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)

Vulnerability to Listeria monocytogenes centers on who has weakened cell-mediated immunity and barriers to infection. Listeria is an intracellular pathogen that can hide inside host cells and spread from cell to cell, so clearing the infection relies heavily on T-cell–mediated responses and intact mucosal defenses. Pregnant women experience immune changes that dampen cell-mediated immunity to tolerate the fetus, making them more susceptible to invasive Listeria and placental transmission. Newborns have immature, developing immune systems, which also limits their ability to fight off intracellular bacteria. The elderly show age-related decline in immune function, and immunocompromised individuals (due to disease or therapy) have diminished capacity to control intracellular pathogens. In contrast, healthy young adults generally have stronger immune defenses and are less likely to develop severe invasive disease from Listeria. So the statement that healthy young adults are especially vulnerable does not fit the pattern of who is most at risk.