In interviews, the people Ms. Williams contacts regard her with suspicion and hostility, a scenario well known to journalists. She is, after all, asking them whom they have sex with. Truthful answers could destroy relationships, expose illegal behaviors, unloose cascades of shame.

What should she do with that information? Like journalists, she is bound by strict ethical codes. Test, treat, notify. Do not disclose. Do not judge.

I watched as a woman in her 50s, stuck in a loveless, sexless marriage, told Ms. Williams that she’d gotten syphilis from her boyfriend. The woman assumed investigators found her through him. (She knew I was a journalist.) Made sense to me. Ms. Williams, poker-faced, kept probing.

Later Ms. Williams told me the woman had been lying. But ethically, the investigator could not confront the woman with what she knew — including the identity of the actual informant and the toxic tangle of her relationships. All had been shared in confidentiality.

Similarly, I often cannot write much of what people tell me.

There are obvious differences between our professions. Like the part where she draws blood from her subjects with a syringe. My main instruments are a pad and pen.

And though I have had frightening moments — interviewing murderers and wife beaters, reporting alone at night in places where I should not have been — her job, in a state where gun owners can carry concealed weapons, can be terrifying daily. Looking for people who work hard not to be found, she has been chased off by drug dealers, lunging dogs, a pig.

Another difference: I certainly become emotionally steeped in the reporting of each article. (Ask my beleaguered family.) Then I get to shake it off and move on.