Etiology of community-acquired pneumonia in patients admitted to an infectious diseases hospital: a retrospective epidemiological study

The etiology of pneumonia remains a subject of close interest for researchers and practicing physicians. Many authors have noted a low rate of etiological identification for community-acquired pneumonia in the Russian Federation. Sample-based researches in these conditions are an important source of information. The purpose . To analyze the etiological structure of community-acquired pneumonia among hospitalized patients. Materials and Methods . The epidemiological retrospective descriptive observational research was conducted. We analyzed medical records (electronic health records) of patients (adults and children) hospitalized with pneumonia in the period from January 2024 and December 2024, inclusive at infectious diseases hospital in Moscow. The etiology of pneumonia was considered based on the patient’s final diagnosis. The sample size was 4,807. Inclusion criteria were: laboratory-confirmed diagnosis of community-acquired pneumonia, influenza with pneumonia, or COVID-19 with pneumonia; biological material was collected within the first 24 hours of hospitalization. Exclusion criteria included: patients with diagnoses “pneumonia without specifying the pathogen “; “pneumonia in diseases classified elsewhere”; patients with HIV infection, viral hepatitis B and/or C; and patients hospitalized at other medical organizations in the previous 14 days for a period of more than 48 hours. Data were analyzed using descriptive statistics. Statistical processing was carried out in the IBM SPSS Statistics 20 program, visualization in Microsoft Excel. Results. The most frequent etiologies of communityacquired pneumonia among hospitalized patients were: M. pneumoniae (28.7%; 95% CI 27.3–30.2), SARS-CoV-2 (21.1%; 95% CI 19.8–22.4), S. pneumoniae (11.8%; 95% CI 10.8–12.8), H. influenzae (10.7%; 95% CI 9.7–11.7), and rhinovirus (5.6%; 95% CI 4.9–6.3), with other pathogens occurring less frequently. Mixed etiology pneumonia accounted for 19.4% (95% CI 17.8–21.1) of cases. The predominant pathogens varied by age group: S. pneumoniae, H. influenzae, and M. pneumoniae prevailed among children; M. pneumoniae was the leading cause in adults aged 18–34; S. pneumoniae, H. influenzae, and M. pneumoniae were most common in the 35–64 age group; SARS-CoV-2, S. pneumoniae, and H. influenzae predominated in the 65–84 group; and SARS-CoV-2, influenza viruses, S. pneumoniae, and H. influenzae were most prevalent in patients aged 85 and older. A shift in the prevailing pathogen was observed throughout the year: from January to March, viral pneumonias had the highest proportion (caused by influenza in January, and SARS-CoV-2 and non-influenza respiratory viruses in February and March). Bacterial pathogens (S. pneumoniae, H. influenzae, etc.) predominated during the spring-summer period (April to July), while M. pneumoniae was most prevalent from August to November, followed by an increase in influenza-related pneumonia cases in December. Conclusion . In conclusion, the most frequent pathogens of community-acquired pneumonia among hospitalized patients in 2024 were M. pneumoniae, SARS-CoV-2, S. pneumoniae, H. influenzae, and rhinovirus. The results demonstrate varying levels of pathogen significance across different age groups, seasonal shifts in the predominant agents throughout the year, and a substantial proportion of mixedetiology pneumonia cases.