Clinical Study of Parapertussis Following the COVID-19 Pandemic

Background: Bordetella parapertussis ( B. parapertussis ) has been reported to cause symptoms similar to those of Bordetella pertussis ( B. pertussis ) infection, but there have been few reports of B. parapertussis infection in Japan, and many details remain unknown. Methods: We compared the clinical characteristics of patients aged 15 years or younger who tested positive for B. parapertussis or B. pertussis using the multiplex PCR method (FilmArray Respiratory Panel 2.1) between April 2021 and December 2025. Results: B. parapertussis was detected in 128 specimens (0.96%), of which 108 (84.4%) were co-detected with other pathogens. B. pertussis was detected in 39 specimens (0.24%), of which 24 (61.5%) were co-detected. In this study, the epidemic periods of B. parapertussis and B. pertussis did not overlap. The median ages of B. parapertussis –positive and B. pertussis –positive cases were 4 and 10 years, respectively. Comparing the clinical symptoms of B. parapertussis –positive cases with those of B. pertussis –positive cases, symptoms characteristic of pertussis, such as paroxysmal coughing, cough-induced vomiting, whooping, and apnea, were significantly less common in B. parapertussis –positive cases. About 80% of cases positive for B. pertussis were diagnosed as typical pertussis, while none of the cases positive for B. parapertussis were diagnosed as pertussis. Conclusions: The detection of B. parapertussis does not necessarily mean that the patient will exhibit symptoms of pertussis. It is also important to consider the possibility that the symptoms are caused by other pathogens.