SEATTLE — A major study testing whether Americans would take their H.I.V. drugs every day if they were paid to do so has essentially failed, the scientists running it announced Tuesday at an AIDS conference here.

Paying patients in the Bronx and in Washington — where infection rates are high among poor blacks and Hispanics — up to $280 a year to take their pills daily improved overall adherence rates very little, the study’s authors said.

The hope was that the drugs would not only improve the health of the people taking them, but help slow the spread of H.I.V. infections. H.I.V. patients who take their medicine regularly are about 95 percent less likely to infect others than patients who do not. The Centers for Disease Control and Prevention estimates that only a quarter of all 1.1 million Americans with H.I.V. are taking their drugs regularly enough to not be infectious.

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