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Tuberculin Skin Test Reaction and Body Mass Index in Old Age Home Residents in Hong Kong

Authors

  • Moira Chan-Yeung MB,

    1. From the Divisions of *Respiratory MedicineGeriatrics, Department of Medicine, University of Hong Kong, Hong Kong, ChinaDepartment of Medicine and Therapeutics, Prince of Wales Hospital, Hong Kong, China§Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Hong Kong, ChinaTuberculosis and Chest Service, Public Health Services Branch, Centre for Health Protection, Department of Health, Hong Kong, China
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  • David L. K. Dai MBBS,

    1. From the Divisions of *Respiratory MedicineGeriatrics, Department of Medicine, University of Hong Kong, Hong Kong, ChinaDepartment of Medicine and Therapeutics, Prince of Wales Hospital, Hong Kong, China§Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Hong Kong, ChinaTuberculosis and Chest Service, Public Health Services Branch, Centre for Health Protection, Department of Health, Hong Kong, China
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  • Amy H. K. Cheung MSc,

    1. From the Divisions of *Respiratory MedicineGeriatrics, Department of Medicine, University of Hong Kong, Hong Kong, ChinaDepartment of Medicine and Therapeutics, Prince of Wales Hospital, Hong Kong, China§Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Hong Kong, ChinaTuberculosis and Chest Service, Public Health Services Branch, Centre for Health Protection, Department of Health, Hong Kong, China
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  • Felix H. W. Chan MBBCh, MSc,

    1. From the Divisions of *Respiratory MedicineGeriatrics, Department of Medicine, University of Hong Kong, Hong Kong, ChinaDepartment of Medicine and Therapeutics, Prince of Wales Hospital, Hong Kong, China§Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Hong Kong, ChinaTuberculosis and Chest Service, Public Health Services Branch, Centre for Health Protection, Department of Health, Hong Kong, China
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  • Kai-Man Kam MB,

    1. From the Divisions of *Respiratory MedicineGeriatrics, Department of Medicine, University of Hong Kong, Hong Kong, ChinaDepartment of Medicine and Therapeutics, Prince of Wales Hospital, Hong Kong, China§Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Hong Kong, ChinaTuberculosis and Chest Service, Public Health Services Branch, Centre for Health Protection, Department of Health, Hong Kong, China
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  • Cheuk-Ming Tam MB,

    1. From the Divisions of *Respiratory MedicineGeriatrics, Department of Medicine, University of Hong Kong, Hong Kong, ChinaDepartment of Medicine and Therapeutics, Prince of Wales Hospital, Hong Kong, China§Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Hong Kong, ChinaTuberculosis and Chest Service, Public Health Services Branch, Centre for Health Protection, Department of Health, Hong Kong, China
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  • Chi-Chiu Leung MB

    1. From the Divisions of *Respiratory MedicineGeriatrics, Department of Medicine, University of Hong Kong, Hong Kong, ChinaDepartment of Medicine and Therapeutics, Prince of Wales Hospital, Hong Kong, China§Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Hong Kong, ChinaTuberculosis and Chest Service, Public Health Services Branch, Centre for Health Protection, Department of Health, Hong Kong, China
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Address correspondence to Prof. Moira Chan-Yeung, Department of Medicine, 4/F, Professorial Block, Queen Mary Hospital, Hong Kong SAR, China. E-mail: mmwchan@hkucc.hku.hk

Abstract

OBJECTIVES: To study the relationship between body mass index (BMI) and tuberculin skin test (TST) reaction in predicting the development of active tuberculosis (TB).

DESIGN: A follow-up study.

SETTING: Old age homes.

PARTICIPANTS: Three thousand six hundred five residents who took part in a screening program for TB and had two-step TST using two units of the tuberculin PPD-RT23.

MEASUREMENTS: Rate of development of active TB in these residents over an average follow-up period of 2.5±1.25 years.

RESULTS: After one-step and two-step testing, 46.3% and 69.6% of residents, respectively, had positive TST reactions (≥10 mm). Thirty-four residents developed active TB (323 per 100,000 person-years) during follow-up. The only significant risk factors associated with development of active TB were positive TST according to one-step testing (adjusted odds ratio (OR)=2.91, 95% confidence interval (CI)=1.26–6.74) and a BMI less than 18.5 (adjusted OR=3.15, 95% CI=1.45–6.86). Residents with a BMI less than 18.5 and a negative TST also had greater risk of active TB than residents with a BMI greater than 18.5 and negative TST (adjusted OR=4.36, 95% CI=1.04–18.3), whereas those with a positive TST had the highest risk (adjusted OR=10.2, 95% CI=2.63–39.4). Two-step testing increased the sensitivity but reduced the specificity of TST in identifying active TB on follow-up.

CONCLUSION: In the elderly population, interpretation of TST should take into consideration the BMI of the individual. A positive TST according to one-step but not two-step testing was useful in predicting the development of active TB on follow-up.

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