Abstract
This review presents critical insights into the clinical and epidemiological aspects of participation of various causative agents of opportunistic infections in the formation of complex comorbidity in humans. Clinical and epidemiological aspects are important components of complex comorbidity due to wide occurrence, causing negative impact on human health and population reproduction. The data on the relative incidence of mono- and concurrent-infections are heterogeneous. The causative agents of opportunistic infections can persist in the human body, cause latent endogenous infections, and engage in intracellular parasitism. A high level of circulation of opportunistic infections pathogens creates the conditions for atypical forms of multisystemic pathology. Broad clinical polymorphism and low specificity cause untimely diagnosis. Low tension of anti-infection immunity is associated with the low protective activity of pathogens and mosaicism of antigens. Examples of complex comorbidity with the involvement of herpes viruses can be a combination of EpsteinBarr virus and Corynebacterium diphtheriae, cytomegalovirus and infectious mononucleosis and a combination with Streptococcus pneumoniae, Haemophilus influenzae type b. The combination of cytomegalovirus infection can occur with either one infectious disease or multiple ones (for example, metapneumovirus infection, S. pneumoniae, Bordetella pertussis, and H. influenzae). Mycoplasmosis can have a course of specific polyetiological infections in combination with viruses, bacteria, fungi, and protozoa. The authors also paid attention to the manifestation forms of pneumocystosis in the impairment of the immune status of the body (combination with toxoplasmosis, blastocystosis, etc.). The possibility of association of blastocysts with Staphylococcus spp., Klebsiella pneumoniae, and Lamblia intestinalis has been shown, and the roles of anisacidosis and chlamydial infection in the formation of complex comorbidity are also discussed. Complex comorbidity requires increased attention to diagnosis, assessment of epidemiological determinants, and the organization of epidemiological studies for its analysis.