A norovirus outbreak occurs at an assisted-living facility. Which immediate public-health action best prioritizes protection of the highest-risk residents?

Close the facility permanently and immediately transfer all residents to different long-term care centers regardless of symptom status, without waiting for case confirmation.

Recommend residents drink more fluids and continue communal dining because the outbreak will stop on its own; focus only on symptomatic residents receiving supportive care in place without altering food service practices.

Isolate symptomatic residents, exclude symptomatic staff from food handling, intensify hand hygiene and surface disinfection, and notify public health authorities.

Provide prophylactic antibiotics to all residents and staff because antibiotics will prevent viral spread and are the fastest way to stop gastrointestinal outbreaks in institutional settings.