Intervention implementation
At each village clinic visit, to prevent control contamination, the study drugs were dispensed and taken after meals under direct observation by trained village doctors. Participants had no access to prescription drugs by themselves. During the pre-specified six-week phase, participants in the preventive treatment group were allowed to take the medicine within three days in case of interruptions. However, for the last dose, considering the need for more physical examination and information collection, participants were allowed for seven days’ delay in order to improve the adherence [