The rates of conversion to negative PCR results ( PCR conversion ) were 66.2 % in the benznidazole group and 33.5 % in the placebo group at the end of treatment , 55.4 % and 35.3 % , respectively , at 2 years , and 46.7 % and 33.1 % , respectively , at 5 years or more ( P < 0.001 for all comparisons ) .