The Centers for Disease Control and Prevention on Monday added 13 cases to the year's tally, down from about 20 cases in each of the previous two weeks.
Three-quarters of this year's cases are tied to an outbreak that started in December at Disneyland in California. Five of the latest cases are linked to Disneyland.
The source of that outbreak has not yet been identified. The strain behind it has been seen in at least 14 countries. Measles cases in the U.S. usually are brought in and spread by travellers from countries where measles is more common.
CDC update: http://www.cdc.gov/measles/cases-outbreaks.html