Biomedical subjects

M Y Wong

Publications and source records attributed to M Y Wong.

At least 19 recordsLinked to original sources

PubMed2005

Tuberculin response in BCG vaccinated schoolchildren and the estimation of annual risk of infection in Hong Kong.

BACKGROUND: In Hong Kong there has been nearly universal neonatal BCG vaccination coverage since 1980. METHOD: 21 113 schoolchildren aged 6-9 years were skin tested with one unit of tuberculin (PPD RT-23) using the intradermal technique during a routine BCG revaccination programme. Information on sex, date of birth, date of tuberculin testing, and tuberculin reaction size at 72 hours was retrieved. The annual risk of tuberculous infection (ARTI) was estimated by three different approaches. RESULTS: Significantly higher tuberculin positive rates were found in girls and with increasing age at all commonly used cut-off points (5, 10, and 15 mm). Using a cut-off point of > or =10 mm and the formula 1- (1 - tuberculin positive rate)(1/age), the ARTI was estimated to be 1.93% (95% CI 1.84 to 2.03) for girls and 1.41% (95% CI 1.33 to 1.50) for boys. Using the differences in the tuberculin positive rate between the 6-7 year and 8-9 year age groups, the ARTI became 1.90% (95% CI 1.09 to 2.70) and 1.84% (95% CI 1.15 to 2.54) for girls and boys, respectively. When the prevalence of infection was estimated by locating a secondary peak of the tuberculin reaction distribution curve at 15 mm and assuming a symmetrical distribution of reaction sizes among those infected around this peak, the corresponding ARTI was much lower at 0.52% (95% CI 0.46 to 0.59) and 0.43% (95% CI 0.37 to 0.49) for girls and boys, similar to that estimated indirectly from the prevalence of disease. CONCLUSION: The ARTI as estimated by conventional methods was unexpectedly high among BCG vaccinated children and did not agree with that anticipated from the annual incidence of active disease. Further studies are needed to address the discrepancies, including the possible interaction between BCG and other environmental stimuli.

Age Factors↗

PubMed2005

Directly observed treatment of tuberculosis in Hong Kong.

OBJECTIVE: To evaluate the local use of out-patient directly observed treatment (DOT) for tuberculosis (TB) control. SETTING: Seventeen government chest clinics managing around 80% of TB patients in Hong Kong. METHOD: A retrospective cohort. TB patients registered for treatment from 1 July to 31 August 2000 were followed up for 2 years. Baseline socio-demographic and clinical characteristics were correlated with adherence to DOT, mode of treatment and treatment outcomes. RESULTS: Of 988 patients, respectively 142, 140 and 21 switched to non-DOT within 2 months, 2-6 months and after 6 months. More Chinese patients than ethnic minorities switched to non-DOT within the first 2 months (15.2% vs. 0%, P = 0.001). Geographical inconvenience (31.7%) was the primary reason for switching initially, with increasing proportions giving no specific reason after the second month. Patients staying on DOT in the first 2 months had a significantly higher cure rate than those not on DOT, in both univariate (92.7% vs. 83.9%, P = 0.002) and multivariate analysis (OR = 2.5, P = 0.001). Subsequent switching, intermittent or daily regimen did not appear to affect the outcome. CONCLUSION: Significant numbers of patients failed to stay on DOT, and those staying initially had a better outcome.

Aged↗

PubMed2004

Correlated measurement error--implications for nutritional epidemiology.

BACKGROUND: In nutritional epidemiology, it is common to fit models in which several dietary variables are included. However, with standard instruments for dietary assessment, not only are the intakes of many nutrients often highly correlated, but the errors in the estimation of the intake of different nutrients are also correlated. The effect of this error correlation on the results of observational studies has been little investigated. This paper describes the effect on multivariate regression coefficients of different levels of correlation, both between the variables themselves and between the errors of estimation of these variables. METHODS: Using a simple model for the multivariate error structure, we examine the effect on the estimates of bivariate linear regression coefficients of (1) differential precision of measurement of the two independent variables, (2) differing levels of correlation between the true values of the two variables, and (3) differing levels of correlation between the errors of measurement of the two variables. As an example, the prediction of plasma vitamin C levels by dietary intake variables is considered, using data from the European Prospective Investigation of Cancer (EPIC) Norfolk study in which dietary intake was estimated using both a food frequency questionnaire (FFQ) and a 7-day diary (7DD). The dietary variables considered are vitamin C, fat, and energy, with different approaches taken to energy adjustment. RESULTS: When the error correlation is zero, the estimates of the bivariate regression coefficients reflect the precision of measurement of the two variables and mutual confounding. The sum of the observed regression coefficients is biased towards the null as in univariate regression. When the error correlation is non-zero but below about 0.7, the effect is minor. However, as the error correlation increases beyond 0.8 the effect becomes large and highly dependent on the relative precision with which the two variables are measured. At the extreme, the bivariate estimates can become indefinitely large. In the example, the error correlation between fat and energy using the FFQ appears to be over 0.9, the corresponding value for the 7DD being approximately 0.85. The error correlation between vitamin C and fat, and vitamin C and energy, appears to be below 0.5 and smaller for the 7DD than for the FFQ. The impact of these error correlations on bivariate regression coefficients is large. The effect of energy adjustment differs widely between vitamin C and fat. CONCLUSION: High levels of error correlation can have a large effect on bivariate regression estimates, varying widely depending on which two variables are considered. In particular, the effect of energy adjustment will vary widely. For vitamin C, the effect of energy adjustment appears negligible, whereas for fat the effect is large indicating that error correlation close to one can partially remove regression dilution due to measurement error. If, for fat intake, energy adjustment is performed by using energy density, the partial removal of regression dilution is achieved at the expense of substantial reduction in the true variance.

Ascorbic Acid↗

PubMed2004

Estimation of magnitude in gene-environment interactions in the presence of measurement error.

The design of studies aimed at identifying the interaction between genetic and environmental determinants in disease risk is attracting increased attention. In this paper, we study the effect of errors on measuring exposures and the effect of assessing genotype at one locus on the association of a continuous outcome measure with continuous exposures and genotype. The estimation of misclassification errors in assessing genotypes from a separate study is proposed. If the exposure measurement error is substantial, then even relatively small errors in genotyping within limits that are often quoted can have an appreciable effect on interaction estimates. We, thus, consider a method for correcting the measurement errors when the interaction between the exposures and the genetic factor is significant. Finally, we present an epidemiological example to demonstrate the importance of correcting measurement errors.

Alleles↗

PubMed2004

Wireless capsule endoscopy in Chinese patients with suspected small bowel diseases.

OBJECTIVE: To evaluate the use of wireless capsule endoscopy in Chinese patients. DESIGN: Retrospective analysis. SETTING: University teaching hospital, Hong Kong. PATIENTS: Twenty-eight patients who had undergone wireless capsule endoscopy between December 2002 and December 2003. MAIN OUTCOME MEASURES: Diagnoses according to findings of capsule endoscopy and complications from the procedure. RESULTS: The mean age of the 28 patients (15 men and 13 women) was 60.0 (standard deviation, 18.3) years. The indications for capsule endoscopy were obscure gastro-intestinal bleeding (n=16), unexplained iron-deficiency anaemia (n=9), and recurrent abdominal pain (n=3). Half of the patients had abnormal endoscopy findings that may account for their presenting symptoms. The most common abnormality was angioectasia of the small bowel. Small bowel ulcers and erosions were also noted in three patients with obscure bleeding. In contrast, none of the patients with recurrent abdominal pain had abnormal capsule endoscopy. No complications arose from the procedure. CONCLUSIONS: Wireless capsule endoscopy is a safe and useful mode of investigation for the diagnosis of obscure gastro-intestinal bleeding in Chinese patients.

Abdominal Pain↗

PubMed2004

Socio-economic factors and tuberculosis: a district-based ecological analysis in Hong Kong.

BACKGROUND: Relatively little is known about the impact of socio-economic factors on tuberculosis in a metropolitan city with high disease incidence. METHOD: District-specific tuberculosis notification rates for 1995--1997 and 2000--2002 were indirectly sex- and age-adjusted and compared with the socio-economic characteristics in the 1996 by-census and 2001 census. RESULTS: The differences between the 18 districts persisted after 3-year averaging and indirect standardisation. Only the percentage of population born locally, the percentage of the population widowed or divorced and the percentage of households residing in rooms or bedsits were consistently associated with the standardised notification ratios (SNR) for both periods, the first being negatively so (all P < 0.05). In a combined analysis with a general linear model for both periods, birth in China, residence <7 years, speaking other Asian languages, being married and in a single household were also significantly associated with the SNR (all P < 0.05). Using a backward conditional approach, only local birth, being married, and residing in rooms or bedsits were independent predictors of SNR (all P < 0.05). There was no significant association between SNR and socio-economic indices on education, occupation, unemployment and income. CONCLUSION: Socio-economic factors other than simple poverty are affecting the district-specific tuberculosis rates in Hong Kong.

Female↗

PubMed2004

Transurethral resection of prostate (TURP) through the decades--a comparison of results over the last thirty years in a single institution in Asia.

INTRODUCTION: This study was conducted to evaluate the results and complications of transurethral resection of prostate (TURP) over the last 30 years in our institution. MATERIALS AND METHODS: This retrospective study encompasses 3 different eras: 168 patients in the late 70s, 175 patients in the late 80s and 283 patients in the late 90s. All the patients had at least 18 months of follow-up. RESULTS: The mean age from the 1970s, the 1980s and 1999 were 68.8 years, 69.2 years and 69.4 years respectively. The proportion of patients operated on for acute retention fell from 78.6% (132) in the 1970s, to 54% (96) in the 1980s, and 43% (122) in 1999. The mean resection time was 44.8 minutes in 1989 and 41.8 minutes in 1999. The mean weight of prostate resected was 22.1 g in the 1970s, 24.2 g in 1989 and 22.2 g in 1999. 44% (74) required blood transfusion in the 1970s, with 11% (19) in 1989 and 4% (11) in 1999. There were 2 deaths (acute myocardial infarction and pneumonia) in the 1970s, 1 (pneumonia) in 1989 and no mortality in 1999. There were 4 patients with TURP syndrome in the 1970s, 3 in 1989 and 1 in 1999. The incidence of postoperative urinary tract infection (UTI) was 25% (42) in the 1970s, 16% (29) in 1989 and 6% (17) in 1999. CONCLUSIONS: As expertise and experience in TURP progress, the complication rates fall, as evidenced by the lower rates of transfusion, TURP syndrome and postoperative UTI in the later series.

Aged↗

PubMed2003

The detection of gene-environment interaction for continuous traits: should we deal with measurement error by bigger studies or better measurement?

BACKGROUND: The search for biologically relevant gene-environment interactions has been facilitated by technological advances in genotyping. The design of studies to detect interactions on continuous traits such as blood pressure and insulin sensitivity is attracting increasing attention. We have previously described power calculations for such studies, and this paper describes the extension of those calculations to take account of measurement error. METHODS: The model considered in this paper is a simple linear regression relating a continuous outcome to a continuously distributed exposure variable in which the ratio of slopes for each genotype is considered as the interaction parameter. The classical measurement error model is used to describe the uncertainty in measurement in the outcome and the exposure. The sample size to detect differing magnitudes of interaction with varying frequencies of the minor allele are calculated for a given main effect observed with error both in the exposure and the outcome. The sample size to detect a given interaction for a given minor allele frequency is calculated for differing degrees of measurement error in the assessment of the exposure and the outcome. RESULTS: The required sample size is dependent upon the magnitude of the interaction, the allele frequency and the strength of the association in those with the common allele. As an example, we take the situation in which the effect size in those with the common allele was a quarter of a standard deviation change in the outcome for a standard deviation change in the exposure. If a minor allele with a frequency of 20% leads to a doubling of that effect size, then the sample size is highly dependent upon the precision with which the exposure and outcome are measured. rho(Tx) and rho(Ty) are the correlation between the measured exposure and outcome, respectively and the true value. If poor measures of the exposure and outcome are used, (e.g. rho(Tx) = 0.3, rho(Ty) = 0.4), then a study size of 150 989 people would be required to detect the interaction with 95% power at a significance level of 10(-4). Such an interaction could be detected in study samples of under 10 000 people if more precise measurements of exposure and outcome were made (e.g. rho(Tx) = 0.7, rho(Ty) = 0.7), and possibly in samples of under 5000 if the precision of estimation were enhanced by taking repeated measurements. CONCLUSIONS: The formulae for calculating the sample size required to study the interaction between a continuous exposure and a genetic factor on a continuous outcome variable in the face of measurement error will be of considerable utility in designing studies with appropriate power. These calculations suggest that smaller studies with repeated and more precise measurement of the exposure and outcome will be as powerful as studies even 20 times bigger, which necessarily employ less precise measures because of their size. Even though the cost of genotyping is falling, the magnitude of the effect of measurement error on the power to detect interaction on continuous traits suggests that investment in studies with better measurement may be a more appropriate strategy than attempting to deal with error by increasing sample sizes.

Environmental Exposure↗

PubMed2001

Response of the ascorbate-peroxidase of Selenastrum capricornutum to copper and lead in stormwaters.

The green alga Selenastrum capricornutum expresses a unique ascorbate peroxidase, that responds to copper and lead. Attempts were made to test if this peroxidase could be used to monitor the levels of copper and lead in natural waters. When S. capricornutum was exposed to a stormwater sample, the specific activity of the peroxidase in the cell extract was commensurate with the combined copper and lead contents in the sample. The peroxidase responses were also correlated with the 96 hr biomass toxicity assay of S. capricornutum. However, unlike the biomass toxicity assay, the peroxidase activity was not affected by the anions in the samples. The use of this peroxidase can be used as a marker for testing heavy metal toxicity in the water.

Ascorbate Peroxidases↗

PubMed2001

Early extubation after cardiac surgery: emotional status in the early postoperative period.

OBJECTIVE: To compare the emotional state during the first 3 days after coronary artery surgery of patients who had undergone early versus conventional extubation. DESIGN: A prospective, randomized, controlled trial. SETTING: University hospital, single center. PARTICIPANTS: Eligible patients (n = 100) presenting for elective coronary artery surgery, randomized to an early extubation group or a conventional extubation group. INTERVENTIONS: Emotional status was measured by the Hospital Anxiety and Depression Scale (HAD), the Self Assessment Manikin (SAM), and the Multiple Affect Adjective Check List-Revised (MAACL-R). Tests were administered preoperatively and on the 1st and 3rd days postoperatively. MEASUREMENTS AND MAIN RESULTS: Of patients in the conventional extubation group, 30% showed moderate-to-severe depressive symptoms (HAD score >10) on day 3 postoperatively compared with 8% of patients in the early extubation group (p = 0.02). There was a clinically insignificant increase in MAACL-R depression score on the 1st postoperative day within both groups but no other differences within or between groups in SAM or MAACL-R scores. CONCLUSION: Early extubation results in fewer patients displaying depressive symptoms on the 3rd postoperative day but appears to have little effect on other measurements of emotional status. Anesthetic management during coronary artery bypass graft surgery may play an important role in the overall well-being of the patient by decreasing the incidence of postoperative depression.

Affect↗

PubMed2001

Sample size determination for studies of gene-environment interaction.

BACKGROUND: The search for interaction effects is common in epidemiological studies, but the power of such studies is a major concern. This is a practical issue as many future studies will wish to investigate potential gene-gene and gene-environment interactions and therefore need to be planned on the basis of appropriate sample size calculations. METHODS: The underlying model considered in this paper is a simple linear regression and relating a continuous outcome to a continuously distributed exposure variable. RESULTS: The slope of the regression line is taken to be dependent on genotype, and the ratio of the slopes for each genotype is considered as the interaction parameter. Sample size is affected by the allele frequency and whether the genetic model is dominant or recessive. It is also critically dependent upon the size of the association between exposure and outcome, and the strength of the interaction term. The link between these determinants is graphically displayed to allow sample size and power to be estimated. An example of the analysis of the association between physical activity and glucose intolerance demonstrates how information from previous studies can be used to determine the sample size required to examine gene-environment interactions. CONCLUSIONS: The formulae allowing the computation of the sample size required to study the interaction between a continuous environmental exposure and a genetic factor on a continuous outcome variable should have a practical utility in assisting the design of studies of appropriate power.

Effect Modifier, Epidemiologic↗

PubMed2001

An update on percutaneous nephrolithotomy in the management of urinary calculi.

Since its introduction in the 1970s, percutaneous nephrolithotomy has undergone numerous refinements in both instrumentation and technique to become an efficacious and safe procedure for the removal of renal calculi. The aim of this review is to discuss issues raised in publications in the year 2000 regarding percutaneous nephrolithotomy in the management of urinary stone disease.

Humans↗

PubMed2001

Childhood abuse and lifetime psychopathology in a community sample.

OBJECTIVE: The authors assessed lifetime psychopathology in a general population sample and compared the rates of five psychiatric disorder categories between those who reported a childhood history of either physical or sexual abuse and those who did not. METHOD: A modified version of the Composite International Diagnostic Interview and a self-completed questionnaire on child abuse were administered to a probability sample (N=7,016) of Ontario residents 15 to 64 years of age. RESULTS: Those reporting a history of childhood physical abuse had significantly higher lifetime rates of anxiety disorders, alcohol abuse/dependence, and antisocial behavior and were more likely to have one or more disorders than were those without such a history. Women, but not men, with a history of physical abuse had significantly higher lifetime rates of major depression and illicit drug abuse/dependence than did women with no such history. A history of childhood sexual abuse was also associated with higher rates of all disorders considered in women. In men, the prevalence of disorders tended to be higher among those who reported exposure to sexual abuse, but only the associations with alcohol abuse/dependence and the category of one or more disorders reached statistical significance. The relationship between a childhood history of physical abuse and lifetime psychopathology varied significantly by gender for all categories except for anxiety disorders. Although not statistically significant, a similar relationship was seen between childhood history of sexual abuse and lifetime psychopathology. CONCLUSIONS: A history of abuse in childhood increases the likelihood of lifetime psychopathology; this association appears stronger for women than men.

Adolescent↗

PubMed2001

The Singapore General Hospital early clinical experience with the 7.5F flexible ureterorenoscope.

INTRODUCTION: Reduced instrument size, increased flexibility, coupled with improved optics and larger working channels have enhanced the capabilities of the ureterorenoscope. MATERIALS AND METHODS: We present our initial experience with the new 7.5F flexible ureterorenoscope. A total of 29 flexible ureterorenoscopies were performed from July 1995 to December 1997 by a single surgeon. The indications for flexible ureterorenoscopy was therapeutic in 10 (34.5%) patients (all had urolithiasis) whilst it was diagnostic in 19 patients (65.5%). For the diagnostic cohort, 9 (31.0%) patients had haematuria with radiological upper tract filling defect, 8 (27.6%) had radiological upper tract filling defect alone and 2 (6.9%) had ureteropelvic junction narrowing for evaluation. RESULTS: Of the therapeutic cases, all 10 (100%) were stone free at 3 months. Of the diagnostic cases, 12 (63.2%) had normal findings, 4 (21.1%) had urolithiasis and 3 (15.8%) had transitional cell carcinoma (TCC). Of the 3 cases of TCC, one was managed endoscopically. CONCLUSIONS: The smaller calibre and actively deflectable 7.5F flexible ureterorenoscopes facilitate various endoscopic procedures thus broadening the diagnostic and therapeutic scope of the ureterorenoscope.

Adult↗

PubMed2001

Clinics in diagnostic imaging (67). Hydronephrotic horseshoe kidneys with multiple calculi.

Horseshoe kidney is the commonest congenital renal anomaly. Its inherently-poor drainage system renders the patient prone to stone formation. A 56-year-old man with bilateral renal stones in a horseshoe system associated with hydronephrosis is presented. He was treated successfully with bilateral CT-guided percutaneous nephrostomy and percutaneous nephrolithotripsy. Various treatment options, including ESWL, PCNL and open surgery, are discussed.

Humans↗

PubMed2000

Glucose intolerance and physical inactivity: the relative importance of low habitual energy expenditure and cardiorespiratory fitness.

Glucose intolerance and diabetes mellitus are associated with physical inactivity, but it is unclear whether preventive interventions should aim at increasing overall energy expenditure or increasing participation in vigorous, fitness-enhancing activities. Studies aimed at separating and quantifying the effects of these two dimensions of physical activity should use well-validated measurement instruments and employ a study design in which the bivariate error structure of these instruments is determined. In the Isle of Ely Study (Cambridgeshire, United Kingdom), 775 individuals aged 45-70 years in 1994-1997 completed a glucose tolerance test and assessment of 4-day physical activity level (total energy expenditure/basal metabolic rate) by heart rate monitoring, a technique that has been validated against doubly labeled water and whole-body calorimetry. Cardiorespiratory fitness (maximum oxygen uptake (VO2max) per kg)) was measured in a submaximal test. To correct for measurement error, the authors had 190 individuals repeat both tests on three occasions at 4-month intervals. Two-hour glucose level was negatively correlated with physical activity level (men: r = -0.22, p < 0.001; women: r = -0.11, p < 0.05) and VO2max per kg (men: r = -0.18, p < 0.01; women: r = -0.19, p < 0.001) and was positively correlated with age and obesity. The model incorporating bivariate adjustment for measurement error showed that energy expenditure had a major effect on glucose tolerance, but there was less of an effect for cardiorespiratory fitness. These data provide support for public health strategies aimed at increasing overall energy expenditure.

Aged↗

PubMed2000

Bacterial morphotypes and early cellular responses in clinically infected and non-infected sites after combination therapy of guided tissue regeneration and allograft.

OBJECTIVES: To compare the bacterial morphotypes and early cellular responses in periodontally treated sites with and without pus formation after a combination of guided tissue regeneration (GTR) and allograft therapy. METHODS: 45 subjects with 80 sites having periodontal lesions with moderate to deep pockets and angular bone defects participated. 28 treated sites in 25 patients were included in the studies. 14 sites suffered from symptoms and signs of infection with pus formation during the healing period were assigned to the pus (P) group. Another 14 sites had asymptomatic healing and were assigned to the non-pus (NP) group. The GTR membranes were retrieved 4-6 weeks after surgery and processed for SEM examination. The bacterial morphotypes on the membranes were observed and photographed. Bacterial adhesion score (BAS, 0-5) and the presence of leukocytes and fibroblasts were estimated from photographs. RESULTS: The results showed that large numbers of bacteria (high BAS) were present on both sides of the coronal 2/3 of the membrane in both groups, irrespective of clinical conditions. At the apical 1/3 of the membrane, moderate numbers of bacteria were still found on the outer side in the P group. The BAS of rod-shaped bacteria were significantly higher in the P group than that of the NP group on the outer coronal 2/3 of the membrane. The frequency of the presence of fibroblasts (18.5%) at the apical 1/3 of the inner (tooth facing) side of the P group was much lower than that of the same location (28.6-29.6%) in the NP group. The presence of leukocytes and fewer numbers of fibroblasts on the GTR membrane were associated with greater BAS for rod- and filament-shaped bacteria. CONCLUSIONS: GTR membranes are commonly colonized by oral bacteria during retention, even on uncomplicated and tissue covered portions. The overt infection clinically (pus group) of the membrane-allograft treated sites is associated with a significantly elevated BAS of rod-shaped bacteria, and may be closely related to the occurrence of its adverse early healing responses (inflammation, pus formation, fewer fibroblasts and greater accumulation of leukocytes).

Adult↗

PubMed2000

Quantifying the association between habitual energy expenditure and blood pressure.

BACKGROUND: Previous studies have demonstrated an association between physical inactivity and hypertension, but the methods used to assess activity have been subjective and imprecise. Recently methods have become available allowing measurement of energy expenditure in free-living populations. Our aim was to employ these methods to assess the independent association between energy expenditure, cardio-respiratory fitness and blood pressure. METHODS: In a cross-sectional study of 775 people (45-70 years) participating in a continuing population-based cohort study, energy expenditure was assessed by 4 days of heart rate monitoring with individual calibration of the relationship between heart rate and energy expenditure, a method validated against doubly-labelled water and whole body calorimetry. Cardio-respiratory fitness was assessed in a sub-maximal test. To adjust for measurement error in the assessment of usual energy expenditure and fitness, 190 subjects repeated both tests on three further occasions at 4-monthly intervals. RESULTS: A highly significant linear trend in blood pressure was found across quintiles of the physical activity level, the ratio of total energy expenditure to basal metabolic rate. The differences in the mean systolic/diastolic blood pressure between the top and bottom quintile was 6.3/4.4 mmHg in men and 10.7/5.9 mmHg in women. These effects were independent of obesity and cardio-respiratory fitness. Correction for measurement error suggests that the true underlying relationship between usual energy expenditure and blood pressure is stronger still. CONCLUSIONS: These findings are compatible with a strong association between usual energy expenditure and blood pressure and support public health strategies aimed at increasing overall energy expenditure.

Aged↗