I have recently experienced an example of a persistent and rigorous interview that yielded an unexpected payoff. I somehow contracted a Giardia infection, a parasite usually associated with contaminated water. The first questions anyone knowledgeable asks are “Were you drinking out of streams?” and “Were you drinking well water?” because there is a problem in rural areas with contaminated water and wells can become contaminated, especially when there is a lot of flooding, as there was this summer. But I am a city person and only drink tap water. No, I haven’t been camping, I have not been drinking out of streams. I thought maybe there was a sick food service worker? Maybe contaminated tap water in a rural gas station in our trip to Duluth? Hard to know.
It turns out that Giardia is a reportable public health infection, so I got a call this week from a public health student. She asked a ton of detailed questions about symptoms and exactly when I started feeling ill, and exactly what I was doing when I started feeling ill, which was confusing because the symptoms came on quite gradually. But she persisted, cross-examining me this way and that about what symptoms and when. Then we had to go over everywhere I’d been and everything I’d eaten in the suspect period (which was, it turned out, was two weeks earlier than I had been thinking about). This was going on a long time, over 30 minutes, it was starting to hold up dinner, I was getting impatient, but she persisted. What grocery stores do we shop at? Do we eat organic food? Do we go to the farmers market? Do we grow our own food? Do we go to a butcher shop? Where did we eat out in the last two weeks of August? Well, we eat out a lot and I really don’t remember two months ago, and I was rolling my eyes. But then I remembered that we put almost everything on credit card, so I pulled up the credit charge records while she waited and went through the list. There were a lot. She was trying to get me to remember what I ate at each place. Pretty hard to remember what you ate at a Chinese buffet, something we often do for Sunday lunch. What about the steak place? Steak. Then, BINGO. A Baraboo restaurant. We had hamburgers, we think, we both ate the same dinner, my spouse says. What else? Then my spouse says, wait, did you drink at the water fountain at the park? It comes back to me. We were eating dinner in Baraboo (40 miles away) because we’d taken a day trip to go hiking in a canyon near Devil’s Lake that had been washed out a few years ago and, oh yes, there was a hand pump for water and yes, I had drunk and filled my water bottle at it. My spouse had not. That hand pump was almost certainly drawing well water; it would not have been on a municipal water supply. It now seems that was the most likely source of the infection.
This was fascinating. I’m sure these probing phone calls are feed into a database that looks for patterns. If that hand pump was the source, I wasn’t the only one using it that day as I waited in line while others filled their bottles there. My persistent interviewer did not, of course, stop probing once the water pump came up, but she did seem to get less exacting about trying to get me to remember what I’d eaten at each place.
Two interesting methods lessons. One is the persistent probing interview, and why it matters. And the second is that I doubt I ever would have had any way to remember that day in the woods with the hand pump if it wasn’t for the credit card records to jog my memory. There is also the personal lesson to be more careful about using hand pumps in rural areas. And of course, the institutional infrastructure lesson about the importance of public health organizations and protection of watersheds. I remember spending time in Russia where you really cannot drink the tap water because it is all contaminated.
I’m saving this example for methods classes, and sharing it for that reason.