Objective: To perform an epidemiological survey of the first case with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in Pinghu City of Jiaxing City, Zhejiang Province on March 13, 2022, so as to provide insights into the management of coronavirus disease (COVID-19) epidemics. Methods: According to the requirements of the Protocol on Prevention and Control of COVID-19 (8th Edition), epidemiological investigations were performed among 39 cases with SARS-CoV-2 infections in Pinghu City from March 13 to 20, 2022. Cases' demographics, clinical symptoms, history of immunization and exposure were collected, and close contacts were identified. Pharyngeal swabs were sampled from infected cases for detection of SARS-CoV-2 nucleic acid and whole-genome sequencing, and the source of infection and transmission route were investigated. Results: The index case for this COVID-19 epidemic was an imported case from Shanghai Municipality, who infected 6 persons via aerosol transmission when playing in the badminton venue of Pinghu National Fitness Center on March 9; subsequently, one of these infected cases infected another 18 persons when playing in the badminton venue of Jiadian Village Resident's Fitness Center in Zhapu Township on March 12. Sixteen confirmed cases were reported, and all cases were mild; another 23 asymptomatic cases were diagnosed, with no death reported. This epidemic occurred from March 11 to 20, with 3 generations of spread and a median incubation period of 3 days. The SARS-CoV-2 infected cases had a median age of 33.5 (interquartile range, 12.0) years and included 36 cases with a history of COVID-19 vaccination. There were 16 cases with fever, cough, runny nose and sore throat, and 13 cases with imaging features of pneumonia. The effective reproductive number (Rt) of the COVID-19 epidemic was 7.73 at early stage, and was less than 1 since March 21. Whole-genome sequencing identified Omicron BA.2 variant among 33 cases, which had high homology with the index cases. Conclusion This epidemic was a cluster of COVID-19 caused by imported Omicron BA.2 variant infection from Shanghai Municipality, and the COVID-19 transmission was mainly caused by indoor aerosols.

Objective:To investigate effect of reperfusion injury following different ischemic duration on skeletal muscle in rats.Methods:A model of ischemia/reperfusion injury (IRI) was established by unilateral clamping femoral artery and additional application of tourniquet in skeletal muscle of hind limbs in 35 male Wsitar rats. According to different ischemia time, the animals were assigned to 2-hour ischemia and 24-hour reperfusion (I2R24 group), 2.5-hour ischemia and 24-hour reperfusion (I2.5R24 group), 3-hour ischemia and 24-hour reperfusion (I3R24 group), 4-hour ischemia and 24-hour reperfusion (I4R24 group) and sham group, with 7 rats per group. At the end of reperfusion, gastrocnemious tissues and plasma samples were collected and analyzed. The ratio of wet ∶ dry weight (W/D) was used to measure muscle edema. The assay of 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) was conducted to evaluate muscle viability. HE staining was executed to observe histopathological changes. Immunofluorescence staining was performed to assess the levels of C1q, C3b/c, tissue factor (TF), fibrinogen (FN), bradykinin receptor 1 (BR1), BR2, vascular cell adhesion molecule-1 (VCAM-1), E-selectin, fibrinogen-like protein-2 (FGL-2) and myeloperoxidase (MPO) in muscle tissues. ELISA method was used to determine the concentrations of interferonγ (IFN-γ), interleukin7 (IL-7), IL-18, macrophage inflammatory1α (MIP-1α) and monocyte chemotactic protein 1 (MCP-1) in plasma.Results:With prolongation of ischemia time and subsequent reperfusion, tissue edema became severe gradually. The ratio of W/D was 5.3±0.2, 6.1±0.3, 6.9±0.2, 7.6±0.3 in I2R24, I2.5R24, I3R24 and I4R24 groups, higher than that in sham group (4.5±0.1) (all P<0.01). Muscle viability got decreased gradually. Muscle viability was (62.4±3.5)%, (45.3±3.3)%, (35.4±3.4)%, (27.1±5.9)% in I2R24, I2.5R24, I3R24 and I4R24 groups, lower than that in sham group［(93.8±7.2)%］(all P<0.01). Histopathological changes became aggravated gradually. The most severe group was I4R24 group, with the most severe myocyte injury, interstitial edema and extensive inflammatory infiltration, followed by I3R24, I2.5R24 and I2R24 groups in order. There was normal structure integrity and neatly arranged myocyte in sham group. Meanwhile, levels of C1q, C3b, FN, BR1, VCAM-1, E-selectin and FGL-2 got increased gradually. The highest levels for these factors were seen in I4R24 group, followed by I3R24 group, I2.5R24 group, I2R24 group and sham group in order. The rough ratio of the number of positive MPO cells/total cell number under high lens (×200) were increased gradually, with the highest level in I4R24 group, followed by I3R24 group, I2.5R24 group, I2R24 group and sham group in order. However, expression of TF and BR2 were not altered significantly among the groups. Plasma levels of INF-γ, IL-7, IL-18, MIP-1α and MCP-1 elevated gradually with prolongation of ischemia time (all P<0.01). The sequence was the sham group, I2R24 group, I2.5R24 group, I3R24 group and I4R24 groups for levels of these factors from low to high (all P<0.01). Conclusion:Reperfusion after prolongation of ischemia duration can increase the activation of complement, coagulation, kinin and endothelial cells as well as the release of inflammatory factors, and thus aggravate the degree of skeletal muscle tissue injury.