934096911.21741.2073
Impact481625216410.79881.1683
Incidence281519610210.39221.1185
Individual3813734976.57730.713
Infection1813667797010.52991.1339
Intensive Care Unit281504210910.73391.1598
Level2811144928028.30363.0464
Management481118733146.98410.7548
March28070261428.08450.8701
Mortality3811837336318.14881.9547
Need48142831267.56350.8141
Number48172991708.62940.9317
Obesity3804120894.3820.4716

The analytic consequence of 82 keywords with from 69 to 3972 occurrence times.

Figure 6

Discussion

So far, 2019-nCoV has infected one hundred and thirty million people and affected the lives of billions of people. As the understanding of COVID-19 patients continues to develop, clinicians have gradually realized the dangers of the sequelae and complication that COVID-19 patients have. Early detection of possible complication and sequelae of each system will improve clinical outcomes and reduce their incidence. Laboratory and clinical data will be crucial to clarify the pathophysiology and potential damage of 2019-nCoV to various systems. Finally, the various system evaluations of patients after recovery are critical to understanding the natural history of 2019-nCoV in various systems and monitoring potential system sequelae. Therefore, we took the eight major systems as the entry point and analyzed in detail the morbidity and pathogenesis of the possible complication and sequelae of each system of COVID-19 patients (Supplementary Figure 2).

Respiratory Sequelae

The respiratory system is the primary target for attack by 2019-nCoV. Pathological changes occurred in the pulmonary parenchyma, pulmonary vascular endothelium, and alveoli of patients infected with COVID-19 (). There are case reports that the alternations in pulmonary parenchyma caused by 2019-nCoV could induce the occurrence of pneumothorax, leading to severe vasculitis and endotheliitis (). In the tissue section observations of the lung tissue of patients who died from COVID-19, it was found that the alveoli were destroyed and infiltrated by a large number of inflammatory cells, and the pulmonary microvascular was accompanied by a large number of thromboses (, ). Additionally, many patients recovering from COVID-19 still have a cough and shortness of breath after being cured, and severe cases can have extensive fibrosis of the lungs, resulting in severe dyspnea (). The above alternations would cause an imbalance of the ventilatory flow ratio, and there is no evidence that these pathological alterations are reversible. Therefore, patients infected with COVID-19 are impacted with severe pulmonary fibrosis and are still at risk after their nucleic acid test turns negative.

Cardiovascular Complication

Similar to other respiratory infections, pre-existing cardiovascular disease or risk factors increase susceptibility to COVID-19 (). Meanwhile, the mortality of patients with cardiovascular disease is relatively higher (). The cardiovascular diseases of patients infected with 2019-nCoV worsen significantly, and it can even cause new cardiovascular complication. A study from Wuhan, China showed that nearly 20% of patients infected with 2019-nCoV suffered cardiovascular damage and the patients’ conditions would worsen if their IL-6 was elevated (, ). The most serious cardiovascular complication of COVID-19 patients is myocarditis, which is most commonly defined as an elevation of hypersensitivity cardiac troponin I (cTnI) above the 99th percentile of the upper reference limit (). The onset of acute myocarditis results in ischemia and hypoxia and increases the risk of death if it exceeds the bearing capacity of the body (, ). In addition, both tachy- and brady-arrhythmias are known to occur in COVID-19 patients (). However, no study has described the incidence of ST-segment elevation myocardial infarction in COVID-19, but it appears to be low. Angiotensin converting enzyme 2 (ACE2) plays an essential role in the development of cardiovascular diseases (). High expression of ACE2 in COVID-19 patients lead to an imbalance of renin-angiotensin-aldosterone system (RAAS), which participates in the regulation of electrolytes and blood flow (, ). Excessive contraction of blood vessels and acceleration of blood flow increased the risk of hypertension and thrombosis (). In addition, elevated pressure in the peripheral blood increases the afterload on the heart and consequently causes organic pathological alterations of cardiac dilatational hypertrophy (). A study by Frankfurt University Hospital showed that 78 out of 100 survivors of COVID-19 had cardiovascular abnormalities, and 60 of them still had signs of persistent myocardial inflammation more than two months after the diagnosis ().

Neurological Complication

Neurological symptoms are also common in patients infected with 2019-nCoV (, ). Nearly forty percent of patients have neurological manifestations (). Most of these effects are seizures, delirium, and unconsciousness (–). A British study analyzed 153 patients with clinical syndromes related to COVID-19 pneumonia. Many of the patients suffered from new-onset psychosis, neurocognitive syndromes or affective disorders, and changes in mental status, which usually occurred in relatively young patients. Some showed symptoms associated with Guillain-Barre syndrome (–). When this virus infects the brain, viral encephalitis and purulent lesions increase the difficulty of treatment and caused sequelae after treatment (). In addition, the most dangerous condition was that the virus would induce paralysis of the respiratory center, causing apnea and threatening the patient’s life if it invaded the medulla oblongata and pons (). Recent studies indicated that 2019-nCoV can break through the blood-brain barrier and invade the brain, mainly through the nasal cavity and intestines and the virus has been detected in cerebrospinal fluid (–). In addition, it was found in the clinical examination of patients with neurological symptoms that almost all patients on imaging had brain bleeding to different degrees (). Cranial nerve injury leads to a loss of smell, temporary loss of consciousness, and even stroke (–). Local hypoxemia induced by cerebral circulation disorders can lead to permanent alterations of the brain ().

Digestive Complication

The clinical findings indicated that gastrointestinal reactions and liver dysfunction appeared in patients with COVID-19 (59, 60). Inappetence, vomiting, diarrhea and indigestion occurred in the patients. A meta-analysis of patient data from multiple countries revealed that more than half of patients had gastrointestinal reactions (). In addition, in a retrospective analysis of clinical cases, it was reported that 27.3% of patients showed liver biochemistry abnormalities and 3.9% had liver injury (61). The disturbance of the digestive system is attributed to the expression of ACE2 and the ACE2 receptor in digestive ducts (62, 63). The pathogenesis is similar to the complication experienced in the cardiovascular systems. However, most of the gastrointestinal complication caused by COVID-19 disappeared after effective treatment of the pneumonia, with few obvious sequelae. In addition, more noteworthy was the role of intestinal flora in the development of COVID-19. On the one hand, clinical data indicated the intestinal flora was disordered in patients with COVID-19, which lead to the adverse reactions in the gastrointestinal tract (64, 65). On the other hand, the intestinal flora had the potential to promote the activity of anti-inflammation cells in the alveolar and inhibit the progression of pneumonia, which is defined as the “gut-lung axis” (66).

Urinary Complication

The kidney is one of the important target organs causing the high mortality rate of COVID-19 (67). A clinical study entitled “Caution on Kidney Dysfunctions of 2019-nCoV Patients” published on the preprint platform medRxiv stated that 63% of patients showed symptoms of renal insufficiency, and CT scans showed 100% of patients with renal imaging abnormalities. It has been noted that kidney involvement in COVID-19 is frequent and it ranges from mild proteinuria to acute kidney injury (AKI) (68, 69). Numerous studies have indicated a high incidence of AKI in patients with COVID-19, especially in severe cases (70–72). According to clinical statistics, the mortality rate of COVID-19 patients with AKI was three times higher than in patients without kidney injury (73). Microscopic observation of the kidneys of patients who died of COVID-19 found that most patients had obvious renal tubular damage (74). Acute kidney injury significantly contributes to long-term effects on the kidney, such as microalbuminuria and chronic kidney diseases or renal failure, which needs routine dialysis (75). However, no studies have been reported on the long-term renal outcomes among patients recovered from COVID-19 (76). Therefore, it is essential to monitor the renal function of patients who are discharged from the hospital, especially with kidney damage caused by coronaviruses infection in order to improve the prognosis of COVID-19 and to prevent further renal injuries.

The kidney injury was more due to the secondary effect of immune reactions induced by 2019-nCoV rather than any direct effect of the virus (77). In other words, although COVID-19 could invade the kidney cells through the ACE2-dependent pathway, the virus-associated immune response and cytokine secretion were more likely to attack normal cells and cause kidney damage (78). However, this is based on only a consensus of the majority, and the pathogenesis of COVID-19 in kidney damage is still inconclusive. Identifying the reason for the kidney alterations will contribute to increased efficiency of treatment and an improved prognosis.

Endocrine Complication

In terms of the clinical manifestations of patients with COVID-19, most endocrine glands might be affected by the virus, such as the pancreas, adrenal glands, thyroid, etc. (79). Recent studies have indicated that patients with a history of diabetes were more susceptible to 2019-nCoV (80, 81). In addition, the presence of diabetes mellitus increased the risk of requiring critical care (82, 83). It was found in a microscope observation of the adrenal glands of patients with COVID-19 that 46% showed alterations in adrenal gland morphology such as ischemia, hemorrhage, degeneration, and local inflammation (84). Adrenal vascular alterations are likely to be caused by the immune disorder induced by 2019-nCoV (85). In addition, 15% of patients with COVID-19 had thyroid dysfunction (86). This was also attributed to the immunity response and autoimmunity induced by 2019-nCoV (87, 88). Meanwhile, the outbreak of the COVID-19 epidemic might worsen some glandular tumors and delay the timing of treatment (89). The above evidence showed that 2019-nCoV could attack the glands via the immune system, which might be the entry point for the treatment of endocrine complication. If there is no effective treatment, it will further aggravate the condition of diabetes and increase the risk of cancer and other chronic endocrine diseases.

Reproductive Complication

There are obvious sex differences in reproductive complication and sequelae. Recent studies had confirmed ACE2 is abundant in gametocytes, Sertoli cells and spermatogonia stem cells, suggesting the testis is a high-risk organ vulnerable to 2019-nCoV infection (90, 91). Indeed, coronavirus could damage the structure of the testicles and affect male fertility, supported by the detection of coronavirus in the semen of patients, some of whom had complication of orchitis (92). An observational study indicated that 39.1% of male patients with COVID-19 have oligospermia and 60.9% of them have a high inflammatory state in their semen (93). Around 19% of patients at the time of their COVID-19 confirmation were experiencing scrotal discomfort (94). In addition, interstitial oedema and congestion in the testes and epididymis are observed in all deceased COVID-19 patients, which also indicate potential testis injury (93). Compared with male patients, there are relatively few reports on the impact of the coronavirus on the female reproductive system. However, ACE2 has been demonstrated to be widely expressed in the female genital tract and ovary (95, 96), and thereby is likely to affect ovulation and embryonic development in a similar way (97, 98). Due to a lack of attention and limited duration of hospitalization, other reproductive dysfunctions such as infertility and menstrual disorders are difficult to identify. Therefore, follow-up studies and evaluation of reproductive function, especially fertility, is essential among patients recovered from COVID-19.

Skeletal Complication

During the epidemic of SARS, myalgia and muscle weakness were common complication (99). COVID-19 also has a direct impact on the skeletal system together with an indirect action through the regulation of nerves and the blood supply. 2019-nCoV combines with ACE2 and destroys the balance of RAS, which causes degradation of muscle protein and leads to physical dysfunction (100). In addition, infection-mediated deleterious immune responses lead to neurological abnormalities, and a significant increase in serum pro-inflammatory cytokines may lead to skeletal muscle damage (101). In addition, patients with myalgia tend to have higher levels of creatine kinase and lactate dehydrogenase (). Elevated levels of the pro-inflammatory factor interleukin-6 may be responsible for the myalgia and joint pain (102). Osteoimmunology reveals the potential effect of viral infection on the RANK-RANKL system, which increases bone resorption and induces osteoporosis. It is worth noting that after being discharged from the hospital, severe patients may have sequelae of muscle wasting due to the prolonged period spent in bed, and they require progressive rehabilitation training to gradually return to their pre-onset mobility (103). Furthermore, severe patients treated with glucocorticoids may also experience hip joint injuries and femoral head necrosis (104). At present, it seems that the patient’s condition is not effectively controlled, and an overdose of glucocorticoids is given, which may cause sequelae such as osteoporosis and osteonecrosis.

Other Involvement: Psychological Changes

The influence of COVID-19 on mental health due to restricted activity in public should not be ignored. The mental health status reported by patients with COVID-19 appears to be more serious. They fear death and are very prone to negative emotions (105). Unlike SARS survivors, the incidence of depression, anxiety, insomnia, and acute stress in patients with COVID-19 is 75%, 71%, 68%, and 71%, respectively, while the incidence of mental and psychological problems in COVID-19 survivors, 3 months after discharge and 30 months after discharge, is also much higher.

There are two aspects to the psychological complication or sequelae caused by COVID-19. One is that severely ill patients have experienced the fear of death. Even if their bodies recover, some people still have psychological fears. The other is that patients with mild illnesses cause people to fear rejection by others after their recovery. Many people who have recovered from mild illness have nervousness, anxiety, and fear. Regardless of whether they had mild or severe cases, nearly half of survivors have post-traumatic stress disorder, depression, or insomnia and anxiety. Some people cannot return to a normal state.

The mental and psychological problems of medical staff are even more prominent, and the incidence is significantly higher than that of non-medical staff. Among them, nurses have the highest incidence of psychological problems. It is indicated that anxiety among medical staff is 46%, while the incidence among non-medical staff is 8.5%. Other people, including front-line workers and their families, close contacts, and people in isolation, as well as low-income people in the community, are also susceptible to psychological problems, indicating that ordinary citizens also experience poor psychological health in the epidemic. It is shown that in the first five months of the pandemic, Japan’s monthly suicide rate dropped by 14%, but it rose by 16% in the second wave 90, while the suicide rate of women, children, and adolescents has increased even more.

Therefore, in the post-epidemic era, the construction of a mental health system is particularly important. A grid-based community psychological service system should be established, especially in the prevention stage. For example, a three-person psychological service team should be formed in schools, communities and some medical units to screen and serve for the mental health of the population. In addition, mental and psychological education courses should also be introduced in primary and secondary schools to avoid impairments of the mental development of the students.

As is mentioned above, clinical complications and sequelae of COVID-19 were common among survivors during early convalescence. Apart from the clinical characteristics during hospitalization, the outcomes of COVID-19 also vary across different ages and ethnic backgrounds. It was observed in a large cohort of survivors of COVID-19 in Wuhan, China that survivors with old age are especially susceptible to complications or sequelae of COVID-19 compared with younger individuals (106). Indeed, ageing plays an important role in the development of COVID-19 and its complications or sequelae. With age, mitochondrial quality, and function declines, leading to a variety of physiology changes, such as chronic inflammation and defective immune responses to viral infection, which eventually increases the susceptibility to COVID-19 complications and sequelae (107, 108). Likewise, the outcomes of COVID-19 also present certain ethnic and racial differences. It was observed that black patients with COVID-19 usually had higher mortality rates that white patients, which was also noted among pediatric patients. However, the racial disparities are more like to be multifactorial while black race alone was not associated with the high mortality rates (109–111). Black patients had higher prevalence of chronic diseases, such as diabetes, hypertension, chronic renal diseases and so forth. As is mentioned above, patients with pre-existing diseases usually had bad poor clinical outcomes and were with higher risks of various complications and sequelae. Additionally, work environment, living conditions, public insurance and economic conditions were also responsible for the prevalence and mortality rate of COVID-19 (110).

Currently, no specific treatment targeting major complications and sequelae of COVID-19, which is only limited to symptomatic treatment. Additionally, there is even no effective therapy for complications in certain systems, such as the reproductive system. Therefore, current treatment options should be extended in patients with COVID-19 and personalized therapies should be implemented based on the clinical characteristics during hospitalization and also the individual circumstances, such as age and pre-existing diseases. Consequently, it is crucial to development reasonable and effective treatment strategies to restore function of organs which were damaged during the course of COVID. In addition, daily symptom monitoring is necessary for patients discharged from hospital. Routine physical examination is strongly recommended for severe or elderly patients and patients with pre-existing diseases until 6 months after discharge.

There are several limitations that are specific to the use of bibliometric analysis in this study which may be inevitable. It has been only less than two years since the outbreak of COVID-19. Although significant breakthroughs have been made in the understanding COVID-19, there are relatively few literatures focused on the complications and sequelae of COVID-19 that have been published. As a result, only 82 keywords were extracted from the published literatures, which may lead to the inaccuracies in the classification of keywords. In addition, with accumulating evidence indicating that many survivors of COVID-19 are suffered from various complications and sequelae, it is believed that growing numbers of studies will focus on the complications and sequelae of COVID-19. Therefore, there may be discrepancies between our bibliometric analysis and the actual publication situation.

Conclusions

In the context of vaccination and effective medications, there are no obstacles to the elimination of 2019-nCoV. However, the damage of 2019-nCoV to the body has been ignored. We systematically analyzed the complication and sequelae of the eight systems of COVID-19 patients. Most of the complication or sequelae of patients are related to the expression of ACE2 on tissues and organs, which is the target recognized and bound by 2019-nCoV. The RAS axis participates in the regulatory process and leads to systemic disorders when the axis feedback is imbalanced. At the same time, we analyzed various psychological barriers of people in the post-epidemic era. In our study, we pay more attention to the adverse variations to the body caused by 2019-nCoV rather than just the virus itself. In conclusion, the prevention and treatment of complications and sequelae in COVID-19 patients in the post-epidemic era are the top priority, and they should and must attract the close attention of experts and scholars around the world.

Funding

This work was supported by the fellowship of China Postdoctoral Science Foundation [2020M670100ZX].

Publisher’s Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Statements

Author contributions

Conceptualization: LT, KY, JW, and GW. Methodology: KY, GW, and SZ. Investigation: LT, KY, GW, JW, SZ, WD, YM, and YX. Writing – original draft: KY, GW, JW, SZ, WD, YM, and YX. Writing – review and editing: LT, KY, JW, and GW. Supervision: LT, KY, JW, and GW. All authors contributed to the article and approved the submitted version.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fimmu.2021.711741/full#supplementary-material

Supplementary Figure 1

Flow chart of literature filtering involved in this study.

Supplementary Figure 2

Complication and sequelae of COVID-19 patients involved in eight major systems.

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Summary

Keywords

COVID-19, complication, sequelae, eight systems, bibliometric analysis, Web of Science

Citation

Yang K, Wen G, Wang J, Zhou S, Da W, Meng Y, Xue Y and Tao L (2021) Complication and Sequelae of COVID-19: What Should We Pay Attention to in the Post-Epidemic Era. Front. Immunol. 12:711741. doi: 10.3389/fimmu.2021.711741

Received

19 May 2021

Accepted

10 August 2021

Published

03 September 2021

Volume

12 - 2021

Edited by

Julia Kzhyshkowska, Heidelberg University, Germany

Reviewed by

Willy A. Valdivia-Granda, Orion Integrated Biosciences, United States; Shaza Shantier, University of Khartoum, Sudan; Samrat Kumar Dey, Dhaka International University, Bangladesh

Updates

Copyright

*Correspondence: Lin Tao,

†These authors have contributed equally to this work

This article was submitted to Viral Immunology, a section of the journal Frontiers in Immunology

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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