Which laboratory step is used to confirm diphtheria infection and guide isolation?

Which laboratory step is used to confirm diphtheria infection and guide isolation?

• A. Blood culture
• B. PCR to confirm (isolate until 3 negative pharyngeal cultures)
• C. Urine culture
• D. Stool culture

Answer: (B)

Rapid confirmation of diphtheria hinges on detecting the toxigenic Corynebacterium diphtheriae from the pharynx. PCR testing of a throat swab can quickly confirm the presence of the organism and the toxin gene, allowing fast, decisive confirmation of infection. Once confirmed, isolation is continued until three consecutive pharyngeal cultures are negative, usually collected 24 hours apart, to ensure clearance and prevent transmission. Other types of cultures—blood, urine, stool, or non-pharyngeal samples—don’t reliably diagnose diphtheria or determine how long isolation should last.

Rapid confirmation of diphtheria hinges on detecting the toxigenic Corynebacterium diphtheriae from the pharynx. PCR testing of a throat swab can quickly confirm the presence of the organism and the toxin gene, allowing fast, decisive confirmation of infection. Once confirmed, isolation is continued until three consecutive pharyngeal cultures are negative, usually collected 24 hours apart, to ensure clearance and prevent transmission. Other types of cultures—blood, urine, stool, or non-pharyngeal samples—don’t reliably diagnose diphtheria or determine how long isolation should last.