[PCR testing for Bordetella pertussis in household contacts as a diagnostic tool for atypical whooping cough in unvaccinated young infants].

Introduction: False-negative findings of polymerase chain reaction (PCR) for genuine pertussis as well as the numerous atypical forms of whooping cough make it difficult to diagnose this disease in young babies.

Methods: For two years, real-time PCR was performed to test for Bordetella pertussis in 86 infants younger than 6 months hospitalized for apnea or paroxysmal and/or vomiting cough and in 205 of their household contacts, whether or not they coughed.

Results: Group 1 included 30 infants for whom PCR detected B. pertussis (25 of whom were also RSV+). PCR was also positive for at least one household contact in 25/30 families. This group included 16 babies with apnea and 12 who developed a whooping cough during follow-up. Group 2 comprised 12 infants whose PCR was negative while at least one household contact had positive results. Five of these infants had severe apnea and 6 developed a whooping cough. Group 3 included 44 infants (28 RSV +) for whom PCR was negative in the index case and in the household contacts: none developed a whooping cough during follow-up. Only 3 of the 54 positive household contacts had a paroxysmal cough or a typical whooping cough and 12 had no cough at all.

Conclusion: Positive PCR in a household contact, symptomatic or not, is helpful for the diagnosis of atypical whooping cough in young infants.