Routine use of gene amplification for pertussis diagnosis in children

The resurgence of whooping cough observed in France convinced us to develop a specific PCR assay to detect B. pertussis in nasopharyngeal secretions in parallel of the culture. The aim of our study was to show the value of the PCR in routine diagnosis. From November 1996 to August 2000, in two hospitals located in the Yvelines (France), the children consulting for a cough compatible with the diagnosis of whooping cough were included in this study. A questionnaire including clinical, biological and radiological items was completed for each one of these patients. A culture of Bordetella and a detection by PCR of B. pertussis were carried out on each nasopharyngeal aspirate. The diagnosis of whooping cough was retained if the detection was positive in PCR and/or culture. Among the 215 investigated children with suspected cases of whooping cough, the diagnosis was positive for 45 (20.9%), of which 39 were less than one year old (median: three months). Sixteen (35.5,%) were positive at the same time for both the PCR and the culture, 26 (57.8%) for only PCR and three (6.7%) for only culture. The PCR was positive in 93.3% of the cases. The results were obtained with an average time of 48 hours. The culture was positive in 61.2% of the cases with an average time of six days. The monthly distribution of the cases of whooping cough was very inhomogeneous and of epidemic appearance. The majority of the cases was located between two periods: 42% between November 1996 and September 1997 and 40% between November 1999 and August 2000. Among the infected children, 15 were less than two months old and were not yet vaccinated; among the 24 others infants, a delay in the vaccine calendar was noted in 50% of the cases. Four children between six and 14 years old were correctly vaccinated. The evolution was favourable in all the children. The PCR due to its sensitivity, its specificity and its rapidity offers to the clinician a powerful tool for the diagnosis of whooping cough. Nevertheless, the culture must be associated with the PCR, in order to follow the epidemiology and the sensitivity to antibiotics of B. pertussis.