| Summary: | <h4>Background</h4>TB persists despite being relatively easy to detect and cure because the journey from the onset of symptoms to cure involves a series of steps, with patients being lost to follow-up at each stage and delays occurring among patients not lost to follow-up. One cause of drop-off and delay occurs when patients delay or avoid returning to clinic to get their test results and start treatment.<h4>Methods</h4>We fielded two SMS interventions in three Cape Town clinics to see their effects on whether people returned to clinic, and how quickly. One was a simple reminder; the other aimed to overcome "optimism bias" by reminding people TB is curable and many millions die unnecessarily from it. Recruits were randomly assigned at the clinic level to a control group or one of the two SMS groups (1:2:2). In addition to estimating effects on the full sample, we also estimated effects on HIV-positive patients.<h4>Results</h4>SMS recipients were more likely to return to clinic in the requested two days than the control group. The effect was smaller in the intent-to-treat analysis (52/101 or 51.5% vs. 251/405 or 62.0%, p = 0.05) than in the per-protocol analysis (50/97 or 51.5% vs. 204/318 or 64.2%, p = 0.03). The effect was larger among HIV-positives (10/35 or 28.6% vs. 97/149 or 65.1%, p<0.01). The effects of SMS messages diminished as the interval increased: significant effects at the 5% level were found at five and 10 days only among HIV-positives. The second SMS message had larger effects, albeit not significantly larger, likely due in part to lack of statistical power.<h4>Conclusions</h4>At 2 U.S. cents per message, SMS reminders are an inexpensive option to encourage TB testers to return to clinic, especially when worded to counter optimism bias.
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