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  1. Cheong YL, Leitão PJ, Lakes T
    Spat Spatiotemporal Epidemiol, 2014 Jul;10:75-84.
    PMID: 25113593 DOI: 10.1016/j.sste.2014.05.002
    The transmission of dengue disease is influenced by complex interactions among vector, host and virus. Land use such as water bodies or certain agricultural practices have been identified as likely risk factors for dengue because of the provision of suitable habitats for the vector. Many studies have focused on the land use factors of dengue vector abundance in small areas but have not yet studied the relationship between land use factors and dengue cases for large regions. This study aims to clarify if land use factors other than human settlements, e.g. different types of agricultural land use, water bodies and forest are associated with reported dengue cases from 2008 to 2010 in the state of Selangor, Malaysia. From the correlative relationship, we aim to generate a prediction risk map. We used Boosted Regression Trees (BRT) to account for nonlinearities and interactions between the factors with high predictive accuracies. Our model with a cross-validated performance score (Area Under the Receiver Operator Characteristic Curve, ROC AUC) of 0.81 showed that the most important land use factors are human settlements (model importance of 39.2%), followed by water bodies (16.1%), mixed horticulture (8.7%), open land (7.5%) and neglected grassland (6.7%). A risk map after 100 model runs with a cross-validated ROC AUC mean of 0.81 (±0.001 s.d.) is presented. Our findings may be an important asset for improving surveillance and control interventions for dengue.
  2. Cheong YL, Burkart K, Leitão PJ, Lakes T
    Int J Environ Res Public Health, 2013 Nov 26;10(12):6319-34.
    PMID: 24287855 DOI: 10.3390/ijerph10126319
    The number of dengue cases has been increasing on a global level in recent years, and particularly so in Malaysia, yet little is known about the effects of weather for identifying the short-term risk of dengue for the population. The aim of this paper is to estimate the weather effects on dengue disease accounting for non-linear temporal effects in Selangor, Kuala Lumpur and Putrajaya, Malaysia, from 2008 to 2010. We selected the weather parameters with a Poisson generalized additive model, and then assessed the effects of minimum temperature, bi-weekly accumulated rainfall and wind speed on dengue cases using a distributed non-linear lag model while adjusting for trend, day-of-week and week of the year. We found that the relative risk of dengue cases is positively associated with increased minimum temperature at a cumulative percentage change of 11.92% (95% CI: 4.41-32.19), from 25.4 °C to 26.5 °C, with the highest effect delayed by 51 days. Increasing bi-weekly accumulated rainfall had a positively strong effect on dengue cases at a cumulative percentage change of 21.45% (95% CI: 8.96, 51.37), from 215 mm to 302 mm, with the highest effect delayed by 26-28 days. The wind speed is negatively associated with dengue cases. The estimated lagged effects can be adapted in the dengue early warning system to assist in vector control and prevention plan.
  3. Cheah YK, Kee CC, Lim KK, Cheong YL
    J Child Adolesc Psychiatr Nurs, 2024 May;37(2):e12468.
    PMID: 38654575 DOI: 10.1111/jcap.12468
    OBJECTIVE: Adolescent sleep problems are a worldwide public health issue. The present study examines factors associated with worry-related sleep problems among school-going adolescents. The country of interest is Timor-Leste, a low-income country, where studies pertaining to adolescent sleep problems are lacking.

    DESIGN AND MEASURES: Data were analysed from the Global School-Based Student Health Survey Timor-Leste (n = 3455). An ordered probit model was used to assess the effects of demographic, lifestyle, social, and psychological factors on different levels of worry-related sleep problems (i.e., no, mild and severe sleep problems).

    RESULTS: School-going adolescents were more likely to face mild or severe worry-related sleep problems if they were older, passive smokers, alcohol drinkers and moderately active. School-going adolescents who sometimes or always went hungry were more likely to experience worry-related sleep problems than those who did not. Involvement in physical fights, being bullied, and loneliness were positively associated with the probability of having modest or severe worry-related sleep problems.

    CONCLUSION: Age, exposure to second-hand smoke, alcohol consumption, physical activity, going hungry, physical fights, being bullied and loneliness are the important determining factors of adolescent worry-related sleep problems. Policymakers should pay special attention to these factors when formulating intervention measures.

  4. Siti-Futri FF, Rosilawati R, Wan KL, Cheong YL, Nazni WA, Lee HL
    Trop Biomed, 2020 Mar 01;37(1):201-209.
    PMID: 33612731
    The continued absence of an effective and safe tetravalent dengue vaccine and the lack of specific anti-viral treatment have made mosquito vector control using chemical insecticides as the mainstream for dengue prevention and control. However, the long-term use of chemical insecticides may induce resistance. Hence detection of insecticide resistance in dengue vectors is crucially important in ensuring the insecticide-based intervention in dengue control program is still effective and reliable. In this study, the susceptibility status of Aedes aegypti from five selected dengue hotspots in Klang Valley, Malaysia against pyrethroids was determined by employing the World Health Organization (WHO) protocol of adult bioassay. Four types of pyrethroids were tested against adult female Aedes aegypti to determine the knockdown rate, post 24-h adult mortality and resistance ratio. All field-collected Aedes aegypti strains were resistant to the four pyrethroids tested, except for the Taman Sungai Jelok (TSJ) strain. Permethrin exhibited the lowest knockdown rate against Aedes aegypti, followed by deltamethrin, cyfluthrin and lambda-cyhalothrin. This present study indicated the widespread of pyrethroid resistance in Aedes aegypti in Klang Valley, indicating the needs of implementing alternative measures in vector control program. The data in this study can be utilised as an input for insecticide resistance management of Aedes aegypti in Malaysia.
  5. Cheah YK, Zainuddin NH, Kee CC, Lim KH, Omar MA, Cheong YL
    Clin Child Psychol Psychiatry, 2023 Oct;28(4):1341-1357.
    PMID: 36428238 DOI: 10.1177/13591045221142497
    Sexual behaviour and mental health among adolescents are major public health issues. This study examines how lifestyles affect sexual behaviour among school-going adolescents in Malaysia, and the potential mediational role of mental health. It is the first to our knowledge to explore the mediating effect of mental health on sexual behaviour with a focus on a fast-growing developing country. Data were obtained from the National Health and Morbidity Survey 2017 (n = 27,497). Structural equation modelling was utilized to examine depression and anxiety as mediators of the relationships between sexual behaviour and smoking, alcohol drinking and illicit drug use, controlling for sociodemographic factors. Results showed that adolescents who smoked, consumed alcohol, used illicit drugs, and had depression and anxiety were more likely to engage in sexual behaviour than others. Depression and anxiety partially mediated the relationships between sexual behaviour and smoking, and illicit drug use. The association between alcohol drinking and sexual behaviour was fully mediated by depression and anxiety. In conclusion, lifestyles may affect sexual behaviour through mediation of mental health. Therefore, policymakers should take mental health factors into consideration when designing adolescent sexual behaviour preventative interventions.
  6. Lim KH, Cheong YL, Sulaiman N, Yah XY, Mahadzir ME, Lim JH, et al.
    Tob Induc Dis, 2022;20:105.
    PMID: 36474605 DOI: 10.18332/tid/155376
    INTRODUCTION: Measuring the level of nicotine addiction among smokers is an integral part of enhancing smoking cessation as nicotine dependence is one of the barriers to smoking cessation. In this study, we compared the level of agreement between FTND and HSI in detecting high nicotine dependence among daily smokers.

    METHODS: We collected data from participants of a public smoking cessation clinic in Selangor. A trained pharmacist conducted face-to-face interviews with 152 daily smokers using a structured validated questionnaire. Respondents were classified as having high nicotine dependence using both the HSI (score ≥4) and the FTND (score ≥6), and concordance between the two measures, kappa statistics and sensitivity, specificity of the HSI were then determined with the FTND classification as the reference standard.

    RESULTS: The HSI had a substantial agreement with the FTND (Cohen's kappa=0.72) in measuring high levels of nicotine addiction, with good sensitivity (83.3%) and specificity (89.4%).

    CONCLUSIONS: The findings suggest that the HSI can be used instead of the FTND in clinical-based investigations to screen for high nicotine dependence among daily smokers in the clinical setting.

  7. Lim KH, Yun YX, Cheong YL, Sulaiman N, Mahadzir ME, Lim JH, et al.
    Tob Induc Dis, 2023;21:36.
    PMID: 36909814 DOI: 10.18332/tid/159624
    INTRODUCTION: The Fagerström test for nicotine dependence (FTND) was forward-backwards translated into the Malay language (FTND-M) and administered to 152 daily smokers who sought treatment for smoking cessation in government health clinics in Selangor state, Malaysia.

    METHODS: Using confirmatory factor analysis (CFA), four measurement models with the best relative fit were compared, one uni-dimensional model, and three different two-domain (morning and daytime smoking) models.

    RESULTS: The findings indicate that the best model of the FTND-M was a two-domain model, wherein domain one represented morning smoking (time to first cigarette of the day, smoking more in the morning, and which cigarette would you hate to give up) and domain two represented daytime smoking (cigarettes per day, difficulty refraining from smoking, and smoking when ill) which showed good model fit [χ2/df=1.932, goodness of fit (GFI) of 0.967, comparative fix index (CFI) of 0.945, incremental fit index (IFI) of 0.98, Tucker-Lewis index (TLI) of 0.95 and a real mean square end of approximation (RMSEA) of 0.079, and substantial reliability >0.70].

    CONCLUSIONS: This study indicates that the FTND-M can be used to assess these two dimensions of nicotine addiction among daily smokers in a clinical setting.

  8. Lim KH, Ghazali SM, Lim HL, Cheong YL, Kee CC, Heng PP, et al.
    Tob Induc Dis, 2021;19:50.
    PMID: 34177412 DOI: 10.18332/tid/136029
    INTRODUCTION: Secondhand (SHS) smoke exposure has caused various health problems. Therefore, continuous monitoring of SHS exposure is important to determine the efficacy of various anti-tobacco measure implemented. The study aims to compare the prevalence and factor(s) associated with SHS exposure among secondary school-going adolescents in Malaysia during 2012 and 2017.

    METHODS: We derived data from the Global School Health Survey (GSHS) 2012 and GSHS 2017, which was carried out in Malaysia using multistage sampling to select representative samples of secondary school-going adolescents. Both surveys used similar questionnaires to measure SHS exposure. Descriptive and multivariate logistic regression was used to determine the prevalence and factors associated with SHS exposure.

    RESULTS: Approximately four in ten respondents were exposed to SHS in the past week in both surveys (41.5% in GSHS 2012 and 42.0% in GSHS 2017, respectively). Both surveys revealed a significantly higher SHS exposure among respondents who smoked than among non-smokers and higher among males compared to females. The likelihood of SHS exposure in both surveys was also similar, with a higher likelihood of SHS exposure among smoking adolescents and non-smoking adolescents who had at least one smoking parent/guardian, regardless of their own smoking status. Male adolescents had a higher risk of SHS exposure compared to their female counterparts. Meanwhile, SHS risk also increased with age, regardless of smoking status.

    CONCLUSIONS: Our findings suggested that there were no changes in the prevalence of SHS exposure and recorded only a slight change in the factors associated with exposure to SHS among school-going adolescents in Malaysia between the years 2012 and 2017. A more pro-active, extensive and comprehensive programme should be implemented to address the problem of SHS exposure. Parents should be advised to stop smoking or abstain from smoking in the presence of their children, and smoking cessation interventions are necessary for smoking adolescents and their parents.

  9. Lim KH, Cheong YL, Lim HL, Cheong KC, Hashim MHM, Marine AA, et al.
    Tob Induc Dis, 2024;22.
    PMID: 38268983 DOI: 10.18332/tid/176164
    INTRODUCTION: Perception is an essential factor influencing smoking among adolescents. Thus, a valid tool for measuring perception is a requisite in smoking studies. This study further establishes the validity and reliability of a Malay language version of the Perception Towards Smoking Questionnaire (BM-PTSQ) for assessing the perception of smoking among secondary school-going adolescents in Malaysia.

    METHODS: We administered the BM-PTSQ to 669 secondary school students selected through multistage sampling; 60% of respondents were male (n=398), and 69.9% (n=463) were from rural areas. Respondents were aged 13-16 years, 36.4% (n=241) were 13 years, 40.0% (n=265) were 14 years, and 23.6% (n=156) were 16 years old. We used parallel and exploratory factor analysis (EFA) to determine the domains of the questionnaire. In addition, we also employed EFA, confirmatory factor analyses (CFA), and Cronbach's alpha to evaluate the construct validity and reliability of the BM-PTSQ.

    RESULTS: EFA and parallel analysis identified two domains in the BM-PTSQ that accounted for 62.9% of the observed variance, and CFA confirmed the two-domain structure. The two domains' internal consistency scores ranged from 0.702 to 0.80, which suggested adequate reliability.

    CONCLUSIONS: The BM-PTSQ has acceptable psychometric validity and is appropriate for assessing smoking perception and intention among Malaysian secondary school-aged youth. Researchers should further evaluate this tool's applicability in a more sociodemographically diverse population.

  10. Lim KH, Ghazali SM, Lim HL, Kee CC, Cheah YK, Singh BSGP, et al.
    Tob Induc Dis, 2020;18:80.
    PMID: 33013276 DOI: 10.18332/tid/127231
    INTRODUCTION: Periodic surveys on tobacco use patterns and other aspects of tobacco use among school-going adolescents in Malaysia provide information on the effectiveness of anti-smoking measures implemented. However, such information is limited in Malaysia. We investigated the prevalence of smoking and other related aspects among middle-secondary school students in Malaysia from the years 2003-2016 to fill this gap.

    METHODS: We analyzed data from the Global Youth Tobacco Survey (GYTS) 2003, GYTS 2009, and the Tobacco and Electronic Cigarette Survey among Malaysia Adolescents (TECMA) 2016. The surveys employed multistage sampling to select representative samples of adolescents attending secondary school in Malaysia. Data were collected using a pre-validated self-administered anonymous questionnaire adopted from the GYTS.

    RESULTS: Between 2003 and 2016, major changes occurred in which there were reductions in the prevalence of ever smoking, current smoking, and susceptibility to smoking. Reductions were also observed in exposure to SHS in public places and in the home. The proportion of school-going adolescents who support a ban on smoking in public places increased between 2013 to 2016, and there was a significant reduction in the proportion of respondents that were offered 'free' cigarettes by tobacco company representatives. However, there was no difference in the proportion of adolescents who initiated smoking before the age of 10 years and current smokers seeking advice to quit smoking across the time period.

    CONCLUSIONS: Our study indicates that the smoking policies and measures have been effective in reducing smoking prevalence, secondhand smoke exposure, and access to cigarettes, among school-going adolescents in Malaysia. However, measures to reduce smoking initiation and increase smoking cessation need to be strengthened to reduce the burden of smoking-related diseases in Malaysia in the long-term.

  11. Cheong YL, Rosilawati R, Mohd-Khairuddin CI, Siti-Futri FF, Nur-Ayuni N, Lim KH, et al.
    Trop Biomed, 2021 Jun 01;38(2):171-179.
    PMID: 34172707 DOI: 10.47665/tb.38.2.054
    Diseases such as malaria, dengue, Zika and chikungunya remain endemic in many countries. Setting and deploying traps to capture the host/vector species are fundamental to understand their density and distributions. Human effort to manage the trap data accurately and timely is an exhaustive endeavour when the study area expands and period prolongs. One stop mobile app to manage and monitor the process of targeted species trapping, from field to laboratory level is still scarce. Toward this end, we developed a new mobile app named "PesTrapp" to acquire the vector density index based on the mobile updates of ovitraps and species information in field and laboratory. This study aimed to highlight the mobile app's development and design, elucidate the practical user experiences of using the app and evaluate the preliminary user assessment of the mobile app. The mobile app was developed using mobile framework and database. User evaluation of the mobile app was based on the adjusted Mobile App Rating Scale and Standardized User Experience Percentile Rank Questionnaire. The process flows of system design and detailed screen layouts were described. The user experiences with and without the app in a project to study Aedes surveillance in six study sites in Selangor, Malaysia were elucidated. The overall mean user evaluation score of the mobile app was 4.0 out of 5 (SD=0.6), reflects its acceptability of the users. The PesTrapp, a one-stop solution, is anticipated to improve the entomological surveillance work processes. This new mobile app can contribute as a tool in the vector control countermeasure strategies.
  12. Gill BS, Jayaraj VJ, Singh S, Mohd Ghazali S, Cheong YL, Md Iderus NH, et al.
    Int J Environ Res Public Health, 2020 Jul 30;17(15).
    PMID: 32751669 DOI: 10.3390/ijerph17155509
    Malaysia is currently facing an outbreak of COVID-19. We aim to present the first study in Malaysia to report the reproduction numbers and develop a mathematical model forecasting COVID-19 transmission by including isolation, quarantine, and movement control measures. We utilized a susceptible, exposed, infectious, and recovered (SEIR) model by incorporating isolation, quarantine, and movement control order (MCO) taken in Malaysia. The simulations were fitted into the Malaysian COVID-19 active case numbers, allowing approximation of parameters consisting of probability of transmission per contact (β), average number of contacts per day per case (ζ), and proportion of close-contact traced per day (q). The effective reproduction number (Rt) was also determined through this model. Our model calibration estimated that (β), (ζ), and (q) were 0.052, 25 persons, and 0.23, respectively. The (Rt) was estimated to be 1.68. MCO measures reduce the peak number of active COVID-19 cases by 99.1% and reduce (ζ) from 25 (pre-MCO) to 7 (during MCO). The flattening of the epidemic curve was also observed with the implementation of these control measures. We conclude that isolation, quarantine, and MCO measures are essential to break the transmission of COVID-19 in Malaysia.
  13. Rasli R, Cheong YL, Che Ibrahim MK, Farahininajua Fikri SF, Norzali RN, Nazarudin NA, et al.
    PLoS Negl Trop Dis, 2021 Mar;15(3):e0009205.
    PMID: 33755661 DOI: 10.1371/journal.pntd.0009205
    BACKGROUND: In Malaysia, dengue remains a top priority disease and usage of insecticides is the main method for dengue vector control. Limited baseline insecticide resistance data in dengue hotspots has prompted us to conduct this study. The present study reports the use of a map on the insecticide susceptibility status of Aedes aegypti and Aedes albopictus to provide a quick visualization and overview of the distribution of insecticide resistance.

    METHOD AND RESULTS: The insecticide resistance status of Aedes populations collected from 24 dengue hotspot areas from the period of December 2018 until June 2019 was proactively monitored using the World Health Organization standard protocol for adult and larval susceptibility testing was conducted, together with elucidation of the mechanisms involved in observed resistance. For resistance monitoring, susceptibility to three adulticides (permethrin, deltamethrin, and malathion) was tested, as well as susceptibility to the larvicide, temephos. Data showed significant resistance to both deltamethrin and permethrin (pyrethroid insecticides), and to malathion (organophosphate insecticide) in all sampled Aedes aegypti populations, while variable resistance patterns were found in the sampled Aedes albopictus populations. Temephos resistance was observed when larvae were tested using the diagnostic dosage of 0.012mg/L but not at the operational dosage of 1mg/L for both species.

    CONCLUSION: The present study highlights evidence of a potential threat to the effectiveness of insecticides currently used in dengue vector control, and the urgent requirement for insecticide resistance management to be integrated into the National Dengue Control Program.

  14. Nazni WA, Hoffmann AA, NoorAfizah A, Cheong YL, Mancini MV, Golding N, et al.
    Curr Biol, 2019 Dec 16;29(24):4241-4248.e5.
    PMID: 31761702 DOI: 10.1016/j.cub.2019.11.007
    Dengue has enormous health impacts globally. A novel approach to decrease dengue incidence involves the introduction of Wolbachia endosymbionts that block dengue virus transmission into populations of the primary vector mosquito, Aedes aegypti. The wMel Wolbachia strain has previously been trialed in open releases of Ae. aegypti; however, the wAlbB strain has been shown to maintain higher density than wMel at high larval rearing temperatures. Releases of Ae. aegypti mosquitoes carrying wAlbB were carried out in 6 diverse sites in greater Kuala Lumpur, Malaysia, with high endemic dengue transmission. The strain was successfully established and maintained at very high population frequency at some sites or persisted with additional releases following fluctuations at other sites. Based on passive case monitoring, reduced human dengue incidence was observed in the release sites when compared to control sites. The wAlbB strain of Wolbachia provides a promising option as a tool for dengue control, particularly in very hot climates.
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