The measles outbreak that has thus far infected 20 people in three boroughs may have started in hospitals and doctor's offices in Upper Manhattan and the Bronx, according to health officials.

The Times reports this morning that the city's Department of Health suspects the outbreak got its start in medical facilities, and it may have worsened because workers failed to recognize and isolate ailing patients in time. "We know a number of people were exposed and possibly got their infection either at a doctor’s office or at an emergency room where they went and it took more time than it should have for them to be put in an isolation area where they couldn’t possibly infect anyone else,” Dr. Jay Varma, the health department’s deputy commissioner for disease control, told the paper.

Nine children and 11 adults have been diagnosed with the highly contagious viral disease thus far, with a new adult patient confirmed this week. And though authorities haven't named any specific hospitals that may have dropped the ball on identifying the outbreak, New York-Presbyterian Hospital/Columbia University Medical Center in Upper Manhattan confirmed earlier this month that it has treated 10 measles patients, and up to 600 more may have been exposed. A spokesperson for the hospital noted that "to the best of our knowledge, none of the patients who were seen in our emergency room got measles here in our emergency room."

Seven of the children who contracted the disease were too young to be vaccinated, and two were refused vaccination by their parents. Measles was all but eliminated in the United States by the year 2000 thanks to the vaccination, but in 2011 there were 222 measles cases reported. Of the US residents who contracted the virus, 166 were unvaccinated or had unknown vaccination status.