A pathogen similar to Bordetella pertussis is responsible for as many one in six cases of whooping cough, Australian infectious disease specialists have confirmed.
Bordetella holmesii causes a respiratory infection similar to pertussis but mostly in adolescents rather than under fives, researchers at the University of Sydney say.
The novel pathogen is routinely misdiagnosed as pertussis because the current PCR test for the whooping cough pathogen does not distinguish between the two Bordetella species, they write in the journal Pathology.
While B. holmesii has been shown to be account for up to 30% of ‘pertussis’ cases in outbreaks in the US, the incidence of the pathogen in Australia has been unknown until now.
When researchers used a B. holmesii specific PCR test to investigate 802 patients diagnosed with pertussis they found that 46 (6%) of them were actually B. holmesii rather than B pertussis.
The analysis, which covered pertussis samples from 2008-20016 held at the Centre for Infectious Disease and Microbiology Laboratory Services in NSW, found that the incidence of B. holmesii was zero in some years, but around 6-8% in four annual sets of samples and as high as 17% in 2010.
There were no cases of co-infection, showing that the novel pathogen had been hidden from view by being misdiagnosed as pertussis, the researchers said.
They noted that most cases occurred in the 11-18 years age group and there was evidence of person-to-person transmission within households.