"Unfortunately, we're off to a bad year in 2014," state epidemiologist Dr Gil Chavez said, adding that last year during this time only two measles cases were reported. None of the cases till now has been fatal, but measles can be deadly.
California also faced a bad flu season with 278 deaths being confirmed on Friday.
Though measles was eliminated in the US in 2000, as per US Centers for Disease Control and Prevention records, people can get the virus when they come in contact with an infected person. Other ways to contract the disease is while travelling to locations where the disease is common or coming in contact with travellers.
Of the 15 patients, three had been to the Philippines this year, two to India and two others had come in contact with travellers. At present, Philippines is facing a very bad measles outbreak.
Chavez said many people intentionally do not go for measles vaccination and he was concerned about those patients who avoided them. "A myth persists among many parents that the measles vaccine is dangerous. These illnesses continue to make a comeback because we have people who refuse to be vaccinated," he added.
Allegheny County in California got its first measles case since 2009. Health officials said an infected UC Berkeley student travelled on the Bay Area Rapid Transit system on February 14 and he might have spread it to many others.
Some of the symptoms of measles are runny nose, red and watery eyes, cough and a high fever, raised, red rash lasting four to seven days that starts from face and spreads to the neck and other body parts.
In serious cases, measles can cause ear infection, diarrhoea, pneumonia, encephalitis and even death. Pregnant women come under the high-risk group as the disease can cause miscarriages or premature delivery.