Helfenberger, L., R. Fischer, S. Giezendanner, and A. Zeller. “Risk Factors for Peritonsillar Abscess in Streptococcus A-Negative Tonsillitis: A Case Control Study”. Swiss Medical Weekly, vol. 151, no. 0304, Jan. 2021, p. w20404, doi:10.4414/smw.2021.20404.