Model-Based Evaluation of Transmissibility and Intervention Measures for a COVID-19 Outbreak in Xiamen City, China.

Background: In September 2021, there was an outbreak of coronavirus disease 2019 (COVID-19) in Xiamen, China. Various non-pharmacological interventions (NPIs) and pharmacological interventions (PIs) have been implemented to prevent and control the spread of the disease. This study aimed to evaluate the effectiveness of various interventions and to identify priorities for the implementation of prevention and control measures. Methods: The data of patients with COVID-19 were collected from 8 to 30 September 2021. A Susceptible-Exposed-Infectious-Recovered (SEIR) dynamics model was developed to fit the data and simulate the effectiveness of interventions (medical treatment, isolation, social distancing, masking, and vaccination) under different scenarios. The effective reproductive number (Reff ) was used to assess the transmissibility and transmission risk. Results: A total of 236 cases of COVID-19 were reported in Xiamen. The epidemic curve was divided into three phases (Reff = 6.8, 1.5, and 0). Notably, the cumulative number of cases was reduced by 99.67% due to the preventive and control measures implemented by the local government. In the effective containment stage, the number of cases could be reduced to 115 by intensifying the implementation of interventions. The total number of cases (TN) could be reduced by 29.66-95.34% when patients voluntarily visit fever clinics. When only two or three of these measures are implemented, the simulated TN may be greater than the actual number. As four measures were taken simultaneously, the TN may be <100, which is 57.63% less than the actual number. The simultaneous implementation of five interventions could rapidly control the transmission and reduce the number of cases to fewer than 25. Conclusion: With the joint efforts of the government and the public, the outbreak was controlled quickly and effectively. Authorities could promptly cut the transmission chain and control the spread of the disease when patients with fever voluntarily went to the hospital. The ultimate effect of controlling the outbreak through only one intervention was not obvious. The combined community control and mask wearing, along with other interventions, could lead to rapid control of the outbreak and ultimately lower the total number of cases. More importantly, this would mitigate the impact of the outbreak on society and socioeconomics.

Natural history and cycle threshold values analysis of COVID-19 in Xiamen City, China.

Objective: This study elaborated the natural history parameters of Delta variant, explored the differences in detection cycle thresholds (Ct) among cases. Methods: Natural history parameters were calculated based on the different onset time and exposure time of the cases. Intergenerational relationships between generations of cases were calculated. Differences in Ct values of cases by gender, age, and mode of detection were analyzed statistically to assess the detoxification capacity of cases. Results: The median incubation period was 4 days; the detection time for cases decreased from 25 to 7 h as the outbreak continued. The average generation time (GT), time interval between transmission generations (TG) and serial interval (SI) were 3.6 ± 2.6 days, 1.67 ± 2.11 days and 1.7 ± 3.0 days. Among the Ct values, we found little differences in testing across companies, but there were some differences in the gender of detected genes. The Ct values continuous to decreased with age, but increased when the age was greater than 60. Conclusion: This epidemic was started from aggregation of factories. It is more reasonable to use SI to calculate the effective reproduction number and the time-varying reproduction number. And the analysis of Ct values can improve the positive detection rate and improve prevention and control measures.

Synthesis of Au-decorated tripod-shaped Te hybrids for applications in the ultrasensitive detection of arsenic.

Novel Au-decorated Te hybrids with a tripod-shaped planar microstructure were prepared through a two-step hydrothermal process: the synthesis of Te single crystals and the subsequent self-sacrificial reaction of Te template with HAuCl4. Based on the influences of reaction temperature and solvent compositions on the as-obtained microstructures, a plausible mechanism was proposed to account for the formation of the tripod-shaped Te and Au/Te crystals. The as-prepared Au/Te hybrids have the sensitivity of 6.35 µA/ppb in the electrochemical detection of As(III), which represents the highest sensitivity reported in literature. The Au/Te sensor also has a low detection limit of 0.0026 ppb and could work in complex mixtures containing As(III), Cu(II) and other heavy metal ions, exhibiting excellent selectivity on As(III) and Cu(II) ions. The enhanced electrocatalytic property may be attributed to the synergetic interactions between the noble metal and semiconductor and the presence of a large number of active sites on the hybrids surface.

Fabrication of noble-metal catalysts with a desired surface wettability and their applications in deciphering multiphase reactions.

Noble-metal Pd and Pt catalysts with a wide range of surface wettability were fabricated through an electrochemical approach and were characterized with scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and atomic force microscopy. The importance of surface wettability of solid catalysts in multiphase reactions-especially their correlation to the nature of the studied chemical system-was investigated by reducing oxygen in an alkaline solution and oxidizing hydrogen peroxide and sodium formate in alkaline or buffered solutions at the as-prepared catalysts. These experiments illustrate that the nature of a multiphase reaction plays a critical role in determining the influence of surface wettability on the catalyst performance, providing a unique approach to decipher the reaction process. The investigation allows us to gain new insights into the electrochemical oxidation of sodium formate.