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Biomedical subjects

F T Chew

Publications and source records attributed to F T Chew.

At least 37 records · Page 2Linked to original sources
PubMed1999

House dust mite fauna of tropical Singapore.

INTRODUCTION AND AIMS: Sensitization to house dust mites is very common in the tropics. This study evaluated the dust mite fauna in Singaporean homes. METHODS: A total of 134 dust samples from 50 homes were evaluated. Dust mites were isolated, identified and quantified by standard techniques. RESULTS: Dust mites were isolated from 130/134 (97%) samples, with mites identified in all samples from sofas (n = 21) and carpets (n = 13), and 49/50 (98%) and 47/50 (94%) from mattresses and bedroom floors, respectively. All samples from sofas and carpets had more than 500 mites/g compared with 47/50 (94%) and 23/50 (46%) from mattresses and floors, respectively. Blomia tropicalis was the predominant mite (62% of total mites) followed by D. pteronyssinus (16% of total mites). Eight samples had a predominance of Sturnophagoides brasiliensis and Tarsonemus granarius. Other species that accounted approximately 1% of mites identified included D. farinae, Austroglycyphagus malaysiensis, Cheyletus malaccensis, Malayoglyphus intermedius, Suidasia pontifica and Tyrophagus putrescentiae. CONCLUSION: Dust mites were highly prevalent and present in high densities in Singaporean homes with B. tropicalis being the most prevalent species.

Animals↗
PubMed1999

Allergenic differences between the domestic mites Blomia tropicalis and Dermatophagoides pteronyssinus.

BACKGROUND: House dust mite allergens are the most important indoor allergens associated with asthma and rhinitis in Singapore and the tropics. Recent data to suggest that besides the Dermatophagoides spp., the domestic mite Blomia tropicalis (Bt) is also an important source of allergens in these regions. OBJECTIVE: To evaluate the degree of allergenic cross-reactivity between Bt and D. pteronyssinus (Dp). METHODS: Cross-reactivity between extracts of Bt and Dp was evaluated by fluorescent allergosorbent (FAST) inhibition studies and cross enzyme immunoelectrophoresis. Additionally, the major Dp allergens - Der p 1, Der p 2 and Der p 5, were also compared with the Bt extract by dot blot inhibition. Skin prick and intradermal end-point titration were then carried out to compare the homologous allergens of the mite species, Blo t 5 and Der p 5. RESULTS: FAST inhibition studies showed low to moderate cross-reactivity between the two dust mite extracts (maximum cross-inhibition, 60%). Native allergens studied by cross enzyme immunoelectrophoresis using mite allergic sera also showed similar results but with at least four cross-reactive IgE binding antigens. Dot blot inhibition studies using allergens of Dp, Der p 1, Der p 2, and Der p 5, showed little cross-reactivity between these allergens with components of the crude Bt extracts. Further, evaluation of a recombinant allergen of Bt, Blo t 5, showed low levels of cross-reactivity even with its homologous Dp counterpart, Der p 5. CONCLUSION: These results provide evidence that Bt allergens are distinct and have relatively low to moderate cross-reactivity with Dermatophagoides spp. allergens. Bt allergens should therefore be included in the diagnostic panel for the evaluation of allergic disorders in the tropics, and the development of new diagnostic and therapeutic strategies should include allergens of Bt.

Allergens↗
PubMed1999

Geographical comparison of the prevalence of childhood asthma and allergies in Singapore.

A previous study suggested that differences in the prevalence of respiratory illnesses such as asthma in school children in different regions of Singapore were not due to the influence of air pollution or environmental factors but possibly to cultural and socio-economic factors. The effects of socio-economic or demographic variables were, however, not shown in that study. In this study, we set out to discover whether regional differences in the prevalence of atopic diseases such as asthma, rhinitis and eczema in Singapore school children could be explained by different demographic profiles. The prevalence of asthma and allergies were evaluated in 6238 Singapore school children in two age groups (6-7 years [n = 2030] and 12-15 years [n = 4208]). They were from four regions, based on residential post codes. Demographic and socio-economic data were also obtained. The questionnaire of the International Study on Asthma and Allergies in Childhood (ISAAC) was used. The data showed that children residing in the northern regions of Singapore had a significantly lower prevalence of asthma and rhinitis than those in other regions. When controlled for demographic influences (age, sex and race) and socio-economic factors (type of housing), however, the differences between these regions were reduced. No geographical difference in the prevalence of eczema was observed. Thus, geographical differences in the prevalence of asthma and rhinitis in Singapore could in part be explained by demographic and socio-economic differences in the population.

Adolescent↗
PubMed1999

Under-recognition of childhood asthma in Singapore: evidence from a questionnaire survey.

In a recent study on the prevalence of childhood asthma and allergies using the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaires, 6238 Singapore school children in two age-groups, 6-7 years (n = 2030) and 12-15 years (n = 4208), were evaluated. Of the 1856 children who reported asthma-like symptoms (wheezing, exercise-wheezing, persistent nocturnal cough), 919 (49%) had not been diagnosed asthmatic. Of these undiagnosed children, 731 (39%) reported current symptoms of asthma. Under-recognition of asthma was more prevalent among those with persistent nocturnal cough and mild symptoms. In addition, the discordance between wheezing in the last 12 months and a diagnosis of asthma was significantly higher among the younger age-group (6-7 years), but exercise-induced wheezing was less recognized as a symptom of asthma among the older age-group (12-15 years). This study has shown that there is a substantial degree of under-recognition of asthma among school children in Singapore.

Adolescent↗
PubMed1999

The economic cost of asthma in Singapore.

BACKGROUND: Asthma is a common chronic disorder. In Singapore, it is estimated that 140,000 individuals have current asthma and more than 100 individuals die of this disease annually. OBJECTIVE: This study estimates the economic cost of asthma, both direct and indirect, to the patient and community. METHOD: Direct cost estimates were based on all levels of medical care, which included inpatient care, emergency room visits, specialist outpatient and primary healthcare, and medication costs. Indirect costs were estimated from cost of time lost by patients and their families attending to medical needs and the loss of productivity due to absenteeism. These estimates were calculated to the 1992/93 US dollar. RESULTS: The total cost of asthma in Singapore was estimated to be US $33.93 million per annum. This was made up of US $17.22 million in direct costs and US $16.71 million in indirect costs. Inpatient hospitalisation accounted for the largest proportion of direct medical expenditure, approximately US $8.55 million. The loss of productivity from acute asthma accounted for the largest proportion of the indirect costs at US $12.70 million. The cost estimates did not include premature death due to disease. These estimates represent approximately US $238 per asthmatic person per year or US $11.90 per person per year. CONCLUSION: This study shows that the economic cost of asthma is also considerable in populations outside the Western hemisphere, and justifies the need for a concerted effort to reduce asthma morbidity worldwide.

Asthma↗
PubMed1999

Factors associated with increased respiratory symptoms among asthmatic children in Singapore.

Asthma is a common cause of childhood morbidity. The objective of the present study was to evaluate the factors associated with increased asthma morbidity among asthmatic children in Singapore. A cohort of primary school children (n = 6,404, aged 6-13 years) were evaluated using the American Thoracic Society and the Division of Lung Diseases of the National Heart, Lung and Blood Institute, USA (ATS-DLD) respiratory questionnaire. A total of 2,222 of 6,404 children (34.8%) was found to have reported symptoms of wheezing. Of these, 899/2,222 (40.5%) reported symptoms of "increased asthma morbidity". This was associated with the younger age group, male sex and higher socio-economic status. In addition, concurrent or past allergies were strongly associated with increased asthma morbidity, while premature birth and a history of prior childhood respiratory illnesses and Infections were predictive of greater asthma morbidity. No association was found between increased morbidity and presence of domestic pets, parental smoking, childcare attendance, and the season of birth.

Adolescent↗
PubMed1999

Sensitization to Blomia tropicalis and dermatophagoides pteronyssinus-a comparative study between Singapore and Taiwan.

Blomia tropicalis (Bt) and Dermatophagoides pteronyssinus (Dp) are the predominant domestic mites species in Singapore and Taiwan. This study aims to characterize and compare the mite sensitization profiles in both countries. Skin prick tests were performed on 203 Singaporeans with Dp and Bt crude extracts. In vitro IgE and IgG4 reactivity to extracts and specific allergens (Der p 1, Der p 2 Der p 5 and Blo t 5) were determined by immunoassays. Approximately 91% of the tested Singaporeans were skin test positive for both Bt and Dp. Both populations share similar frequencies of in vitro IgE reactivity to all the allergens tested, but they differ in the pattern and magnitude of allergen sensitization. Although Der p 1, Der p 2 and Blo t5 are major sensitizing allergens in both countries, Blo t 5 is a more potent one in Singapore, probably reflecting the high level of exposure to Bt. The unique major Bt and Dp allergens should be included for precise diagnosis and effective immuno-therapeutic treatment of mite allergy in both countries.

Adolescent↗
PubMed1999

Culture of Blomia tropicalis and IgE immunoblot characterization of its allergenicity.

Blomia tropicalis is an important triggering factor for allergic diseases such as asthma, rhinitis and atopic dermatitis in tropical and subtropical regions, which climate favours the growth of this species. Our previous mite fauna study revealed that Blomia tropicalis is the most dominant species present in Singapore house dust The main objective of this study is to establish a mass culture of Blomia tropicalis for further characterization of the antigenic and molecular properties of this mite. Approximately one gram of mites could be obtained for every 300-gram of culture medium by culturing under natural condition with a mean annual temperature of 30 degrees C and a mean relative humidity of 80%, and harvested by modified Tullgren funnel. Allergen characterization by IgE immunoblot analysis with crude mite extracts showed some IgE reactivity differences between Blomia tropicalis mite extract from Singapore and Colombia. The possible reasons for these findings are the quality and source of the mite protein extracts used, or selective differences in the population under evaluation. Further, the atopic sera tested showed differences in the pattern and Intensity of IgE immunoblot reactivity to crude extracts of Blomia tropicalis and Dermatophagoides pteronyssinus, the other highly prevalent mite in Singapore. These data support the existence of species-specific allergens. In conclusion, we have been successful in setting up B. tropicalis mass cultures and have prepared extracts of high allergenicity.

Allergens↗
PubMed1999

Ethnic differences in genetic susceptibility to atopy and asthma.

The genetics of asthma and atopy is complex, but can be approached by studies of both candidate genes and mapping of susceptibility loci. Genetic factors conferring susceptibility to disease may vary among ethnic groups. We present our experience with some candidate gene studies for asthma and atopy and susceptibility locus mapping for linkage to chromosome 5q.

Asian People↗
PubMed1998

Seasonal trends of viral respiratory tract infections in the tropics.

To evaluate the seasonal trends of viral respiratory tract infections in a tropical environment, a retrospective survey of laboratory virus isolation, serology and immunofluorescence microscopy in two large general hospitals in Singapore between September 1990 and September 1994 was carried out. Respiratory tract viral outbreaks, particularly among infants who required hospitalization, were found to be associated mainly with respiratory syncytial (RSV) infections (72%), influenza (11%) and parainfluenza viruses (11%). Consistent seasonal variations in viral infections were observed only with RSV (March-August) and influenza A virus (peaks in June, December-January). The RSV trends were associated with higher environmental temperature, lower relative humidity and higher maximal day-to-day temperature variation. Although the influenza A outbreaks were not associated with meteorological factors, influenza B isolates were positively associated with rainfall. These data support the existence of seasonal trends of viral respiratory tract infections in the tropics.

Adolescent↗
PubMed1998

Awareness of environmental issues and the acceptance of CFC-free inhalers.

With the recent availability of a chlorofluorocarbon (CFC)-free metered dose inhaler (MDI) (Airomir), a patient survey was carried out to evaluate awareness of the role of CFCs in our environment and acceptance of this new inhaler. A questionnaire survey was conducted on parents and guardians of 201 children. Depending on respondents' preference, the interview was conducted in English (71%), Chinese (23%), Malay (5%) or Tamil (1%). A 'taste' test was also conducted on 103 of these children. Only 13% (26/201) of parents/guardians were aware that MDIs contained CFCs. Although 70% of children were in favour of the new taste of the CFC-free inhaler, the cost of the new inhaler was an important consideration for parents and guardians in their decision to switch to the new inhaler. The majority (93%) were willing to switch if its cost were equivalent to their current inhaler. This study has provided pertinent information with regard to acceptance of CFC-free inhalers which should be considered when making the inevitable switch to environmentally friendly inhalers.

Adult↗
PubMed1998

Month of birth and childhood atopic diseases in the tropics.

The relationship between the month of birth and prevalence of diagnosed asthma, asthma-like symptoms (wheezing, nocturnal cough, and exercise wheezing), rhinitis, and eczema was investigated in four cohorts each of primary schoolchildren and secondary school (high school) adolescents in Singapore by questionnaire survey. Significantly increased prevalence rates of diagnosed asthma and asthma-like symptoms were observed in certain birth months of the year for two adolescent cohorts, while significant association between birth month and presence of symptoms of rhinitis was found in a cohort of 6-7-year-olds. However, when demographic factors were taken into consideration by multivariate analysis, only the association between asthma, asthma-like symptoms, and birth month remained significant in one of the adolescent cohorts. There was, therefore, only a weak association between the month of birth and atopic disease in our schoolchildren. The overall seasonal trends, however, did show two main seasons (March-May and September-November) associated with higher prevalence of these diseases.

Adolescent↗
PubMed1998

Risk factors for breakthrough varicella in healthy children.

AIM: To evaluate the risk factors for breakthrough varicella in a follow up study of a cohort of 181 healthy children immunised when aged 9-24 months with a reformulated Oka strain varicella vaccine (SmithKline Beecham Biologicals/Oka). DESIGN: The children were randomised in a double blind manner into one of four groups to receive one of two production lot vaccine batches, at two different titres (high titre, 10(3.9) and 10(4.0) plaque forming units (pfu); low titre (heat exposed), 10(2.7) and 10(2.8) pfu). The overall seroconversion rate after immunisation was 99%. RESULTS: One hundred and sixty-eight patients were available for review after a mean (SD) follow up of 35 (9) months after vaccination. Multivariate analysis indicated that risk factors for breakthrough varicella were household contact with varicella (adjusted odds ratio (OR), 19.89; 95% confidence interval (CI), 18.39 to 21.39), vaccination age of < or = 14 months (adjusted OR, 2.30; 95% CI, 1.69 to 2.90), and receiving low titre (10(2.7) pfu) vaccine (adjusted OR, 2.13; 95% CI, 1.54 to 2.73). All children who developed breakthrough varicella, had a modified varicella illness, except for three, all of whom had received low titre vaccine. CONCLUSION: The identification of young immunisation age (< or = 14 months) and low titre vaccine as risk factors for breakthrough varicella have important implications for the implementation of varicella vaccination programmes in healthy children.

Age Factors↗
PubMed1997

Presence of domestic pets and respiratory symptoms in asthmatic children.

The allergens of domestic pets such as cats, dogs and birds, have been known to sensitive predisposed individuals. In Singapore, approximately 25% to 35% of our atopic populations are sensitised to cat, dog or bird feather allergens. It is not known, however, if the presence of such domestic pets would translate to higher rates of sensitisation, or more importantly, give rise to increased respiratory symptoms. This study evaluated the association between the presence of domestic pets at home and the prevalence of respiratory symptoms among asthmatic children in Singapore. The parents of 1517 doctor-diagnosed asthmatic children were interviewed using the American Thoracic Society-Division of Lung Diseases respiratory questionnaire. More than 20% were found to have domestic pets (cats, dogs or birds) at home. Of these, those with exposure to passive smoke in the home were excluded. A total of 188 current pet owners (cats, dogs and birds) were demographically-matched for sex, race and socio-economic status (type of housing) to those without pets, past or current. Compared to those without pets, asthmatic children with pets at home had a higher prevalence of coughing with cold [relative risk (RR) 1.30; 95% confidence interval (CI) 1.01 to 1.69]; wheezing with cold (RR 1.42; CI 1.07 to 1.90), wheezing with shortness of breath (RR 1.33; CI 1.00 to 1.82), exercise-induced wheezing (RR 1.68; CI 1.10 to 2.56); and increased phlegm production or congestion with cold (RR 1.38; CI 1.00 to 1.91). This study suggests that the presence of domestic pets increases the prevalence of respiratory symptoms in asthmatic children. Those with predisposition to these allergens should avoid having these pets in the home or take specific precautions in avoiding their allergens.

Animals↗
PubMed1997

Prevalence and distribution of indoor allergens in Singapore.

BACKGROUND AND AIMS: Immediate hypersensitivity to indoor allergens is known to be associated with allergic asthma. This study evaluated the prevalence and distribution of six indoor allergens in 956 dust samples obtained from homes, childcare centres, schools, and a hospital in tropical Singapore. Seasonality of mite allergens was also assessed. METHODS: The major allergens of the Dermatophagoides spp. dust mites, Der p 1 and Der f 1; major cat and dog allergens, Can f 1 (dog) and Fel d 1 (cat); and cockroach, Bla g 1, were measured by specific enzyme immunoassays. Allergen levels of the storage mite, Blomia tropicalis (Blo t), were measured by a fluorescent allergosorbent test (FAST) inhibition assay. RESULTS: Our results showed that homes had significantly higher concentrations and prevalence of allergens compared with the other locations, except for Bla g 1, where higher mean levels were found in schools. Within the homes, the highest concentrations of mite allergens were found in mattresses (geometric mean: 1.2 microg/g dust Der p 1; 2717 Allergen Units per gram dust [AU/g] Blo t), and carpets (1.5 microg/g Der p 1; 1620 AU/g Blo t), whilst Bla g 1 was mainly concentrated in the storerooms (geometric mean = 3.5 units/g) and kitchens (geometric mean = 5.1 units/g). The major cat and dog allergens were well distributed and not confined to homes with pets. Their highest levels were found in dust of soft furnishings, carpets and mattresses. There was an absence of significant seasonal variation in Der p 1, Der f 1 and Blo t levels in the homes over a 1 year period. CONCLUSION: The results indicate that compared with public places, the home consitutes a major reservior of indoor allergens. Allergens of the storage mite, B. tropicalis, should be considered as a major allergenic component of dust in Singapore.

Air Pollution, Indoor↗
PubMed1996

Age- and sex-related changes in lymphocyte subpopulations of healthy Asian subjects: from birth to adulthood.

Flow cytometric analysis of lymphocyte subsets were evaluated in 391 healthy Asian subjects ranging in age from birth to 40 years. Lymphocyte subsets were analysed using specific monoclonal antibodies: CD20 (B cells), CD3 and CD2 (T cells), CD16 and CD56+ (NK cells), CD4/CD3+ (helper-inducer T cells), CD8/ CD3+ (suppressor/cytotoxic T cells), HLA-DR expression on CD3 and CD25 (Tac) on CD3. The total white cell count, absolute lymphocyte counts, and B cell percentages peaked in infancy and declined steadily with age. Absolute counts of each subset, which were derived from absolute lymphocyte counts, also followed this trend. Increases with age were seen in the NK, T cell (CD2, CD3), and CD8 percentages. Males tended to have higher NK and CD8 percentages than females, and, conversely, females had higher CD3 and CD4 percentages than males. Comparison of our results with studies involving Caucasian subjects indicated higher NK percentages in our Asian population and lower CD4 absolute counts in the males of our population. These results indicate the presence of age, sex, and probable racial differences in lymphocyte subset expression. Our results may serve as reference standards for the Asian population.

Adolescent↗