title: Seasonal pattern of tuberculosis in Hong Kong.
abstract: BACKGROUND
  Summer predominance of tuberculosis (TB) was reported previously in temperate regions. No consistent data were available for lower latitudes.
  
  
  METHODS
  The monthly TB notification data in Hong Kong from 1991 to 2002 were examined for seasonal fluctuation. A seasonal model was then developed after standardization by period, sex, age, history of TB, form of disease, and bacteriological status.
  
  
  RESULTS
  The raw monthly counts showed remarkably consistent seasonal fluctuation across different periods, sexes, and age groups. A sine model was fitted for 82 104 notifications (adjusted R(2) = 0.373, P < 0.001). A summer peak was observed with seasonal fluctuation of 18.4% (P < 0.001), which was substantially higher than that reported previously for temperate regions. The amplitudes of fluctuation were 35.0, 15.0, 19.0, and 20.2% for those aged < or =14, 15-34, 35-64, and >/=65 years, respectively (all P < 0.001). No gender difference was noted (18.2% vs 19.0%, P = 0.790). Seasonal pattern was detected among new cases (18.6%, P < 0.001), but not retreatment cases (5.2%, P = 0.333). Culture-positive cases showed greater fluctuation than culture-negative cases (29.4% vs 6.4%, P < 0.001). No significant difference was found between pulmonary and extrapulmonary cases (16.8% vs 21.6%, P = 0.356). TB cases notified in summer were more likely to be smear-positive [odds ratio (OR) 1.100, 95% confidence interval (CI) 1.045-1.158, P < 0.001] and culture-positive (OR 1.175, 95% CI 1.121-1.232, P < 0.001) than those notified in winter, even after stratification by other key variables.
  
  
  CONCLUSIONS
  A consistent seasonal pattern was found, with variable amplitudes of fluctuation in different subgroups and differing disease characteristics in different seasons. These observations are suggestive of the presence of a seasonal disease-modifying factor.
authors.affiliation: Tuberculosis and Chest Service, Department of Health, 8 Chaiwan Road 4/F, Shaukiwan, Hong Kong, China. cc_leung@dh.gov.hk
authors.forename: Chi Chiu
authors.initials: CC
authors.lastname: Leung
authors.forename: Wing Wai
authors.initials: WW
authors.lastname: Yew
authors.forename: Thomas Yan Keung
authors.initials: TY
authors.lastname: Chan
authors.forename: Cheuk Ming
authors.initials: CM
authors.lastname: Tam
authors.forename: Chiu Yeung
authors.initials: CY
authors.lastname: Chan
authors.forename: Chi Kuen
authors.initials: CK
authors.lastname: Chan
authors.forename: Nelson
authors.initials: N
authors.lastname: Tang
authors.forename: Kwok Chiu
authors.initials: KC
authors.lastname: Chang
authors.forename: Wing Sze
authors.initials: WS
authors.lastname: Law
mesh_terms: D017677:Age Distribution; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008297:Male; D015233:Models, Statistical; D012621:Seasons; D014376:Tuberculosis / Q000453:epidemiology*