Study design

This was a retrospective observational study of data that were prospectively collected over 20 years in the Hospital Clinic, Barcelona. All adults with a clinical diagnosis of S. pneumoniae pneumonia between January 1996 and December 2016 were included. To aid analysis, we divided the study population into four cohorts by time period: 1997–2001, 2002–2006, 2007–2011, and 2012–2016. For the purpose of publication the Ethics Committee of the Hospital Clinic of Barcelona approved the study (Register: 2009/5451), and the need for written informed consent was waived because of the non-interventional design.