The paper provides etiological description of community-acquired pneumonia at young people in closed groups (armed forces personnel), as well as analysis of pathogenicity, virulence and persistence factors of the aforementioned microbe strains. The authors have studied serotype parameters of pneumococcus strains among patients suffering from community-acquired pneumonia and healthy young people during group formation and in the course of military service, making estimate of their differences in the virulence and persistence factors activity. According to the findings, increase in pneumococcus strains of 14, 6B, 23 serotypes was observed among the suffering patients, while 1, 14, 23, 18N and 19F serotypes were detected among the healthy people during the first year of the service, and their replacement by 23, 9, 14, 15, 19F and 6 A serotypes occurred in the course of the second year.