Dr. Pevzner: It depends on the situation.

It begins by looking at available information, like medical records. The next step may be talking to people who have been sick, or their families. Often samples are collected for testing: food, water, blood. Then they piece together that information to determine what is the cause of what is making people sick, and how can we protect the public’s health.

How often are disease detectives called into action?

Dr. Pevzner: Our disease detectives go into the field to do about 200 investigations a year, domestically and internationally.

With a measles outbreak, is the goal to find Patient Zero?

Dr. Pevzner: Measles is the bad guy. What we’re trying to determine is, how is the crime being committed? In other words, how is measles being spread in a community? What are the behaviors that are leading to the transmission of a vaccine-preventable disease?

How do you take the best available science and really think like an anthropologist, and work on the very complicated social and cultural aspects to how you can make effective interventions?

What illnesses have you encountered as a disease detective?

Dr. Phillips: The West Nile virus. I went running around Staten Island, drawing people’s blood to try to figure out how it was transmitting through that borough.

And there were the anthrax letters.

Later, New York City saw SARS, the 2009 flu, Zika, Ebola, and Legionnaires’ disease, to name a few.

Any unusual ways you’ve found clues as to how a disease was spreading?

Dr. Phillips: There was a hepatitis C outbreak in Brooklyn during my time at the city Health Department. We could not it figure out. We had interviewed everybody, observed how things were being done.