Which of the following is a common symptom indicating a healthcare-associated infection?

Elevated white blood cell count is a common symptom indicating a healthcare-associated infection because it reflects the body's immune response to infection. When an infection occurs, the body produces more white blood cells to combat pathogens, which can lead to a noticeable increase in the white blood cell count. Clinicians often monitor this count as a part of blood tests to help diagnose infections, including those acquired in healthcare settings.

The other options, while they may relate to a patient's overall health status or various conditions, are not as directly indicative of an infection. Low blood pressure can occur in various medical conditions, including severe infections, but it is not a specific indicator of a healthcare-associated infection. A decreased heart rate is generally not associated with infections; rather, it may indicate other medical issues. The natural pain response is also not specific to infections and can occur in numerous contexts, such as injuries or other types of inflammatory conditions.