Age-period-cohort analysis of tuberculosis notifications in Hong Kong from 1961 to 2005

Peng Wu ¹, Benjamin J Cowling ^1*, C Mary Schooling ¹, Irene OL Wong ¹, Janice M Johnston ¹, Chi-Chiu Leung ², Cheuk-Ming Tam ² and Gabriel M Leung ¹

¹ The University of Hong Kong, Hong Kong
² Tuberculosis and Chest Service, Hong Kong

^* To whom correspondence should be addressed. E-mail: bcowling{at}hku.hk.

Accepted 9 October 2007

Abstract

Background: Hong Kong, despite its wealth, excellent vital indices and robust health care infrastructure has a relatively high incidence of tuberculosis (TB) (85.4 per 100,000). Hong Kong residents have also experienced a very rapid and recent epidemiologic transition; the population largely originated from migration by southern Chinese in the mid 20th century. Given, the potentially long latency period of TB infection, we investigated to what extent TB incidence rates reflected the population history and the impact of public health interventions.

Methods: We used an age-period-cohort model to decompose the Hong Kong TB notification rates from 1961 to 2005 into the effects of age, calendar period and birth cohort.

Results: Analysis by age showed a consistent pattern across all the cohorts by year of birth, with a peak in relative risk of TB at 20-24 years of age. Analysis by year of birth showed an increase in relative risk of TB from 1880 to 1900, stable risk until 1910 and then a linear rate of decline from 1910, with an inflection point at 1990 for a steeper rate of decline, while period effects yielded only one inflection during the calendar years 1971-75.

Conclusions: Economic development, social change and DOTS have contributed to TB control in Hong Kong. The linear cohort effect until 1990 suggests that a relatively high, but slowly falling, incidence of TB in Hong Kong will continue into the next few decades.

Keywords: epidemiology, tuberculosis

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