In suspected pertussis, which test best confirms the diagnosis?

• A. Chest X-ray
• B. Bordetella pertussis PCR
• C. Sputum culture
• D. Urine antigen test

Answer: (B)

In suspected pertussis, the best test to confirm the diagnosis is Bordetella pertussis PCR performed on a nasopharyngeal specimen. PCR detects the bacterial DNA and is both highly sensitive and specific, especially during the early stages of the illness when the patient is most contagious. A rapid result helps initiate appropriate antibiotic therapy and limit transmission. While culture can definitively identify the organism and is useful for epidemiology and susceptibility testing, it is slower and less sensitive, particularly if antibiotics have already been started or if the specimen quality isn’t optimal. Imaging like chest X-ray isn’t diagnostic for pertussis itself; it may show complications but cannot confirm the infection. Urine antigen testing is not a reliable diagnostic method for pertussis.