Scientific analysis can detect endemic TB

Tool can spot slow-growing clusters

RFLP analysis is known chiefly as a good tool for finding case clusters when there’s ongoing transmission, but some TB experts like using the technique to pinpoint slow-motion, mini-epidemics that evolve, like a flower opening in time-lapse photography over years, even decades.

RFLP analysis is especially useful where TB is endemic, says Nancy Dunlap, MD, medical director of the Alabama TB control program. "Here in my state, where we have a relatively high background rate of TB, our big problem isn’t outbreak-type situations, where you see lots of cases all at once. Instead, what we’ve got is more like a series of smoldering epidemics that go on for years. You don’t necessarily associate these cases with each other because they occur over such a long period of time."

That means TB controllers can have a hard time pinpointing the site where transmission is continuing to take place, she adds. But by using RFLP, it’s possible to find links that weren’t apparent before. "It’s usually a specific site," Dunlap says. "Often it’s a place where some kind of illicit activity is taking place — a shothouse or maybe a convenience store where people gather to smoke crack in the bathroom." Because of the illicit nature of the goings-on, people are reluctant to name contacts; even if they were willing, they often don’t know one another by name.

By correlating RFLP analysis with demographic information, Dunlap has come up with some interesting clusters, she says. One cluster is composed of elderly people all born in the first decade of the 1900s. "We don’t yet know the association," she says, adding that TB controllers already have ruled out nursing homes because they’re monitored on a regular basis. "But clearly, there’s something there."

There’s really no substitute for RFLP in endemic settings, she says "It’s the only tool I know of that can help you link patients over a long period of time, take out the static, and show you where you need to go to interrupt the transmission."