Which patient population is especially vulnerable to Listeria monocytogenes infection and why?

• A. Pregnant women, neonates, elderly, and immunocompromised individuals due to reduced gastric acidity and immune defenses.
• B. Healthy young adults.
• C. Athletes.
• D. Infants.

Answer: (B)

Listeria monocytogenes infections hit hardest those with weakened cell-mediated immunity. This pathogen is intracellular, so control relies mainly on T-cell–mediated responses and activated macrophages. During pregnancy, immune defenses shift to tolerate the fetus, reducing intracellular pathogen clearance and increasing risk to both mother and fetus. Neonates have immature immune systems, and the elderly experience immune senescence, while immunocompromised individuals (such as those with HIV, cancer, or on immunosuppressive therapy) have diminished ability to contain intracellular bacteria. Because of these immune limitations, invasive listeriosis with possible meningitis or fetal/neonatal infection is most likely in these groups, whereas healthy young adults tend to have robust defenses. Listeria can also spread to the fetus and cross the placental and blood-brain barriers, underscoring why these populations are particularly vulnerable.