title: Relationship between age and prevalence of hepatitis B infection in first-year university students in Hong Kong.
abstract: OBJECTIVE
  To determine the effect of age on the prevalence of hepatitis B virus (HBV) infection during a routine screening programme of first-year students enrolled in Health Sciences Studies at the Chinese University of Hong Kong from 2001 to 2009.
  
  
  METHODS
  In a retrospective cohort study, data on the hepatitis B surface antigen (HBsAg) status was retrieved from the University Health Service and analysed according to the age of the student at testing and year of birth.
  
  
  RESULTS
  Of the 2,688 students enrolled in the study group, 79 (2.9 %) tested positive for HBsAg. The prevalence increased significantly from 0.9, 2.3, 4.3 to 5.5 % for those tested at age ≤ 18, 19, 20 and ≥ 21 years, respectively (p < 0.001). On logistic regression analysis, taking age ≤ 18 years and year of birth before 1983 (before the availability of HBV vaccination) as the reference group, HBV infection increased progressively with age, with an adjusted odds ratio of 3.36 [95 % confidence interval (CI) 1.01-11.23], 6.04 (95 % CI 1.74-20.98) and 11.61 (95 % CI 3.20-42.13) for age 19, 20 and ≥ 21 years, respectively. There was no significant change in the odds ratio after adjustment for the year of birth before and after introduction of the vaccination programme.
  
  
  CONCLUSIONS
  Among the university students enrolled in our study, the overall prevalence of HBV infection before and after the introduction of HBV vaccination was lower than the 10 % found in the general population. There was, however, a significant progressive increase with age at testing from ≤ 18 to ≥ 21 years, suggesting a previously overlooked contribution of horizontal transmission to the high prevalence of HBV infection found in our adult population.
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong, People's Republic of China.
authors.forename: S S H
authors.initials: SS
authors.lastname: Suen
authors.forename: T T
authors.initials: TT
authors.lastname: Lao
authors.forename: O K
authors.initials: OK
authors.lastname: Chan
authors.forename: T K
authors.initials: TK
authors.lastname: Lau
authors.forename: T Y
authors.initials: TY
authors.lastname: Leung
authors.forename: P K S
authors.initials: PK
authors.lastname: Chan
mesh_terms: D000293:Adolescent; D000367:Age Factors; D016001:Confidence Intervals; D005260:Female; D006509:Hepatitis B / Q000453:epidemiology* / Q000517:prevention & control; D006514:Hepatitis B Surface Antigens / Q000097:blood; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D017589:Immunization Programs; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D015995:Prevalence; D012189:Retrospective Studies; D013334:Students / Q000706:statistics & numerical data*; D014495:Universities; D055815:Young Adult
chemical_list: D006514:Hepatitis B Surface Antigens