INTRODUCTIONThe world's first rotavirus vaccine, Rotashield or RRV-TV, was registered in the US in 1998, but withdrawn within a year because of an observed association with intussusception (IS). Surveillance for IS has consequently become important in safety monitoring of new-generation rotavirus vaccines during development. Post-marketing surveillance is also important, and requires the availability of local baseline epidemiology data on IS.

MATERIALS AND METHODSAn eight-year study of IS in children under 2 years of age in Singapore was performed by retrospective review of admissions to KK Women's and Children's Hospital, the main paediatric hospital, from 1997 to 2001, followed by prospective surveillance of all hospitals from 2001 to 2004, using the case definition of the Brighton Collaboration Intussusception Working Group.

RESULTSThe average IS incidence was 60 per 100,000 in under-ones, and 32 per 100,000 in under-twos, with a downward trend between 1999 and 2004. Ninety-two per cent of subjects were aged below one year, with 51% aged 6 months to 11 months. The mean age at which IS occurred increased from 6.4 months to 12.5 months over the study period. The male-to-female ratio was 1.3:1. No trend in IS numbers was observed over different months of the year.

CONCLUSIONIS in Singapore shows no seasonality, but has demonstrated a trend of decreasing incidence in recent years. While highest in the first year of life, the risk of IS is increasing in the second year of life. Males have a slightly higher risk.

Child, Preschool ; Female ; Humans ; Immunization Programs ; Incidence ; Infant ; Infant, Newborn ; Intussusception ; chemically induced ; epidemiology ; Male ; Prospective Studies ; Retrospective Studies ; Risk Assessment ; Risk Factors ; Rotavirus ; immunology ; Rotavirus Infections ; prevention & control ; Rotavirus Vaccines ; adverse effects ; Singapore ; epidemiology ; Vaccination ; adverse effects

INTRODUCTIONUnderstanding baseline epidemiology of intussusception (IS) in different geographical settings is important for the safety assessment of rotavirus vaccines. This paper presents IS surveillance data from Singapore between 1997 and 2007, including the period between November 2005 and December 2007 when rotavirus vaccines (primarily Rotarix) were available to newborns in Singapore.

MATERIALS AND METHODSCase ascertainment, collection, analyses and presentation of IS data was done as per recommendations of the Brighton Collaboration Working Group. For estimating the IS incidence rate in infants, live births for the years of the study were used as denominators, while for incidence in children age <2 years, the expected numbers of infant deaths occurring between 1 and 2 years of age was deducted from the combined live births for the 2 years, to obtain the denominator.

RESULTSThe incidence of IS among children aged <1 year throughout this 10-year period was higher than the incidence of IS in children between 1 and 2 years of age. In 2005, 2006 and 2007, the incidence of IS per 100,000 was 39.9, 26.4 and 35.6 in children aged <1 year and 26.2, 23.8 and 28.7 in children <2 years.

CONCLUSIONThis IS surveillance study provides reassuring preliminary evidence that there is no increase in the incidence of IS in Singapore after the introduction of rotavirus vaccines (including Rotarix) in Singapore.

Adolescent ; Child ; Child, Preschool ; Female ; Humans ; Incidence ; Infant ; Infant, Newborn ; Intussusception ; epidemiology ; prevention & control ; virology ; Male ; Population Surveillance ; Risk Assessment ; Rotavirus Vaccines ; Singapore ; epidemiology ; Time Factors