Ciprofloxacin used at study entry independently predicted invasive Candida infection ( adjusted hazard ratio = 2.1 [ 1.1-4 .1 ] ) ; the risk gradually increased with duration of ciprofloxacin therapy : six of 384 in patients not exposed ( 1.6 % ) , eight of 212 ( 3.8 % ) when used for 1-2 days ( hazard ratio = 2.5 ; 95 % CI , 0.9-7 .3 ) , and 31 of 493 ( 6.3 % ) when used for 3 days ( hazard ratio = 3.8 ; 95 % CI , 1.6-9 .3 ; p = 0.002 ) .