Factbox: What you need to know about the measles epidemic in the United States

(Reuters) – The United States this year recorded 764 measles cases in 23 states. This is the largest epidemic since public health officials declared the eradication of the disease in 2000, according to the Center for Disease Control and Prevention.

The CDC is expected to publish Monday updated figures on the number of cases registered so far this year.

The following facts relate to the epidemic:

* Public health officials attribute the resurgence of measles to the spread of misinformation about vaccines. A vocal fringe of parents opposes vaccines, convinced, contrary to scientific studies, that their ingredients can cause autism.

* The largest outbreaks are concentrated in New York, which recorded 466 cases, mainly in the Jewish Orthodox community of the Williamsburg district, and in Rockland County, northern New York, with 224 cases. These figures include infections from last year and are not directly comparable to the CDC figures.

* Other outbreaks are underway in California, Michigan, New Jersey, Georgia and Maryland.

* The disease is highly contagious and can be fatal, killing one or two in 1000 children who contract it, according to the CDC. It can also cause permanent hearing loss or intellectual disability. This is the biggest risk for young unvaccinated children.

* The 2000 United States declaration that measles had been eradicated meant that the disease was no longer present in the country all year round. Measles remains common in some countries of Europe, Asia and Africa and unvaccinated travelers in these countries can bring it back to the United States. The current epidemics are due to visits to Israel and Ukraine.

* New York City officials said 22,833 people had received the measles, mumps and rubella (MMR) vaccine in affected areas since the start of the outbreak in October. The city has begun to fine non-vaccinated adults.

* Lawmakers from Oregon, New Jersey, Iowa, Vermont and Minnesota are considering legislation to eliminate non-medical exemptions for unvaccinated children to attend public schools. Only three states currently prohibit all non-medical exemptions: California, Mississippi and West Virginia.

* To obtain a collective immunity protecting people who are unable to be vaccinated against measles, such as infants and people whose immune system is compromised, 90% to 95% of the population must be vaccinated.

Sources: US CDC, World Health Organization, state and city public health offices in New York, California and Michigan, National Conference of State Legislatures.