SARS-CoV-2 seroprevalence in the urban population of Qatar: An analysis of antibody testing on a sample of 112,941 individuals

ABSTRACTBackgroundQatar has experienced a large SARS-CoV-2 epidemic. Our first objective was to assess the proportion of the urban population that has been infected with SARS-CoV-2, by measuring the prevalence of detectable antibodies. Our second objective was to identify predictors for infection and for having higher antibody titers.MethodsResidual blood specimens from individuals receiving routine and other clinical care between May 12-September 9, 2020 were tested for anti-SARS-CoV-2 antibodies. Associations with seropositivity and higher antibody titers were identified through regression analyses. Probability weights were applied in deriving the epidemiological measures.ResultsWe tested 112,941 individuals (∼10% of Qatar’s urban population), of whom 51.6% were men and 66.0% were 20-49 years of age. Seropositivity was 13.3% (95% CI: 13.1-13.6%) and was significantly associated with sex, age, nationality, clinical-care type, and testing date. The proportion with higher antibody titers varied by age, nationality, clinical-care type, and testing date. There was a strong correlation between higher antibody titers and seroprevalence in each nationality, with a Pearson correlation coefficient of 0.85 (95% CI: 0.47-0.96), suggesting that higher antibody titers may indicate repeated exposure to the virus. The percentage of antibody-positive persons with prior PCR-confirmed diagnosis was 47.1% (95% CI: 46.1-48.2%), severity rate was 3.9% (95% CI: 3.7-4.2%), criticality rate was 1.3% (95% CI: 1.1-1.4%), and fatality rate was 0.3% (95% CI: 0.2-0.3%).ConclusionsFewer than two in every 10 individuals in Qatar’s urban population had detectable antibodies against SARS-CoV-2 between May 12-September 9, 2020, suggesting that this population is still far from the herd immunity threshold and at risk from a subsequent epidemic wave.</jats:sec

Chemical Kinetic Study of the Oxidation of Isocetane (2,2,4,4,6,8,8-Heptamethylnonane) in a Jet-stirred Reactor: Experimental and Modeling

The kinetics of oxidation of isocetane (2,2,4,4,6,8,8-heptamethylnonane), a cetane number reference fuel, was studied experimentally in a jet-stirred reactor (JSR) at 10 atm and a constant residence time of 1 s, over the temperature range 770−1070 K, and for variable equivalence ratios (0.5, 1, and 2). Concentration profiles of reactants, stable intermediates, and final products were obtained by probe sampling followed by online and offline gas chromatography analyses and online Fourier transformed infrared spectrometry. The oxidation of this fuel in these conditions was modeled using computer-generated semidetailed kinetic reaction mechanisms. A reasonable representation of the kinetics of oxidation of isocetane and the formation of the main products under the present JSR conditions could be obtained. However, the prediction of most of the intermediates was poor as a result of the use of too simplified lumped chemistry in these schemes. This indicates needs for additional model development that could benefit from the present experimental database

Kinetics of Oxidation of a Reformulated Jet Fuel (1-Hexanol/Jet A-1) in a Jet-Stirred Reactor: Experimental and Modeling Study

International audienc

Synthetic Jet Fuel Combustion: Experimental and Kinetic Modeling Study

International audienceFischer-Tropsch liquid fuels synthesized from syngas, also called synthetic paraffinic jet fuel (SPK), can be used to replace conventional petroleum-derived fuels in jet engines. Whereas currently syngas is mostly produced from coal of natural gas, its production from biomass has been reported. These synthetic liquid fuels contain a very high fraction of iso-alkanes, while conventional jet fuels contain large fractions of n-alkanes, cycloalkanes (naphtenes), and aromatics. In that contest, a jet-stirred reactor (JSR) was used to study the kinetics of oxidation of a 100% SPK and a 50/50 SPK/Jet A-1mixture over a broad range of experimental conditions (10 atm, 560 to 1030K, equivalence ratios of 0.5 to 2, 1000 ppm of fuel). The temperature was varied step-wise, keeping the mean residence time in the JSR constant and equal to 1s. Three combustion regimes were observed over this temperature range: the cool-flame oxidation regime (560-740K), the negative temperature coefficient (NTC) regime (660-740K), and the high-temperature oxidation regime (>740K). More than 15 species were identified and measured by Fourier transform infrared spectrometry (FTIR), gas chromatography/ mass spectrometry (CG/MS), flame ionization detection (FID), and thermal conductivity detection (TCD). The results consisting of concentration profiles of reactants, stable intermediates and products as a function of temperature showed similar kinetics of oxidation for the fuels considered, although the 100% SPK was more reactive. A surrogate detailed chemical kinetic reaction mechanism was used to model these experiments and ignition experiments taken from the literature. The kinetic modeling showed reasonable agreement between the data and the computations whereas model improvements could be achieved using more appropriate surrogate model fuels. Kinetic computations involving reaction paths analyses and sensitivity analyses were used to interpret the results

Profil particulier des zymodèmes de Leishmania infantum causant la leishmaniose viscérale en Tunisie

Archives des Bulletins de la Société de Pathologie Exotique - SPE (http://www.pathexo.fr/1845-bulletin.html?id_bull=94&id_volume=232&L=1)International audienceThe isoenzymatic typing of 16 stocks of Leishmania, isolated from Tunisian visceral leishmaniasis (VL) cases, revealed that all strains belonged to Leishmania (L.) infantum species. Although zymodeme MON-1 was predictably the most frequent (9 cases), it came as a surprise that L. infantum MON-24 was responsible of about third of cases. This latter zymodeme, while previously reported in Tunisia, Algeria and Spain, was assumed to be a dermotropic and the few cases of VL that it caused occurred always in HIV infected patients. L. infantum MON-80, occasionally reported during both cutaneous and VL of immunocompetent infants was identified in 2 patients. This report confirms that in addition to the more common L. infantum MON-1, zymodeme MON-24 has a substantial role in generating VL in immunocompetent infants in Tunisia.Le typage iso-enzymatique de 16 souches de leishmanies isolées chez des enfants tunisiens atteints de leishmaniose viscérale (LV) a révélé qu'en plus du classique Leishmania (L.) infantum MON-1, identifié chez 9 patients, le zymodème L. infantum MON-24 a été trouvé dans 5 cas. Bien que ce zymodème ait déjà été incriminé dans la genèse de quelques cas de LV infantile en Algérie, en Tunisie et en Espagne, une proportion aussi élevée, 31,2%, était inattendue. En effet, L. infantum MON-24 a été jusque-là considéré comme plutôt dermotrope et les quelques cas de LV qui lui sont rapportés sont survenus le plus souvent chez des individus immunodéprimés infectés par le VIH.Par ailleurs, L. infantum MON-80, déjà signalé au cours de formes aussi bien cutanées que viscérales, a été identifié chez 2 patients

Experimental Study of the Oxidation of N -Tetradecane in a Jet-Stirred Reactor (JSR) and Detailed Chemical Kinetic Modeling

International audienc

Retrofitting Heat Exchanger Network of Industrial Ethylene Glycol Plant using Heat Integration based on Pinch Analysis

Heat integration by pinch method is used to modify the heat exchanger network of an industrial ethylene glycol plant. The aim is to reduce the energy cost by operating the plant close to the maximum energy recovery. Pinch analysis identified a pinch temperature of 483 K, a minimum heating utility of 13,490.9 MJ/ton EO, and a minimum cooling utility of 25,697 MJ/ton EO. Using the pinch decomposition diagram and the standard procedure for matching hot and cold streams, a retrofit of the heat exchangers network is developed. The modified heat exchanger network reduces the external cooling duty by 45.5% and the external heating duty by 93.3%. This promising cost savings provide enough justification for restructuring the existing ethylene glycol plant. Moreover, an additional 6% reduction in the external cooling duty can be achieved by integrating the steam turbine below the pinch point