Rapid diagnosis of pertussis in young infants: comparison of culture, PCR, and infant's and mother's serology

The contribution of maternal pertussis serology comparing prepartum serum to serum collected during the infant's disease to the diagnosis of pertussis in infants was evaluated for 28 pairs of young infants with pertussis syndrome and their mothers and was compared to those of culture and PCR. Infants had a nasopharyngeal aspiration tested by PCR, and acute and convalescent sera were collected during their disease. Mothers had a first acute serum collected concomitantly with the infant's acute serum, and both acute sera were compared to a prepartum serum. Sera were analyzed by immunoblotting for the detection of anti-pertussis toxin (PT) antibodies. Serological evidence of pertussis in infants was assessed as either an increase in anti-PT antibody levels between the mother's prepartum and acute sera or the presence of antibodies in the infant's acute serum and their absence in both the mother's acute and prepartum sera. Culture and PCR sensitivity were 43 and 89%, respectively. Most infants (18 of 24) had no pertussis antibody detectable in their acute sera, confirming a delayed immune response at this age. A comparison of infant's and mother's serology, using prepartum serum, rapidly confirmed the diagnosis in 57% of the cases. Although less sensitive than PCR, this serological method should be used for a rapid diagnosis of pertussis in young infants when culture and PCR are either not available or negative.