Haemophilus influenzae type b infections in Hong Kong

A 5-year territory-wide retrospective survey of invasive Haemophilus influenzae type b (Hib) diseases in Hong Kong established that the annual incidence for children <5 years old was 2.7 per 100 000 [95% confidence interval (CI), 2.0 to 3.5]. However, the corresponding annual incidence in Vietnamese refugees in Hong Kong was 42.7 per 100 000 (95% CI 17.2 to 87.9), giving a relative risk of 18.5 (95% CI 8.3 to 41.0). The nasopharyngeal carriage rate of Hib was zero in 621 healthy Chinese children and 1.3% (95% CI 0.04 to 2.63%) in 300 healthy Vietnamese refugees 2 months to 5 years old in Hong Kong. The corresponding carriage rate of nontypable H. influenzae was 5.8% (95% CI 1.4 to 7.6%) in Chinese and 65.4% (95% CI 58.9 to 69.8) in Vietnamese. In a larger study of 1812 healthy Chinese children between 6 months and 5 years of age investigated by throat swabs, again no Hib was isolated but 141 children (7.8%) were found to be carriers of non-type b H. influenzae. In a study of 596 healthy Chinese children and adults, 25% had the protective level of anti-Hib antibody of >0.15 mu g/ml by 1 year and 90% had reached >0.15 mu g/ml by 6 years of age. There was some evidence that these "natural" antibodies against Hib in Hong Kong Chinese were cross-reacting antibodies against antigens on other encapsulated bacteria.