Microbiological characterization of Streptococcus pneumoniae and non-typeable Haemophilus influenzae isolates as primary causes of acute otitis media in Bulgarian children before the introduction of conjugate vaccines - Setchanova, L P; Kostyanev, T; Alexandrova, A B; Mitov, I G; Nashev, D; Kantardjiev, T (Ann Clin Microbiol Antimicrob, 2013)