In a PCR assay of DNA isolated from a nasopharyngeal swab, amplification using primers to IS481 was positive and using primers to IS1001 was negative. All controls were acceptable. Which of the following organisms was present in this sample?

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The presence of IS481 in the DNA isolated from a nasopharyngeal swab is highly specific for Bordetella pertussis, the causative agent of pertussis (whooping cough). IS1001 primers, on the other hand, are specific for Bordetella holmesii, a closely related but less common species that can also be found in respiratory samples. The negative result for IS1001 rules out B. holmesii as a possible cause of the patient's symptoms. Choice B, Bordetella parapertussis, can also cause a milder form of pertussis but is less commonly detected in clinical samples. Choice D, Legionella pneumophila, is an unrelated bacteria that causes Legionnaires' disease, a severe form of pneumonia.

In a PCR Assay of DNA Isolated from a Nasopharyngeal