[Advance on theoretical epidemiology models research of prevention and control of COVID-19].

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.

[Typical case analysis of COVID-19 cluster epidemic in Shaanxi, 2020].

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.

[The status and related factors of myopia for children and adolescents aged 5-18 years old in Shaanxi Province in 2018].

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 ï¼»58.6%(5 830/9 949)ï¼½ was higher than that of boys ï¼»58.6% (3 416/5 830)ï¼½ (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 yuanï¼»OR (95%CI):1.58(1.34-1.87)ï¼½.

[WITHDRAWN: Potential false-positive rate among the 'asymptomatic infected individuals' in close contacts of COVID-19 patients].

Editor office's response for Ahead of Print article withdrawn The article "Potential false-positive rate among the 'asymptomatic infected individuals' in close contacts of COVID-19 patients" was under strong discussion after pre-published. Questions from the readers mainly focused on the article's results and conclusions were depended on theoretical deduction, but not the field epidemiology data and further researches were needed to prove the current theory. Based on previous discussions, the article was decided to be offline by the editorial board from the pre-publish lists. 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.

A flow cytometric comparison of DNA content and glutathione levels in hepatocytes of English sole (Parophyrs vetulus) from areas of differing water quality.

English sole (Parophyrs vetulus) in Puget Sound, Washington, USA are at risk of hepatocarcinogenesis specifically in areas adjacent to polluting industrial effluents. A question concerning population and ecosystem survival is whether any of the effects of etiopathologic change are reversible. This has been approached by looking for evidence of tumor accelerating effects in an exposed population. Cellular parameters were determined by flow cytometry for hepatocytes of English sole. Cells containing hyperdiploid DNA not present in fish from reference waters, Port Madison, were found in all non-tumor-bearing and tumor bearing fish taken from a polluted site, Eagle Harbor, where incidence of hepatic neoplasia approaches 30%. Induction of altered DNA content in the exposed general hepatocyte population suggests environmental induction rather than an association with lesions per se. In contrast, glutathione levels in hepatocytes (0.8-3.2 nmol/mg protein), were little influenced by the exposure site, consistent with the apparent lack of protection against chemically induced carcinogenesis in English sole. Association of altered DNA content with exposure site is significant for its potential contribution to biological acceleration and evidence of tumor promotion found at the tissue and organismic levels. The results support the notion that hepatocarcinogenesis in English sole in Eagle Harbor has a multi-year exposure etiology, in which potentially reversible accelerating influences have a role, and that glutathione conjugation is an inadequate mode of detoxification for these fish.

Asymmetrical pairings of transposons in and proximal to the white locus of Drosophila account for four classes of regularly occurring exchange products.

An explanation for the origins of four classes of regularly occurring duplication and deficiency chromosomes is provided through examination of their molecular structures. The duplications and deficiencies occur as the reciprocal products of crossing-over, following two different patterns of asymmetrical synapsis between transposons positioned in and proximal to the white locus of Drosophila melanogaster. Three copies of the retrovirus-like transposon roo are involved in the exchanges. Evidence suggests that transposon-mediated asymmetrical exchange is a general phenomenon in eukaryotes, which adds significantly to the effects of transposons in the restructuring of eukaryotic genomes.

A revision of the cytology and ontogeny of several deficiencies in the 3A1-3C6 region of the X chromosome of Drosophila melanogaster.

The cytology and developmental attributes of 18 deficiency mutations in the 3A1-3C6 region of the salivary gland X chromosome of Drosophila melanogaster have been investigated. The cytological limits of several older deficiencies have been revised and clarified and several new deficiencies are characterized. The deficiency mutants, withone possible exception, show a lethal phase in the late embryonic period or the early first larval instar. In contrast, the earliest acting point mutation lethals exposed by these deficiencies generally exhibit a somewhat later, post-embryonic lethality, perhaps indicating that the deficiencies are having some cumulative or synergistic impact on development. However, even with this difference in time of lethality, it is still possibleto conclude that it is not the absolute size of the deficiency but rather the character of the loci delected that determines the impact on development. Observations on the morphology of lethal embryos shows that while this analysis is internally consistent, it does not agree with earlier work. None of the 3A1-3C6 deficiencies causes any major teratologies during embryogenesis. Furthermore, the "earliest acting" gene in this region does not lie in band 3C1 but is most likely associated with bands3A8-10.

Lethality patterns and morphology of selected lethal and semi-lethal mutations in the zeste-white region of Drosophila melanogaster.

Aspects of the developmental genetics of lethal and semi-lethal mutants representing 13 complementation groups (cistrons) in the 3A-3C region of the X chromosome of Drosophila melanogaster are given. Each of these cistrons is associated with a particular chromomere in the salivary gland chromosome. Mutants within each cistron have similar lethality patterns and morphological attributes, and the characteristics of a given cistron are distinct with respect to other cistrons. These results provide additional evidence that only one function is associated with each chromomere.-The results of the lethality pattern analysis are also compared with previous studies of lethal mutants of Drosophila.

The anatomy and function of a segment of the X chromosome of Drosophila melanogaster.

An average size chromomere of the polytene X chromosome of Drosophila melanogaster contains enough DNA in each haploid equivalent strand to code for 30 genes, each 1,000 nucleotides long. We have attempted to learn about the organization of chromosomes by asking how many functional units can be localized within a chromomere. This was done by 1) recovery of mutants representative of every cistron in the 3A2-3C2 region; 2) the characterization of the function of each mutant type and grouping by complementation tests; 3) the determination of the genetic and cytological position of each cistron by recombination and deletion mapping. The data clearly show one functional group per chromomere. It is postulated that a chromomere is one cistron within which much of the DNA is regulatory in function.