Clinical and Laboratory Diagnosis for Naegleria fowleri Infection

What to know

  • Primary amebic meningoencephalitis (PAM) is a rare but nearly always fatal brain infection caused by the ameba Naegleria fowleri.
  • PAM is diagnosed using laboratory tests.
  • The tests are available in only a few laboratories in the United States, including CDC.
High resolution of Naegleria fowleri ameba in a person's cerebrospinal fluid

Diagnosing Naegleria fowleri infection

Clinicians ‎

For 24/7 diagnostic assistance, specimen collection guidance, shipping instructions, and treatment recommendations, contact the CDC Emergency Operations Center at 770-488-7100

PAM is diagnosed by detecting Naegleria fowleri amebas using different tests offered by only a few U.S. laboratories, including CDC. The tests include:

  • A polymerase chain reaction (PCR) test that detects Naegleria fowleri in a patient's cerebrospinal fluid (CSF) or tissue
  • Immunohistochemical (IHC) testing and indirect immunofluorescent (IIF) staining that use specific antibodies against Naegleria fowleri to detect the ameba
  • Direct visualization by examining CSF under a microscope. Naegleria fowleri can be identified in CSF smears or cultures using hematoxylin and eosin (H&E), periodic acid-Schiff (PAS), trichrome, Giemsa, or Wright-Giemsa stains. Note: A Gram stain should be avoided since Naegleria fowleri can be destroyed during heat fixation.
High resolution of a person's cerebrospinal fluid. Two arrows point to Naegleria fowleri amebas
Naegleria fowleri amebas in a patient's cerebrospinal fluid. Photos: Dr. James Roberts, Children's Healthcare of Atlanta

CDC offers diagnostic assistance for Naegleria fowleri infection to physicians and scientists through DPDx and the Free-Living and Intestinal Amebas (FLIA) Lab.

Morphology experts at DPDx can evaluate microscopic images. Scientists at the FLIA laboratory provide diagnostic assistance using molecular and immunofluorescence assays.