Pertussis notifications in Australia, 1991 to 1997

Although pertussis is a vaccine-preventable disease, it has been epidemic in Australia since 1993 and recently claimed the lives of four children under three months of age. We reviewed national notifications of pertussis from 1991 to 1997 and found notification rates ranged from 2.0 per 100,000 population in 1991 to a peak of 30.5 per 100,000 population in 1994 despite pertussis vaccination coverage approaching 90% for the three-dose primary course. We found that notification rates were highest in infants (< 1 year of age) and school aged children (5-14 years of age). Although there was a resurgence of pertussis in 1996, age-specific notification rates decreased for children aged 1-7 years and it appears that the diphtheria-tetanus-pertussis (DTP) booster introduced as a fifth dose at 4-5 years may be having an effect. We raise the possibility that the current whole cell pertussis vaccine may be providing only short-term immunity and that our results may reflect low or inadequate vaccine coverage among both the population at large and the individual cases. We identify gaps in the national surveillance system which require attention including under-reporting and the need for information on vaccination status of notified cases; method of diagnosis; and date of birth or age in months to identify the proportion of infants in the highest risk group, that is under six months of age.