Pertussis--going, going, but not gone: thirteen year trends in the incidence of pertussis in the Republic of Ireland and North Eastern Health Board.

Pertussis or whooping cough is caused by Bordetella pertussis. Complications of pertussis include pneumonia, seizures, encephalopathy and death. Diagnostic tests include pernasal swab culture, serology, direct immuno-fluorescent assay (DFA) and polymerase chain reaction (PCR). At present, the majority of cases are diagnosed clinically. DTaP immunisation uptake has considerably reduced disease incidence. We describe national and NEHB reported cases of pertussis over a 13 year period from 1988 to 2000 inclusive and we also describe in detail all pertussis admissions to Our Lady of Lourdes Hospital, Drogheda from 1998 to 2000 inclusive. From 1988 to 2000 inclusive, all pertussis cases notified nationally and in the NEHB region were tabulated and studied from data obtained from the Department of Public Health, NEHB and the NDSC, together with national and NEHB DTaP immunisation rates. All admissions to Our Lady of Lourdes Hospital, Drogheda with a diagnosis of pertussis from 1998 to 2000 inclusive were studied in detail by retrospective medical record review and the results were later analysed using the Epi-Info Version 6.0 statistical package. National notified pertussis cases had fallen from 1170 cases in 1988 to 150 cases in 2000. There was a striking rise in pertussis nationally in 1989 to 2217 cases and this directly related to the sharp fall in DTaP immunisation uptake at that time due to adverse publicity. Current 5-in-1 immunisation rates are between 80% to 85% nationally, and 88% for the NEHB region. NEHB pertussis notifications rose from 72 cases in 1988 to 328 in 1989 and this directly reflected the national trend; in 2000 there were only 13 notifications. In the NEHB region between 1998 and 2000 inclusive, there were only 26 notified cases of pertussis, 17 of which were admitted to hospital. Only 1/17 (6%) had a positive pernasal swab culture. There were no deaths. Pertussis is under-diagnosed and is still largely a clinical diagnosis. There has been an approximate ten-fold decrease in pertussis incidence rates over the 13 year study period both nationally and in the NEHB region. Current DTaP immunisation rates in the NEHB region of 88%, and of between 80% to 85% nationally are insufficient to confer 'herd immunity' and thus young infants will continue to be at risk.