Risk factors associated with COVID-19 infection: a retrospective cohort study based on contacts tracing.

This study aimed to estimate the attack rates, and identify the risk factors of COVID-19 infection. Based on a retrospective cohort study, we investigated 11,580 contacts of COVID-19 cases in Guangdong Province from 10 January to 15 March 2020. All contacts were tested by RT-PCR to detect their infection of SARS-COV-2. Attack rates by characteristics were calculated. Logistic regression was used to estimate the risk factors of infection for COVID-19. A total of 515 of 11,580 contacts were identified to be infected with SARS-COV-2. Compared to young adults aged 20-29 years, the infected risk was higher in children (RR: 2.59, 95%CI: 1.79-3.76), and old people aged 60-69 years (RR: 5.29, 95%CI: 3.76-7.46). Females also had higher infected risk (RR: 1.66, 95%CI: 1.39-2.00). People having close relationship with index cases encountered higher infected risk (RR for spouse: 20.68, 95%CI: 14.28-29.95; RR for non-spouse family members: 9.55, 95%CI: 6.73-13.55; RR for close relatives: 5.90, 95%CI: 4.06-8.59). Moreover, contacts exposed to index case in symptomatic period (RR: 2.15, 95%CI: 1.67-2.79), with critically severe symptoms (RR: 1.61, 95%CI: 1.00-2.57), with symptoms of dizzy (RR: 1.58, 95%CI: 1.08-2.30), myalgia (RR: 1.49, 95%CI: 1.15-1.94), and chill (RR: 1.42, 95%CI: 1.05-1.92) had higher infected risks. Children, old people, females, and family members are susceptible of COVID-19 infection, while index cases in the incubation period had lower contagiousness. Our findings will be helpful for developing targeted prevention and control strategies to combat the worldwide pandemic.

Succession sequence of lactic acid bacteria driven by environmental factors and substrates throughout the brewing process of Shanxi aged vinegar.

Lactic acid bacteria (LAB) are essential microbiota for the fermentation and flavor formation of Shanxi aged vinegar, a famous Chinese traditional cereal vinegar that is manufactured using open solid-state fermentation (SSF) technology. However, the dynamics of LAB in this SSF process and the underlying mechanism remain poorly understood. Here, the diversity of LAB and the potential driving factors of the entire process were analyzed by combining culture-independent and culture-dependent methods. Canonical correlation analysis indicated that ethanol, acetic acid, and temperature that result from the metabolism of microorganisms serve as potential driving factors for LAB succession. LAB strains were periodically isolated, and the characteristics of 57 isolates on environmental factor tolerance and substrate utilization were analyzed to understand the succession sequence. The environmental tolerance of LAB from different stages was in accordance with their fermentation conditions. Remarkable correlations were identified between LAB growth and environmental factors with 0.866 of ethanol (70 g/L), 0.756 of acetic acid (10 g/L), and 0.803 of temperature (47 °C). More gentle or harsh environments (less or more than 60 or 80 g/L of ethanol, 5 or 20 g/L of acetic acid, and 30 or 55 °C temperature) did not affect the LAB succession. The utilization capability evaluation of the 57 isolates for 95 compounds proved that strains from different fermentation stages exhibited different predilections on substrates to contribute to the fermentation at different stages. Results demonstrated that LAB succession in the SSF process was driven by the capabilities of environmental tolerance and substrate utilization.

[Determination of erythromycin residue in pork samples using molecularly imprinted solid phase extraction coupled with high performance liquid chromatography].

Molecularly imprinted polymers (MIPs) for erythromycin (ERY) were prepared by precipitation polymerization, using ERY as template molecule, methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker and methanol/acetonitrile (1:4, v/v) as porogens. The characterization of the prepared MIPs and non-imprinted polymers (NIPs) were evaluated by scanning electron microscope (SEM) and equilibrium adsorption experiment. The results showed that the MIPs possessed the specific adsorptivity toward ERY. Scatchard analysis revealed that the apparent maximum binding capacity (Qmax) and the dissociation content (Kd) to ERY were as follows: Qmax1 = 45.24 mg/g, Kd1 = 0.028 g/L; Qmax2 = 87.53 mg/g, Kd2 = 0.20 g/L. Using the prepared MIPs as selective adsorbent, the proposed molecularly imprinted solid phase extraction (MISPE) coupled with high performance liquid chromatography (HPLC) was successfully applied to determine ERY residue in pork samples. A linear correlation was obtained over a range of 0.5-50 mg/L (r2 = 0.999 4), and the limit of detection was 0.2 mg/kg (S/N = 3). The spiked recoveries of ERY were 95.2%-104.2% with the relative standard deviations (RSDs) of less than 5%. The proposed method is selective, sensitive and reliable for the analysis of ERY residue in pork samples.

Determination of trace 2,4-dinitrophenol in surface water samples based on hydrophilic molecularly imprinted polymers/nickel fiber electrode.

A rapid, sensitive and selective electrochemical method was proposed for the determination of 2,4-dinitrophenol (2,4-DNP) in surface water samples, using hydrophilic molecular imprinted polymers (MIPs) as the recognition element and nickel (Ni) fiber as the catalytic element. Hydrophilic MIPs were synthesized using 2,4-DNP as the template, acrylamide as the monomer, glycidilmethacrylate as the pro-hydrophilic co-monomer and acetonitrile as the solvent. Hydrophilic modification could enhance the accessibility of 2,4-DNP to the imprinted cavities and improve the selective recognition properties of traditional MIPs in water medium. Subsequently, hydrophilic MIPs/Ni fiber electrode was prepared to determine trace 2,4-DNP by cyclic voltammetry. The parameters affecting the analytical performance were investigated. Under optimized conditions, the linear range was 0.7-30 µg L⁻¹ and the detection limit was 0.1 µg L⁻¹. Finally, the proposed method was applied to measure 2,4-DNP in surface water samples. The spiked recoveries were changed from 91.3% to 102.6% and the RSD was not higher than 5.1%. There was no statistically significant difference between the results obtained by the proposed method and the traditional chromatographic method.

Online coupling of molecularly imprinted solid-phase extraction to HPLC for determination of trace tetracycline antibiotic residues in egg samples.

An automated system has been developed for the determination of trace tetracycline antibiotics (TCs) in egg samples, based on online molecularly imprinted solid-phase extraction (MISPE) coupling with high-performance liquid chromatography (HPLC). Oxytetracycline and chlortetracycline were chosen as mixed templates to synthesize highly selective molecularly imprinted polymers for online extraction. Under the optimal online MISPE-HPLC condition, 10 mL egg samples were injected into the MISPE column and then the matrix was washed out. By rotating the switching valve, TCs were transferred to the analytical column and then separated by HPLC. Because sample pretreatment and chromatographic separation were carried out simultaneously, the whole analytical time (18 min) was significantly shortened compared with conventional offline techniques. The detection limits ranged from 0.8 to 1.3 ng/g. The enhancement factors were in the range of 159-410. The spiked recoveries of TCs in real egg samples ranged from 91.6 to 107.6% and the relative standard deviations (RSDs) were not higher than 4.0%.

Rapid and selective determination of urinary lysozyme based on magnetic molecularly imprinted polymers extraction followed by chemiluminescence detection.

A rapid, low cost and selective chemiluminescence method coupled with magnetic molecularly imprinted polymers extraction was developed to detect lysozyme in human urine samples. Compared with traditional solid-phase extraction, this method could achieve selective extraction for the lysozyme, avoid the time consuming elution from a column or centrifugation steps, and then showed great potential in the high-throughput screening of clinical samples. The parameters affecting the performance of extraction and chemiluminescence were investigated. Under optimal conditions, the whole analytical procedure was completed within 12 min and spiked recovery ranged from 90.1% to 103.7% (R.S.D.≤6.7%). The limit of quantitation was 5 ng mL(-1). Furthermore, the results obtained by the proposed method were linearly correlated to those by commercial lysozyme detection kit (r=0.9595). Finally, the validated method was used to measure the urinary lysozyme of renal disease patients and healthy controls. The results confirmed the reliability and practicality of the protocol and revealed a good perspective of this method for biological sample analysis.

Magnetic molecularly imprinted nanoparticles for recognition of lysozyme.

Molecular imprinting is an attractive technique for preparing mimics of natural, biological receptors. Nevertheless, the imprinting of macromolecule remains a challenge due to their bulkiness and sensitivity to denaturation. In this work, we presented a method for preparing multifunctional lysozyme-imprinted nanoparticles (magnetic susceptibility, molecular recognition and environmental response). The magnetic susceptibility was imparted through the successful encapsulation of Fe3O4 nanoparticles. Selective lysozyme recognition depended on molecularly imprinted film. Moreover, it was also a hydrophilic stimuli-responsive polymer, which could undergo a reversible change of imprinted cavity in response to a small change in the environmental conditions. Thus, magnetic molecularly imprinted nanoparticles had high adsorption capacity (0.11 mg mg(-1)), controlled selectivity and direct magnetic separation (22.1 emicro g(-1)) in crude samples. After preconcentration and purification with magnetic MIPs nanoparticles, a sensitive chemiluminescence method was developed for determination of lysozyme in human serum samples. The results indicated that the spiked recoveries were changed from 92.5 to 113.7%, and the RSD was lower than 11.8%.

Preparation of mixed-templates molecularly imprinted polymers and investigation of the recognition ability for tetracycline antibiotics.

We developed in the present study a set of molecularly imprinted polymers (MIPs) by precipitation polymerization, using four members of tetracycline antibiotics (TCs) as templates (Oxytetracycline, Tetracycline, Chlortetracycline and Doxycycline). Then, based on the imprinting effect of different MIPs (TCs), Oxytetracycline and Chlortetracycline were chosen as mixed-templates to synthesize high selective MIPs for recognition of a family of analytes. And the characterization of obtained MIPs was analyzed by FESEM analysis, Brunauer-Emmett-Teller (BET) method, polymer size analysis, and determination of swelling ratio and COOH capacity. It was shown that the optimal imprinting factors of TCs on mixed-templates MIPs were more than 6.0 and the maximum binding amount of TCs were about 27 micromol g(-1) (Oxytetracycline), 35 micromol g(-1) (Tetracycline), 35 micromol g(-1) (Chlortetracycline) and 39 micromol g(-1) (Doxycycline), respectively. Finally, the mixed-templates MIPs were shown to be promising for on-line solid-phase extraction-HPLC-UV determination of trace TCs in foodstuffs. With a sample loading volume of 10 mL, the enhancement factors were in the range of 159-410.

[A quantitative method for simultaneous assay of four flavones with one marker in Radix Scutellariae].

OBJECTIVE: To develop a quantitative method for simultaneously determining four flavones in Radix Scutellariae, by using one chemical standard substance. METHOD: The relative correction factors (RCF) of four flavones were determined by HPLC-DAD. Within the linear ranges, the values of RCF at 274 nm of wogonoside, baicalein, and wogonin to baicalin, were 0.7467, 0.5638, 0.4351, respectively. And the contents of baicalin in 27 samples of Scutellaria baicalensis were authentically determined by the external standard method, and the contents of the three other flavones were calculated according to their RCF. The contents of these four flavones in the all samples were determined with the external standard method. RESULT: The RCF had a good reproducibility (RSD 0.66%-2.83%). No significant differences between the quantitative results by the above two methods were observed. CONCLUSION: It is a fast, convenient, and accurate method to determine multi-components especially when some authentic standard substances were unavailable. It can be used as a method to control the quality of Radix Scutellariae.

[Determination of zizybeoside II of Ziziphus jujuba by HPLC].

OBJECTIVE: To develop a quantitative method for determination of zizybeoside II in Ziziphus jujuba. METHOD: The samples were separated at 30 degrees C on a Zorbax SB-C18 column eluted with methanol-water (20 : 80) as the mobile phase. Flow rate was set at 1.0 mL x min(-1) and the detection wavelength was set at 210 nm. RESULT: The calibration curve was linear within the range from 0.046 to 0.582 microg (r = 0.999 9) and the average recovery was 97.2%. 12 batches of the crude drugs purchased from different areas were determined and the contents of zizybeoside II in Fructus Jujubae were fluctuated from 0.013% to 0.041%. CONCLUSION: The method is simple, repeatable and could be used for the quality control of Z. jujuba.