Kaplan SL, Center KJ, Barson WJ, Ling-Lin P, Romero JR, Bradley JS, Tan TQ, Hoffman JA, Peters TR, Gurtman A, Scott DA, Trammel J, Gruber WC, Hulten KG, Mason EO. Multicenter surveillance of Streptococcus pneumoniae isolates from middle ear and mastoid cultures in the 13-valent pneumococcal conjugate vaccine era. Clin Infect Dis. 2015 May 01; 60(9):1339-45.