Yersinia pestis infections are most commonly found in which U.S. region?

Yersinia pestis, the bacterium that causes plague, is most commonly associated with the southwestern regions of the United States, particularly New Mexico, Arizona, and California. These states have the environmental conditions and ecosystems that support the presence of the fleas that typically carry Yersinia pestis, as well as the rodent populations that serve as reservoirs for the bacterium.

The geographic distribution of plague cases in the U.S. historically aligns with areas where these vectors are prevalent. Surveillance and epidemiological data consistently show that the majority of reported cases are concentrated in the southwestern states, making this choice a well-supported response based on patterns of infection and ecological factors specific to this region. Other regions mentioned in the other answer choices have shown very few or no significant cases of plague, which highlights the distinct habitat and vector dynamics that make the southwestern states the primary area for Yersinia pestis infections.