Patients infected with atypical pathogens ( hazard ratio [ HR ] , 0.33 ; 95 % CI , 0.13-0 .85 ) or with Pneumonia Severity Index ( PSI ) category IV pneumonia ( HR , 0.81 ; 95 % CI , 0.59-1 .10 ) were less likely to reach clinical stability with monotherapy , whereas patients not infected with atypical pathogens ( HR , 0.99 ; 95 % CI , 0.80-1 .22 ) or with PSI category I to III pneumonia ( HR , 1.06 ; 95 % CI , 0.82-1 .36 ) had equivalent outcomes in the 2 arms .