Take your meds: Paper tests reveal hidden codes (above) when exposed to the urine of patients who have taken tuberculosis medication. The codes can be numerical sequences or bar codes (below image). Credit: Christopher Harting

Drug-resistant tuberculosis is a major public-health problem in poor nations. While antibiotics can effectively treat TB, they cause nausea and other side effects, and many patients stop taking them a month or two into the six-month treatment regimen. That can foster drug-resistant forms of the infection, which are deadlier and more expensive to treat.

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