Objective:To analyze the epidemiological characteristics of reinfection of 2019-nCoV and influencing factors, and provide evidence for effective prevention and control of COVID-19 epidemic.Methods:The incidence data of COVID-19 in Ningbo from January 1, 2020 to November 30, 2022 were collected from the infectious disease surveillance system of Chinese information system for disease control and prevention. The incidence of reinfection of 2019-nCoV was investigated by using questionnaire. logistic regression analysis was used to analyze the influences of gender, age, time interval from the first infection, history of underlying disease, 2019-nCoV vaccination dose and disease severity on the reinfection.Results:A total of 897 previous 2019-nCoV infection cases were investigated, of which 115 experienced the reinfection of 2019-nCoV, the reinfection rate was 12.82%. The interval between the two infections M( Q1, Q3) was 1 052 (504, 1 056) days. Univariate analysis showed that age, 2019-nCoV vaccination dose, history of underlying disease, type of 2019-nCoV variant causing the first infection, time interval from the first infection and severity of the first infection were associated with the reinfection rate (all P<0.05). Multivariate logistic regression analysis showed that the risk for reinfection in age group 30- years was higher than that in age group ≥60 years ( OR=2.10, 95% CI: 1.11-3.97). No reinfection occurred in those with time interval from the first infection of <6 months, and the risk for reinfection was higher in those with the time interval of ≥12 months than in those with the time interval of 6- months ( OR=6.68, 95% CI: 3.46-12.90). The risk for reinfection was higher in the common or mild cases than in the asymptomatic cases ( OR=2.64, 95% CI: 1.18-5.88; OR=2.79, 95% CI: 1.27-6.11). Conclusion:The time interval from the first infection was an important influencing factor for the reinfection of 2019-nCoV, and the probability of the reinfection within 6 months was low.

Objective:To investigate the infection rate in close contacts of COVID-19 patients before and after the last negative nucleic acid test, evaluate the effect of dynamic nucleic acid test in determining the infectivity of COVID-19 patients.Methods:Dynamic nucleic acid test results of COVID-19 cases were collected in a retrospective cohort study. COVID-19 cases with negative nucleic acid test results before their first positive nucleic acid tests were selected as study subjects. Close contacts of the index cases and the secondary close contacts were kept isolation for medical observation to assess their risk of infection.Results:This study included 89 confirmed cases from two local COVID-19 epidemics in Ningbo. A total of 5 609 close contacts were surveyed, the overall infection rate was 0.20%. No close contacts of the COVID-19 cases before the last negative nucleic acid test were infected, and the infection rate in the close contacts of the COVID-19 cases after the last negative nucleic acid test was 1.33%, all of these close contacts lived together with the index cases. No secondary close contacts were infected.Conclusion:COVID-19 patient becomes infectious after the last nucleic acid is negative, and has no infectivity before the last nucleic acid negative.

Objective:To investigate the local epidemic of COVID-19 caused by 2019-nCoV Delta variant in Zhenhai district of Ningbo, identify the transmission chain and provide reference for the prevention and control of COVID-19 epidemic.Methods:The incidence data of COVID-19 in Zhenhai from 6 to 18 December, 2021 were collected in field investigation. Field epidemiological investigation was conducted to understand the epidemiological characteristics of COVID-19 cases and analyze the transmission chains.Results:The first case might be infected with 2019-nCoV through direct or indirect exposure when passing through a medium-risk area, then a family cluster was caused, and the epidemic spread through close contacts of family members with others such as work, daily life, and moxibustion. The epidemic lasted for 14 days, and 74 confirmed COVID-19 cases were reported. The median incubation period was 4.0(3.0,5.8)d. All the cases were in a chain of transmission for more than 6 generations, and the intergenerational interval was 3.5(2.0,5.3)d. The gene sequencing result indicated that the pathogen was Delta AY.4 variant of 2019-nCoV. Both the epidemiological investigation and the gene sequencing results supported that the local COVID-19 epidemic in Zhenhai was associated with the COVID-19 epidemic in Shanghai.Conclusions:The transmission chain of this epidemic was clear. Delta AY.4 variant has obvious characteristic to cause case clusters in families, places with poor ventilation, and residential communities. It is suggested to strengthen the health management in key areas and key populations, and increase the frequency of nucleic acid testing.

Objective:To investigate the association of single nucleotide polymorphism at the estrogen receptor 1(ESR1) gene rs1801132 with the risk of brick-tea type skeletal fluorosis.Methods:The typical brick-tea type fluorosis areas in Qinghai, Xinjiang, and Inner Mongolia were selected as the survey sites for a cross-sectional study. An epidemiological questionnaire was conducted by the staffs on the sites for participants older than 16 years, and physical examination and X-ray diagnosis were performed. Brick tea, blood, and urine samples were collected at the same time. The diagnosis of skeletal fluorosis through X-ray was based on the "Diagnostic Criteria for Endemic Skeletal Fluorosis" (WS/T 192-2008); The determination of tea's fluoride and urinary fluoride was performed by fluoride ion-selective electrode method; gene sequencing analysis of rs1801132 locus of ESR1 gene was done by Sequenom MassARRAY flight mass spectrometry system.Results:A total of 994 patients were included in this study. The total prevalence of skeletal fluorosis was 23.9% (238/994). The prevalence of skeletal fluorosis in Tibetans(39.9%, 123/308) was higher than those of Mongolian and Han nationality [22.2% (58/261), 13.4% (57/425), χ 2=20.435, 67.811, P < 0.05]. Based on binary logistic analysis, the daily tea fluoride intake ≤ 3.5 mg, urinary fluoride content ≤1.6 mg/L, and age ≤45 years were used as the reference groups, and then, when the daily tea fluoride intake > 7.0 mg ( OR=2.865, 95% CI: 1.923-4.268), urinary fluoride content > 1.6-3.2 mg/L ( OR=2.368, 95% CI: 1.686-3.326) and > 3.2 mg/L ( OR=3.559, 95% CI: 2.401-5.276), the age > 45-65 years old ( OR=2.361, 95% CI: 1.603-3.477) and > 65 years old ( OR=4.556, 95% CI: 2.845-7.296), the risk of fluorosis was higher than that of the reference group, respectively. When the daily tea fluoride intake was > 3.5-7.0 mg and the level of urinary fluoride was > 1.6-3.2 mg/L, G allele had a protective effect on skeletal fluorosis in Mongolian population (adjusted OR=0.207, 95% CI: 0.044-0.974); when the daily tea fluoride intake was > 3.5-7.0 mg, gender was male group, G allele had a protective effect on skeletal fluorosis in Han population (adjusted OR=0.315, 95% CI: 0.112-0.887). Conclusion:The single nucleotide polymorphism of the rs1801132 locus at the ESR1 gene may be associated with the risk of susceptibility to brick-tea type skeletal fluorosis in Mongolian and Han nationality.

Objective:To study and establish a high-throughput and rapid detection method for fluorine ion content in water based on 96-well plate and microplate reader, and to evaluate its performance.Methods:According to the principle of blue ternary complex formed by reaction of fluorine ion with fluorine reagent and lanthanum nitrate, the absorbance of the complex at the wavelength of 650 nm was proportional to the concentration of fluoride ion, and the content of fluoride ion in water samples was quantitatively determined by microplate reader. The accuracy, precision and detection limit of the method were evaluated by the standard recovery rate method and the reference material method.Results:The linear correlation coefficient of the standard curve of this method was > 0.999; the standard recovery rates of different concentrations were 99.00% - 103.33% in the accuracy experiment of this method, and the average recovery rate was 101.08%. In the standard material method, the measured values are all within the calibration range of the standard solution. The relative standard deviation of water samples with different concentrations was ≤10% in the precision experiment and the detection limit was 0.06 mg/L.Conclusion:The method has good accuracy and precision, low detection limit and small sample consumption, and this method can greatly improve the detection efficiency.

Objective To investigate the relationship between Cytochrome P-450 1A1 (CYP1A1) gene polymorphism and the ethnic differences to brick-tea fluorosis and the gene-environment interaction.Methods Inhabitants over the age of 16 years old in Inner Mongolia,Qinghai and Xinjiang were investigated.The questionnaire survey included basic information,dietary survey and total fluoride intake,and peripheral venous blood was collected.The CYP1A1 gene single nucleotide polymorphism (SNP) genotyping was determined using mass spectrometry;the diagnosis of skeletal fluorosis was based on the X-ray method;combined genetic factors with environmental factors,the interaction of gene-environment was analyzed.Results In the 1 414 copies of whole blood samples (308 Tibetans,290 Kazakhs,261 Mongolians,425 Han people,130 Russians),CYP1A1 genes rs1048943 sites were typed into AA,AG and GG genotypes,and gene distribution met Hardy-Weinberg equilibrium (P ＞ 0.05).The frequencies of genotypes AA,AG and GG in Tibetans were 55.8％ (172/308),37.3％ (115/308) and 6.8％ (21/308),respectively;the frequencies of the three genotypes in Kazakhs were 69.7％ (202/290),27.6％ (80/290) and 2.8％ (8/290),respectively;the frequencies of the three genotypes in Mongolians were 60.5％ (158/261),36.0％ (94/261) and 3.4％ (9/261),respectively;the frequencies of the three genotypes in Han people were 60.9％ (259/425),33.6％ (143/ 425) and 5.4％ (23/425),respectively;the frequencies of genotypes in Russians were 72.3％ (94/130),26.9％ (35/130) and 0.8％ (1/130),respectively;the differences of the three genotype frequencies between different ethnic groups were statistically significant (x2 =24.757,P ＜ 0.05).The skeletal fluorosis detection rates in different ethnic from high to low were Tibetans (39.94％,123/308),Kazakhs (33.79％,98/290),Mongolians (22.22％,58/261),Han people (13.41％,57/425) and Russians (8.46％,11/130),and the differences were statistically significant (x2 =100.156,P＜ 0.05).Skeletal fluorosis detection rates of different genotypes were AA (24.18％,214/885),AG/GG (25.14％,133/529),the difference was not statistically significant between the groups (x2 =0.165,P ＞ 0.05).After the ethnic stratification,the differences were also not statistically significant (P ＞ 0.05).Only in the group of Tibetans whose urine fluoride level was 1.6-3.2 mg/L and Mongolians under age 45 were found that the G gene was one of the risk factors in skeletal fluorosis [OR =2.035,95％ CI (1.003-4.128);OR =5.602,95％CI (1.461-21.479)];G gene might be a protective factor in the Mongolians aged 45 years and over [OR =0.422,95％CI(0.190-0.938)].Conclusion This study does not find a positive correlation between CYP1A1 gene polymorphism and the ethnic differences to bricktea fluorosis.

Objective To investigate the effects of fluoride on trabecular bone of the tibia and lumbar in BALB/c mice.Methods Totally 64 four-week-old BALB/c mice were randomly divided into 4 groups by weight,16 per group:control group (treated with distilled water) and 3 sodium fluoride (NaF) exposure groups (treated with NaF at 25,50 and 100 mg/L F-),respectively.At 12 weeks,mice were killed and blood,two hind limbs and lumbar were collected.Bone fluoride content and incidence rates of dental fluorosis were determined.Serum content of alkaline phosphatase (AKP) and acid phosphatase (ACP) were detected by micro enzyme labeled method.The ultrastructure of osteoblasts and osteoclasts in lumbar were observed via transmission electron microscope.The pathological changes of the trabecular bone of the tibia and the lumbar were observed under optical microscope,the percentage of trabecular area (％Tb.Ar) was measured with Image-Pro Plus (IPP) software.Results Bone fluoride contents of low,middle and high fluoride groups [(1 828.62 ± 102.93),(3 308.27 ± 185.63),(4 933.36 ± 301.16) mg/kg] were higher than that of the control group [(775.23 ± 92.56) mg/kg,all P ＜ 0.05].The incidences of dental fluorosis in the 4 groups were 0(0/16),47％(7/15),93％(14/15) and 100％(16/16),respectively;the difference was statistically significant (x2 =27.23,P ＜ 0.05).In middle and high fluoride groups,serum AKP [(18.30 ± 1.99),(24.50 ± 3.14) king unit/100 ml] and ACP [(11.97 ± 1.73),(11.31 ± 1.46) king unit/100 ml] were significantly higher than those of control [(14.63 ± 1.21),(9.07 ± 1.47) king unit/100 ml,respectively,all P ＜ 0.05].Under the electron microscope,osteoblast had developed organelles in each fluoride group,rough endoplasmic reticulum,Golgi body,and mitochondria were abundant,and nucleolus was obvious in the osteoblast.Osteoclast was rich in mitochondria,ruffled border clear and distributed phagocytic vacuoles in low fluoride group and middle fluoride group.Compared with the control group (17.03 ± 3.73),HE staining of tibia ％Tb.Ar in high fluoride group (28.79 ± 8.26) was significantly increased (P ＜ 0.05).The lumbar spine ％Tb.Ar in low,middle and high fluoride groups (15.87 ± 2.59,18.28 ± 0.89,21.99 ± 1.81) were higher than that of the control group (12.06 ± 1.76,all P ＜ 0.05].Conclusions BALB/c mice could be used as a model of skeletal fluorosis.Osteoblast and osteoclast are activated in BALB/c mice with skeletal fluorosis.Bone formation is more obvious than bone resorption and bone mass is increased.What is more,bone mass has increased more significantly in the lumbar spine of mice.

Objective To explore the effects of different doses of sodium fluoride (NaF) on cartilage lesion and expression of interleukin-6 (IL-6) in serum and cartilage tissue of Balb/c mice.Methods Sixty-four 5-week-old male Balb/c mice were divided into 4 groups based on body weight via the random number table method and 16 mice were in each group.The mice in control group were fed with distilled water,and experimental animals in low,middle and high fluoride groups were fed with distilled water containing NaF 25,50 and 100 mg/L,respectively.The mice were weighed once a week and fed for three months to establish the drinking water fluorosis model.The fluoride contents in spine were detected via the fluorin-ion selective electrode method.The pathological changes in articular cartilage and epiphyseal plate cartilage were observed through optical microscope.The levels of serum IL-6 and souble IL-6 receptor (sIL-6R) were detected via the enzyme-linked immunosorbent assay.The expression of IL-6 protein in articular cartilage and epiphyseal plate cartilage was examined by immunohistochemistry.Results From the sixth week of the experiment,compared with other 3 groups,the body weight of high fluoride group decreased significantly (all P ＜ 0.05);from the seventh week,compared with control and low fluoride groups,the body weight of middle fluoride group decreased significantly (all P ＜ 0.05);throughout the experiment,compared with control group,the body weight of low fluoride group had not changed significantly (all P ＞ 0.05).The fluoride contents of bone in control group,low fluoride group,middle fluoride group and high fluoride group were (842.46 ± 89.27),(1 705.05 ± 105.76),(2 614.17 ± 156.10) and (3 444.58 ± 233.69) mg/kg,respectively.The differences between groups were statistically significant (F =309.716,P ＜ 0.05),and fluoride contents of bone increased with increase of fluoride doses (all P ＜ 0.05).Under optical microscope,the cartilage tissue of control group was normal,while articular cartilage and epiphyseal plate cartilage showed different degrees of cartilage ossification in fluorosis mice and the changes increased with the increase of fluoride doses.The levels of serum IL-6 in control group,low fluoride group,middle fluoride group and high fluoride group were (5.98 ± 1.43),(7.54 ± 2.16),(5.25 ± 1.97) and (6.31 ±-1.36) ng/L,respectively.The differences between groups were statistically significant (F =3.840,P ＜ 0.05),low fluoride group was significantly higher than control group (P ＜ 0.05),and middle fluoride group was significantly lower than low fluoride group (P ＜ 0.05).The levels of serum slL-6R in control group,low fluoride group,middle fluoride group and high fluoride group were (0.83 ± 0.20),(0.93 ± 0.23),(0.82 ±0.27) and (0.92 ± 0.28) μg/L,respectively.The differences between groups were not statistically significant (F =0.738,P ＞ 0.05).Immunohistochemical results showed that articular cartilage full-layer cells in each group expressed IL-6 protein especially in the middle layer of chondrocytes,while IL-6 protein only expressed in hypertrophic chondrocytes of epiphyseal plate cartilage.Comparing with other groups,IL-6 positive cells were the most and had the deepest staining in low fluoride group.Conclusions Different doses of NaF could not only cause cartilage lesion,but also change the expression of IL-6 in serum and cartilage tissue of Balb/c mice.The results indicate that IL-6 may be involved in the cartilage lesion caused by fluoride.

Objective Through the research and analysis of guangdong medical college affiliated hospital orthopaedic hospitalized patients with a diagnosis of osteoporosis in Zhanjiang,this paper provide theoretical basis for the prevention of osteoporosis frac-ture.Methods The elderly aged over 40 years old,living in this area for a long time.Data was collected from August 2012 to Feb-ruary 2014,hospitalized patients in guangdong medical college affiliated hospital were diagnosed with osteoporosis.Contents include general situation survey,medical examination,venous blood tests and bone mineral density testing.Results Fracture group average age is older than the non fracture group;the fracture group lumbar spine bone mineral density(LSBMD)and femoral neck bone min-eral density(FNBMD)T value and Z value and serum calcium group is greater than the fracture and the differences were statistically significant(P <0.05).Fracture group in gender divided into two groups for comparison,in which women older than men,and the difference was statistically significant(P <0.05),male LSBMD T and Z values and FNBMD T value is greater than the female and the difference was statistically significant(P <0.05).According to the 10 year age group,Each age group compared with the frac-ture number and non fracture number,in the age group of 70-80 fracture number were the most;All age groups in LSBMD,FNB-MD,serum calcium(Ca)and VitD compared,non fracture group is most higher than that of fracture group.The influence factors of the fractures for non conditional Logistic regression analysis,age,LSBMD,FNBMD T value increased were risk factors for fracture, VitD,FNBMD,LSBMD T value increased were protective factors of fracture.Conclusion Need as soon as possible to prevent osteo-porosis,especially before the age of 40,try to improve the peak bone density,to prevent the occurrence of osteoporosis in the future.

AIM: To study the effects of spirulina (Spirin) in the prevention of liver fibrosis in rats.　METHODS: Wistar rats were divided into three groups: control group(n=8); CCl4 group(n=8), spirulina group(n=8). CCl4 group and spirulina group rats were induced by 40% CCl4 olive oil solution into models of liver fibrosis, meanwhile spirulina group was given the feed with spirulina powder for 12 wk. Liver histological changes, hydroxyproline(HYP) content in liver tissues, serum procollagen type Ⅲ(PC-Ⅲ) and hyaluronic acid(HA) levels were observed. 　RESULTS: The pathological studies showed that the liver fibrosis degree of spirulina group was obviously lighter than that of CCl4 group. Spirulina group had significantly lower levels of HYP(174 μg*g-1±37 μg*g-1), PC-Ⅲ(140 μg*L-1±37 μg*L-1) and HA(262 μg*L-1±92 μg*L-1) than those of CCl4 group (243 μg*g-1±49 μg*g-1, 274 μg*L-1±69 μg*L-1 and 484 μg*L-1±114 μg*L-1, respectively).　CONCLUSION: The experimental evidence suggests that spirulina can prevent the formation of liver fibrosis.