Wednesday, October 27, 2010

Changing Seroprevalence of Hepatitis B Virus Markers of Adults in Singapore


Original Article

Changing Seroprevalence of Hepatitis B Virus Markers of Adults in Singapore

Wei Wei Hong,1MBBS, MPH, Li Wei Ang,1MSc(Statistics), Jeffery L Cutter,1MMed (PH), MSc (Epidemiology), FAMS, Lyn James,1MBBS, MMed
(PH), FAMS, Suok Kai Chew,2MSc(PH), MSc(Epidemiology), FAMS, Kee Tai Goh,3MSc (PH), MD, FAMS

1 Communicable Diseases Division, Ministry of Health, Singapore
2 Health Services Group, Ministry of Health, Singapore
3 Offi ce of the Director of Medical Services, Ministry of Health, Singapore
Address for Correspondence: Dr Hong Wei Wei, Communicable Diseases Division, Ministry of Health, Singapore.


Introduction: We presented the fi ndings from 2 seroprevalence studies conducted 6 years
apart, so as to determine changes in the hepatitis B surface antigen (HBsAg) positivity rate
and immunity to hepatitis B virus (HBV) among Singapore residents aged 18 to 69 years, and
to assess the impact of a 4-year catch-up hepatitis B immunisation programme for adolescents
and young adults launched in 2001.

Materials and Methods:
Two hepatitis B seroprevalence studies (HBSS) were conducted in 1999 and 2005 based on stored blood samples collected from
4698 participants aged 18 to 69 years during the national health survey (NHS) 1998 and from
3460 participants during the NHS 2004, respectively. Serology for HBsAg, hepatitis B e antigen
(HBeAg) and antibody to HBsAg (anti-HBs) were tested by enzyme immunoassay in HBSS 1999
and electrochemiluminescence in HBSS 2005.

The overall age-standardised prevalence
of HBsAg among Singapore residents aged 18 to 69 years decreased signifi cantly from 4.0%
in HBSS 1999 to 2.8% in HBSS 2005 (P = 0.002). The age-standardised prevalence of HBsAg
in males (4.9% in 1999) and Chinese (4.7% in 1999) both decreased signifi cantly to 2.7% and
2.8%, respectively in 2005. The overall age-standardised population immunity to HBV (anti-
HBs >10mIU/ml) increased from 39.7% in 1999 to 42.1% in 2005 (P = 0.019). In particular, the
age-specifi c prevalence of anti-HBs showed a signifi cant increase among those in the age group
of 18 to 29 years from 27.9% in 1999 to 41.7% in 2005 (P <0.001) and among those in the age
group of 30 to 39 years from 39.9% in 1999 to 44.7% in 2005 (P = 0.021).

There was an overall decline in the HBsAg positivity rate as well as an overall increase in population
immunity to HBV. Following the 4-year catch-up immunisation programme, there was a signifi -
cant increase in the immunity to HBV infection in the younger population aged 18 to 29 years.

Ann Acad Med 2010;39:591-8

In Singapore, epidemiological surveillance and research
on hepatitis B virus (HBV) infection were initiated when
acute viral hepatitis was made a notifi able disease under
the Infectious Diseases Act in 1976. Based on the fi ndings
of epidemiological investigations of reported cases and the
results of seroepidemiological studies, a national hepatitis
B prevention and control programme was formulated and
implemented.1 Immunisation against HBV infection forms
the cornerstone of the programme, alongside the other
activities which include surveillance, routine antenatal
screening and screening of voluntary blood donors for
HBV carriers, adoption of universal precautions and public

The hepatitis B immunisation programme, introduced in
mid-1983, was initially targeted at the high-risk groups such
as healthcare workers but later also included babies born to
HBV carrier mothers from 1 October 1985 onwards.2 From
1 September 1987, the childhood immunisation programme
was extended to include all newborns. The coverage rate
for infants who have completed the full course of 3 doses
before 1 year of age increased from 50% in 1988 to 91%
in 1994 and since 2005, at least 95% of children under 2
years of age have been immunised against hepatitis B.3
The herd immunity of the childhood population, based
on a seroprevalence survey conducted in 1998/1999,4 was
90% in children below 5 years of age and 77% in children
aged between 5 and 14 years of age and no cases of acute
hepatitis B has been reported in children below 15 years
of age since 1997.3 The prevalence of hepatitis B surface
antigen (HBs Ag) in Chinese children aged between 5 and
9 years was 5.7 % in 19725 and 3.4% in 19871 but none
of the primary school children 6 years of age was tested
positive in 1993.6

However, HBV infection remains an important public
health problem among the adult population in Singapore. A
recent study estimated that the annual costs of chronic HBV
infection and its complications such as chronic hepatitis,
liver cirrhosis and liver cancer amounted to US$279 million
and draws attention to the continuing fi nancial burden of
the disease in Singapore.7

In 1999, a hepatitis B seroprevalence study (HBSS 1999)
of the adult population aged 18 to 69 years was conducted
using stored blood sample from the national health survey
(NHS) 1998.8 A key fi nding from this study was that the
majority of the younger age group of 18 to 29 years old
had no immunity to HBV infection as indicated by a low
seroprevalence of antibody to HBsAg (anti-HBs) (27.9%)
in this age group. Based on these fi ndings, the School
Health Services of the Health Promotion Board (HPB)
implemented a 4-year hepatitis B catch-up immunisation
programme which was targeted at the student population
born before 1987 and who were likely to have missed the
national hepatitis B childhood immunisation programme.
During the same period, the HPB also embarked on a mass
media programme to increase public awareness on the risks
of HBV infection and the importance of immunisation
against hepatitis B. Education materials were distributed to
the students, parents and the public together with publicity
over the television, radio and newspapers.

The largely school-based voluntary catch-up immunisation
programme was launched in January 2001 for students in
secondary schools, junior colleges, centralised institutes,
institutes of technical education, polytechnics and
universities. In 2001/2002, fulltime national servicemen
were also offered hepatitis B screening and immunisation
at 35 Singapore Armed Forces medical centres. In 2004,
the programme was also extended to the students in 18
special schools.

At the end of the 4-year immunisation programme, a total
of 221,873 youths (students and national servicemen) had
participated, of whom 127,108 were tested seronegative
for various HBV markers. Among the seronegative youths,
108,576 (85.4%) completed at least one dose of hepatitis B
immunisation and 99,333 (78.1%) completed all the 3 doses.
We undertook another national seroepidemiological
survey on hepatitis B in 2005 (HBSS 2005) to assess
the changing seroprevalence of HBV markers in the
adult population in Singapore by comparing the fi ndings
with those of HBSS 1999. Special reference was made
on the impact of the catch-up hepatitis B immunisation

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