MATHEMATICAL-MODELS OF HAEMOPHILUS-INFLUENZAE TYPE-B

A review of empirical studies and the development of a simple theoreti cal framework are used to explore the relationship between Haemophilus influenzae type b (Hib) carriage and disease within populations. The models emphasize the distinction between asymptomatic and symptomatic infection. Maximum likelihood methods are used to estimate parameter v alues of the models and to evaluate whether models of infection and di sease are satisfactory. The low incidence of carriage suggests that pe rsistence of infection is only compatible with the absence of acquired immunity to asymptomatic infection. The slight decline in carriage ra tes amongst adults is compatible with acquired immunity, but could be a consequence of reduced contacts. The low rate of disease observed in adulthood cannot be explained if protection from disease is a product of previous detectable exposure to Hib alone. We estimate an R-0 of 3 .3 for Hib in developed countries, which suggests that current immuniz ation programmes may eliminate the infection. Analysis of the disease data set suggests the absence of maternal immunity and increased susce ptibility to disease in the oldest age classes.