The primary diagnostic specimen for detecting Naegleria fowleri infection is a:

• A. Thick blood smear
• B. Cerebrospinal fluid sediment
• C. Corneal scraping
• D. Skin biopsy

Answer: (B)

Naegleria fowleri causes a rapidly progressive brain infection, so the most reliable way to confirm it is to look for the organism directly in the central nervous system. A sample of cerebrospinal fluid obtained by lumbar puncture is the primary diagnostic specimen because the parasite invades the CNS and is detectable there. On examination of CSF sediment, the characteristic trophozoites can be seen with direct wet mount or stained preparations, and confirmation can be further supported by PCR or antigen testing on CSF. Other specimens listed don’t reflect the site of infection: a thick blood smear targets blood parasites, a corneal scraping is used for ocular amoebae, and a skin biopsy wouldn’t reveal CNS infection.