Pertussis is common in nonvaccinated infants hospitalized for respiratory syncytial virus infection

Background: There is some evidence that Bordetella pertussis can cause co-infection with respiratory syncytial virus (RSV). Subjects and Methods: RSV etiology was studied by antigen detection in 117 infants < 6 months of age, who were hospitalized for respiratory tract infection during an RSV epidemic. B. pertussis etiology was studied by polymerase chain reaction in those 88 in whom parents or nurses reported cough. Results: RSV was found in 91 (78%) infants and B. pertussis in 9 (8%) infants. In 7 cases, there was mixed RSV-pertussis infection. In retrospective analysis, RSV and mixed RSV-pertussis cases could not be separated by clinical characteristics. Conclusions: Co-infection caused by B. pertussis was present in 8% of infants, aged < 6 months, who were hospitalized for RSV infection. To avoid under-diagnosis, pertussis should be considered in all nonvaccinated infants with lower respiratory tract infection.