Detection of Bordetella pertussis by polymerase chain reaction and culture in the nasopharynx of erythromycin-treated infants with pertussis.

Background. Pertussis is a highly contagious respiratory disease and the most serious effects occur in young infants. Recently it has been shown that rapid and highly specific PCR can be a useful diagnostic tool for detection of pertussis infection. To our knowledge there are no previous studies concerning the disappearance of Bordetella pertussis DNA from the nasopharynx during antimicrobial treatment. Methods. We studied prospectively how rapidly live B. pertussis organisms and DNA of these bacteria disappear from the nasopharynx during erythromycin therapy in unvaccinated infants. Eighty-five nasopharyngeal swabs obtained from nine erythromycin-treated infants with pertussis on consecutive days during hospitalization were tested by PCR and culture. The PCR products were further analyzed by Southern hybridization. Results. On the fourth day of treatment 56% of the samples were positive by culture and 89% by PCR, whereas after 7 days the rates were 6 and 56%, respectively. In seven of nine patients PCR remained positive for 1 to 7 days longer than culture. The follow up study also showed the semiquantitative nature of the PCR assay. The intensity of the PCR products in agarose gel usually weakened with time during erythromycin therapy. Conclusions. The results of this study show that PCR assay can achieve the specific diagnosis of pertussis infection in a large proportion of infants even when antimicrobial treatment has killed the organisms and culture is no longer positive.