INVASIVE HAEMOPHILUS-INFLUENZAE TYPE-B DISEASE IN THE OXFORD REGION (1985-91)

For a seven year period (1985-91) clinical and epidemiological data we re prospectively collected on children aged <10 years with microbiolog ically confirmed invasive Haemophilus influenzae type b infection in t he Oxford region to study the epidemiology of the disease and determin e the potential impact of early primary immunisation in infants. Compu ter records of primary immunisations given to these cases were retrosp ectively analysed and, where necessary, hospital and general practitio ner records were searched to determine the immunisation history. Over the seven year period, 416 cases of invasive H influenzae type b disea se were reported. Widescale immunisation against H influenzae type b b egan in 1991 as part of a regional trial. The estimated annual inciden ce for invasive disease between 1985 and 1990 was 35.5 cases per 100 0 00 children aged less than 5 years; for H influenzae type b meningitis it was 25.1 per 100 000 children aged less than 5 years. The cumulati ve risks for invasive disease and meningitis by the fifth birthday wer e one in 560 and one in 800 respectively. The majority of disease (71% ) occurred in children less than 2 years of age with the peak monthly incidences at 6 and 7 months of age. The overall mortality was 4.3% an d 50% of these deaths occurred suddenly. Most (91%) of the children ha d received at least one primary immunisation against diphtheria, tetan us, and pertussis before H influenzae type b infection and there was o nly one case of parental refusal of immunisation. None had received H influenzae type b immunisation. Given a vaccine uptake of 90% by 5 mon ths of age it is estimated that at least 82% of the H influenzae type b infections could have been prevented. Extrapolated nationally, 1150 cases of infection and 50 deaths could be prevented each year by routi ne primary immunisation.