Measles is caused by the measles virus, which can be spread through the air by coughing or sneezing.
This, the HSE says, is why measles outbreaks are occurring in Ireland and across Europe.
It is also 15 times a record low recorded in 2016.
The Washington State Health Department hasn't identified "patient zero" in the Clark County measles outbreak that has tallied 50 confirmed cases in Clark County and 55 total cases in Washington and OR since January 1.
Vaccination remains the most effective method for preventing measles, according to the Bell County Health District. Measles infection can have serious complications such as pneumonia, seizures and encephalitis (inflammation of the brain). According to the World Health Organization, before the introduction of measles vaccination in 1963, the virus caused 2.6 million deaths every year.
So far in the USA this year, about 80 cases of measles have been reported, with two outbreaks ongoing in Washington and NY states. In Madagascar, officials say more than 50,000 people have been infected with measles in recent months and more than 300 people, mostly children, have died as a result.
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Across the US, 10 states - California, Colorado, Connecticut, Georgia, Illinois, New Jersey, New York, Oregon, Texas and Washington - reported 79 confirmed measles cases in January, according to the Centers for Disease Control and Prevention.
Measles infections in Europe hit a decade high in 2018, despite more children than ever before receiving vaccinations. Measles is highly contagious and early identification remains a critical public health measure to reduce the spread of the disease. Orders of measles vaccines in the county reached 3,150 in January.
These new Multnomah County cases are linked to the Clark County outbreak.
The orders represent only state-supplied vaccines requested through the federal Vaccines for Children program, which provides free immunizations to children who otherwise couldn't afford them.
The percentage of children receiving the first dose of the vaccine also increased, to 95%.
"This outbreak has put people at real risk", said Ann Thomas, public health physician at the Oregon Health Authority.