SUNScholar - Browsing by Author "Van Helden, P. D."

Browsing by Author "Van Helden, P. D."

Now showing 1 - 13 of 13

Factors influencing peak expiratory flow in teenage boys
(Health & Medical Publishing Group, 2001) Van Helden, S. N.; Hoal-van Helden, E. G.; Van Helden, P. D.
Background. Peak expiratory flow (PEF) is a useful measure of pulmonary health status and is frequently utilised in asthma management. Reduction in PEF is usually indicative of onset of asthma symptoms. However, use can be made of PEF values only if normal values are known. The definition of normal range is always difficult and may vary between regions and be affected by a variety of factors. Objective. To establish PEF values for teenage boys in a Cape Town suburb and examine factors that possibly influence this measurement. Setting. A high school for boys in the southern suburbs of Cape Town. Methods. Measurements of PEF were taken for 124 boys. Subjects were approximately 16 years old and apparently healthy at the time of survey. Further details were provided by means of a questionnaire. Results. PEF ranged from 350 to 760 1/min, with a mean (± standard deviation (SD) of 539 ± 68 1/min. Factors expected to influence PEF included height and mass, whereas unexpected factors included sport intensity and academic grade. A trend to reduced peak flow was already evident in boys who smoked and boys from homes where a parent smoked. Regression analysis suggested peak flow differences in our population compared with the standard reference. Conclusion. Interpretation of results obtained from peak-flow instruments should take into account additional knowledge concerning the individual. Further surveys of the South African population and of different groups should be done to establish local standards and factors influencing PEF.
Identification of a major locus, TNF1, that controls BCG-triggered TNF production by leukocytes in an area hyperendemic for tuberculosis.
(UNIV CHICAGO PRESS, 1427 E 60TH ST, CHICAGO, USA, IL, 60637-2954, 2013) Cobat, A.; Hoal, E. G.; Gallant, C. J.; Simkin, L.; Black, G. F.; Stanley, K.; Ja�s, J-P.; Yu, T. H.; Boland-Auge, A.; Grange, G.; Delacourt, C.; Van Helden, P. D.; Casanova, J-L.; Abel, L.; Alcais, A.; Schurr, E.
Incidence of heat-labile enterotoxin-producing Escherichia coli detected by means of polymerase chain reaction amplification
(Health & Medical Publishing Group, 1994) Winterbach, R.; Van Helden, P. D.; Janse Van Rensburg, J.; Victor, T.
Diarrhoea can be caused by many different organisms, some of which are notoriously difficult to identify. One of these is enterotoxin-producing Escherichia coli. Recently a new diagnostic technique that uses polymerase chain reaction DNA amplification was developed for detection of the 'A' subunit of the labile enterotoxin-producing E. coli gene. This technique was used to evaluate the incidence of heat-labile (LT+) enterotoxin-producing E. coli in the causation of diarrhoea. The results from this study showed that LT+ E. coli is a cause of diarrhoea in the western Cape and that 5,3% of non-diagnosed diarrhoea patients in Tygerberg Hospital were infected with this pathogen. This represented less than 1% of the total number of cases of diarrhoea investigated in this hospital. The peak coincides with the wetter months in this locality and the infection rate is lower than that reported in most other countries. Given the low incidence of occurrence of this organism we do not recommend routine implementation of the diagnostic procedure. However, this test may be useful at times, e.g. to ascertain the source of a diarrhoea epidemic.
Interferon : the clinical experience
(Health & Medical Publishing Group, 1983) Van Helden, P. D.
Recent trials with interferon, in particular those using pure, recombinant interferon, have provided us with improved data (compared with those obtained in early studies) and show that interferon does hold some promise as a therapeutic agent. When used in the treatment of viral disease, interferon has shown itself to be quite effective in reducing viral titres. While not as effective against cancer, interferon has limited tumour growth, reduced the appearance of metastases and led to a general improvement in patient condition in many cases. This article discusses some of the recent results obtained with interferon in the treatment of viral disease and cancer.
Mixed strain Mycobacterium tuberculosis infections: implications for tuberculosis treatment and control.
(AMER SOC MICROBIOLOGY, 1752 N ST NW, WASHINGTON, USA, DC, 20036-2904, 2012) Cohen, T.; Van Helden, P. D.; Wilson, D.; Colijn, C.; McLaughlin, M. M.; Abubakar, I.; Warren, Rob
Mutations and other Risk indicators for Oesophageal Cancer among two distinct groups.
(2005) Burger, H.; Barnard, D.; Van Helden, P. D.; Victor, T. C.; Abel, S.; Gelderblom, W. C. A.; Rossouw, G.; Wilken, E.; Marasas, W. F.O
Mycobacteria and disease in Southern Africa
(Wiley Online Library, 2013) Botha, L.; Gey van Pittius, N. C.; Van Helden, P. D.
The genus Mycobacterium consists of over 120 known species, some of which (e.g. M. bovis and M. tuberculosis) contribute extensively to the burden of infectious disease in humans and animals, whilst others are commonly found in the environment but may rarely if ever be disease‐causing. This paper reviews the mycobacteria found in southern Africa, focussing on those in the M. tuberculosis complex as well as the non‐tuberculous mycobacteria (NTM), identifying those found in the area and including those causing disease in humans and animals, and outlines some recent reports describing the distribution and prevalence of the disease in Africa. Difficulties in diagnosis, host preference and reaction, immunology and transmission are discussed.
Resistance to pyrazinamide and ethambutol compromises MDR/XDR-TB treatment
(Health and Medical Publishing Group (HMPG), 2009-11) Hoek, K. G. P.; Schaaf, H. S.; Gey van Pittius, N. C.; Van Helden, P. D.; Warren, R. M.
Rifampicin resistance in Mycobacterium tuberculosis : rapid detection and implications in chemotherapy
(Health & Medical Publishing Group, 1996-01) Pretorius, G. S.; Sirgel, F. A.; Schaaf, H. Simon; Van Helden, P. D.; Victor, T. C.
Objectives. Tuberculosis treatment and susceptibility testing are cumbersome, especially in the case of multidrug-resistant (MDR) Mycobacterium tuberculosis. It is known that mutations in the rpoB gene of M. tuberculosis lead to resistance to rifampicin (RMP). In this study an attempt was made to apply molecular techniques for rapid detection of antibiotic resistance in clinical isolates of M. tuberculosis. Design. settings and subjects. RMP-resistant clinical isolates of M. tuberculosis from South Africa (N = 120) with unique resistant patterns were selected for calculation of resistance frequencies, and 74 MDR isolates of M. tuberculosis from different geographical origins were used for microbiological and molecular analysis. The polymerase chain reaction (PCR) technique was applied for amplification of a previously described region around a cluster of mutations in the rpoB gene, and single-stranded conformational polymorphism (SSCP) analysis was optimised to screen for mutations in the amplified region. Results. The results showed that an optimised PCR-SSCP procedure could detect a cluster of mutations in the rpoB gene (for RMP resistance) in 95% of RMP-resistant isolates. This procedure could therefore be used in the prediction of RMP resistance. Evidence was obtained that these mutations can be screened for directly from BACTEC cultures or even directly from Ziehl-Neelsen-positive sputum samples. Statistical analysis also showed that this locus can be used to predict the presence of an MDR isolate, which may have important implications in decisions concerning chemotherapy. Conclusions. It is currently not feasible to test all tuberculosis cases, but application of the PCR-SSCP technology in the prediction of multidrug resistance in M. tuberculosis isolates may be important in patients, especially where frequencies are high for drug-resistant isolates. This methodology could reduce the time required for sensitivity testing from approximately 6-12 weeks to a few days.
Tuberculosis research : the way forward
(Health & Medical Publishing Group, 1996) Beyers, A. D.; Donald, P. R.; Van Helden, P. D.; Ehlers, M. R. W.; Steyn, L.; Mizrahi, V.
Tuberculosis is back on the world stage with a vengeance, perhaps at least partly as a consequence of complacency about the threat it posed in the recent past.
The use of the polymerase chain reaction test in the diagnosis of tuberculosis
(Health & Medical Publishing Group, 1991) Van Helden, P. D.; Du Toit, R.; Jordaan, A.; Taljaard, B.; Pitout, J.; Victor, T.
Current techniques for laboratory diagnosis of tuberculosis have some serious limitations. These include the high cost and time required for the current assays. The development of a rapid, sensitive, specific and low-cost assay is therefore of considerable importance. We report here the development and laboratory testing of a polymerase chain reaction DNA-based diagnostic test for the presence of Mycobacterium tuberculosis in sputum. The assay shows a high level of sensitivity and specificity and requires considerably less capital, consumables and time inputs than existing laboratory tests. We believe this technology is ready for large-scale evaluation and use, particularly in hospital-based laboratories.
Whole genome sequencing reveals genomic heterogeneity and antibiotic purification in Mycobacterium tuberculosis isolates
(BioMed Central, 2015-10) Black, P. A.; De Vos, M.; Louw, G. E.; Van der Merwe, R. G.; Dippenaar, A.; Streicher, Elizabeth M.; Abdallah, A. M.; Sampson, S. L.; Victor, T. C.; Dolby, T.; Simpson, J. A.; Van Helden, P. D.; Warren, Robin M.; Pain, A.
Background: Whole genome sequencing has revolutionised the interrogation of mycobacterial genomes. Recent studies have reported conflicting findings on the genomic stability of Mycobacterium tuberculosis during the evolution of drug resistance. In an age where whole genome sequencing is increasingly relied upon for defining the structure of bacterial genomes, it is important to investigate the reliability of next generation sequencing to identify clonal variants present in a minor percentage of the population. This study aimed to define a reliable cut-off for identification of low frequency sequence variants and to subsequently investigate genetic heterogeneity and the evolution of drug resistance in M. tuberculosis. Methods: Genomic DNA was isolated from single colonies from 14 rifampicin mono-resistant M. tuberculosis isolates, as well as the primary cultures and follow up MDR cultures from two of these patients. The whole genomes of the M. tuberculosis isolates were sequenced using either the Illumina MiSeq or Illumina HiSeq platforms. Sequences were analysed with an in-house pipeline. Results: Using next-generation sequencing in combination with Sanger sequencing and statistical analysis we defined a read frequency cut-off of 30 % to identify low frequency M. tuberculosis variants with high confidence. Using this cut-off we demonstrated a high rate of genetic diversity between single colonies isolated from one population, showing that by using the current sequencing technology, single colonies are not a true reflection of the genetic diversity within a whole population and vice versa. We further showed that numerous heterogeneous variants emerge and then disappear during the evolution of isoniazid resistance within individual patients. Our findings allowed us to formulate a model for the selective bottleneck which occurs during the course of infection, acting as a genomic purification event. Conclusions: Our study demonstrated true levels of genetic diversity within an M. tuberculosis population and showed that genetic diversity may be re-defined when a selective pressure, such as drug exposure, is imposed on M. tuberculosis populations during the course of infection. This suggests that the genome of M. tuberculosis is more dynamic than previously thought, suggesting preparedness to respond to a changing environment.
Widespread use of incorrect PCR ramp rate negatively impacts multidrug-resistant tuberculosis diagnosis (MTBDRplus)
(Nature Publishing Group, 2018) Derendinger, B.; De Vos, M.; Nathavitharana, R. R.; Dolby, T.; Simpson, J. A.; Van Helden, P. D.; Warren, Robin M.; Theron, G.
ENGLISH ABSTRACT: The scale-up of rapid drug resistance testing for TB is a global priority. MTBDRplus is a WHO-endorsed multidrug-resistant (MDR)-TB PCR assay with suboptimal sensitivities and high indeterminate rates on smear-negative specimens. We hypothesised that widespread use of incorrect thermocycler ramp rate (speed of temperature change between cycles) impacts performance. A global sample of 72 laboratories was surveyed. We tested 107 sputa from Xpert MTB/RIF-positive patients and, separately, dilution series of bacilli, both at the manufacturer-recommended ramp rate (2.2 °C/s) and the most frequently reported incorrect ramp rate (4.0 °C/s). Mycobacterium tuberculosis-complex DNA (TUB-band)-detection, indeterminate results, accuracy, and inter-reader variability (dilution series only) were compared. 32 respondents did a median (IQR) of 41 (20–150) assays monthly. 78% used an incorrect ramp rate. On smear-negative sputa, 2.2 °C/s vs. 4.0 °C/s improved TUB-band positivity (42/55 vs. 32/55; p = 0.042) and indeterminate rates (1/42 vs. 5/32; p = 0.039). The actionable results (not TUB-negative or indeterminate; 41/55 vs. 28/55) hence improved by 21% (95% CI: 9–35%). Widespread use of incorrect ramp rate contributes to suboptimal MTBDRplus performance on smear-negative specimens and hence limits clinical utility. The number of diagnoses (and thus the number of smear-negative patients in whom DST is possible) will improve substantially after ramp rate correction.

Browsing by Author "Van Helden, P. D."

Results Per Page

Sort Options