Objective: As the prevention and control of COVID-19continues to advance, the active nucleic acid test screening in the close contacts of the patients has been carrying out in many parts of China. However, the false-positive rate of positive results in the screening has not been reported up to now. But to clearify the false-positive rate during screening is important in COVID-19 control and prevention. Methods: Point values and reasonable ranges of the indicators which impact the false-positive rate of positive results were estimated based on the information available to us at present. The false-positive rate of positive results in the active screening was deduced, and univariate and multivariate-probabilistic sensitivity analyses were performed to understand the robustness of the findings. Results: When the infection rate of the close contacts and the sensitivity and specificity of reported results were taken as the point estimates, the positive predictive value of the active screening was only 19.67%, in contrast, the false-positive rate of positive results was 80.33%. The multivariate-probabilistic sensitivity analysis results supported the base-case findings, with a 75% probability for the false-positive rate of positive results over 47%. Conclusions In the close contacts of COVID-19 patients, nearly half or even more of the 'asymptomatic infected individuals’ reported in the active nucleic acid test screening might be false positives.

In 2018, the myopia detection rate of children and adolescents aged 5-18 years old in Shaanxi Province was 54.9% (11 060/20 144). The myopia detection rate of girls ［58.6%(5 830/9 949)］ was higher than that of boys ［58.6% (3 416/5 830)］ ( P<0.001). In children and adolescents, the myopia detection rate increased with the age before their 16 years old, and saw a stable or downward trend after the age of 16. After adjusting the confounding factors, the myopia detection rate of children and adolescents from regions with per capita GDP>100 000 yuan was higherthan that of children and adolescents from regions with per capita GDP<50 000 yuan［ OR (95% CI):1.58(1.34-1.87)］.

In 2018, the myopia detection rate of children and adolescents aged 5-18 years old in Shaanxi Province was 54.9% (11 060/20 144). The myopia detection rate of girls ［58.6%(5 830/9 949)］ was higher than that of boys ［58.6% (3 416/5 830)］ ( P<0.001). In children and adolescents, the myopia detection rate increased with the age before their 16 years old, and saw a stable or downward trend after the age of 16. After adjusting the confounding factors, the myopia detection rate of children and adolescents from regions with per capita GDP>100 000 yuan was higherthan that of children and adolescents from regions with per capita GDP<50 000 yuan［ OR (95% CI):1.58(1.34-1.87)］.

Objective:By analyzed the transmission patterns of 4 out of the 51 COVID-19 cluster cases in Shaanxi province to provide evidences for the COVID-19 control and prevention.Methods:The epidemiological data of RT-PCR test-confirmed COVID-19 cases were collected. Transmission chain was drawn and the transmission process was analyzed.Results:Cluster case 1 contained 13 cases and was caused by a family of 5 who traveled by car to Wuhan and returned to Shaanxi. Cluster case 2 had 5cases and caused by initial patient who participated family get-together right after back from Wuhan while under incubation period. Cluster case 3 contained 10 cases and could be defined as nosocomial infection. Cluster case 4 contained 4 cases and occurred in work place.Conclusion:Higher contact frequency and smaller places were more likely to cause a small-scale COVID-19 cluster outbreak, with potential longer incubation period. COVID-19 control strategies should turn the attention to infection prevention and control in crowded places, management of enterprise resumption and prevention of nosocomial infection.

COVID-19 has brought a significant impact to the global health system, and also opportunities and challenges to epidemiological researches. Theoretical epidemiological models can simulate the process of epidemic in scenarios under different conditions. Therefore, modeling researches can analyze the epidemical trend of COVID-19, predict epidemical risks, and evaluate effects of different control measures and vaccine policies. Theoretical epidemiological modeling researches provide scientific advice for the prevention and control of infectious diseases, and play a crucial role in containing COVID-19 over the past year. In this study, we review the theoretical epidemiological modeling researches on COVID-19 and summarize the role of theoretical epidemiological models in the prevention and control of COVID-19, in order to provide reference for the combination of mathematical modeling and epidemic control.
COVID-19 ; Communicable Diseases/epidemiology* ; Humans ; Models, Theoretical ; SARS-CoV-2