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.

1. GBD 2021 Lower Respiratory Infections and Antimicrobial Resistance Collaborators. Global, regional, and national incidence and mortality burden of non-COVID-19 lower respiratory infections and aetiologies, 1990-2021: a systematic analysis from the Global Burden of Disease Study 2021. Lancet Infect Dis. 2024; 24(9): 974-1002. doi:10.1016/S1473-3099(24)00176-2

2. Bernadeta Dadonaite, Max Roser Pneumonia, 2024.: [Electronic resource]. – on October 10 2025. – URL: https://ourworldindata.org/pneumonia (date accessed: 10.11.2025)

3. On the state of sanitary and epidemiological well-being of the population in the Russian Federation in 2024: State report. Moscow: Federal Service for Supervision of Consumer Rights Protection and Human Welfare, 2025; – с. 424. (In Russ.)

4. Community-acquired pneumonia in adults: clinical recommendations of the Russian Federation [Electronic resource] /Ministry of Health of Russia; approved 2024. URL: https://cr.minzdrav.gov.ru/preview-cr/654_2 (date accessed: 10.11.2025)

5. Viral pneumonia: clinical recommendations of the Russian Federation [Electronic resource] / Ministry of Health of Russia; approved 2024. URL: https://cr.minzdrav.gov.ru/preview-cr/838_1. (date accessed: 10.11.2025)

6. Briko N.I., Korshunov V.A., Lomonosov K.S. Pneumococcal infection in the Russian Federation: the state of the problem. Bulletin of RAMS. – 2021; – 76(1): 28–42. doi: https://doi.org/10.15690/vramn1404 (In Russ.)

7. Popova A.Y., Yezhlova E.B., Demina Y.V., Omariev Z.M. Epidemiology and prevention of community-acquired pneumonia//Infectious diseases: news, opinions, training. 2019; – Т.8, – № 2. – С. 43-48. doi: 10.24411/2305-3496-2019-12005 (In Russ.)

8. Linok A.P., Kulikova M.M., Solomay T.V., Linok A.V., Semenenko A.V., Nikitina G.Y. Current trends in the development of the epidemic process of community-acquired pneumonia and their connection with upper respiratory tract infections. Epidemiology and infectious diseases. Topical issues. – 2024; – 2: 13-20. DOI: https://dx.doi.org/10.18565/epidem.2024.14.2.13-20 (In Russ.)

9. Zakharenkov I.A., Rachina S.A., Dekhnich N.N., et al. Etiology of heavy community-acquired pneumonia in adults: results of the first Russian multicenter research//Therapeutic Archive. – 2020. – Т. 92. – №1. – C. 36-42. doi: 10.26442/00403660.2020.01.000491 (In Russ.)

10. Rachina S.A., Kupryushina O.A., Strelkova D.A., Avdeev S.N., et al., Etiology of community-acquired pneumonia in hospitals of the Russian Federation after the COVID-19 pandemic: results of a multicenter prospective study Clinical microbiology and antimicrobial chemotherapy. – 2024; – 26(2):141-147. Doi: 10.36488/cmac.2024.2.141-147 (In Russ.)

11. Tsoumani E, Carter JA, Salomonsson S, Stephens JM, Bencina G. Clinical, economic, and humanistic burden of community acquired pneumonia in Europe: a systematic literature review. Expert Rev Vaccines. – 2023; – 22(1): 876-884. doi:10.1080/14760584.2023.2261785

12. Meyer Sauteur PM; European Society of Clinical Microbiology and Infectious Diseases Study Group for Mycoplasma and Chlamydia Infections (ESGMAC) Mycoplasma pneumoniae Surveillance (MAPS) study group. Mycoplasma pneumoniae: re-emergence and beyond. Lancet Microbe. – 2025 Nov; – 6(11):101191. doi: 10.1016/j.lanmic.2025.101191.

13. Rowlands RS, Meyer Sauteur PM, Beeton ML, On Behalf Of The Escmid Study Group For Mycoplasma And Chlamydia Infections Esgmac. Mycoplasma pneumoniae: not a typical respiratory pathogen. J Med Microbiol. – 2024 Oct; – 73(10): 001910. doi: 10.1099/jmm.0.001910.

14. Chubukova O.A., Shkarin V.V. Features of epidemiology of community-acquired pneumonia with combined etiology//Medical almanac. – 2017. – №4 (49). (In Russ.)

15. Rachina S.A., Kupryushina O.A., Yasneva A.S., Volosovtsova E.S., Strelkova D.A., Avdeev S.N., Frangu R.K., Merzheva Z.M., Samokhina A.S., Yeryshva D.S., Tikhonova M.A., Yatsyshina S.B. What do we know about mycoplasma pneumonia? // Practical pulmonology. – 2023. – № 3. – С. 20-30. (In Russ.)

16. On the state of sanitary and epidemiological well-being of the population in the Russian Federation in 2023: State report. Moscow: Federal Service for Supervision of Consumer Rights Protection and Human Welfare, 2024. – 364 p. (In Russ.)

17. MU 3.1.2/4.2.3973-23 “Epidemiological surveillance of community-acquired pneumonia”

18. Order of the Federal State Statistics Service of 13.12.2024 No. 639 On approval of forms of federal statistical observation No. 1 and No. 2 “Information on infectious and parasitic diseases “ and instructions (In Russ.)

19. Bobrova O.P., Zyryanov S.K., Chernaya V.V., Statsenko M.V., Parygina O.A. Implementation of microbiological monitoring for predicting the multidrug-resistant phenotype of respiratory isolates based on risk factor analysis in patients with community-acquired pneumonia. Real-World Data & Evidence. 2025;5(2):58-71. (In Russ.) https://doi.org/10.37489/27823784-myrwd-074.

20. Gadsby NJ, Musher DM. The Microbial Etiology of Community-Acquired Pneumonia in Adults: from Classical Bacteriology to Host Transcriptional Signatures. Clin Microbiol Rev. – 2022 Dec 21; – 35(4):e0001522. doi: 10.1128/cmr.00015-22. Epub 2022 Sep 27.