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T P Ng

Publications and source records attributed to T P Ng.

At least 19 recordsLinked to original sources
PubMed1995

Asthma in chemical workers exposed to aliphatic polyamines.

Following the identification of an index case of occupational asthma, we assessed the respiratory morbidity in 12 workers exposed to aliphatic polyamines in a chemical factory and in 60 unexposed workers in three other workplaces. Many amine workers reported symptoms of chronic cough (7/12), chronic phlegm (9/12), wheezing (4/12) and exertional breathlessness (3/12). These were significantly more frequent in exposed than in unexposed workers (P < 0.01). They also had significantly greater diurnal variation in peak expiratory flow rates (DV-PEFR) than the unexposed workers (P < 0.01). All four amine workers with wheezing reported onset of symptoms after employment at the factory, and all had DV-PEFR greater than 15%, compared to only one control worker (P < 0.01). A second case of occupational asthma was confirmed by bronchial challenge test. The study indicated a very high risk of asthma and chronic airways disease and a need for stringent measures to protect the health of industrial workers exposed to aliphatic amines in Singapore.

Adult↗
PubMed1995

Ventilatory function measured with the Micro Spirometer: performance evaluation and reference values.

The performance of the Micro Spirometer was compared with that of the Vitalograph by assessing the extent of agreement between the instruments and the repeatability of measurements with each instrument. The Micro Spirometer tended to give lower readings of forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and peak expiratory flow rate (PEFR) than the Vitalograph, with wide limits of agreement. The values of these ventilatory functions measured with the Micro Spirometer were, therefore, not directly comparable with those obtained from the Vitalograph, and it is also not satisfactory to predict readings on the Micro Spirometer from those made on the Vitalograph. In the management of asthma patients, the PEFR would still be preferably measured with the mini Wright peak flow, given its low cost and established reliability compared with the standard Wright peak flow meter. The Micro Spiromoter has the practical advantages of portability, ease of operation and relative cheapness for the baseline and long-term assessment of FEV1 and FVC in ambulatory care, as well as in epidemiological studies. However, local users should not employ reference values provided by the manufacturer or those published in the literature, but those reported in this paper.

Adolescent↗
PubMed1994

Risks of asthma associated with occupations in a community-based case-control study.

The aim of this study was to identify occupational risk groups which might usefully be targeted for occupational asthma surveillance and control, using a community-based case-control approach. Data on previous and current occupations held by subjects were analyzed for 787 adult patients with bronchial asthma and 1591 nonasthmatic patient controls, aged 20-54 years, belonging to the three major races (Chinese, Malays, and Indians) in five outpatient primary care polyclinics. Odds ratios (OR) and 95% confidence intervals (95% CI) of association were adjusted for sex, age, race, smoking, and clinical atopy. No associated risks of asthma were found for clerical or sales workers in general. Significantly reduced risks of association with asthma were found for professional, technical, administrative, and managerial occupations (OR, 0.62; 95% CI, 0.47-0.82). The associated risks of asthma were generally elevated for service workers (OR, 1.35; 95% CI, 1.04-1.74) and manufacturing production and related workers (OR, 1.49; 95% CI, 1.23-1.81). Among them, increased risks were observed for cleaners, particularly municipal cleaners and sweepers (OR, 1.91; 95% CI, 1.22-2.99), textile workers (OR, 5.83; 95% CI, 1.93-17.57), garment markers (OR, 1.61; 95% CI, 1.01-2.58), electrical and electronic production workers (OR, 1.36; 95% CI, 1.06-1.75), printers (OR, 2.24; 95% CI, 1.17-4.31), and construction/renovation workers (OR, 2.24; 95% CI, 1.30-3.85). The odds ratio of association of asthma with exposures in service and production-related occupations overall, relative to the "nonexposed" reference group of nonmanual professional/technical, administrative/managerial, clerical, and sales occupations, was estimated to be 1.72 (95% CI, 1.36-2.19); the estimated population attributable risk was 0.33 (95% CI, 0.22-0.44).

Adult↗
PubMed1994

Biological monitoring of exposure to low concentrations of styrene.

A field study was conducted on 39 male workers exposed to styrene at concentrations below 40 ppm (time weighted average, TWA). Analyses were carried out on environmental air, exhaled air, blood, urine, and two major urinary metabolites of styrene: mandelic acid (MA) and phenylglycoxylic acid (PGA). Head space gas chromatography (GC) with a flame ionization detector (FID) was used for determination of styrene in blood and urine. Postexposure exhaled air was analyzed using capillary GC. Environmental styrene exposure was measured by personal sampling using carbon cloth personal samplers. Urinary metabolites of styrene were determined by high pressure liquid chromatograph (HPLC). When the end-of-shift breath, blood, and urine styrene levels were compared with environmental TWA values, blood styrene correlated best with styrene in air (r = 0.87), followed by breath styrene (r = 0.76). Poor correlation (r = 0.24) was observed between environmental styrene exposure and urine styrene. When styrene metabolites were compared with environmental styrene, the sum of urinary MA and PGA correlated better with styrene in air than MA or PGA alone. The correlations between urinary metabolites and environmental styrene improved when corrected for the specific gravity of urine. Even better correlations were observed when the urinary metabolites were corrected for creatinine. The correlation coefficients for environmental styrene and end-of-shift MA, PGA, and MA+PGA were 0.83, 0.84, and 0.86, respectively. The correlation coefficients between environmental styrene and next morning urinary metabolites fell to 0.47, 0.61, and 0.65 for MA, PGA, and MA+PGA, respectively. These results suggest that determination of the total MA and PGA in urine samples is preferred than separate measurements of MA or PGA. The good correlation between environmental exposure and styrene in the exhaled air also suggests that breath styrene level can be a useful indicator for low level styrene exposure, as the method is specific, noninvasive, and rapid. Urinary styrene seems to be a less reliable indicator for low level styrene exposure.

Adult↗
PubMed1994

Impairment of color vision among workers exposed to low concentrations of styrene.

A field study was conducted among 21 male workers exposed to styrene of concentration below 30 ppm in a fiber-reinforced plastic boat manufacturing plant. Twenty-one male workers with similar age groupings, years of education, and social and occupational state served as referents. The mean end-of-shift urinary mandelic acid (MA) and phenylglycoxylic acid (PGA) for the exposed workers were 84 mg/g creatinine and 66 mg/g creatinine, respectively. The Lanthony D-15 Hue Desaturated Panel was used to evaluate color discrimination of the exposed and referent groups. The results of the test were expressed as total color difference score (TCDS). The exposed workers' mean TCDS (a higher score denotes poorer color discrimination ability) was significantly (p < 0.0006) higher than the referents'. Neurobehavioral tests were also conducted, using the World Health Organization's Neurobehavioral Core Test Battery (NCTB). All the results of the NCTB were poorer for the exposed than for the referents. However, significant differences were observed only for Digit Span, Digit Symbol, and Benton Visual Retention tests. These results suggest that low exposure to styrene could affect some psychometric performance and may impair color vision.

Adult↗
PubMed1994

Epidemiology of allergic rhinitis and its associated risk factors in Singapore.

BACKGROUND: Few studies have evaluated the relationship between allergic rhinitis and risk factors in the environment which promote aeroallergenic exposures, but knowledge of these are of practical importance from the point of view of community prevention. METHOD: A cross-sectional population-based study of 2868 adults aged 20-74 years was carried out. Allergic rhinitis was defined as the self-reported presence, in the previous year, of usual nasal blockage and discharge apart from colds or the flu, provoked by allergens, with or without conjunctivitis. RESULTS: Allergic rhinitis was reported by 4.5% of the subjects. Higher crude prevalences were observed in males, younger adults, Indians compared to Chinese and Malays, those with higher socioeconomic status, and in three of five residential areas studied. Significant environmental factors included cockroach infestation, occupational exposure, past smoking habit, outdoor air pollution, and frequent heavy exposure to cooking fumes. Keeping pets, having rugs or carpets in the home, and passive exposure to tobacco smoke showed weak and statistically insignificant associations. There was no apparent association with use of mosquito coils or incense. The significant determinants after multivariate adjustment of all risk factors were age, race, flat size, area of residence, cockroach infestation, past smoking, and occupational and cooking fumes exposure. CONCLUSION: The study underscores the importance of environmental control of inhalational exposure to common allergens and irritants in the prevention of allergic rhinitis.

Adult↗
PubMed1994

Postural stability of workers exposed to lead.

OBJECTIVE: To detect, with a computerised postural sway measurement system, any significant deviation of postural sway parameters among lead workers compared with a control group. METHODS: Postural stability was investigated with a computerised postural sway measurement system in 60 workers exposed to lead with a duration of exposure of 84 (range 3-366) months and 60 controls. Sway parameter data were collected with an Advanced Mechanical Technology computerised biomechanics platform system. RESULTS: The mean current blood lead concentration was 36.0 (range 6.4 to 64.5) micrograms/dl for the exposed workers and 6.3 (range 3.1 to 10.9) micrograms/dl for the 14 controls. There was no significant difference between the groups for the postural sway parameters obtained when the eyes were open. Significant differences were found for Xs, Ys (SDs of the coordinates of the centre of pressure); Xm, Ym (mean deviation of the coordinates of the centre of pressure); Rm (average displacement of Xi, Yi, from Xo, Yo); L (length of sway path); Vel (mean velocity of the centre of pressure along its path); Ao (area included within the path of the centre of pressure); Ae (95% confidence elliptical area). The Romberg ratios (the relation between eyes closed and open) for the Vel, L, Ao and Ae of the exposed workers were also significantly different from the controls. CONCLUSION: The study showed that workers exposed to lead had significantly poorer postural stability than the controls. Lead may affect certain parts of the whole sensory neural axis resulting in postural instability when the visual input is cut off. Based on current blood lead concentrations, we were not able to obtain any significant association with the postural sway parameters.

Adult↗
PubMed1994

Prevalence of asthma and risk factors among Chinese, Malay, and Indian adults in Singapore.

BACKGROUND: The prevalence and morbidity of asthma vary greatly among different ethnic communities and geographical locations, but the roles of environmental and genetic factors are not fully understood. The differences in prevalence of adult asthma among Chinese, Malay, and Indian ethnic groups in Singapore were examined, and the extent to which these could be explained by personal and environmental factors were investigated. METHODS: A stratified disproportionate random sample (n = 2868) of Chinese (n = 1018), Malays (n = 967), and Indians (n = 883) of both sexes was drawn from households in five public housing estates, and an interviewer administered questionnaire was used to determine cumulative and current prevalence of "physician diagnosed asthma" (symptoms with a physician diagnosis of asthma). RESULTS: Lifetime cumulative prevalence (standardised to the general population) of "physician diagnosed asthma" was 4.7% in men and 4.3% in women; 12 month period prevalences were 2.4% and 2.0%, respectively. Cumulative prevalence of asthma was significantly higher in Indians (6.6%) and Malays (6.0%) than in Chinese (3.0%); period prevalences of asthma were 4.5% in Indians, 3.3% in Malays, and 0.9% in Chinese. Ownership of cats or dogs was more frequent in Malays (15.4%) and Indians (11.2%) than in Chinese (8.8%). Rugs and carpets were also more frequently used by Malays (52.2%) and Indians (40.7%) than by Chinese (8.9%). Current smoking prevalences were higher in Malays (27.3%) than in Indians (19.4%) and Chinese (23.0%). Malays and Indians did not have higher rates of atopy (11.1% and 15.2%, respectively) than Chinese (15.4%). Adjustment for these factors in multivariate analyses reduced the greater odds of asthma in Malays and Indians, but not to a significant extent. CONCLUSIONS: There are ethnic differences in the prevalence of asthma in Singapore which are not entirely explained by differences in smoking, atopy, or other risk factors. Other unmeasured environmental factors or genetic influences are likely to account for residual differences in the prevalence of asthma.

Adult↗
PubMed1994

Understanding asthma: patient survey.

Eight hundred and two adult patients attending five randomly selected polyclinics in Singapore were interviewed to assess their understanding of asthma. Knowledge of asthma mechanism and its medications was poor with a mean score of 1.4 (median: 1) out of a total score of 6. About a third knew that asthma is due to narrowing of airways and a quarter knew the action of bronchodilators. Only 4.4% (27) knew that steroids decrease airway swelling or inflammation. The best knowledge score was associated with subjects who had the highest education, who had a family history and who had been exposed to pamphlets and books. Incorrect use of prophylaxis was also evident with only one-third (37%) using steroid inhalers regularly as prescribed. Only half (54.5%) of those with no schooling used the correct inhaler technique. Doctors were a source of information for only 49.9% (400) of the patients and it was those with the highest education who were most likely to get information from the doctors. Pamphlets were a source of information for less than one-fifth (16.2%) of the subjects. Greater emphasis should be given to patient education by doctors to help patients understand asthma and its treatment. Important target groups are the older, lesser educated and the moderate or severe patients on steroid inhalers.

Adult↗
PubMed1994

Silica and lung cancer: a continuing controversy.

The question whether silica is carcinogenic is not new, but there has been a resurgence of research over the last two decades with the use of more powerful epidemiological methodologies. There is sufficient evidence for the carcinogenicity of crystalline silica in animals. A large number of cohort and case-control studies consistently suggest a modest excess of lung cancer in workers with occupational silica exposure (relative risk less than 2). However, in many studies, the association is confounded by exposures to cigarette smoke, and environmental cocarcinogens like radon daughters, polyaromatic hydrocarbons and asbestos. The excess risk of lung cancer is more pronounced in workers with silicosis (relative risk of 2 to 4). Silica may act as a direct carcinogen or indirectly by the adsorption of cocarcinogens such as polyaromatic hydrocarbons from cigarette smoke or industrial pyrolysis products, and/or by impairing pulmonary clearance, thereby increasing the effective dose and duration of exposure to these carcinogens. Pulmonary fibrosis itself may be a precursor to the development of lung cancer.

Animals↗
PubMed1994

Outpatient adult bronchial asthma in Singapore.

OBJECTIVES: To describe the clinical pattern and drug use in adult bronchial asthma seen in Government polyclinics (primary health care centres). DESIGN: A cross-sectional study using a structured questionnaire. SETTING: The five largest Government polyclinics in Singapore. SUBJECTS: Eight hundred and two subjects aged between 21-58 years drawn from the register of outpatient attendances. The response rate was 63%. RESULTS: The mean age of the study subjects was 37.4 years and the mean age of onset was 19.2 years. Thirty-three percent had onset of asthma under 10 years old. The most commonly reported trigger factors were cold drinks (67%), a change of temperature or humidity (65%), influenza or colds (65%), house dust (58%) and cigarette smoke (37%). In 27%, the work environment was a provoking factor. One-fifth had attacks every night or every day. About half of the patients had FEV1 under 80% of predicted. In the past year, 10% had 4 or more acute attacks requiring emergency attendance, 18% had one or more hospital admissions and 21% had sickness absence from asthma for one week or more. Of the 186 subjects who needed bronchodilators/inhalers 3 times or more a day, only 19.3% were on inhaled steroids. CONCLUSIONS: Considerable morbidity existed amongst outpatient asthmatics. Inhaled steroids appeared to be under-used.

Adult↗
PubMed1994

Lifestyle and behavioural risk factors associated with asthma morbidity in adults.

We studied the association between morbidity and personal lifestyle/behavioural factors that predispose to exposure to known environmental precipitants of asthma, in a group of asthmatics (n = 787) in primary-care clinics. Clinical severity of asthma was determined by questions regarding the frequency of daytime or nocturnal attacks, the number of visits to primary care or hospital emergency departments for treatment of acute attacks, and the number of hospitalizations, as well as the amount of sick leave in the past year. Questions concerning risk factors included ethnicity, clinical atopic status (current rhinitis/eczema), smoking, occupation, keeping of pets, rugs and carpets, use of brooms, burning of mosquito coils or incense, and outdoor air pollution, as well as the patient's knowledge of asthma care. The most significant independent predictors of asthma morbidity, identified from multivariate logistic regression analyses, were current keeping of either pets or rugs/carpets (OR 1.49; 95% CI 1.12-1.99), and current high-risk occupations (OR 0.59, 95% CI 0.40-0.89). A multiplicity of interacting factors and behavioural responses appear to influence the effects of allergens and other environmental precipitants on asthma morbidity in patients.

Adult↗
PubMed1994

Epidemiology of chronic (perennial) rhinitis in Singapore: prevalence estimates, demographic variation and clinical allergic presentation.

We conducted a population-based study involving a stratified cluster disproportionate random sample of 2868 adults aged 20 to 74 years selected from five housing estates (Yishun, Toa Payoh, Jurong East, Geylang/Eunos and Bukit Merah). Chronic rhinitis was defined as the usual presence of symptoms of blocked or running nose, apart from colds or the flu, lasting for more than a year. Allergic rhinitis was considered to be present if these symptoms were associated with conjunctivitis or recognisable provocation by commonly known allergens, namely house dust, dogs, cats, birds, pollen, or medicines. The estimated general population prevalence of chronic rhinitis was 10.8% (95% confidence interval (CI) 8.8-12.7). Higher prevalences were noted in males, in younger adults, in Indians and Chinese, in those with higher socio-economic status, and in Toa Payoh, Jurong East and Geylang/Eunos. The prevalence of allergic rhinitis was 5.5% (95% CI 4.5-6.5). The most common 'allergenic' factor in allergic rhinitis was house dust (73%); provocation by birds, cats or dogs (5%), grass or tree pollens (5%), and medicine (5%) was less common but likely to have been under-recognised. Provocation by change in temperature (54%) and early in the morning (64%) was equally frequent in both 'allergic' and 'non-allergic' rhinitis; cigarette smoke, petrol and diesel fumes, food and work environment were less common (4-12%). Allergic rhinitis was highly significantly associated with asthma (13.9% in allergic rhinitis, 4.4% in non-allergic rhinitis, and 2.2% in non-rhinitic subjects).

Adult↗
PubMed1993

Respiratory symptoms and lung function effects of domestic exposure to tobacco smoke and cooking by gas in non-smoking women in Singapore.

STUDY OBJECTIVES: To investigate the effects of passive exposure to tobacco smoke and gas cooking at home on respiratory symptoms and lung function of non-smoking women. SETTING: Evidence on the effects of passive smoking and exposure to nitrogen dioxide from gas cooking on the respiratory health of adults is limited and variable. Over 97% of women in Singapore do not smoke, and a principal source of indoor air pollution for housewives is passive smoking and gas cooking. DESIGN: This was a cross sectional (prevalence) study of a population based sample of 2868 adults aged 20 to 74 years in Singapore. A structured questionnaire administered by trained interviewers was used to collect data on passive smoking, gas cooking, respiratory symptoms, and other relevant variables. Passive smoking was defined as exposure to cigarette smoke from one or more members of the household who had ever smoked. Gas cooking was defined in terms of the weekly frequency of gas cooking, as well as the frequency with which the respondent's kitchen was filled with heavy cooking fumes (rarely, occasionally, often). Forced expiratory volume in one second (FEV1) was measured by using a portable Micro-spirometer. Multivariate analyses were used to estimate relative odds of association for respiratory symptoms and FEV1 effect, with adjustment for potential confounding variables. PARTICIPANTS: Of a total of 1438 women in the sample, 1282 women who had never smoked provided questionnaire data and 1008 women provided acceptable readings of FEV1 for analysis. MAIN RESULTS: Passive smoking was significantly associated with greater relative odds of usual or chronic cough and phlegm, wheezing, and breathlessness on exertion, as well as lower FEV1. Greater relative odds of respiratory symptoms were also associated with the weekly frequency of gas cooking, although these results were statistically insignificant. Chronic cough and phlegm and breathlessness on exertion, however, were significantly associated with the frequency with which the kitchen was filled with heavy cooking fumes. A lower FEV1 was found in women who cooked frequently (more than thrice a week). CONCLUSION: Domestic exposure to cigarette smoke and gas cooking is associated with increased risks of respiratory symptoms and impairment of lung function in non-smoking women in Singapore.

Adult↗
PubMed1993

Further evidence of human silica nephrotoxicity in occupationally exposed workers.

It has previously been shown that granite workers with heavy exposure to silica had glomerular and proximal tubular dysfunction evidenced by increased urinary excretions of albumin, alpha-1-microglobulin (AMG), and beta-N-acetyl-glucosaminidase (NAG). The investigation was replicated in another group of granite workers to further elucidate the exposure effect relation. The urinary excretion of albumin, alpha-1-microglobulin (AMG), beta-2-microglobulin (BMG), and beta-N-acetyl-glucosaminidase (NAG) was determined in two groups of granite workers with low and high exposure to silica. Low molecular weight proteinuria and enzymuria were significantly correlated with duration of exposure in the high but not the low exposure group. These increases were most pronounced in those with 10 or more years of heavy exposure, and in those with radiological evidence of pulmonary fibrosis, particularly those with rounded small opacities denoting classical silicosis. These results provide further evidence that prolonged and heavy exposure to silica is associated with nephrotoxic effects in granite workers.

Acetylglucosaminidase↗
PubMed1992

Small airways function of silica-exposed workers.

Small airways obstruction may be present for many years before chronic airway obstruction becomes evident. Several spirometric indices, especially flow rates at low lung volumes, may reflect the status of small airways. Time domain indices, by using moments analysis of the volume time spirogram, have also been shown to be sensitive indicators of small airways obstruction. In this study, we have applied the various spirometric indices as well as time domain indices to a group of granite quarry workers without radiographic evidence of silicosis or physiological evidence of obstruction to the larger airways. The aim was to evaluate small airways function in relation to dust exposure in subjects with normal ratio of the forced expiratory volume in one second to the forced vital capacity (FEV1/FVC) and normal FVC. The volume-time spirograms of 140 quarry workers were digitized using an electronic digitizer connected to a microcomputer where flow and time domain indices were computed. The workers were divided into three exposure groups based on their occupational history. With adjustment for age, height, and smoking status, all the time domain indices showed significant small airways obstruction with increasing dust exposure. Smokers had greater degree of airways obstruction than the non-smokers, with a similar trend of increase in small airways obstruction in relation to higher exposure. Our present study suggests that small airways obstruction is present among silica exposed workers in the absence of radiological evidence of silicosis and large airways obstruction. There was also evidence of increasing small airways obstruction in higher dust exposure group. Our study also suggests that time domain indices are more sensitive to small airways obstruction.

Adult↗
PubMed1992

Predictors of mortality in silicosis.

The mortality of a cohort of 1487 male patients with silicosis in a population-based register followed up from 1980 to 1986 was evaluated with reference to the mortality rates of the general male population. A striking excess of deaths from all causes (observed 368, standardized mortality ratio, SMR 3.00) was noted. Seventy-four percent of the deaths were due to respiratory conditions and complications directly or indirectly related to silicosis. The risk of death was especially higher than expected in younger patients under 45 years of age. Patients with simple silicosis of profusion category 1 did not appear to be at any increased risk of death relative to the general population, but increasing excesses of death were associated with greater extent of simple and conglomerate disease. These increased mortality risks were observed in tuberculosis-free patients as well as in those who never smoked. For the same extent of silicotic disease, the risk of death was higher if tuberculosis occurred. There was no evidence, however, that patients who smoked were more likely to suffer a worse mortality outcome than those who did not. Age at diagnosis, extent of silicotic disease and the occurrence of tuberculosis were therefore strong predictors of mortality in patients with silicosis.

Adult↗