A 7-year-old child presents to the emergency department with a sore throat, low-grade fever, and a thick, gray membrane covering their tonsils and throat. The parent reports that the child was not vaccinated due to personal beliefs. Which of the following actions is most appropriate for the nurse to take first?
Perform a throat culture and await results.
Start intravenous broad-spectrum antibiotics.
Quarantine the patient and notify public health authorities.
Administer diphtheria antitoxin immediately.