<prompt> Most common organism causing UI in adult?H influenzaStap aureusStrepto pneumoniaStreptococcus pyogenes  <response>: Ans. is d i.e., Streptococcus pyogenes Most common cause of upper respiratory tract infection is viral infection. Rhinovirus is the most common cause. Among the bacteria, group A beta-hemolytic streptococci streptococcus pyogenes is the most common cause. And most common type of infection is pharyngitis. 