Abstract
Bordetella holmesii, an emerging pathogen, can be misidentified as Bordetella pertussis by routine polymerase chain reaction (PCR). In some reports, up to 29% of the patients diagnosed with pertussis have in fact B. holmesii infection and invasive, non-respiratory B. holmesii infections have been reported worldwide. This misdiagnosis undermines the knowledge of pertussis' epidemiology, and may lead to misconceptions on pertussis vaccine's efficacy. Recently, the number of whooping cough cases has increased significantly in several countries. The aim of this retrospective study was to determine whether B. holmesii was contributing to the increase in laboratory-confirmed cases of B. pertussis in Switzerland. A multiplex species-specific quantitative PCR assay was performed on 196 nasopharyngeal samples from Swiss patients with PCR-confirmed Bordetella infection (median age: 6 years-old, minimum 21 days-old, maximum 86 years-old), formerly diagnosed as Bordetella pertussis (IS481+). No B. holmesii (IS481+, IS1001−, hIS1001+) was identified. We discuss whether laboratories should implement specific PCR to recognize different Bordetella species. We conclude that in Switzerland B. holmesii seems to be circulating less than in neighboring countries and that specific diagnostic procedures are not necessary routinely. However, as the epidemiological situation may change rapidly, periodic reevaluation is suggested.
Highlights
Pertussis outbreaks are reported worldwide and Bordetella pertussis is detected by polymerase chain reaction (PCR) with increasing frequency in nasopharyngeal (NP) samples of symptomatic patients
Respiratory infection with B. holmesii can be misidentified as B. pertussis by PCR because both genomes contain the insertion sequence IS481 targeted by PCR assays routinely used in most laboratories
The IS481 target is highly sensitive for B. pertussis: its genome contains .50 copies of the IS481 sequence, but it is not species-specific: it is present in the genome of B. holmesii (8–10 copies), and in some animal isolates of B. bronchiseptica
Summary
Pertussis outbreaks are reported worldwide and Bordetella pertussis is detected by polymerase chain reaction (PCR) with increasing frequency in nasopharyngeal (NP) samples of symptomatic patients. Respiratory infection with B. holmesii can be misidentified as B. pertussis by PCR because both genomes contain the insertion sequence IS481 targeted by PCR assays routinely used in most laboratories. This misdiagnosis of B. holmesii as B. pertussis is common: in a recent large quality control test, only one out of 24 European laboratories properly identified a B. holmesii strain [4]
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