Chris Chao, MD
The incubation period of measles is 10-12 days. A patient is not contagious during this time. Once an infected individual develops symptoms (including fever), they are highly contagious with a transmission rate of 90%.
KOPLIK SPOTS ARE THE EARLY SIGNS OF MEASLES
Koplik spots occur 1-4 days before the exanthem and occur in up to 70% of patients with measles. They are typically not painful, which may differentiate Koplik spots from aphthous ulcers or herpangina. Koplik spots initially present as bluish white “grains of salt on a red background” opposite the molars on the buccal mucosa. Spots may extend to the entire buccal mucosa before disappearing as the rash begins.
A patient with measles is contagious during the prodrome period up to 5 days after the rash onset. By the time the characteristic rash develops, the patient has been contagious for several days. A patient is contagious when Koplik spots develop.
Since Koplik spots occur before the characteristic rash of measles develops, prompt recognition of Koplik spots is critically important to limit the spread.
To identify Koplik spots, you must look for it, and this includes doing a comprehensive oral exam on a potentially non-cooperative child.
References:
Zenner, D, Nacul L, “Predictive power of Koplik’s spots for the diagnosis of measles” J Infecti Dev Ctries 2012 Mar 12;6(3):271-5
CDC: measles https://www.cdc.gov/measles/index.html
