This article is more than 5 years old. Information may no longer be current.
Duration of pertussis PCR positivity a median of 58 days
Click Here to Manage Email Alerts
There is a median duration of 58 days for Bordetella pertussis PCR positivity, according to recent study findings published in the Journal of the Pediatric Infectious Diseases Society.
Bryan L. Stone, MD, MS, of the division of pediatric inpatient medicine, department of pediatrics at the University of Utah School of Medicine, and colleagues evaluated children younger than 18 years with positive B. pertussis PCR (index cases; n=14) and close contacts with at least 7 days of cough illness without a known etiology (associated cases; n=35). Participants provided nasopharyngeal samples for PCR testing at baseline, then weekly for 3 weeks, followed by testing monthly or every other month from symptom onset until samples were negative.
Bryan L. Stone
Fifty-one percent of associated cases were PCR-positive. Including negative baseline samples more than 21 days after symptom onset, 31 PCR-positive participants and three PCR-negative participants were included in analysis.
Samples were positive from days 4 to 172 following symptom onset, and conversion to negative samples occurred between 22 and 207 days in PCR-positive participants.
Out of 34 participants who provided 50 PCR samples, 34 received either erythromycin or azithromycin.
“B. pertussis PCR may remain positive in 50% of patients for >50 days after the onset of symptoms, despite antibiotic treatment and clinical improvement,” the researchers wrote. “Testing for B. pertussis by PCR when clinical suspicion of infection exists may be useful weeks after symptoms onset; respiratory illness testing strategies need to include consideration that persistent positive B. pertussis PCR results may confuse the diagnosis in nonpertussis infection.”
Bryan L. Stone, MD, MS, can be reached at bryan.stone@hsc.utah.edu.
Disclosure: The study was funded in part by the Primary Children’s Medical Center Foundation.
Perspective
Back to Top
Roger Baxter, MD
I found this a helpful study, in both a clinical and research context. Clinically, we often wonder if a person with prolonged cough has pertussis, and this study is reassuring that, even after several weeks (when many patients present), the test can be useful. For research, we use the test as a marker of infection, and there has been concern that many people with pertussis might have a false negative test if they present late, leading to misclassification and diluting the vaccine effectiveness estimates. Once again, this is reassuring.
I agree with the researchers’ conclusions that this makes repeat testing pretty useless, but in my experience patients rarely like to go through the nasopharyngeal test again, once they’ve had the pleasure of a 3-inch swab up their nose.
Click Here to Manage Email Alerts