Tuesday, March 10, 2009

Microbes and Genetics

This morning on the way in to the office, I caught a story on NPR about the role of genetics in susceptibility to infectious diseases.

What factors in the host make the host more susceptible to particular germs than others? This question is often asked of me. I once investigated an elementary school outbreak of coxsackie virus. The school nurse called me: She had more than 100 vomiting kids. Could I help? I grabbed an intern (new on the job), and called the sanitarian to meet me out there. Upon arrival, we were confronted with a hallway lined with little kids puking in trash cans.

Here's the thing about a bunch of kids puking: It is really, really difficult to figure out who is actually sick and who is sick because of the sight/smell/sound of everyone else throwing up. The school nurses call it WGA. They have "what's going around." We focused on those who first succumbed.

They were mostly first graders. The little epidemiologists had already determined this was all a result of the hot dogs they had eaten in the cafeteria the day before. I remember school cafeteria hot dogs. I get why they were pegged. Nonetheless, the intern and I set about conducting our own interviews. We tried to focus on the teachers. Who among them were sick? What did they eat? Was it different from the well teachers? We interviewed some of the kids too. Next time you talk to a first grader, ask her what she ate for lunch the day before. Recall bias is a challenge! Despite the children's insistence that the hot dogs were the problem, statistically in our case control study we did not find that to be the case. No particular food stuck out as the likely culprit.

This outbreak appeared to be point-source -- in other words, they were probably all infected at the same time by the same source. All of the children and teachers who got sick did so within a couple of hours of each other. Interestingly, once they all recovered there were not any more cases.

The sanitarians had better luck. They identified a cafeteria worker who had been sick for a few days before all this, and came to work with active diarrhea. Was she our index case? Schools are required to save a tray of all the foods served for at least a week just in case something like this happens. We took the tray and sent it to the lab. The lab found a high coliform count (in other words, fecal contamination).

In the end we hypothesized that the sick cafeteria worker had contaminated hands (wash your hands people!!) and spread her germs all over the cafeteria. It didn't matter what the kids ate; the contamination was probably not contained to one food item.

Of all the kids, only one went to the doctor, so despite the puking drama, the kids were not that sick. But the one kid who went to the doctor actually went to the emergency room. He was diagnosed with viral myocarditis, an infection of his heart, as a result of coxsackie virus.

We don't know for sure that the other children has coxsackie virus. The samples that were taken were unfortunately tested for bacterial infections only and all came back negative. But outbreaks like this are certainly not unheard of. But if the outbreak was due to coxsackie, why is it that some of the children experienced mild gastrointestinal symptoms, but this one child was hospitalized because the virus entered his heart? Perhaps the answer is that some people are genetically more susceptible to certain infectious diseases than others.

1 comment:

  1. You are SO cool to have such a blog-worthy job. What a great gig! ;)