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![Text Box: SEROEPIDEMIOLOGY OF HAEMOPHILUS INFLUENZAE TYPE B [Hib] INFECTION IN SINGAPORE
Chan SH, Tan KL, Dong F, Khoo C, Poerschke G, Szymanski S, Dargan J
Faculty of Medicine National University of Singapore; MSD Singapore, MSD Asia Ltd., Merck & Co, Inc., PA, USA
Objective: To study polyribosylribitol phosphate antibody (anti-PRP) levels as a surrogate of Hib exposure/infection in Singaporean infants and children who are not vaccinated against Hib.
Methods: From April 1996 to December 1997, a serum sample was obtained from each of 1163 healthy children (birth to 16 years of age). Sera were tested at Merck Research Laboratories (USA) for anti-PRP using a Farr-type Radioimmunoassay.
Results: Ethnic groups: Chinese 77%, Malays 17%, Indians and others 6% reflecting the ethnic group proportions in the community.
Age Range N GMT in 米g/ml of anti-PRP 95% Confidence interval 米g/ml undetectable anti-PRP %
Cord blood 78 0.77 0.56 每1.05 15 [12/78]
2 每 6 months 25 0.17 0.10 每 0.25 44 [11/25]
2 每 18 months 122 0.2 0.14 每0.24 35 [43/122]
1.5 每 6 years 401 0.42 0.14 每 1.0 2 [78/401]
6 每 16 years 464 0.794 0.5 每 1.1 6 [29/464]
Conclusion: The observed anti-PRP pattern is similar to that described in Western countries prior to the introduction of Hib conjugate vaccines, but it does not explain the very low incidence of reported Hib disease (<5/100,000/year) in Singapore. Maternal antibody to Hib in infants fell fast, to very low levels between 2- 6 months and remained at low levels to 18 months of age, suggesting that many infants are susceptible to Hib infection. Development of anti-PRP at older ages implies that Hib is circulating. Natural exposure appears to begin from 1.5 years, rising fast after ~6 years, coinciding with school entry. This suggests that Hib exposure in children results in subclinical infections.](./2408_files/image001.gif)
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