After adjusting for potential confounders , we found that the risk of HIV seroconversion among participants who were daily smokers of crack cocaine increased over time ( period 1 : hazard ratio [ HR ] 1.03 , 95 % confidence interval [ CI ] 0.57-1.85 ; period 2 : HR 1.68 , 95 % CI 1.01-2.80 ; and period 3 : HR 2.74 , 95 % CI 1.06-7.11 ) .
O O O O O O O O O O O O B-DiseaseOrPhenotypicFeature I-DiseaseOrPhenotypicFeature O O O O O O O B-ChemicalEntity I-ChemicalEntity O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O