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Biomedical subjects

M A Lewis

Publications and source records attributed to M A Lewis.

At least 55 records · Page 3Linked to original sources
PubMed2000

Modeling and analysis of stochastic invasion processes.

In this paper we derive spatially explicit equations to describe a stochastic invasion process. Parents are assumed to produce a random number of offspring which then disperse according to a spatial redistribution kernel. Equations for population moments, such as expected density and covariance averaged over an ensemble of identical stochastic processes, take the form of deterministic integro-difference equations. These equations describe the spatial spread of population moments as the invasion progresses. We use the second order moments to analyse two basic properties of the invasion. The first property is 'permanence of form' in the correlation structure of the wave. Analysis of the asymptotic form of the invasion wave shows that either (i) the covariance in the leading edge of the wave of invasion asymptotically achieves a permanence of form with a characteristic structure described by an unchanging spatial correlation function, or (ii) the leading edge of the wave has no asymptotic permanence of form with the length scales of spatial correlations continually increasing over time. Which of these two outcomes pertains is governed by a single statistic, phi which depends upon the shape of the dispersal kernel and the net reproductive number. The second property of the invasion is its patchy structure. Patchiness, defined in terms of spatial correlations on separate short (within patch) and long (between patch) spatial scales, is linked to the dispersal kernel. Analysis shows how a leptokurtic dispersal kernel gives rise to patchiness in spread of a population.

Animals↗
PubMed2000

Venous thromboembolism and oral contraceptive use: a methodological study of diagnostic suspicion and referral bias.

BACKGROUND: In studies of oral contraceptive oral contraceptive use and risk of venous thromboembolism, bias related to heightened diagnostic suspicion and preferential referral of oral contraceptive users has been an issue. The aim of our study was to determine the presence and potential impact of diagnostic suspicion and referral bias. METHODS: We conducted a case/non-case study in 21 regional study centers in Germany and, in parallel, a conventional case-control study using the same cases but randomly selected population controls from the same areas. Women with symptoms compatible with venous thromboembolism were included in the study between 1994 and 1999, and classified as cases or non-cases (first reference group) according to the diagnostic work-up (case/non-case study). A second reference group consisted ofpopulation controls (conventional case-control study as an internal comparison for the case/non-case study): 606 cases, 462 non-cases and 2942 population controls aged 15-49 years. Adjusted unconditional regression analyses were performed. RESULTS: Adjusted odds ratios for venous thromboembolism in oral contraceptive users were systematically higher in the classical case-control study compared to the case/non-case approach (using the same cases) across all subgroup analyses (e.g. for idiopathic cases, the odds ratio was 67% higher in the case-control study: 4.33 (95% confidence interval (CI) 3.27-5.74) versus 2.60 (95% CI 1.75-3.88)). We found a significantly increasing trend of oral contraceptive use in four categories of increasingly sophisticated diagnostic tests that were applied to 1067 women with a suspicion of venous thromboembolism, irrespective of the outcome. Stratified analysis showed the diagnostic level to be a confounder. CONCLUSION: In our population-based study with the possibility of internal comparison, we found clear evidence that diagnostic suspicion and referral bias does play an important role in case-control studies of venous thromboembolism risk among oral contraceptive users. This underlines the importance of making an effort to avoid this bias when designing a new study.

Adolescent↗
PubMed2000

Isolation and identification of Candida from the oral cavity.

A number of methods of sampling the oral cavity for the presence of candida have been developed. Such techniques play an important role in the diagnosis and management of oral candidosis. In the past, identification of candida isolated from the oral cavity has usually been limited to the genus Candida or to the species C. albicans. However, with the recognition that Candida species differ in the production of putative virulence factors and sensitivity to antifungal agents, greater emphasis has been placed on identification of isolates to species level. As a result a range of commercially available systems for yeast identification can now be used in conjunction with traditional identification procedures.

Antifungal Agents↗
PubMed2000

Macrorestriction fingerprinting of "Streptococcus milleri" group bacteria by pulsed-field gel electrophoresis.

Although isolates of the "Streptococcus milleri" group (SMG) of bacteria are regarded as members of the commensal microflora of the body, they are frequently encountered in purulent infections from a range of body sites. The genetic diversity of 91 epidemiologically unrelated SMG isolates (including 37 commensal strains and 49 disease-associated strains) was analyzed by macrorestriction fingerprinting (MF). The genomes were digested with SmaI and ApaI independently, and fragments were resolved by pulsed-field gel electrophoresis. Similarities between banding profiles were determined, and strains were clustered on this basis into dendrograms. In common with other commensal species that have been examined by MF, considerable genetic diversity was revealed. In addition, the clustering of strains tended to support the current taxonomic position of this heterogeneous group. The present study has shown that MF is a powerful tool for characterization of SMG strains and that its use is likely to be of great value in epidemiological and population genetic studies of this group of bacteria.

DNA Fingerprinting↗
PubMed2000

Immunisation against varicella in end stage and pre-end stage renal failure. Trans-Pennine Paediatric Nephrology Study Group.

OBJECTIVES: To investigate the seroconversion rate and duration of persistence of protective antibody titres after varicella immunisation in children with renal failure. DESIGN: 32 children (25 end stage and 7 pre-end stage renal failure) were immunised using 2 x 2,000 plaque forming unit doses of varicella vaccine 3 months apart. Varicella antibody titres were measured by enzyme linked immunosorbent assay. RESULTS: All children initially seroconverted after immunisation. At a mean follow up of 20.3 months, 23 of 28 had protective antibody titres, 4 children having died of unrelated causes. Two children required a third booster dose. 11 children underwent renal transplantation; 10 had protective titres at the time of transplantation and, at a mean of 23.4 months after immunisation, 6 currently have protective titres. Minor side effects occurred after 11 vaccine doses in 9 children. No child developed varicella, despite 10 clear episodes of exposure to the wild-type virus. CONCLUSIONS: Varicella immunisation in children with end stage and pre-end stage renal failure results in a high rate of seroconversion and persistence of protective antibody titres. More widespread use of the vaccine before renal transplantation is recommended.

Antibodies, Viral↗
PubMed1999

Seizures following renal transplantation in childhood.

Few studies have investigated the incidence of seizures following renal transplantation in childhood. The aim of this study was to determine this incidence and to identify risk factors. Retrospective casenote analysis was carried out on 119 transplants performed in 109 children over 10 years. Twenty-one transplants (in 20 children) were complicated by seizures, the majority of which occurred in the first 55 days after transplantation. Seizures were more common in the 5- to 10-year-old age group (P=0.03), but were no more common in those with a prior history of seizure (P=0.69). Their aetiology was predominantly multifactorial; hypertension (n=15), fever/infection (n=4) and acute allograft rejection (n=6) were commonly identified risk factors; 2 were secondary to intracerebral pathology. Most seizures were short lived, required minimal therapy and had a good long-term neurological outcome. In conclusion, seizures are relatively common following paediatric renal transplantation. Parents are now routinely counselled of this risk.

Adolescent↗
PubMed1999

Social control in personal relationships: impact on health behaviors and psychological distress.

This study examines associations among social control, health behavior change, and psychological distress. Social control refers to interactions between social network members that entail regulation, influence, and constraint. Social control is predicted to have dual effects leading to better health practices while also arousing psychological distress. A random sample of 242 individuals answered questions about health practices, overall exposure to social control in their networks, and social control attempts made by a specific network member. Analyses yielded mixed support for the hypotheses, but analyses of responses to the social control attempts of a specific network member did reveal that social control predicted less health-compromising behavior and more health-enhancing behavior as well as more distress. The results suggest that social control warrants greater attention in efforts to understand how personal relationships influence health.

Adult↗
PubMed1999

Effect of environmental haemin upon the physiology and biochemistry of Prevotella intermedia R78.

The effect of environmental haemin on the physiology and biochemistry of Prevotella intermedia R78 grown in batch culture was assessed. Extent and rate of growth increased as the environmental haemin concentration was raised. In addition, cell morphology was predominantly cocco-bacillary when cultured in high haemin environments, while bacillary forms were prevalent in low haemin conditions (< 2.5 mumol l-1). Cells harvested from low haemin environments produced greater numbers of extracellular vesicles and greater amounts of peptidolytic activity, haemagglutinating potential and haemin binding activity when compared with cells harvested from high haemin conditions. The results of the present study indicate that aspects of the biochemistry and physiology of P. intermedia are influenced by changes in environmental haemin levels.

Culture Media↗
PubMed1999

Circulating vascular endothelial growth factor is not increased during relapses of steroid-sensitive nephrotic syndrome.

BACKGROUND: An uncharacterized circulating factor that increases vascular permeability has previously been described in childhood steroid-sensitive nephrotic syndrome (SSNS). The aim of this study was to determine whether this factor is vascular endothelial growth factor (VEGF), the recently described endothelial cell mitogen and enhancer of vascular permeability. METHODS: Plasma and urine VEGF levels were measured in children with SSNS in both relapse and remission and in normal age- and sex-matched controls. Semiquantitative reverse transcriptase-polymerase chain reaction studies investigating VEGF mRNA expression were performed on peripheral blood mononuclear cells isolated from children with SSNS in relapse and controls. In two experimental models (one-hour and three-day follow-up postinfusion), Sprague-Dawley rats were intravenously administered 50 microg rVEGF to determine whether this induced either proteinuria or glomerular histologic change. RESULTS: Plasma VEGF levels and urine VEGF/creatinine ratios were not elevated in SSNS relapse compared with remission and control samples. Peripheral blood mononuclear cell VEGF mRNA expression was no different in SSNS patients compared with controls. The administration of VEGF to rats induced an acute reversible fall in systemic blood pressure but did not result in the development of either proteinuria or glomerular histologic change. CONCLUSION: Increased circulating VEGF levels are not responsible for the proteinuria observed during relapses of SSNS. Further studies are warranted to investigate intrarenal VEGF expression.

Adrenal Cortex Hormones↗
PubMed1999

Bladder augmentation surgery--what about the malignant risk?

Augmentation cystoplasty has become a common surgical treatment for the neuropathic bladder. However, malignancy in bladder augmentations has been well-described and in time is estimated to occur in 1.3% of cases. We surveyed 36 paediatric surgeons from the UK with a special interest in paediatric urology to ascertain how many bladder augmentations were being performed in children each year and whether the surgeons were warning patients/parents of the malignant risks involved with this surgery. Over 150 bladder augmentations were being performed in the UK each year. Surgeons surveyed were concerned about the malignant risks and nearly all agreed that a Central Registry of patients with bladder augmentations should be established to keep track of developments.

Child↗
PubMed1999

The differential risk of oral contraceptives: the impact of full exposure history.

Previous discussions have indicated that the small increases of risk of venous thromboembolism (VTE) associated with newer combined oral contraceptives (third generation, containing desogestrel and gestodene) may be attributed to bias due to cohort effects. In a case-control analysis, this may produce an overestimate of risk of newer preparations. In 10 centres in Germany and the UK, the Transnational Study analysed data from 502 women aged 16-44 years with VTE, and from 1864 controls matched for 5-year age group and region. Information on lifetime exposure history from all subjects was added to the dataset used in previous analyses and entered into a Cox regression model with time-dependent covariates. Based on 17 622 continuous exposure episodes comprising 47 914 person-years of observation, the adjusted hazard ratio (equivalent to odds ratio, OR) of VTE for the comparison of current users of third-generation versus current users of second-generation (primarily levonorgestrel compounds) combined oral contraceptives was 0.8 (0.5 to 1.3). The OR obtained in standard case-control analysis had been 1.5 (1.1 to 2.1). Adjustment for past exposures includes more information and appears more valid than the standard cross-sectional analysis. Using this approach, the Transnational Study data show no evidence for an increased risk of VTE with third- compared with second-generation combined oral contraceptives.

Adolescent↗
PubMed1999

Mannitol and frusemide in the treatment of diuretic resistant oedema in nephrotic syndrome.

Three children (two girls aged 7 and 9 years, and one boy aged 4 years) with diuretic resistant oedema in steroid resistant nephrotic syndrome were treated with a combination of intravenous mannitol and frusemide. All three responded with loss of oedema of 10% to 30% of body weight over one week. There were no complications of hypertension or hypovolaemia. Mannitol-frusemide combination is a safe, inexpensive, and effective treatment for diuretic resistant oedema. Its use in other conditions and in developing countries (where the availability and purity of 20% albumin is limited) needs to be explored.

Child↗
PubMed1999

Adherence of Candida albicans to oral epithelial cells differentiated by Papanicolaou staining.

OBJECTIVE: To examine the relative adherence of Candida albicans to oral epithelial cells differentiated by Papanicolaou staining. METHODS: Oral epithelial cells were collected from 10 healthy adults (five male, five female) and counted. Equal volumes of oral epithelial cells and candida were mixed and incubated. The epithelial cells from this mix were collected by filtration through 10 microns polycarbonate membrane filters. Cells retained on the membrane filters were stained with crystal violet followed by Papanicolaou stain. The number of yeast attached to each of 100 red, orange, and green staining oral epithelial cells was determined by direct microscopic examination. RESULTS: C albicans had a higher level of adherence (p < 0.001) to red staining oral epithelial cells (mean (SD) number of candida attached to 100 oral epithelial cells 562 (159)) than to cells staining either orange (105 (47)) or green (161 (66)). CONCLUSIONS: Oral epithelial cell variability for candidal adherence is confirmed. The technique provides an opportunity to examine the relation between oral epithelial cell type and oral candidosis in specific groups, such as tobacco smokers, where increased epithelial cell keratinisation and candidal colonisation has been reported.

Adult↗