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Biomedical subjects

W W Yew

Publications and source records attributed to W W Yew.

At least 19 recordsLinked to original sources
PubMed2006

Smoking and tuberculosis among silicotic patients.

The aim of the present study was to investigate the relationship between smoking and tuberculosis (TB) among high-risk silicotic patients in Hong Kong. A cohort of 435 silicotic patients tuberculin tested from 1995-2002 was prospectively followed-up until the end of 2005. Baseline characteristics were analysed with respect to positive tuberculin reaction (> or =10 mm) at baseline and subsequent development of TB. Smoking, alcohol use and body mass index were independent predictors of positive tuberculin reaction at baseline in multiple logistic regression analysis. Total cigarette pack-yrs did not demonstrate any significant effect. The annual incidences of TB were 1,841, 2,294 and 4,181 per 100,000 for never-, ex- and current smokers, respectively. On Cox proportional hazard analysis, current smokers have a significantly higher risk of TB than other silicotic patients (adjusted hazard ratio (95% confidence interval (CI)): 1.96 (1.14-3.35)) after controlling for age, alcohol use, tuberculin status, treatment for latent TB infection and other relevant background/disease factors. A significant dose-response relationship was also observed with the daily number of cigarettes currently smoked. Smoking cessation may reduce 32.4% (95% CI: 6.5-54.0) of the risk. Smoking increases the risk of both tuberculosis infection and subsequent development of the disease among silicotic patients.

Age Factors↗
PubMed2006

Standard anti-tuberculosis treatment and hepatotoxicity: do dosing schedules matter?

A nested case-control study was conducted in order to examine whether dosing schedules of standard pyrazinamide-containing anti-tuberculosis (TB) treatment (standard treatment) might affect hepatotoxicity. The present authors retrospectively identified all patients with hepatitis using biochemical criteria from a cohort of 3,007 clinic patients who commenced anti-TB treatment from January 1 to June 30, 2001. Each case with hepatitis between 1-9 weeks post-TB treatment was compared using conditional logistic regression analysis with two controls selected randomly from patients without hepatitis in the same period and matched by sex, age and standard treatment. Impacts of sex and age were examined by logistic regression analysis of cases and patients without hepatitis. Hepatitis occurred in 167 patients, of whom 96 qualified as cases. A conditional logistic risk model identified hepatitis B surface antigen carriage as the only risk factor (odds ratio (95% confidence interval (CI)) 1.8 (1.1-3.1)). Logistic regression analysis showed that sex was nonsignificant but ageing increased the odds of hepatitis. The risk of hepatitis increased from 2.6% (1.9-3.5%) to 4.1% (3.2-5.3%) as age exceeded 49 yrs. Dosing schedules in the first 9 weeks have little impact on hepatotoxicity. If patients at risk of both hepatitis and relapse receive standard treatment, daily dosing is preferable.

Adult↗
PubMed2005

Smoking and tuberculosis: the epidemiological association and immunopathogenesis.

There is increasing evidence of a link between tuberculosis and smoking. This paper reviews the epidemiological evidence from the UK, China, India and the USA, summarizing some of the main papers which indicate an association. Where an association has been found there seems to be an increase in tuberculosis case rates of between two- and four-fold for those smoking in excess of 20 cigarettes a day, but it may be difficult to control for other factors, particularly alcohol consumption. The final part of the paper reviews possible mechanisms. A likely possibility is that nicotine turns off the production of TNF-alpha by the macrophages in the lungs, rendering the patient more susceptible to the development of progressive disease from latent Mycobacterium tuberculosis infection.

Adolescent↗
PubMed2005

Molecular diagnostics in tuberculosis.

Molecular diagnostics in tuberculosis has enabled rapid detection of Mycobacterium tuberculosis complex in clinical specimens, identification of mycobacterial species, detection of drug resistance, and typing for epidemiological investigation. In the laboratory diagnosis of tuberculosis, the nucleic acid amplification (NAA) test is rapid and specific but not as sensitive as culture of mycobacteria. The primary determinant of successful NAA testing for tuberculosis depends on the shedding of mycobacterial DNA in secretions from caseating granulomas and its dissemination into sterile body fluids or tissue biopsies. In multibacillary diseases with a high mycobacterial load, a positive Ziehl-Neelsen smear with a positive NAA test is diagnostic of active tuberculosis, whereas a positive Ziehl-Neelsen smear with a negative NAA test in the absence of inhibitors would indicate nontuberculous mycobacterial disease. The role of the NAA test is more important in paucibacillary diseases with low mycobacterial loads. The presence of polymerase chain reaction (PCR) inhibitors, however, especially in extrapulmonary specimens, may produce false-negative results. Although this problem can be overcome to some extent by extra extraction steps, the additional processing invariably leads to the loss of mycobacterial DNA. To circumvent this problem, a brief culture augmentation step is carried out before the NAA test is performed, which can enhance the mycobacterial load while concomitantly diluting inhibitors, thereby maintaining the sensitivity of the test without excessively increasing turnaround time.

Microbial Sensitivity Tests↗
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

Chest radiograph screening for tuberculosis in a Hong Kong prison.

SETTING: Long-stay prisoners are not regularly screened for TB in Hong Kong. OBJECTIVE: To evaluate tuberculosis (TB) screening in prison. METHOD: All prisoners in a maximum security prison as of 31 October 2001 were screened by chest radiograph (CXR), except for those being followed up for TB or examined by CXR in the last 6 months. RESULTS: A total of 814 male prisoners aged 34.6 +/- 9.6 (mean +/- SD) years were successfully screened. Of 53 cases (6.51%) with radiographic abnormalities, 10 active TB cases (8 culture-negative, 2 culture-positive) were diagnosed, giving an overall yield of 1.23% (95%CI 0.59-2.26). There was no statistical difference in age, ethnicity, place of birth or residency status between those with and those without TB (all P > 0.05). Incarceration > or = 2 years, being in current prison > or = 2 years and not having CXR in last 2 years were associated with TB in univariate analysis (all P < 0.05), but only the last remained an independent predictor in multiple logistic regression (OR 16.8, 95%CI 2.1-132.9, P = 0.008). In that group, the yield was 3.1% (95%CI 1.42-5.89). No further cases were detected in the subsequent 2 years. CONCLUSION: CXR screening of long-stay prisoners gave a high yield in this study.

Adult↗
PubMed2005

Socio-demographic and geographic indicators and distribution of tuberculosis in Hong Kong: a spatial analysis.

OBJECTIVE: To determine the socio-demographic and geographic indicators responsible for the distribution and transmission of tuberculosis (TB) in Hong Kong using geographical information system (GIS) technology. MATERIALS AND METHODS: All patients with bacteriologically proven TB over a period of 3 years (May 1999-April 2002) residing within Hong Kong Island were studied. Molecular characterisation of their sputum isolates by IS6110-based restriction fragment length polymorphism (RFLP) technique was performed. Socio-demographic data were derived from the 2001 Hong Kong population census. Geographic coordinates of patients' addresses were linked to the GIS; large street block groups (LSBGs) were the units of analysis. RESULTS: Of 2387 patients with bacteriologically confirmed TB, 2332 had valid addresses distributed in 430 LSBGs in Hong Kong Island. Of the five socio-demographic indicators studied, significant correlations were found between the rate of TB in an LSBG and low educational attainment, elderly population and low-income household, but not population density or unemployment. The five socio-demographic indicators were not different between LSBG with clustered cases and those with unique cases. CONCLUSION: Low educational attainment, old age and poverty were significant determinants of the rate of TB in different parts of Hong Kong, while none of the socio-demographic indicators was related to disease transmission.

Aged↗
PubMed2004

Direct detection of rifampin-resistant mycobacterium tuberculosis in respiratory specimens by PCR-DNA sequencing.

This study evaluated the feasibility of a molecular strategy based on identification of Mycobacterium tuberculosis by IS6110 PCR or Cobas Amplicor PCR, and rpoB PCR-DNA sequencing of the 81-bp rifampin resistance determining region (RRDR) for direct detection of rifampin resistance in respiratory specimens. A collection of 2,138 respiratory specimens and 352 nonduplicate M. tuberculosis isolates (including 233 isolates from the evaluated respiratory specimens and an additional collection of 119 stored isolates) from Southern China was investigated. Using culture as the reference test, the overall diagnostic sensitivities of an acid-fast bacillus (AFB) smear, Cobas Amplicor PCR, IS6110 PCR were 54.5% (156 of 286), 86.7% (248 of 286), and 89.2% (255 of 286), respectively. The sensitivities of the rpoB PCR for the specimens with positive AFB smears and with positive PCR results in the IS6110 PCR and/or Cobas Amplicor PCR were 100% (156 of 156) and 92.3% (239 of 259), respectively. Of the 352 nonduplicate M. tuberculosis isolates, the agar proportion method for rifampin reported 39 resistant strains. Full agreement (352 of 352) was found with the agar proportion method and the genotype inferred from the rpoB DNA sequencing data for rifampin. Thirty-nine mutations of nine distinct kinds, eight point mutations, and one deletion within the RRDR were found in the 39 resistant strains. For the direct DNA sequencing performed on rpoB PCR-positive respiratory specimens, the concordance with the agar proportion method and the subsequent PCR-sequencing for the culture isolate was 100%. This strategy has potential application for direct and rapid diagnosis of rifampin-resistant M. tuberculosis in IS6110 PCR or Cobas Amplicor PCR-positive respiratory specimens.

Antibiotics, Antitubercular↗
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↗
PubMed2003

Recent developments in the treatment of tuberculosis.

The history of chemotherapy of tuberculosis commenced in 1944 with the discovery of streptomycin. Currently, short-course chemotherapy comprising rifampicin, isoniazid, pyrazinamide and ethambutol/streptomycin administered under directly observed settings for 6 months (initially all four drugs followed by the former two drugs), constitutes the cornerstone treatment for pulmonary tuberculosis. Multi-drug resistant tuberculosis requires alternative chemotherapy, ideally in the form of individualised regimens, for management. To improve on the duration of chemotherapy for drug-susceptible tuberculosis and to achieve better treatment for multi-drug resistant tuberculosis as well as latent tuberculosis infection, there arises a genuine need for new drugs. The quest for new agents is, however, impeded by obstacles. Hopefully, tackling these through collaborative public-private partnerships on an international scale will lead to a fruitful outcome.

Animals↗
PubMed2003

Smoking and tuberculosis in Hong Kong.

OBJECTIVE: To study the relationship between smoking and tuberculosis in Hong Kong. METHOD: Indirect sex and age adjustment was used to compare the prevalence of ever smokers between a sample of 851 patients from the 1996 tuberculosis notification registry and the general population. The clinical characteristics of smokers and non-smokers were compared by stratified univariate analysis and multiple logistic regression. RESULTS: Tuberculosis patients were more likely to have smoked than population controls. The respective odds ratios for ever smoking between tuberculosis patients and population controls were 2.44 and 2.08 for males and females aged 16-64 (Mantel-Haenszel weighted OR = 2.40, P < 0.001), and 2.09 and 2.83 for males and females aged > or = 65 (Mantel-Haenszel weighted odds ratio = 2.19, P < 0.001). Male sex, age > or = 65, working at onset of illness, regular alcohol use, drug abuse and absence of contact history were associated with ever smokers (all P < 0.05). Ever smokers were more likely to have cough (OR 1.69), dyspnoea (OR 1.84), upper zone involvement (OR 1.67), cavity (OR 1.76), miliary lung involvement (OR 2.77), positive sputum culture (OR 1.43), but less isolated extrathoracic involvement (OR 0.31), even after controlling for the confounding background variables (all P < 0.05). CONCLUSION: There was a consistent association between smoking and tuberculosis. More aggressive lung involvement was also found among ever smokers.

Adolescent↗
PubMed2002

Clinically significant interactions with drugs used in the treatment of tuberculosis.

Clinically significant interactions occurring during antituberculous chemotherapy principally involve rifampicin (rifampin), isoniazid and the fluoroquinolones. Such interactions between the antituberculous drugs and coadministered agents are definitely much more important than among antituberculous drugs themselves. These can be associated with consequences even amounting to therapeutic failure or toxicity. Most of the interactions are pharmacokinetic rather than pharmacodynamic in nature. The cytochrome P450 isoform enzymes are responsible for many interactions (especially those involving rifampicin and isoniazid) during drug biotransformation (metabolism) in the liver and/or intestine. Generally, rifampicin is an enzyme inducer and isoniazid acts as an inhibitor. The agents interacting significantly with rifampicin include anticoagulants, anticonvulsants, anti-infectives, cardiovascular therapeutics, contraceptives, glucocorticoids, immunosuppressants, psychotropics, sulphonylureas and theophyllines. Isoniazid interacts principally with anticonvulsants, theophylline, benzodiapines, paracetamol (acetaminophen) and some food. Fluoroquinolones can have absorption disturbance due to a variety of agents, especially the metal cations. Other important interactions of fluoroquinolones result from their enzyme inhibiting potential or pharmacodynamic mechanisms. Geriatric and immunocompromised patients are particularly at risk of drug interactions during treatment of their tuberculosis. Among the latter, patients who are HIV infected constitute the most important group. This is largely because of the advent of new antiretroviral agents such as the HIV protease inhibitors and the non-nucleoside reverse transcriptase inhibitors in the armamenterium of therapy. Compounding the complexity of drug interactions, underlying medical diseases per se may also contribute to or aggravate the scenario. It is imperative for clinicians to be on the alert when treating tuberculosis in patients with difficult co-morbidity requiring polypharmacy. With advancement of knowledge and expertise, it is hoped that therapeutic drug monitoring as a new paradigm of care can enable better management of these drug interactions.

AIDS-Related Opportunistic Infections↗