The Centers for Disease Control and Prevention (CDC) said Tuesday afternoon that 107 people from 21 states, including California, have reported contracting the measles.
The other states included are Arkansas, Connecticut, Florida, Illinois, Indiana, Kansas, Louisiana, Maryland, Michigan, Missouri, Nevada, New Jersey, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Tennessee, Texas, and Washington.
This number will likely outpace the number of measles cases reported in 2017.
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There were 118 cases in 2017, and only 86 the year before that.
The last outbreak was in 2015 when 188 people contracted measles.
The outbreak was linked to an amusement park in California where it is thought that a traveler from overseas brought it to the U.S.
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Measles is an airborne virus that spreads through coughing and sneezing.
Symptoms show up in 10-14 days after exposure. The symptoms last 7-10 days and include a high fever, cough, runny nose, and red eyes followed by a rash that typically starts on the face and spreads to the rest of the body.
According to the CDC, some people may suffer from severe complications, such as pneumonia and brain swelling which could result in hospitalization or death.
CDC monitoring measles in 21 states, including California