SUNScholar - Browsing by Author "Bekker, A."

Browsing by Author "Bekker, A."

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Bayesian highest posterior density intervals for the availability of a system with a 'rest-period' for the repair facility
(SAIIE, 2001) Yadavalli, V. S. S.; Bekker, A.; Mostert, P. J.; Botha, M.
In this paper Bayesian estimation for the steady state availability of a one-unit system with a rest-period for the repair facility is studied. The assumption is that the repair facility takes rest with probability p after each repair completion and the facility does not take the same with probability (l - p). The prior information is assumed to be vague and the Jeffreys' prior is used for the unknown parameters in the system. Gibbs sampling is used to derive the posterior distribution of the availability and subsequently the highest posterior density (HPD) intervals. A numerical example illustrates these results.
Berekening van a posteriori-verdeling in Bayes-analise : toepassing in 'n betroubareheidstelsel wat afwisselend gebruik word
(AOSIS, 2002) Yadavalli, V. S. S.; Mostert, P. J.; Bekker, A.; Botha, M.
Bayesian estimation is presented for the stationary rate of disappointments, D∞, for two models (with different specifications) of intermittently used systems. The random variables in the system are considered to be independently exponentially distributed. Jeffreys’ prior is assumed for the unknown parameters in the system. Inference about D∞ is being restrained in both models by the complex and non-linear definition of D∞. Monte Carlo simulation is used to derive the posterior distribution of D∞ and subsequently the highest posterior density (HPD) intervals. A numerical example where Bayes estimates and the HPD intervals are determined illustrates these results. This illustration is extended to determine the frequentistical properties of this Bayes procedure, by calculating covering proportions for each of these HPD intervals, assuming fixed values for the parameters.
Central-line-associated bloodstream infections in a resource-limited South African neonatal intensive care unit
(Health and Medical Publishing Group, 2017) Geldenhuys, C.; Dramowski, Angela; Jenkins, A.; Bekker, A.
Background. The rate of central-line-associated bloodstream infection (CLABSI) in South African (SA) public sector neonatal intensive care units (NICUs) is unknown. Tygerberg Children’s Hospital (TCH), Cape Town, introduced a neonatal CLABSI surveillance and prevention programme in August 2012. Objectives. To describe CLABSI events and identify risk factors for development of CLABSI in a resource-limited NICU. Methods. A retrospective case-control study was conducted using prospectively collected NICU CLABSI events matched to four randomly selected controls, sampled from the NICU registry between 9 August 2012 and 31 July 2014. Clinical data and laboratory records were reviewed to identify possible risk factors, using stepwise forward logistic regression analysis. Results. A total of 706 central lines were inserted in 530 neonates during the study period. Nineteen CLABSI events were identified, with a CLABSI rate of 5.9/1 000 line days. CLABSI patients were of lower gestational age (28 v. 34 weeks; p=0.003), lower median birth weight (1 170 g v. 1 975 g; p=0.014), had longer catheter dwell times (>4 days) (odds ratio (OR) 5.1 (95% confidence interval (CI) 1.0 - 25.4); p=0.04) and were more likely to have had surgery during their NICU stay (OR 3.5 (95% CI 1.26 - 10); p=0.01). Significant risk factors for CLABSI were length of stay >30 days (OR 20.7 (95% CI 2.1 - 203.2); p=0.009) and central-line insertion in the operating theatre (OR 8.1 (95% CI 1.2 - 54.7); p=0.03). Gram-negative pathogens predominated (12/22; 54%), with most isolates (10/12; 83%) exhibiting multidrug resistance. Conclusion. The TCH NICU CLABSI rate is similar to that reported from resource-limited settings, but exceeds that of high-income countries. Prolonged NICU stay and central-line insertion in the operating theatre were important risk factors for CLABSI development. Intensified neonatal staff training regarding CLABSI maintenance bundle elements and hand hygiene are key to reducing CLABSI rates.
Data for indirect load case estimation of ice-induced moments from shaft line torque measurements
(Elsevier, 2018) De Waal, R. J. O.; Bekker, A.; Heyns, P. S.
ENGLISH ABSTRACT: During ice navigation, blade measurements of ice-induced moments on ship propellers, are challenged by the harsh operating environment. To overcome this problem, shaft line measurements are performed inboard, and the required propeller loads are subsequently estimated using a dynamic model and the solution of an inverse problem. The inverse problem is mathematically ill-posed and requires the determination of the ice-induced moment on the propeller blades from shaft line measurements. Full-scale torsional response data is presented as calculated from indirect strain measurements on the shaft line of a polar supply and research vessel. The vessel operated on a 68-day voyage between Cape Town and Antarctica and spent almost 11 days in sea ice with observed concentrations above 90% and a maximum thickness of 3 m. Data for five ice-induced load cases are presented, including the shaft torque from indirect measurements and the estimated ice-induced moment, which is obtained by solving an ill-posed inverse problem. The ice-induced moments on the propeller are obtained by approximating the drive-train as a viscously damped, elastic lumped mass model. The ice-induced moment is then determined through existing approaches to solving the ill-conditioned inverse problem. The lumped mass model is presented along with algorithms to solve the inverse problem, including truncated singular value decomposition, truncated generalized singular value decomposition and Tikhonov׳s method. The resulting time series data for the inversely calculated ice-induced moments is published to provide industry with load cases for ice-going propulsion design.
Electric vehicle sound stimuli data and enhancements
(Elsevier, 2018) Swart, D. J.; Bekker, A.; Bienert, J.
Data for six electric vehicle WOT interior sound measurements and eight enhanced sound signatures are presented. The measurement of electric vehicle interior sound signature data and the enhancement of these stimuli are documented in this data article. The procedures and equipment that were used to record the data, as well as the transposition, harmony and order addition, frequency filtering and modulation enhancement techniques that were applied to these stimuli are explained in detail. The transient frequency content of the 12 sound stimuli is presented in acoustic spectrograms along with the audio files in.mp3 format.
Infectious disease exposures and outbreaks at a South African neonatal unit with review of neonatal outbreak epidemiology in Africa
(Elsevier, 2017) Dramowski, Angela; Aucamp, M.; Bekker, A.; Mehtar, Shaheen
Background: Hospitalized neonates are vulnerable to infection, with pathogen exposures occurring in utero, intrapartum, and postnatally. African neonatal units are at high risk of outbreaks owing to overcrowding, understaffing, and shared equipment. Methods: Neonatal outbreaks attended by the paediatric infectious diseases and infection prevention (IP) teams at Tygerberg Children’s Hospital, Cape Town (May 1, 2008 to April 30, 2016) are described, pathogens, outbreak size, mortality, source, and outbreak control measures. Neonatal outbreaks reported from Africa (January 1, 1996 to January 1, 2016) were reviewed to contextualize the authors’ experience within the published literature from the region. Results: Thirteen outbreaks affecting 148 babies (11 deaths; 7% mortality) over an 8-year period were documented, with pathogens including rotavirus, influenza virus, measles virus, and multidrug-resistant bacteria (Serratia marcescens, Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci). Although the infection source was seldom identified, most outbreaks were associated with breaches in IP practices. Stringent transmission-based precautions, staff/parent education, and changes to clinical practices contained the outbreaks. From the African neonatal literature, 20 outbreaks affecting 524 babies (177 deaths; 34% mortality) were identified; 50% of outbreaks were caused by extended-spectrum β-lactamase-producing Klebsiella pneumoniae. Conclusions: Outbreaks in hospitalized African neonates are frequent but under-reported, with high mortality and a predominance of Gram-negative bacteria. Breaches in IP practice are commonly implicated, with the outbreak source confirmed in less than 50% of cases. Programmes to improve IP practice and address antimicrobial resistance in African neonatal units are urgently required.
NeoCLEAN : a multimodal strategy to enhance environmental cleaning in a resource-limited neonatal unit
(BMC (part of Springer Nature), 2021-02-12) Dramowski, A.; Aucamp, M.; Bekker, A.; Pillay, S.; Moloto, K.; Whitelaw, A. C.; Cotton, M. F.; Coffin, S.
Background: Contamination of the hospital environment contributes to neonatal bacterial colonization and infection. Cleaning of hospital surfaces and equipment is seldom audited in resource-limited settings. Methods: A quasi-experimental study was conducted to assess the impact of a multimodal cleaning intervention for surfaces and equipment in a 30-bed neonatal ward. The intervention included cleaning audits with feedback, cleaning checklists, in-room cleaning wipes and training of staff and mothers in cleaning methods. Cleaning adequacy was evaluated for 100 items (58 surfaces, 42 equipment) using quantitative bacterial surface cultures, adenosine triphosphate bioluminescence assays and fluorescent ultraviolet markers, performed at baseline (P1, October 2019), early intervention (P2, November 2019) and late intervention (P3, February 2020). Results: Environmental swabs (55/300; 18.3%) yielded growth of 78 potential neonatal pathogens with Enterococci, S. marcescens, K. pneumoniae, S. aureus and A. baumannii predominating. Highest aerobic colony counts were noted from moist surfaces such as sinks, milk kitchen surfaces, humidifiers and suction tubing. The proportion of surfaces and equipment exhibiting no bacterial growth increased between phases (P1 = 49%, P2 = 66%, P3 = 69%; p = 0.007). The proportion of surfaces and equipment meeting the ATP “cleanliness” threshold (< 200 relative light units) increased over time (P1 = 40%, P2 = 54%, P3 = 65%; p = 0.002), as did the UV marker removal rate (P1 = 23%, P2 = 71%, P3 = 74%; p < 0.001). Conclusion: Routine environmental cleaning of this neonatal ward was sub-optimal at baseline but improved significantly following a multimodal cleaning intervention. Involving mothers and nursing staff was key to achieving improved environmental and equipment cleaning in this resource-limited neonatal unit.
Neonatal listeriosis during a countrywide epidemic in South Africa : a tertiary hospital’s experience
(Health & Medical Publishing Group, 2018) Dramowski, Angela; Lloyd, L. G.; Bekker, A.; Holgate, S.; Aucamp, M.; Reddy, K.; Finlayson, H.
Background. A countrywide epidemic of Listeria monocytogenes (LM) in South Africa began in the first quarter of 2017, rapidly becoming the world’s largest LM outbreak to date. Methods. We describe the clinical course of neonates with culture-confirmed LM infection admitted to a tertiary neonatal unit at Tygerberg Hospital, Cape Town (1 January 2017 - 31 January 2018). Current epidemic LM cases were compared with a historical cohort of sporadic neonatal LM cases at our institution (2006 - 2016). The global literature on epidemic neonatal LM outbreaks (1 January 1978 - 31 December 2017) was reviewed. Results. Twelve neonates (median gestational age 35 weeks, median birth weight 2 020 g) were treated for confirmed LM bacteraemia in 2017/18, presenting at a median age of 0.5 days. In 5 cases, neurolisteriosis was suspected. Three neonates died (25.0%) v. 8/13 neonatal deaths (61.6%) in the sporadic listeriosis cohort (2006 - 2016) (p=0.075). The institution’s neonatal LM infection incidence increased significantly in 2017 from a historical rate of 0.17/1 000 live births to 1.4/1 000 (p<0.001). During the current LM epidemic, the crude neonatal fatality rate exceeded the average calculated global epidemic neonatal LM mortality (3/12 (25.0%) v. 50/290 (17.2%); p=0.448). Possible factors contributing to the high mortality rate in this epidemic LM neonatal cohort may include more virulent disease associated with sequence type 6 and the predominance of early-onset disease. Conclusions. Epidemic neonatal listeriosis at Tygerberg Hospital was associated with a predominance of bacteraemic, early-onset disease. Listeriosis-associated mortality rates were higher than previously published, but lower than the rate in a historical institutional cohort.
Non-contact experimental methods to characterise the response of a hyper-elastic membrane
(Springer Open, 2017-07-24) Kamper, M.; Bekker, A.
Background: Membranes often feature in dynamic structures. The design of such structures generally includes the evaluation of their dynamic characteristics, such as natural frequecies and mode shapes. Methods: The quasi-statics ad dyamic responses of thin rubber sheeting were investigated through non-contact experimental techniques. The rubber sheeting was modelled as a membrane structure and the material was assumed to be hyper-elastic, isotopic and incompressible. Two hyper-elastic material models were considered, namely the Mooney-Rivlin model and the Neo-Hookean model. The natural frequencies and mode shapes of the hyprt-elastic membrane were anatically and numerically calculated by assuming small linear vibrations and an equi-bi-axial stress state in the membrane. To validate the mathematical analyses, experimental modal analysis was performed where the vibration response was measured with a laser Doppler vibrometer. Results and conclusions: The analytical model, shows that the natural frequencies of the membrane depend on the initial stretch. Mathematical and experimental results agree well at the lower modes. However, measurement resolution is found to be a vital factor which limits the extraction of closely spaced modes due to difficulties with the accurate identification of nodal line in a purely experimental approach.
Prevalence of and risk factors for retinopathy of prematurity in a cohort of preterm infants treated exclusively with non-invasive ventilation in the first week after birth
(Health & Medical Publishing Group, 2013-01-14) Van der Merwe, S. K.; Freeman, N.; Bekker, A.; Harvey, J.; Smith, J.
Objectives. To determine the current prevalence of retinopathy of prematurity (ROP) in premature babies treated with non-invasive ventilation at Tygerberg Children’s Hospital, Parow, Cape Town, South Africa, and to identify risk factors associated with the development of ROP. Methods. A retrospective medical records review of infants screened for ROP during a 2-year period (January 2009 - December 2010). Infants who did not receive invasive ventilation during the first week of life were included. Twenty-four previously reported risk factors for the development of ROP were identified for use in a multivariate logistic regression (MLR) analysis. Results. A total of 356 patients were included. The overall prevalence of ROP was 21.8% and that of clinically significant ROP (CSROP) 4.4%. The risk factors with a statistically significant association with the development of ROP on MLR analysis were severe apnoea (p=0.0005) and decreasing birth weight (p=0.0382). Conclusions. There is a low prevalence of ROP in the cohort of preterm infants treated exclusively with non-invasive ventilation in the first week of life. The risk factors of importance in our population were severe apnoea and lower birth weight. Birth weight is a practical and reproducible variable that can be used to aid development of ROP screening criteria.
Tuberculosis transmission in a hospitalised neonate : need for optimised tuberculosis screening of pregnant and postpartum women
(Health & Medical Publishing Group, 2019) Zenhausern, J.; Bekker, A.; Wates, M. A.; Schaaf, H. S.; Dramowski, A.
ENGLISH ABSTRACT: A recent fatal case of confirmed nosocomial tuberculosis (TB) transmission to a neonate in a kangaroo mother care (KMC) unit highlighted the infection risk to hospitalised neonates in South Africa, a high-burden TB setting. The index case was a 9-week-old infant who presented to another hospital’s intensive care unit with severe respiratory distress shortly after discharge from the KMC unit. Contact tracing identified that the infant had been exposed to a postpartum woman with undiagnosed pulmonary TB while in the KMC unit. Molecular testing confirmed nosocomial transmission between the index case and the presumed source case in the KMC unit. We describe the subsequent process of tracing other TB-exposed infants and mothers, the difficulty in confirming TB infection/disease in pregnancy, and the provision of isoniazid preventive therapy in this cohort. We discuss the practical implementation of TB screening approaches in maternity and neonatal wards in high-burden TB settings.

Browsing by Author "Bekker, A."

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