Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the ongoing coronavirus disease 2019 (COVID-19) pandemic. Alongside investigations into the virology of SARS-CoV-2, understanding the fundamental physiological and immunological processes underlying the clinical manifestations of COVID-19 is vital for the identification and rational design of effective therapies. Here, we provide an overview of the pathophysiology of SARS-CoV-2 infection. We describe the interaction of SARS-CoV-2 with the immune system and the subsequent contribution of dysfunctional immune responses to disease progression. From nascent reports describing SARS-CoV-2, we make inferences on the basis of the parallel pathophysiological and immunological features of the other human coronaviruses targeting the lower respiratory tract - severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV). Finally, we highlight the implications of these approaches for potential therapeutic interventions that target viral infection and/or immunoregulation.

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The trinity of COVID-19: immunity, inflammation and intervention.

Although COVID-19 is most well known for causing substantial respiratory pathology, it can also result in several extrapulmonary manifestations. These conditions include thrombotic complications, myocardial dysfunction and arrhythmia, acute coronary syndromes, acute kidney injury, gastrointestinal symptoms, hepatocellular injury, hyperglycemia and ketosis, neurologic illnesses, ocular symptoms, and dermatologic complications. Given that ACE2, the entry receptor for the causative coronavirus SARS-CoV-2, is expressed in multiple extrapulmonary tissues, direct viral tissue damage is a plausible mechanism of injury. In addition, endothelial damage and thromboinflammation, dysregulation of immune responses, and maladaptation of ACE2-related pathways might all contribute to these extrapulmonary manifestations of COVID-19. Here we review the extrapulmonary organ-specific pathophysiology, presentations and management considerations for patients with COVID-19 to aid clinicians and scientists in recognizing and monitoring the spectrum of manifestations, and in developing research priorities and therapeutic strategies for all organ systems involved.

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Extrapulmonary manifestations of COVID-19.

An outbreak of severe Kawasaki-like disease at the Italian epicentre of the SARS-CoV-2 epidemic: an observational cohort study.

COVID-19 pathophysiology: A review.

The COVID-19 pandemic has shown a markedly low proportion of cases among children1–4. Age disparities in observed cases could be explained by children having lower susceptibility to infection, lower propensity to show clinical symptoms or both. We evaluate these possibilities by fitting an age-structured mathematical model to epidemic data from China, Italy, Japan, Singapore, Canada and South Korea. We estimate that susceptibility to infection in individuals under 20 years of age is approximately half that of adults aged over 20 years, and that clinical symptoms manifest in 21% (95% credible interval: 12–31%) of infections in 10- to 19-year-olds, rising to 69% (57–82%) of infections in people aged over 70 years. Accordingly, we find that interventions aimed at children might have a relatively small impact on reducing SARS-CoV-2 transmission, particularly if the transmissibility of subclinical infections is low. Our age-specific clinical fraction and susceptibility estimates have implications for the expected global burden of COVID-19, as a result of demographic differences across settings. In countries with younger population structures—such as many low-income countries—the expected per capita incidence of clinical cases would be lower than in countries with older population structures, although it is likely that comorbidities in low-income countries will also influence disease severity. Without effective control measures, regions with relatively older populations could see disproportionally more cases of COVID-19, particularly in the later stages of an unmitigated epidemic. A new epidemiological study shows reduced susceptibility to SARS-CoV-2 and decreased risk of developing severe symptoms in people aged younger than 20 years, suggesting that children have limited contribution to spread of COVID-19.

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Age-dependent effects in the transmission and control of COVID-19 epidemics.

OBJECTIVE: To identify the epidemiological characteristics and transmission patterns of pediatric patients with the 2019 novel coronavirus disease (COVID-19) in China. METHODS: Nationwide case series of 2135 pediatric patients with COVID-19 reported to the Chinese Center for Disease Control and Prevention from January 16, 2020, to February 8, 2020, were included. The epidemic curves were constructed by key dates of disease onset and case diagnosis. Onset-to-diagnosis curves were constructed by fitting a log-normal distribution to data on both onset and diagnosis dates. RESULTS: There were 728 (34.1%) laboratory-confirmed cases and 1407 (65.9%) suspected cases. The median age of all patients was 7 years (interquartile range: 2–13 years), and 1208 case patients (56.6%) were boys. More than 90% of all patients had asymptomatic, mild, or moderate cases. The median time from illness onset to diagnoses was 2 days (range: 0–42 days). There was a rapid increase of disease at the early stage of the epidemic, and then there was a gradual and steady decrease. The disease rapidly spread from Hubei province to surrounding provinces over time. More children were infected in Hubei province than any other province. CONCLUSIONS: Children of all ages appeared susceptible to COVID-19, and there was no significant sex difference. Although clinical manifestations of children’s COVID-19 cases were generally less severe than those of adult patients, young children, particularly infants, were vulnerable to infection. The distribution of children’s COVID-19 cases varied with time and space, and most of the cases were concentrated in Hubei province and surrounding areas. Furthermore, this study provides strong evidence of human-to-human transmission.

https://pediatrics.aappublications.org/content/pediatrics/early/2020/03/16/peds.2020-0702.1.full.pdf

Epidemiology of COVID-19 Among Children in China.

BACKGROUND
Metagenomic next-generation sequencing (mNGS) has the potential to become a complementary, if not essential, test in some clinical settings. However, the clinical application of mNGS in a large population of children with various types of infectious diseases (IDs) has not been previously evaluated.


METHODS
From April 2019 to April 2021, 640 samples were collected at a single pediatric hospital and classified as ID [479 (74.8%)], non-ID [NID; 156 (24.4%)], and unknown cases [5 (0.8%)], according to the final clinical diagnosis. We compared the diagnostic performance in pathogen detection between mNGS and standard reference tests.


RESULTS
According to final clinical diagnosis, the sensitivity and specificity of mNGS were 75.0% (95% CI: 70.8%-79.2%) and 59.0% (95% CI: 51.3%-66.7%), respectively. For distinguishing ID from NID, the sensitivity of mNGS was approximately 45.0% higher than that of standard tests (75.0% vs 30.0%; P < 0.001). For fungal detection, mNGS showed positive results in 93.0% of cases, compared to 43.7% for standard tests (P < 0.001). Diagnostic information was increased in respiratory system samples through the addition of meta-transcriptomic sequencing. Further analysis also showed that the read counts in sequencing data were highly correlated with clinical diagnosis, regardless of whether infection was by single or multiple pathogens (Kendall's tau b = 0.484, P < 0.001).


CONCLUSIONS
For pediatric patients in critical condition with suspected infection, mNGS tests can provide valuable diagnostic information to resolve negative or inconclusive routine test results, differentiate ID from NID cases, and facilitate accurate and effective clinical therapeutic decision-making.

Diagnostic Performance of Metagenomic Next-Generation Sequencing in Pediatric Patients: A Retrospective Study in a Large Children's Medical Center.

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SIRT2 functions as a histone delactylase and inhibits the proliferation and migration of neuroblastoma cells

Evaluation of acute kidney injury by urinary tissue inhibitor metalloproteinases-2 and insulin-like growth factor-binding protein 7 after pediatric cardiac surgery

Objective To evaluate the risk of major infections in children with newly diagnosed childhood-onset systemic lupus erythematosus (cSLE). Methods Predictors of major infections were identified by the multivariable logistic regression. Major infection free was defined as no major infection events within 6 months after the diagnosis of cSLE. The Kaplan–Meier survival plot was performed. A prediction model for major infection events was established and examined by receiver operating characteristic (ROC) curve analysis. Results A total of 98 eligible patients were recorded in the medical charts. Sixty-three documented events of major infections were found in 60 (61.2%) cSLE patients. Furthermore, 90.5% (57/63) of infection events occurred within the first 6 months after the diagnosis of cSLE. The high SLEDAI (SLEDAI >10), lupus nephritis and lymphocyte count <0.8×109/L were predictors for major infections. The CALL score (Children with high disease activity [SLEDAI >10], lymphopenia, and LN) was defined by the number of predictors. Patients were then categorized into two groups: low-risk (score 0–1) and high-risk (score 2–3). Patients in the high-risk group had higher rates of the major infection occurrence than those in the low-risk group during the 6 months after the diagnosis of the cSLE (P<0.001) (HR:14.10, 95% CI 8.43 to 23.59). The ROC curve analysis indicated that the CALL score was effective both in the whole cSLE cohort [area under the curve (AUC) = 0.89, 95% CI: 0.81–0.97] and in the subgroup of lung infections (n = 35) (AUC = 0.79, 95% CI: 0.57–0.99). Conclusion High disease activity, LN and lymphopenia were predictors for major infections in newly diagnosed cSLE patients. Specific predictors help identify the cSLE patients with the high risk of major infections. The CALL score could be a useful tool to stratify cSLE patients in practice.

Xi Mo

Papers

Epidemiology of COVID-19 Among Children in China.

Diagnostic Performance of Metagenomic Next-Generation Sequencing in Pediatric Patients: A Retrospective Study in a Large Children's Medical Center.

SIRT2 functions as a histone delactylase and inhibits the proliferation and migration of neuroblastoma cells

Evaluation of acute kidney injury by urinary tissue inhibitor metalloproteinases-2 and insulin-like growth factor-binding protein 7 after pediatric cardiac surgery

Major Infections of Newly Diagnosed Childhood-Onset Systemic Lupus Erythematosus