Short-range airborne route dominates exposure of respiratory infection during close contact

A susceptible person experiences the highest exposure risk of respiratory infection when he or she is in close proximity with an infected person. The large droplet route has been commonly believed to be dominant for most respiratory infections since the early 20th century, and the associated droplet precaution is widely known and practiced in hospitals and in the community. The mechanism of exposure to droplets expired at close contact, however, remains surprisingly unexplored. In this study, the exposure to exhaled droplets during close contact (< 2 m) via both the short-range airborne and large droplet sub-routes is studied using a simple mathematical model of expired flows and droplet dispersion/deposition/inhalation, which enables the calculation of exposure due to both deposition and inhalation. The short-range airborne route is found to dominate at most distances studied during both talking and coughing. The large droplet route only dominates when the droplets are larger than 100 m and when the subjects are within 0.2 m while talking or 0.5 m while coughing. The smaller the exhaled droplets, the more important the short-range airborne route. The large droplet route contributes less than 10% of exposure when the droplets are smaller than 50 m and when the subjects are more than 0.3 m apart, even while coughing. Practical implicationsOur simple but novel analysis shows that conventional surgical masks are not effective if most infectious viruses are contained in fine droplets, and non-conventional intervention methods such as personalised ventilation should be considered as infection prevention strategies given the possible dominance of the short-range airborne route, although further clinical evidence is needed. NomenclatureO_ST_ABSSubscriptC_ST_ABSi Droplets of different diameter groups (i = 1, 2, ..., N) LD Large droplet route SR Short-range airborne route SymbolsA0 Area of source mouth [m2] AE Aspiration efficiency [-] Ar0 Archimedes number [-] bg Gaussian half width [m] bt Top-hat half width [m] CD Drag coefficient [-] CI Specific heat of liquid [J*kg-1*K-1] Cs Specific heat of solid [J*kg-1*K-1] CT Correction factor for diffusion coefficient due to temperature dependence [-] dd Droplet diameter [m] dd0 Droplet initial diameter [m] de1 Major axis of eye ellipse [m] de2 Minor axis of eye ellipse [m] dh Characteristic diameter of human head [m] dm Mouth diameter [m] dn Nostril diameter [m] D{infty} Binary diffusion coefficient far from droplet [m2*s-1] DE Deposition efficiency [-] eLD Exposure due to large droplet route [L] eSR Exposure due to short-range airborne route [L] g Gravitational acceleration [m*s-2] Iv Mass current [kg*s-1] IF Inhalation fraction [-] Kc Constant (=0.3) [-] Kg Thermal conductivity of air [W*m-1*K-1] LS Exposure ratio between large droplet and short-range airborne [-] Lv Latent heat of vaporization [J*kg-1] md Droplet mass [kg] mI Mass of liquid in a droplet [kg] ms Mass of solid in a droplet [kg] M0 Jet initial momentum [m4*s-2] MW Molecular weight of H2O [kg*mol-1] MF Membrane fraction [-] n Number of droplets [n] n0 Number of droplets expelled immediately at mouth [n] Nin Number of droplets entering the inhalation zone [n] Nm Number of droplets potentially deposited on mucous membranes [n] Nt Total number of released droplets [n] Nu Nusselt number [-] p Total pressure [Pa] pv{infty} Vapour pressure distant from droplet surface [Pa] pvs Vapour pressure at droplet surface [Pa] Qjet Jet flow rate [m3*s-1] r Radial distance away from jet centreline [m] rd Droplet radius [m] R Radius of jet potential core [m] Rg Universal gas constant [J*K-1*mol-1] s Jet centreline trajectory length [m] Sin Width of region on sampler enclosed by limiting stream surface [m] Sh Sherwood number [-] Stc Stokes number in convergent part of air stream [-] Sth Stokes number for head [-] Stm Stokes number for mouth [-] t Time [s] T0 Initial temperature of jet [K] T{infty} Ambient temperature [K] Td Droplet temperature [K] u0 Initial velocity at mouth outlet [m*s-1] ud Droplet velocity [m*s-1] ug Gaussian velocity [m*s-1] ugas Gas velocity [m*s-1] ugc Gaussian centreline velocity [m*s-1] uin Inhalation velocity [m*s-1] ut Top-hat velocity [m*s-1] vp Individual droplet volume considering evaporation [m3] x Horizontal distance between source and target [m] z Jet vertical centreline position [m] {rho}0 Jet initial density [kg*m-3] {rho}{infty}Ambient air density [kg*m-3] {rho}d Droplet density [kg*m-3] {rho}g Gas density [kg*m-3] {Delta}{rho}Density difference between jet and ambient air [kg*m-3] g Gas dynamic viscosity [Pa*s] {varphi}Sampling ratio in axisymmetric flow system [-] c Impaction efficiency in convergent part of air stream [-]

Risk factors of incision infection and spinal canal hematoma after lumbar posterior surgery / 中华骨科杂志

Objective To analyze the risk factors of incision infection and spinal canal hematoma after lumbar spinal posterior surgery.Methods Data of 33 patients with incision infection and 25 patients with spinal canal hematoma after posterior surgery for lumbar spinal disease from January 2010 to December 2014 were retrospectively analyzed.For the patients with incision infection,20 of them were males and 13 were females,with an average age of 58.85±8.76 years (range 38-79 years).Of these patients,5 were diagnosed with lumbar disc herniation,9 with lumbar spondylolisthesis,15 with lumbar spinal stenosis and 4 with lumbar vertebral fracture.For patients with spinal canal hematoma,17 of them were males and 8 were females,with a mean age of 60.96±11.37 (range,38-77).The diagnoses of them were lumbar disc herniation in 18 patients,spondylolisthesis in 3 patients and spinal stenosis in 4 patients.From the same period database,patients who underwent lumbar posterior lumbar surgery with no postoperative complications were selected by 3:1 ratio as the control group according to age,gender and diagnosis.Results For patients with incision infection,it was found that diabetes mellitus,preoperative RBC,hemoglobin,total protein,albumin,serum calcium,operation time,number of segment fusion,intraoperative blood loss,postoperative WBC,RBC,hemoglobin and platelet were significantly different from those with non-infection group.Moreover,multivariate logistic analysis showed that diabetes mellitus (OR=3.716,P=0.032),preoperative serum calcium (OR＜ 0.001,P=0.001),intraoperative blood loss (OR=1.002,P=0.014),postoperative hemoglobin (OR=0.923,P=0.018) and postoperative platelet (OR=1.007,P=0.017) were independent risk factors for postoperative incision infection.For patients with spinal canal hematoma,it was found that patients' preoperative total protein,albumin,serum calcium,platelet,operation time,intraoperative blood loss and postoperative total protein were significantly different from non-hematoma group.Multivariate logistic analysis showed that preoperative serum calcium (OR＜ 0.001,P=0.001),preoperative total protein (OR=1.298,P=0.043),intraoperative blood loss (OR=1.003,P=0.021) and postoperative total protein (OR=1.080,P=0.028) were independent risk factors for postoperative spinal canal hematoma.Conclusion The preoperative diabetes mellitus,serum calcium,intraoperative blood loss,postoperative hemoglobin and platelet were important risk factors for lumbar incision infection.And preoperative serum calcium,total protein,intraoperative blood loss and postoperative total protein were the risk factors for spinal canal hematoma.

A survey on distribution and drug resistance of pathogens causing nosocomial infection in general intensive care unit / 中国中西医结合急救杂志

Objective To investigate the distribution and drug resistance of pathogens in intensive care unit (ICU) so as to provide scientific basis for antibiotic adoption and the prevention and control of nosocomial infections. Methods The various specimens collected from the patients admitted into ICU in the First People's Hospital of Shunde Affiliated to the South Medical University from January 2007 to December 2014 were used to isolate the pathogens that might cause nosocomial infections and retrospectively analyze their clinical distribution and drug resistance. Kirby-Bauer paper diffusion and minimal inhibitory concentration (MIC) methods were applied to test the drug sensitivity, and according to National Committee for Clinical Laboratory Standards/Clinical and Laboratory Standards Institute (NCCLS/CLSI) standard, the results were identified.Results The sputum was the major specimen source in ICU, accounting for 68.8%, followed by urine (12.4%) and blood (6.8%). All together 557 pathogens in ICU causing nosocomial infections were isolated of which there were 377 gram-negative (G-) bacilli (67.7%), 103 gram-positive (G+) cocci (18.5%), and 77 fungi (13.8%). Among G- bacilli, the top three wereAcinetobacter baumannii (34.5%), Klebsiella pneumonia (17.8%), andPseudomonas aeruginosa (13.0%). Beside carbapenem, the drug resistance rates of Acinetobacterbaumannii to other antibiotics were more than 40%. The main G+ coccus causing nosocomial infection wasSaphylococcus aureus (36.9%) in ICU. The drug resistance rates ofSaphylococcus aureus to penicillin, gentamicin and erythromycin were higher than 50%. In 77 fungus strains,Candida albicans was ranked the first, accounting for 41.6%.Conclusion The main infection site in ICU is primarily respiratory tract, the G- bacilli are the predominate pathogens, and the drug resistance to antibiotics found in this report is serious, so clinically, the antibiotics should be properly used to avoid the occurrence of pathogenic strain with drug tolerance.

miRNA-129-5p regulates the targets of the VCP gene expression in human osteosarcoma cells / 医学研究生学报

Objective High expression of the valosin-containing protein ( VCP) gene can enhance the metastasis of osteosar-coma via the AKT/PI3K/NF-KappaB/MMP-9 signaling pathway, but the molecular mechanisms underlying the up-regulation of VCP in osteosarcoma cells remains unknown .This study aimed to determine whether miRNA-129-5p can regulate the VCP expression and its targets in human osteosarcoma cells . Methods The microRNA target-predicting software TargetScanhuman 6.2 ( http://www.tar-getscan.org/) was used to predict the possible targets of miRNA-129-5p on the VCP gene.Then, two recombinant gene report vectors containing the wild VCP gene 3′UTR ( psi-VCP vector ) and mutant VCP gene 3′UTR ( psi-VCPmut vector ) were constructed , se-quenced, and identified.The human osteosarcoma U2-OS cells were co-transfected with miRNA-129-5p mimic and psi-VCP vector or psi-VCPmut vector, respectively.A non-specificity mimic transfection served as negative control , and the luciferase activity was detec-ted in each group. Results The software prediction showed only one conserved function site of miRNA-129-5p on the VCP gene 3′UTR163-169 bp.Luciferase activity was significantly lower in the psi-VCP vector +miRNA-129-5p transfection group (15.529 ± 1.902) than in the VCP control group (21.781 ±0.854), VCP mutation experimental group (19.978 ±1.377), and VCP mutation control group (21.952 ±1.516) (P<0.05), with no remarkable difference between the VCP mutation control and VCP control groups (P=0.276). Conclusion miRNA-129-5p can probably regulate the targets of the VCP gene in human osteosarcoma U 2-OS cells.

Preparation of chitosan scaffold with different deacetylated degrees and evaluation of the degradation characteristics / 生物医学工程学杂志

The chitosan scaffolds with different deacetylated degree were prepared in this study. The morphology of scaffolds were observed using SEM, and the porosity, the water absorbing swelling ratio and the degradation were examined both in vitro and in vitro. The results showed that the chitosan scaffolds with different deacetylated degree exhibited three-dimensional structure with high porosity. With increasing of deacetylated degree, their porosities were 93.46%, 90.02% and 86.71%, respectively. The swelling ratios of chitosan scaffolds were 820%, 803% and 772%, respectively. At the fourth week, the degradation rates were 30.44%, 22.08% and 17.10% in vitro, respectively; while the corresponding rates were 57.48%, 40.23%, 29.53% in vivo respectively. The degradation rate of chitosan scaffold was negatively correlated to deacetylated degree. Furthermore, it showed that the speed of degradation in vivo was faster than that in vitro. We concluded that controlling the deacetylated degree of chitosan can provide a well-matched degradable scaffold material for the reparation of cartilage defects.

The construction and identification of prokaryotic expression vector pQE30-EWS-FLI1 / 重庆医科大学学报

Objective:To construct Ewing's sarcoma EWS-FLI1 gene prokaryotic expression vector.Methods:The target gene of EWS-FLI1 was obtained by RT-PCR method after the total RNA was extracted from Ewing's sarcoma A673 cells.The site sequences of restrictive endonuclease SacⅠand Hind Ⅲ were introduced into the upstream and downstream of target gene respectively.The target gene fragment were cloned into pMD18-T and transformed into E.Coli JM109.Screened positive clones were confirmed by PCR,restrictive endonuclease digestion and DNA sequencing.The EWS-FLI1 gene was sequentially subcloned into prokaryotic expression vector pQE30,and the recombinant plasmid pQE30-EWS-FLI1 was confirmed by restrictive endonuclease digestion and DNA sequencing.The proteins,expressed in E.coli JM109 transformed with EWS-FLI1recombinant plasmid under IPTG induction,were characterized by SDS-PAGE and Western-blot.Results:PCR result indicated that an amplified DNA fragment was in size of 1.5 kb.Restrictive endonuclease digestion analysis indicated that the target gene was in size of 1.5 kb.DNA sequencing analysis demonstrated that sequence of target gene accorded with anticipated one.The EWS-FLI1 with a molecular weight of 54 kD was highly expressed in pQE30-EWS-FLI1.Western blot proved that the expressed product had the antigenicity of EWS-FLI1.Conclusion:The recombinant prokaryotic expression vector pQE30EWS-FLI1 is constructed successfully,which will contribute to the further research of EWS-FLI1.

Comparison of continuous versus intermittent warm blood cardioplegia during coronary artery bypass grafting / 中华麻醉学杂志

Objective To examine the difference in myocardial protection provided by continuous and intermittent warm blood cardioplegia during coronary artery bypass (CAB) .Methods Thirty ASA Ⅰ-Ⅱ patients undergoing CAB with warm CPB were randomly divided into two groups : (A) continuous warm blood cardioplegia ( n = 15) and (B) intermittent warm blood cardioplegia ( n = 15) . During CPB the body temperature was maintained at 33℃ -34℃ . Arterial blood samples were taken before skin incision (T0) , 1 h after going on CPB (T1 ) and 6h , 24h after coming off CPB (T2, T3 ), for determination of plasma concentration of cardiac troponin T (cTnT) using ELISA method. A small piece of myocardium was obtained from right ventricle (about 1g ) before aortic crass-clamping and after the aortic clamp was removed for determination of myocardial ATP content and ultrastractural examination. Results The demographic data were comparable between the two groups. Plasma cTnT level increased significantly at T1 and T2 as compared with the baseline values (T0) and then returned to normal level at T3 in both groups. The cTnT level was significantly higher in group B than that in group A at T2 (6h after weaning from CPB)The myocardial ATP content decreased significantly after aortic clamp was removed as compared with that before cross-clamping of aorta, but myocardial ATP content in group A was significantly higher than that in group B after release of arotic clamp. Mitochondria score was significantly higher after release of aortic cross-clamp than that before aortic cross-clamping.Conclusion Continuous warm blood cardiaplegia is superior to intermittent warm blood cardioplegia during CPB in terms of myocardial protection.