Her vocal cords are seen to be grossly oedematous. What is the SINGLE next most appropriate investigation?

A 13 year old girl complains of a 3 day history of hoarseness of voice associated with dry cough. She presents with a fever and malaise. On direct laryngoscopy, her vocal cords are seen to be grossly oedematous. What is the SINGLE next most appropriate investigation?

A. None required
B. Sputum for acid-fast bacilli
C. Blood culture
D. Cervical spine X-ray
E. Bronchoscopy

This is a likely case of a common cold. No further investigations or management is required.