upper respiratory tract infection
It can cause the vocal cords to be swollen and unable to vibrate normally
for two to three weeks. That is why people will be hoarse for that period of time after an
upper respiratory tract infection.
After an illness it is necessary to allow the vocal cords to heal. You are recommended voice rest,
vigorous hydration (lots of fluids), and suppressing cough (cough causes more sheering force on the vocal cords and thus more damage).
Use of a humidifier that helps to keep the vocal cords moist.
Moist vocal cords can vibrate more easily so David has been orderd to stay off the phone and get plenty of rest.