Antimicrobial susceptibilities of 1,684 Streptococcus pneumoniae and 2,039 Streptococcus pyogenes isolates and their ecological relationships: results of a 1-year (1998-1999) multicenter surveillance study in Spain - Perez-Trallero,E.; Fernandez-Mazarrasa,C.; Garcia-Rey,C. (Antimicrob Agents Chemother, 2001)