What is the best method to identify Bordetella pertussis?

• A. Gram stain
• B. Regan-Lowe medium
• C. Polymerase chain reaction
• D. Serology

Answer: (C)

Detecting Bordetella pertussis most effectively comes from directly identifying its genetic material in patient samples. Polymerase chain reaction achieves rapid, highly sensitive, and specific detection from nasopharyngeal specimens, enabling early diagnosis and prompt treatment. It can detect the organism even when there are only small numbers of bacteria and before colonies grow in culture, which is crucial during the early stages of pertussis.

Gram stain is not reliable for this organism because B. pertussis is a small, faintly staining gram-negative coccobacillus and is often not visualized well in clinical specimens. Regan-Lowe medium culture has historic value and is specific, but it is slow (days to obtain growth) and less sensitive, especially if antibiotics have already been started or if specimen collection quality is suboptimal. Serology can be helpful later in the course or in outbreak investigations, but it is not ideal for acute diagnosis since antibodies take time to develop and results can be confounded by vaccination or prior exposure.

So, the best method for identifying Bordetella pertussis in the acute setting is PCR.