Meningococcal carriage and cerebrospinal meningitis after MenAfriVac mass immunization in Burkina Faso

The aims of this study were to evaluate the impact of conjugate vaccine A, MenAfriVac, on Neisseria meningitidis (Nm) asymptomatic carriage and cerebrospinal meningitis in three health districts (Bogodogo, Kaya, and Dandé) of Burkina Faso. Asymptomatic carriage of Nm was assessed by performing cross-sectional studyrepeated (rounds 1 to 10) before and after introduction of the conjugate vaccine against serogroup A of N. meningitidis (NmA), MenAfriVac. In each round at least 1,500 people were enrolled in each district for a month. Data oncases of meningococcal meningitis in the three studied health districts were collected through meningitides epidemiological surveillance of Burkina Faso.Nm was identified in680 of 23,885 throat swabs before vaccination (2. 84%)withNmYasthe dominant serogroup(1.87%). During the same period (2009 and 2010), 891 cases of suspected meningitis were reported in the three health districts among whom 42 were due toNm (4.71%) withNmX (3.70%) asthe most frequently identified serogroup. After vaccination, Nm was identified in 1117 of 27,245 pharyngeal samples (6.42%); NmX (4.42%) wasthe dominantserogroup. From 2011 to 2013, 965 cases of suspected meningitis were reported in all health facilities in the three studied health districts located in the geographical study area; 91 was due toNm (9.43%) andNmWasthe most commonserogroup(52 cases= 5.38%).After introduction of conjugate vaccine A (MenAfriVac), the NmAserogroup almost disappeared both in asymptomatic carriers and in patients with cerebrospinal meningitis. However the presence of the NmW and NmXserogroups, which appear to have replaced serogroup A, is very worrying with regard to meningitis prevention and control in Burkina Faso. It appears necessary to strengthen surveillance and laboratory diagnosis of the different meningococcal serogroups circulating in Africa.Keywords: meningococcal meningitis, serogroups W and X, meningococcal carriage, MenAfriVac

Why oral antiseptic mouth rinsing before sputum collection cannot reduce contamination rate of mycobacterial culture in Burkina-Faso

Background: Tuberculosis (TB) diagnosis by culture in most resource-limited settings is hampered by high contamination rate varying up to 31%. Reduction of oral microorganism loads by mouth rinse with antiseptic before sputum collection showed a reduction of contamination. Moreover, knowing the characteristic of residual contaminant microorganisms would be an asset to understand contamination issues. Objectives: The aim of this study was to evaluate the effects of mouth rinsing with chlorhexidine on mycobacteria culture contaminations and to characterize morphologically the residual contaminants. Methods: We consecutively included 158 patients in a TB center. Each of them supplied two sputa: The first before mouth rinse, and the second after 60sec of mouth rinsing with chlorhexidine (0.1%). Petroff method and Lowenstein-Jensen media were used for sputum decontamination and inoculation respectively. The contamination rates were compared, and the type of residual contaminants were characterized and compared. Results: The contamination rate did not differ before and after the mouth rinse (respectively 58/150 (39 %) vs 61/150 (41 %), p=0.7). The major residual contaminants were Gram positive spore forming bacteria (94%). Conclusion: Chlorhexidine mouth rinsing before sputum collection did not reduce mycobacterial culture contamination rate. This is probably due to spore forming bacteria, highlighted as major residual contaminants. DOI: https://dx.doi.org/10.4314/ahs.v19i1.3 Cite as: Kabore A, Tranchot-Diallo J, Sanou A, Hien H, Daneau G, Gomgnimbou MK, Meda N, Sangar\ue9 L. Why Oral antiseptic mouth rinsing before sputum collection cannot reduce contamination rate of mycobacterial culture in Burkina-Faso. Afri Health Sci. 2019;19(1): 1321-1328. https://dx.doi.org/10.4314/ahs.v19i1.

Impact of mass administration of azithromycin as a preventive treatment on the prevalence and resistance of nasopharyngeal carriage of Staphylococcus aureus

Staphylococcus aureus is a major cause of serious illness and death in children, indicating the need to monitor prevalent strains, particularly in the vulnerable pediatric population. Nasal carriage of S. aureus is important as carriers have an increased risk of serious illness due to systemic invasion by this pathogen and can transmit the infection. Recent studies have demonstrated the effectiveness of azithromycin in reducing the prevalence of nasopharyngeal carrying of pneumococci, which are often implicated in respiratory infections in children. However, very few studies of the impact of azithromycin on staphylococci have been undertaken. During a clinical trial under taken in 2016, nasal swabs were collected from 778 children aged 3 to 59 months including 385 children who were swabbed before administration of azithromycin or placebo and 393 after administration of azithromycin or placebo. Azithromycin was given in a dose of 100 mg for three days, together with the antimalarials sulfadoxine-pyrimethamine and amodiaquine, on four occasions at monthly intervals during the malaria transmission season. These samples were cultured for S. aureus as well as for the pneumococcus. The S. aureus isolates were tested for their susceptibility to azithromycin (15 g), penicillin (10 IU), and cefoxitine (30 g) (Oxoid Ltd). S. aureus was isolated from 13.77% (53/385) swabs before administration of azithromycin and from 20.10% (79/393) six months after administration (PR = 1.46 [1.06; 2.01], p = 0.020). Azithromycin resistance found in isolates of S. aureus did not differ significantly before and after intervention (26.42% [14/53] vs 16.46% [13/79], (PR = 0.62 [0.32; 1.23], p = 0.172). Penicillin resistance was very pronounced, 88.68% and 96.20% in pre-intervention and in post-intervention isolates respectively, but very little Methicillin Resistance (MRSA) was detected (2 cases before and 2 cases after intervention). Monitoring antibiotic resistance in S. aureus and other bacteria is especially important in Burkina Faso due to unregulated consumption of antibiotics putting children and others at risk

Polymorphisms in immunoregulatory genes and the risk of histologic chorioamnionitis in Caucasoid women: a case control study

BACKGROUND: Chorioamnionitis is a common underlying cause of preterm birth (PTB). It is hypothesised that polymorphisms in immunoregulatory genes influence the host response to infection and subsequent preterm birth. The relationship between histologic chorioamnionitis and 22 single nucleotide polymorphisms in 11 immunoregulatory genes was examined in a case-control study. METHODS: Placentas of 181 Caucasoid women with spontaneous PTB prior to 35 weeks were examined for histologic chorioamnionitis. Polymorphisms in genes IL1A, IL1B, IL1RN, IL1R1, tumour necrosis factor (TNF), IL4, IL6, IL10, transforming growth factor beta-1 (TGFB1), Fas (TNFRSF6), and mannose-binding lectin (MBL2) were genotyped by polymerase chain reaction and sequence specific primers. Multivariable logistic regression including demographic and genetic variables and Kaplan-Meier survival analyses of genotype frequencies and pregnancy outcome were performed. RESULTS: Sixty-nine (34%) women had histologic evidence of acute chorioamnionitis. Carriage of the IL10-1082A/-819T/592A (ATA) haplotype [Multivariable Odds ratio (MOR) 1.9, P = 0.05] and MBL2 codon 54Asp allele (MOR 2.0, P = 0.04), were positively associated with chorioamnionitis, while the TNFRSF6-1377A/-670G (AG) haplotype (MOR 0.4, P = 0.03) and homozygosity for TGFB1-800G/509T (GT) haplotype (MOR 0.2, P = 0.04) were negatively associated. CONCLUSION: These findings demonstrate that polymorphisms in immunoregulatory genes IL10, MBL2, TNFRSF6 and TGFB1 may influence susceptibility to chorioamnionitis

Etude par émission acoustique et dilatométrie d'électrodes à base de silicium pour batteries Li-ion

To increase the energy density of Li-ion batteries, especially for the electric vehicle market, the development of new electrode materials is required. Silicon is a particularly interesting material, thanks to its high specific capacity (3579mAh/g, ten times higher than the capacity of graphite). Nevertheless, upon lithiation, silicon undergoes an important expansion (300% vs 10% for graphite). This leads to the cracking of the Si particles and fracturing of the electrode film. These induces electrical disconnections upon cycling, resulting in a poor cycle life. To improve the cyclability of the Si based electrodes, it is important to better understand/quantify their mechanical degradation. Conventional post mortem analyses are insufficient for that purpose. The objective of this work is to develop and use in operando analyses techniques. Therefore, we established protocols to characterize composite electrodes by electrochemical measurements coupled with either acoustic emission (AE) or dilatometry measurements. The evolution of the acoustic activity upon cycling showed that the cracking of the micrometric Si particles and of the composite film mainly occurs during the first cycle and is initiated in the early stage of the lithiation. Very few AE signals are detected in the following cycles. The signal analysis leads to the identification of three types of signals depending to their peak frequency. High frequency signals were associated with surface micro-cracking of the Si particles at the beginning of lithiation. Medium and low frequency signals were respectively attributed to the fracturing of the electrode film and bulk macro-cracking of the Si particles at the end of lithiation. An electrode thickness expansion of 170% was measured by electrochemical dilatometry for our electrodes prepared at pH3 versus 300% for electrodes prepared at pH7. The different mechanical behavior is explained by the formation of covalent bonds between the CMC binder and Si particles at pH3, which increases the mechanical stability of electrodes. This was confirmed by the measurement of their hardness and Young’s modulus. Therefore, pH3 electrodes display a higher capacity retention. It was also demonstrated that a decrease of the Si particle size does not necessarily lead to an improvement of the electrode cycle life. Indeed, we observed a significant decrease of the electrode cycle life when the Si particle size is decreased from 230 to 85 nm. This can be explained by a lack of CMC binder in relation with the higher surface area of the smaller Si particles, leading to a lower mechanical resistance of the electrode film. Within the first cycles, Si 85 nm based electrodes suffer from important cracking and exfoliation. This was confirmed by in operando dilatometry and acoustic measurements, and post mortem SEM observations.Afin d’augmenter la densité d’énergie des batteries Li-ion, en particulier pour le marché des véhicules électriques, il est nécessaire de développer des matériaux d’électrode plus performants. Le silicium, dont la capacité spécifique (3579mAh/g) est dix fois supérieure à celle du graphite, est un matériau particulièrement prometteur. Néanmoins, lors de sa lithiation, il subit une forte expansion volumique (280% contre 10% pour le graphite) conduisant à la décrépitation des particules de Si et à la fissuration/décohésion de l’électrode. Il en résulte une diminution notable de la durée de vie de l’anode. Pour améliorer la tenue au cyclage des électrodes, il est nécessaire de bien comprendre/quantifier leur dégradation morphologique, ce que permettent difficilement des analyses post mortem conventionnelles. Notre objectif est d’utiliser et de développer des outils permettant d'étudier in operando la dégradation de ces électrodes. Nous avons mis en œuvre des protocoles de caractérisation in operando couplant des mesures électrochimiques à l’émission acoustique d’une part et à la dilatométrie d’autre part. Le suivi de l’activité acoustique au cours du cyclage de l’électrode a montré que les particules de Si micrométrique constituant cette électrode se fracturent dès le début de la lithiation, et que la fissuration de l’électrode se produit progressivement tout au long de la 1ère lithiation. Peu d’activité acoustique est détectée par la suite. Par l’analyse des signaux acoustiques, trois types de signaux ont été identifiés, se différenciant principalement selon leur fréquence de pic. Les signaux de hautes fréquences sont associés principalement aux micro-fractures des particules en début de lithiation, et les signaux à moyennes et basses fréquences sont respectivement attribuées à la fissuration de l’électrode et aux macro-fractures des particules de Si en fin de lithiation. L’étude dilatométrique a montré une expansion volumique maximale de ~170% avec une encre tamponnée à pH3 versus 300% si l’électrode est préparée à pH7. Cette différence s’explique par la formation de liaisons cohésives entre le liant CMC et les particules de Si lorsque l’électrode est préparée à pH 3, améliorant sa résistance mécanique. Ce qui a été confirmé par des mesures d’indentation. Ainsi, l’électrode formulée à pH 3 montre une meilleure cyclabilité. Enfin, nous avons démontré qu’une diminution notable de la durée de vie de l’électrode est observée lorsque la taille initiale des particules de Si est réduite de 230 à 85nm. Nous expliquons ce résultat inattendu par une quantité insuffisante de CMC par rapport à la surface spécifique plus élevée des particules de taille plus faible. De fait, sa résistance mécanique est insuffisante et conduit à une fissuration et une exfoliation importantes de l’électrode. Ceci est appuyé par les mesures de dilatométrie, d’émission acoustique et des observations MEB

Acoustic emission and dilatometry study of silicon based electrodes for Li-ion batteries

Afin d’augmenter la densité d’énergie des batteries Li-ion, en particulier pour le marché des véhicules électriques, il est nécessaire de développer des matériaux d’électrode plus performants. Le silicium, dont la capacité spécifique (3579mAh/g) est dix fois supérieure à celle du graphite, est un matériau particulièrement prometteur. Néanmoins, lors de sa lithiation, il subit une forte expansion volumique (280% contre 10% pour le graphite) conduisant à la décrépitation des particules de Si et à la fissuration/décohésion de l’électrode. Il en résulte une diminution notable de la durée de vie de l’anode. Pour améliorer la tenue au cyclage des électrodes, il est nécessaire de bien comprendre/quantifier leur dégradation morphologique, ce que permettent difficilement des analyses post mortem conventionnelles. Notre objectif est d’utiliser et de développer des outils permettant d'étudier in operando la dégradation de ces électrodes. Nous avons mis en œuvre des protocoles de caractérisation in operando couplant des mesures électrochimiques à l’émission acoustique d’une part et à la dilatométrie d’autre part. Le suivi de l’activité acoustique au cours du cyclage de l’électrode a montré que les particules de Si micrométrique constituant cette électrode se fracturent dès le début de la lithiation, et que la fissuration de l’électrode se produit progressivement tout au long de la 1ère lithiation. Peu d’activité acoustique est détectée par la suite. Par l’analyse des signaux acoustiques, trois types de signaux ont été identifiés, se différenciant principalement selon leur fréquence de pic. Les signaux de hautes fréquences sont associés principalement aux micro-fractures des particules en début de lithiation, et les signaux à moyennes et basses fréquences sont respectivement attribuées à la fissuration de l’électrode et aux macro-fractures des particules de Si en fin de lithiation. L’étude dilatométrique a montré une expansion volumique maximale de ~170% avec une encre tamponnée à pH3 versus 300% si l’électrode est préparée à pH7. Cette différence s’explique par la formation de liaisons cohésives entre le liant CMC et les particules de Si lorsque l’électrode est préparée à pH 3, améliorant sa résistance mécanique. Ce qui a été confirmé par des mesures d’indentation. Ainsi, l’électrode formulée à pH 3 montre une meilleure cyclabilité. Enfin, nous avons démontré qu’une diminution notable de la durée de vie de l’électrode est observée lorsque la taille initiale des particules de Si est réduite de 230 à 85nm. Nous expliquons ce résultat inattendu par une quantité insuffisante de CMC par rapport à la surface spécifique plus élevée des particules de taille plus faible. De fait, sa résistance mécanique est insuffisante et conduit à une fissuration et une exfoliation importantes de l’électrode. Ceci est appuyé par les mesures de dilatométrie, d’émission acoustique et des observations MEB.To increase the energy density of Li-ion batteries, especially for the electric vehicle market, the development of new electrode materials is required. Silicon is a particularly interesting material, thanks to its high specific capacity (3579mAh/g, ten times higher than the capacity of graphite). Nevertheless, upon lithiation, silicon undergoes an important expansion (300% vs 10% for graphite). This leads to the cracking of the Si particles and fracturing of the electrode film. These induces electrical disconnections upon cycling, resulting in a poor cycle life. To improve the cyclability of the Si based electrodes, it is important to better understand/quantify their mechanical degradation. Conventional post mortem analyses are insufficient for that purpose. The objective of this work is to develop and use in operando analyses techniques. Therefore, we established protocols to characterize composite electrodes by electrochemical measurements coupled with either acoustic emission (AE) or dilatometry measurements. The evolution of the acoustic activity upon cycling showed that the cracking of the micrometric Si particles and of the composite film mainly occurs during the first cycle and is initiated in the early stage of the lithiation. Very few AE signals are detected in the following cycles. The signal analysis leads to the identification of three types of signals depending to their peak frequency. High frequency signals were associated with surface micro-cracking of the Si particles at the beginning of lithiation. Medium and low frequency signals were respectively attributed to the fracturing of the electrode film and bulk macro-cracking of the Si particles at the end of lithiation. An electrode thickness expansion of 170% was measured by electrochemical dilatometry for our electrodes prepared at pH3 versus 300% for electrodes prepared at pH7. The different mechanical behavior is explained by the formation of covalent bonds between the CMC binder and Si particles at pH3, which increases the mechanical stability of electrodes. This was confirmed by the measurement of their hardness and Young’s modulus. Therefore, pH3 electrodes display a higher capacity retention. It was also demonstrated that a decrease of the Si particle size does not necessarily lead to an improvement of the electrode cycle life. Indeed, we observed a significant decrease of the electrode cycle life when the Si particle size is decreased from 230 to 85 nm. This can be explained by a lack of CMC binder in relation with the higher surface area of the smaller Si particles, leading to a lower mechanical resistance of the electrode film. Within the first cycles, Si 85 nm based electrodes suffer from important cracking and exfoliation. This was confirmed by in operando dilatometry and acoustic measurements, and post mortem SEM observations

Etude par émission acoustique et dilatométrie d'électrodes à base de silicium pour batteries Li-ion

To increase the energy density of Li-ion batteries, especially for the electric vehicle market, the development of new electrode materials is required. Silicon is a particularly interesting material, thanks to its high specific capacity (3579mAh/g, ten times higher than the capacity of graphite). Nevertheless, upon lithiation, silicon undergoes an important expansion (300% vs 10% for graphite). This leads to the cracking of the Si particles and fracturing of the electrode film. These induces electrical disconnections upon cycling, resulting in a poor cycle life. To improve the cyclability of the Si based electrodes, it is important to better understand/quantify their mechanical degradation. Conventional post mortem analyses are insufficient for that purpose. The objective of this work is to develop and use in operando analyses techniques. Therefore, we established protocols to characterize composite electrodes by electrochemical measurements coupled with either acoustic emission (AE) or dilatometry measurements. The evolution of the acoustic activity upon cycling showed that the cracking of the micrometric Si particles and of the composite film mainly occurs during the first cycle and is initiated in the early stage of the lithiation. Very few AE signals are detected in the following cycles. The signal analysis leads to the identification of three types of signals depending to their peak frequency. High frequency signals were associated with surface micro-cracking of the Si particles at the beginning of lithiation. Medium and low frequency signals were respectively attributed to the fracturing of the electrode film and bulk macro-cracking of the Si particles at the end of lithiation. An electrode thickness expansion of 170% was measured by electrochemical dilatometry for our electrodes prepared at pH3 versus 300% for electrodes prepared at pH7. The different mechanical behavior is explained by the formation of covalent bonds between the CMC binder and Si particles at pH3, which increases the mechanical stability of electrodes. This was confirmed by the measurement of their hardness and Young’s modulus. Therefore, pH3 electrodes display a higher capacity retention. It was also demonstrated that a decrease of the Si particle size does not necessarily lead to an improvement of the electrode cycle life. Indeed, we observed a significant decrease of the electrode cycle life when the Si particle size is decreased from 230 to 85 nm. This can be explained by a lack of CMC binder in relation with the higher surface area of the smaller Si particles, leading to a lower mechanical resistance of the electrode film. Within the first cycles, Si 85 nm based electrodes suffer from important cracking and exfoliation. This was confirmed by in operando dilatometry and acoustic measurements, and post mortem SEM observations.Afin d’augmenter la densité d’énergie des batteries Li-ion, en particulier pour le marché des véhicules électriques, il est nécessaire de développer des matériaux d’électrode plus performants. Le silicium, dont la capacité spécifique (3579mAh/g) est dix fois supérieure à celle du graphite, est un matériau particulièrement prometteur. Néanmoins, lors de sa lithiation, il subit une forte expansion volumique (280% contre 10% pour le graphite) conduisant à la décrépitation des particules de Si et à la fissuration/décohésion de l’électrode. Il en résulte une diminution notable de la durée de vie de l’anode. Pour améliorer la tenue au cyclage des électrodes, il est nécessaire de bien comprendre/quantifier leur dégradation morphologique, ce que permettent difficilement des analyses post mortem conventionnelles. Notre objectif est d’utiliser et de développer des outils permettant d'étudier in operando la dégradation de ces électrodes. Nous avons mis en œuvre des protocoles de caractérisation in operando couplant des mesures électrochimiques à l’émission acoustique d’une part et à la dilatométrie d’autre part. Le suivi de l’activité acoustique au cours du cyclage de l’électrode a montré que les particules de Si micrométrique constituant cette électrode se fracturent dès le début de la lithiation, et que la fissuration de l’électrode se produit progressivement tout au long de la 1ère lithiation. Peu d’activité acoustique est détectée par la suite. Par l’analyse des signaux acoustiques, trois types de signaux ont été identifiés, se différenciant principalement selon leur fréquence de pic. Les signaux de hautes fréquences sont associés principalement aux micro-fractures des particules en début de lithiation, et les signaux à moyennes et basses fréquences sont respectivement attribuées à la fissuration de l’électrode et aux macro-fractures des particules de Si en fin de lithiation. L’étude dilatométrique a montré une expansion volumique maximale de ~170% avec une encre tamponnée à pH3 versus 300% si l’électrode est préparée à pH7. Cette différence s’explique par la formation de liaisons cohésives entre le liant CMC et les particules de Si lorsque l’électrode est préparée à pH 3, améliorant sa résistance mécanique. Ce qui a été confirmé par des mesures d’indentation. Ainsi, l’électrode formulée à pH 3 montre une meilleure cyclabilité. Enfin, nous avons démontré qu’une diminution notable de la durée de vie de l’électrode est observée lorsque la taille initiale des particules de Si est réduite de 230 à 85nm. Nous expliquons ce résultat inattendu par une quantité insuffisante de CMC par rapport à la surface spécifique plus élevée des particules de taille plus faible. De fait, sa résistance mécanique est insuffisante et conduit à une fissuration et une exfoliation importantes de l’électrode. Ceci est appuyé par les mesures de dilatométrie, d’émission acoustique et des observations MEB

Impact of the slurry pH on the expansion/contraction behavior of silicon/carbon/carboxymethylcellulose electrodes for li-ion batteries

cited By 10International audienceElectrochemical dilatometry experiments were performed on silicon/carbon/carboxymethylcellulose (Si/C/CMC) composite electrodes prepared with pH7 and buffered pH3 slurries. It was shown that the pH3 electrode better accommodates the severe volume change of the micrometric Si particles, inducing a much better capacity retention with cycling (70% after 10 cycles compared to only 6% for the pH7 electrode). During the first discharge (lithiation), a maximum electrode thickness expansion of ∼170% was observed for the pH3 electrode compared to ∼330% for the pH7 electrode. A lower irreversible expansion was also observed at the end of the 1st cycle (∼50% compared to ∼180%forthepH7 electrode). It was explained by the fact that the pH3 of the slurry, which is known to favor the formation covalent bonds between the Si particles and the CMC chains, greatly improves the cohesive strength of the electrode as supported by the higher hardness and elastic modulus of the pH3 electrode. When the discharge capacity was limited to 1200 mAh g-1, a progressive and irreversible swelling of thepH3 electrode was observed upon prolonged cycling, which was attributed to the accumulation of solid electrolyte interface (SEI) products. © The Author(s) 2016. Published by ECS

In-situ acoustic emission study of Si-based electrodes for Li-ion batteries

cited By 11International audienceThe mechanical degradation of a Si powder (∼2 μm) based electrode is investigated by acoustic emission (AE). AE signals are mainly detected during the first lithiation, suggesting that electrode cracking mainly occurs during this period. The formation of the solid electrolyte interface (SEI) is not very acoustically emissive, in contrast to the Si particle cracking which is initiated in the early stage of the lithiation in accordance with a core - shell lithiation mechanism. An increase of the AE activity is observed at the end of the discharge when the c-Li15Si4 phase is formed and during the charge when the potential reaches ∼0.45 V, corresponding to the delithiation of c-Li15Si4. From a clustering procedure, three types of signals are identi fied: type-1 signals consisting of a succession of very short waveforms with high peak frequency (∼700 kHz) are primarily detected when the Si lithiation is initiated and are ascribed to the nucleation of surface microcracks on the Si particles; type-2 signals (peak frequency ∼400 kHz), present all during the Si lithiation, are attributed to the propagation of cracks through the Si particles and into the composite film; type-3 signals (peak frequency ∼200 kHz), detected when the potential reaches 60 mV, are ascribed to the accentuation of the electrode cracking due to the c-Li15Si4 formation. © 2014 Elsevier B.V. All rights reserved