Streptococcus pneumoniae in hospitalized patients with pneumonia: epidemiology and implications

Background Streptococcus pneumoniae (SP) is a major cause of pneumonia worldwide representing a significant problem from the public health viewpoint. The aim of our study was to assess the frequency of SP in hospitalized patients with pneumonia and investigate its relationship with patients' characteristics. Methods A deterministic record linkage of hospital discharge and microbiology laboratory surveillance databases of a teaching hospital in Rome was used to identify all patients over 15 years old (y) with a diagnosis of pneumonia and a microbiological ascertainment between November 2010 and March 2013. Pneumonia ICD-9-CM codes were used to identify the study population. The frequency of SP was assessed with respect to patients' characteristics. Results 1216 (64% males) of a mean age 65 (SD = 18) y patients with pneumonia were identified. Of them, 707 (58%) had a positive microbiological result. Among the latter, mixed bacterial co-infections were detected in 552 (74%) cases. The most frequently isolated organism was SP in 288 (41%) cases. Nevertheless, SP was the sole isolated agent in only 6 (0.8%) cases. There were no significant differences between men and women with respect to the frequency of SP. Eventually, the frequency of SP among patients with a positive microbiological result was higher in the age group 15-64 y than in 65+ y (45% vs 37%, p = 0.038). When considering only subjects with at least one comorbidity the frequency of SP was higher among the 15-64 y age group (53% vs 44% in 15-64 y and 65+ y respectively, p = 0.040). Conclusions Our study revealed that SP was the most frequent isolated pathogen in hospitalized patients with pneumonia. However, the SP coexistence with other pathogens was present in the vast majority of cases. Interestingly, SP was highly frequent among people with comorbidities, in particular in the age group 15-64 y. This emphasizes the importance of vaccination in this group of patients. Key messages This study shows that more than 40% of pneumonia with a positive microbiological result are caused by Streptococcus pneumoniae. Preventive strategies to limit Streptococcus pneumoniae infections among adults and individuals affected by comorbidities are needed.