Incubation Period Estimation,Superspreading Potentials And Clinical Prognosis Analysis Of SARS-CoV-2 And Its Variant Strain

Objective: Epidemiological contact tracing data of cases infected with SARS-Co V-2B.1.617.2(Delta)variants from July to August 2021 in Nanjing and Yangzhou,Jiangsu Province,were analyzed to characterize the incubation period and superspreading potential of the Delta variants,and the effects of age,sex,and disease severity on incubation period were investigated by multivariate regression analysis and subgroup analysis.By modeling and analyzing the clinical characteristics of the indicators of critically ill patients with novel coronavirus pneumonia(COVID-19)in a hospital in Urumqi,Xinjiang,we screened the influential factors affecting the inability of critically ill patients with COVID-19 to be transferred out of the ICU within a short period of time,thus informing the prognosis of the disease.Methods: We collected contact tracing data for laboratory-confirmed cases of SARS-Co V-2 B.1.617.2(Delta)infections from July to August 2021 on the official websites of the Health Committee of Nanjing and Yangzhou,Jiangsu Province.The incubation distribution of the Delta variants was estimated by using a likelihood-based approach and adjusting for interval-censored observations.The effects of age,sex,and disease severity on incubation were described by multivariate logistic regression models using interval censoring.The superspreading potential of the Delta variants was assessed by modeling the spread of the epidemic as a typical branching process,controlled for transmission heterogeneity by a negative binomial distribution model,and subgroup analysis was performed by different exposure settings and ages.A generalized linear mixed effect model was developed to screen for influential factors affecting the transfer of critically ill COVID-19 patients out of the ICU using Laplace approximation parameter estimation based on great likelihood estimation.Results: The mean incubation period for SARS-Co V-2 B.1.617.2(Delta)was estimated to be 6.64 days(95% CI: 6.27-7.00)by analysis.We found that the mean incubation period was relatively longer in female cases with heavy and critical cases than in male cases with light and common cases,respectively.The incubation of the Delta variants was found to be associated with disease severity,i.e.,there was a slight decrease in the probability of developing severe disease for each additional day of incubation of the Delta variants,with an adjusted dominance ratio OR of0.88(95% CI: 0.71-1.07).We estimated that 14%(95% CI: 11%-16%)of the most infectious cases were responsible for 80% of transmission events in Nanjing and Yangzhou,of which 74%(95% CI: 69%-78%)had 0 offspring secondary cases.In addition,we found that cases in mahjong house had superspreading potential,with 5% of cases generating 80%of total transmission secondary cases.Analysis by building a GLMM model yielded four influencing factors that affected the inability of critically ill COVID-19 patients to be transferred out of the ICU within a short period of time: age(0.949,95% CI: 0.930-0.968),CRP(0.984,95% CI: 0.978-0.989),Cr(1.027,95% CI: 1.018-1.035)and LDH(0.993,95%CI: 0.991-0.996),where the OR of age,CRP and LDH were less than 1,indicating that these three factors were protective factors and that the estimates were negative,indicating that as age,CRP and LDH levels decreased,COVID-19 critically ill patients were more likely to be transferred out of the intensive care unit within a short period of time.Conversely,Cr was a risk factor with an OR greater than 1,indicating that as Cr levels increased,COVID-19 critically ill patients had a greater probability of being transferred out of the intensive care unit within a short period of time.Conclusion: In this study,the incubation period of SARS-Co V-2 B.1.617.2(Delta)strain was found to vary by age and disease severity.These findings provide additional information on the incubation of Delta variantss.Under strict COVID-19 outbreak control measures and aggressive COVID-19 nucleic acid testing,the Delta variants still exhibits great potential for superspreading.Therefore,enhanced surveillance of disease transmissibility,especially in high-risk settings for superspreading,will be key to mitigating epidemics caused by emerging variant strains.In the process of transferring COVID-19 patients to ICU for treatment,clinicians can analyze the reasons for the decrease in Cr index and the increase in Age,CRP,LDH index in patients,so that the causes can be quickly diagnosed and treated,thus allowing patients to be transferred out of ICU in a short period of time.