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?
Start intravenous broad-spectrum antibiotics.
Administer diphtheria antitoxin immediately.
Perform a throat culture and await results.
Quarantine the patient and notify public health authorities.