“The biggest issue has been to identify those 10 percent,” said Dr. Eliud Wandwalo, senior coordinator for TB at the nonprofit Global Fund. “We don’t have any good indicator to show you which of these people who are infected might progress and become sick.”

For many people who are healthy, or who simply feel healthy, the drugs have been a tough sell.

For decades, the standard course has been an antibiotic called isoniazid that kills the bacteria causing TB only when they are replicating. The drug must be taken daily for nine months, in the hope of catching the bacteria as they multiply, and it can cause numbness, nausea and fever. Isoniazid also can cause liver toxicity, so people taking it are advised not to drink alcohol for the entire nine months.

“Traditionally, completion rates have been very poor,” said Dr. Alison Grant, an epidemiologist at the London School of Hygiene & Tropical Medicine.

Doctors sometimes decline to prescribe the antibiotic because of worries about exposing otherwise healthy people to the side effects, or contributing to a rise in drug-resistant bacteria if patients don’t complete the full course.

Both those concerns are unfounded, said Dr. Grant. Doctors “just stay away from it, despite the evidence showing otherwise.”

In the past decade, scientists have come up with two shorter courses: a drug called rifampin taken every day for four months; or a combination of isoniazid and rifapentine, taken once weekly for three months.

Still, for some people, remembering to take the pills — and all 11 pills together — once a week can be more challenging than taking them every day, Dr. Grant said.