Statistical Inference for Linear Mediation Models with High-dimensional Mediators and Application to Studying Stock Reaction to COVID-19 Pandemic (preprint)

Mediation analysis draws increasing attention in many scientific areas such as genomics, epidemiology and finance. In this paper, we propose new statistical inference procedures for high dimensional mediation models, in which both the outcome model and the mediator model are linear with high dimensional mediators. Traditional procedures for mediation analysis cannot be used to make statistical inference for high dimensional linear mediation models due to high-dimensionality of the mediators. We propose an estimation procedure for the indirect effects of the models via a partial penalized least squares method, and further establish its theoretical properties. We further develop a partial penalized Wald test on the indirect effects, and prove that the proposed test has a $\chi^2$ limiting null distribution. We also propose an $F$-type test for direct effects and show that the proposed test asymptotically follows a $\chi^2$-distribution under null hypothesis and a noncentral $\chi^2$-distribution under local alternatives. Monte Carlo simulations are conducted to examine the finite sample performance of the proposed tests and compare their performance with existing ones. We further apply the newly proposed statistical inference procedures to study stock reaction to COVID-19 pandemic via an empirical analysis of studying the mediation effects of financial metrics that bridge company's sector and stock return.

Clinical Course and Risk Factors for Liver Injury of Severe and Critical Patients With COVID-19 (preprint)

Background: Information regarding the clinical course of COVID-19 patients with liver injury is very limited, especially in severe and critical patients. The objective of this study was to describe the characteristics and clinical course of liver function in patients admitted with severe and/or critical SARS-CoV-2 infection, as well as explore the risk factors that affect liver function in the enrolled COVID-19 patients.Methods: Information on clinical characteristics of 63 severe and critical patients with confirmed COVID-19 were collected and analyzed.Results: The incidence of abnormal aspartate aminotransferase, alanine aminotransferase, and total bilirubin in the critical group was significantly higher than in the severe group (respectively 81.48%, 81.49%, 62.67%, and 45.71%, 63.88%, 22.86%, p＜0.05). The time for liver function parameters to reach their extremes was approximately 2-3 weeks after admission. The independent factors associated with liver injury were patients with invasive ventilators, decreased percentages of neutrophils, lymphocytes and monocytes, and sequential organ failure assessment (SOFA) score ≥ 2 (p＜0.05).Conclusions: Abnormal liver tests are commonly observed in severe and critical patients with COVID-19. The patients with severe illness should be closely observed to monitor liver function parameters, particularly when they present with independent risk factors of liver injury.

Detection of SARS-CoV-2 nucleic acid in CSF by ultrahigh depth sequencing in a patient with COVID-19 and neurological dysfunction: a case report (preprint)

Background: SARS-Coronavirus-2 (SARS-CoV-2), the pathogen of coronavirus disease 2019 (COVID-19), not only infects the respiratory tract, but also other organs. About a third of the inpatients of COVID-19 have neurological symptoms and in vitro experiments revealed that SARS-CoV-2 could infect human neural progenitor cells and brain organoids. However, the traditional test often reports negative owing to the low number of virus in the cerebrospinal fluid. To date, timely diagnosis of central nervous system infection of SARS-CoV-2 remains a challenge.Case presentation: On day 14 of COVID-19, seizures, maxillofacial convulsions, intractable hiccups and significant increase in intracranial pressure developed in a 56-year-old man. The RT-PCR of SARS-CoV-2 was negative. SARS-CoV-2 nucleic acid were detected in cerebrospinal fluid (CSF) by ultrahigh depth sequencing. The patient was successfully treated after 14 days of mechanical ventilation and treatment of pneumonia and neurological dysfunction.Conclusions: This case suggests SARS-CoV-2 can invade the central nervous system and relevant examinations with CSF including ultrahigh depth sequencing of SARS-CoV-2 are needed among COVID-19 patients with neurological dysfunction.

Carboxypeptidase B Inhibits Over-activation of Anaphylatoxin-neutrophil Extracellular Trap Axis in COVID-19 Patients (preprint)

Background: Thrombosis and coagulopathy are highly prevalent in severe patients with COVID-19 and increase the risk of death. Immunothrombosis has recently been demonstrated to contribute to the thrombotic events in COVID-19 patients with coagulopathy. Neutrophil extracellular traps (NETs) are primary components of immunothrombosis, whereas the mechanism of NET formation remains unclear. We aim to explore the clinical roles of NETs and the regulation of complement on the NET formation in COVID-19. Methods: : We recruited 135 COVID-19 patients and measured plasma levels of C5, C3, cell-free DNA and myeloperoxidase-DNA. We detected complement-induced NET formation by immunofluorescent staining and evaluated the cytotoxicity to vascular endothelial HUVEC cells by CCK-8 assay. Results: : We found that the plasma levels of complements (C3 and C5) and NETs were closely related to coagulopathy and multiple organ dysfunction in patients with COVID-19. By using anti-C3a and anti-C5a antibodies, we revealed that the complement component anaphylatoxins in the plasma of COVID-19 patients strongly induced NET formation. The pathological effect of the anaphylatoxin-NET axis on the damage of vascular endothelial cells could be relieved by recombinant carboxypeptidase B (CPB), a stable homolog of enzyme CPB2 which can degrade anaphylatoxins to inactive products. Conclusions: : Over-activation in anaphylatoxin-NET axis plays a pathological role in COVID-19. Early intervention in anaphylatoxins might help prevent thrombosis and disease progression in COVID-19 patients.

Clinical Course and Risk Factors for Liver Injury of Severe and Critical Patients With COVID-19: A Single-centered, Retrospective, Observational Study (preprint)

Background: The information regarding the clinical course of COVID-19 patients with liver injury is very limited, especially in severe and critical patients. The objective of this study was to describe the characteristics and clinical course of patients admitted with severe and/or critical SARS-CoV-2 infection in liver function, as well as explore the risk factors that affect liver function in the enrolled COVID-19 patients.Methods: Information on clinical characteristics of 63 severe and critical patients with confirmed COVID-19 were collected and analyzed.Results: The incidence of abnormal aspartate aminotransferase, alanine aminotransferase, and total bilirubin in the critical group was obviously higher than in the severe group (81.48%, 81.49%, 62.67%, and 45.71%, 63.88%, 22.86%, respectively, p＜0.05). The time for liver parameters to reach their peak or trough was approximately 2-3 weeks. No significant difference was observed in cycle threshold values of open reading frame 1ab and nucleocapsid protein gene on admission or at the peak among liver injury group, abnormal group and normal group (p＞0.05). Patients with invasive ventilator, decreased percentage of neutrophil, lymphocyte and monocyte, and SOFA score ≥ 2 (p＜0.05) were the independent factors associated with liver injury.Conclusions: Abnormal liver tests are commonly observed in severe and critical patients with COVID-19. The time of 2-3 weeks after admission should be paid attention to patients with critical COVID-19 in case of the occurrence of liver injury. As independent risk factors for the occurrence of liver injury, regarding decreased ratio of neutrophils, lymphocytes and monocytes, the requirement of invasive ventilator, and SOFA score ≥2 , patients with these abnormal parameters should be of particular concerned during hospitalization.

Impaired cellular immunity to SARS-CoV-2 in severe COVID-19 patients (preprint)

The World Health Organization has declared SARS-CoV-2 virus outbreak a world-wide pandemic. Individuals infected by the virus exhibited different degrees of symptoms, the basis of which remains largely unclear. Currently, though convalescent individuals have been shown with both cellular and humoral immune responses, there is very limited understanding on the immune responses, especially adaptive immune responses, in patients with severe COVID-19. Here, we examined 10 blood samples from COVID-19 patients with acute respiratory distress syndrome (ARDS). The majority of them (70%) mounted SARS-CoV-2-specific humoral immunity with production of neutralizing antibodies. However, compared to healthy controls, the percentages and absolute numbers of both NK cells and CD8+ T cells were significantly reduced, accompanied with decreased IFN{gamma} expression in CD4+ T cells in peripheral blood from severe patients. Most notably, we failed in detecting SARS-CoV-2-specific IFN{gamma} production by peripheral blood lymphocytes from these patients. Our work thus indicates that COVID-19 patients with severe symptoms are associated with defective cellular immunity, which not only provides insights on understanding the pathogenesis of COVID-19, but also has implications in developing an effective vaccine to SARS-CoV-2.

Comparative therapeutic efficacy of interferon and combination Kaletra plus interferon alpha-2b against SARS-CoV-2 (preprint)

Background: The outbreak of coronavirus disease 2019 (COVID-19) posed an enormous threat to public health. The use of antiviral drugs in patients with this disease have triggered people’s attentions. Whether interferon alfa-2b or Kaletra plus interferon alfa-2b treatment can against SARS-CoV-2 was unknown.Methods: This is a retrospective cohort study of 123 laboratory-confirmed COVID-19 patients between Jan.13 2020 and Apr. 23. All patients received standard supportive care and regular clinical monitoring, patients were assigned to standard care group (n=12), interferon alfa-2b group (n=44), and combination Kaletra plus interferon alfa-2b group (n=67) according to their therapies. The primary endpoint for this study was the duration of oxygen-support requirement and virus clearance time. The associations of therapies with these outcomes were assessed by Cox proportional hazards regression. Results: Baseline clinical and laboratory characteristics were similar among 3 groups (p＞0.05). There was no significant association of Kaletra /interferon alfa-2b with faster SARS-CoV-2 RNA clearance (HR, 0.85 [95% CI, 0.45–1.61]; P = 0.61 in interferon alfa-2b group vs HR, 0.59 [95% CI, 0.32–1.11]; P = 0.10 in Kaletra plus interferon alfa-2b group). The duration of oxygen-support requirement in therapy groups similarly showed no significant association. There were no differences among 3 groups in the incidence of adverse events (p＞0.05).Conclusions: In patients with confirmed SARS-CoV-2 infection, no benefit was observed with interferon alfa-2b and Kaletra plus interferon alfa-2b treatment beyond standard care. Further trials in appropriately randomized design may contribute to validate the effective role and safety profile of the test drugs. 

Neutrophil-to-Lymphocyte Ratio Predicts Severe Illness Patients with 2019 Novel Coronavirus in the Early Stage (preprint)

Background: Severe ill patients with 2019 novel coronavirus (2019-nCoV) infection progressed rapidly to acute respiratory failure. We aimed to select the most useful prognostic factor for severe illness incidence. Methods: The study prospectively included 61 patients with 2019-nCoV infection treated at Beijing Ditan Hospital from January 13, 2020 to January 31, 2020. Prognostic factor of severe illness was selected by the LASSO COX regression analyses, to predict the severe illness probability of 2019-CoV pneumonia. The predictive accuracy was evaluated by concordance index, calibration curve, decision curve and clinical impact curve. Results: The neutrophil-to-lymphocyte ratio (NLR) was identified as the independent risk factor for severe illness in patients with 2019-nCoV infection. The NLR had a c-index of 0.807 (95% confidence interval, 0.676-0.38), the calibration curves fitted well, and the decision curve and clinical impact curve showed that the NLR had superior standardized net benefit. In addition, the incidence of severe illness was 9.1% in age [≥] 50 and NLR < 3.13 patients, and half of patients with age [≥] 50 and NLR [≥] 3.13 would develop severe illness. Based on the risk stratification of NLR with age, the study developed a 2019-nCoV pneumonia management process. Conclusions: The NLR was the early identification of risk factors for 2019-nCoV severe illness. Patients with age [≥] 50 and NLR [≥] 3.13 facilitated severe illness, and they should rapidly access to intensive care unit if necessary.