Let Me Out!

Earlier this month, commuters in the San Francisco area were warned that they may have been exposed to the highly contagious disease measles after a student at University of California, Berkeley attended class and rode the Bay Area Rapid Transit (BART) while contagious. The student, who was unvaccinated, likely contracted the disease while traveling abroad. Take a virus that can remain viable in the air of an enclosed space (like a classroom or subway car) or on surfaces for up to about two hours, a large student population of a university like UC Berkeley, and hundreds of thousands of commuters each day and you have a lot of people that were likely exposed to one of the most contagious viruses known to infect humans. Just look at BART alone, which sees roughly 390,000 riders each day. Of course, not all of those will ride in the same car as the student, but we can expect that at the very least, several hundred people would have been exposed to measles each time he rode. Cars hold about 60-70 people, the virus lingers for a couple hours, lots of people getting on and off during that period, it adds up. We could see additional cases popping up over the next week or two. And that's not the only case that California has seen. As of February 21, there have been 15 cases of measles, with the youngest being only 5 months old, according to a CDPH teleconference. Compare this to last year, when there were only 2 cases by the same date.

Those 15 cases make up the majority of the 24 cases seen nationwide to date, with other cases seen in Hawaii, Massachusetts, New York, Oregon, Pennsylvania, Texas, Washington and Wisconsin. The cases are in those who traveled to other countries where there are current measles outbreaks (e.g., the Philippines) or where measles is endemic (e.g., India) or among those who have had contact with someone bringing the virus back from another country. Since measles was eliminated from circulation in the U.S. in 2000, the outbreaks we have seen since then have been due to importation by unvaccinated individuals, some too young to be vaccinated, and others intentionally unvaccinated. Note that none of the outbreaks in recent years has been started by a fully immunized individual. With the risk posed by importation of the disease, I started to think about what role quarantine might play in mitigating potential harm to the public.