Masking and allocation concealment.
Masking was achieved via the use of a placebo that was identical in appearance, taste, and smell to the azithromycin. The formulation of the two medications was the same except for the active ingredient. To facilitate both masking and allocation concealment, study medication bottles were labeled with one of eight treatment letters, with four letters randomly assigned to correspond to azithromycin and four to placebo. Medication labels were identical except for the randomly assigned treatment letter. Each unique study identification number that was assigned to participants after enrollment was randomized to one of the eight treatment letters. The treatment letter was only revelated after enrollment and baseline procedures were complete, and the child was treated with a medication bottle labeled with the corresponding treatment letter. Study participants, caregivers, staff, and investigators were masked to treatment allocation.