Which exposure history would support a diagnosis of primary amebic meningoencephalitis?

• A. Leukemia with chemotherapy
• B. Hiking in the desert of Southwest United States
• C. Swimming in warm stagnant water
• D. Visits to Massachusetts and the North-east

Answer: (C)

PAM results from infection with Naegleria fowleri, a thermophilic free-living ameba that lives in warm freshwater and soil. Humans become infected when contaminated water goes up the nose during activities like swimming or diving, allowing the organism to reach the brain and cause rapid meningoencephalitis. That nasal exposure to warm water is the key link to PAM.

Swim in warm stagnant water fits best because it provides the conditions and route for Naegleria fowleri to enter the body. The other scenarios don’t align with this infection’s typical exposure: being immunocompromised from chemotherapy predisposes to other pathogens, desert hiking isn’t associated with this organism, and travel to the Northeast isn’t the classic exposure setting for PAM, which is more common in warmer regions and seasons.