In the meantime, researchers are working on getting better at identifying TDR, so doctors will know what they're up against if one of their patients has a highly resistant strain of TB. A lab can easily test whether a strain is resistant to the so-called "first line" of TB drugs, but detecting more highly resistant forms of the bacteria is more difficult.
"There are not yet accepted assays for detecting resistance against second-line drugs," van Helden says. Often, doctors will have to wait months to determine whether a patient is actually responding to treatment. That's what happened in Naidoo's case: For a while, he was taking drugs that weren't having any affect on his disease.
Today, Naidoo has permanent lung scarring, but he's otherwise healthy. The scars on his skin have begun to fade, and he recently started running again. He says the experience has allowed him to become a better TB doctor because he can empathize with patients. But many of his colleagues who have been infected as a result of their work have left the field.
"Doctors and nurses are exposed so routinely to sick patients," he says. "We put our lives at risk every day."