California is currently in the midst of a historic measles outbreak, with 49 cases confirmed since the beginning of the year, compared to only four cases during the same time in 2013. Orange County is the hardest-hit county, with 21 confirmed cases of the measles–over double any other county. But the most surprising fact might be that, according to Orange County Public Health (OCPH), over half of Orange County's confirmed cases–11–can be traced back to one person.
Who — and why — is Orange County's Patient Zero?
The Center for Disease Control (CDC) and Prevention declared measles eradicated in the United States in 2000, and since then, California has only seen between four and 40 cases per year. With 49 cases by the end of March, this outbreak is already the worst measles outbreak California has seen since the disease was eradicated.
OCPH knows who Patient Zero is, but can't release any information–city, hospital, race, social economic status–due to patient privacy laws. But we do know this: Vaccination rates are the highest in North County, with Anaheim being the city with the most vaccinated students. South County school districts, on the other hand, have the highest rates of non-vaccination.
To attend elementary school in California, children have to have two rounds of the MMR vaccine–both on or before their first birthday–unless their parents fill out a personal belief waver. Multiple Orange County clinics offer low- and no-cost vaccinations to low-income families. A full list can be found on the OCPH website. Approximately 99 percent of people who receive both doses eventually develop immunity to the disease, according to the CDC.
Of the OC five kids who came down with measles, none of them were vaccinated. There other 16 cases were adults, five of which are healthcare workers. There have been seven total hospitalizations this year in Orange County for measles. State-wide, nearly half of this year's measles cases are from unvaccinated children. The disease is highly contagious–according to Occucare International, 90 percent of un-immune people who come in close contact with someone with measles will contract it.
Though the disease was eliminated from the United States, it can still be a threat, especially to travelers who visit countries where measles is still prevalent. Of California's 49 cases, 11 patients had travelled outside of North or South America, including to parts of the world where outbreaks are actively occurring or where measles is widespread, according to the California Department of Public Health. Of the patients without international travel, 30 had contact with known measles cases, three had contact with international travelers and 5 are under investigation to identify potential sources.