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Respiratory tract infections (acute respiratory infections, ARI) can cause bacteria, viruses and fungi. Among bacterial pathogens, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, representatives of the Enterobacteriaceae family, Legionella pneumophila, causative agents of pertussis and diphtheria are more common. Among the viral pathogens of ARI, the representatives of four families of RNA-containing viruses (orthomixoviruses, paramyxoviruses, coronaviruses and picornaviruses) and two families of DNA-containing viruses (adenovirus, parvoviruses) are of greatest importance. Children of preschool age are subject to ARI, on average, 4-8 times a year, schoolchildren - 2-6 times a year, adults - 2-3 times a year. In contingents of often ill children, episodes of acute respiratory infections are registered 10 to 12 times a year. ARI can occur in mild, medium-heavy and severe (croup, bronchitis, bronchiolitis, pneumonia) forms.
General indications for laboratory testing for the purpose of conducting etiological diagnosis of acute respiratory disease is the presence of a patient with a sharply developed disease with local symptoms of respiratory tract infection in the presence of general toxication syndrome.
Infectious diseases of the respiratory tract must be differentiated from other diseases / conditions of non-infectious nature (allergy, pulmonary embolism, endocarditis of the tricuspid valve, bronchiolitis obliterans, systemic vasculitis, lung infarction, pulmonary eosinophilia, etc.) based on the results of clinical radiology and laboratory tests. It should be taken into account that pneumonia can develop due to infection by pathogens of especially dangerous and natural focal infections (ornithosis, Ku-fever, pulmonary form of anthrax, tularemia, etc.), therefore it is necessary to carefully collect and analyze the epidemiological anamnesis. In individuals with a decreased activity of the immune system, ARDs can also cause enteroviruses, herpes viruses, cytomegalovirus, candida, aspergillus, cryptococci, pneumocysts. It is necessary to conduct differential diagnosis of pertussis infection from acute bronchitis caused by other pathogens. Differential diagnosis of influenza and other acute respiratory infections is possible only with the help of laboratory research methods.
Laboratory tests used for the purpose of etiological diagnosis of upper and lower respiratory tract infections include direct (detection of the pathogen, its genome and AH) and indirect (detection of AT) diagnostic methods.
Microscopy (bacterioscopy) of Gram-smear smear and CSF allows to determine only the dominant morphotype of a potential bacterial pathogen. The value of the method and the tasks to be solved differ depending on which clinical material is selected from which locus of the organism. The purpose of researching the material from sterile loci - blood, CSF, pleural fluid, etc., is to determine the dominant morphotype of a potential bacterial pathogen and the relationship to Gram stains. In addition, the nature of the inflammatory reaction (leukocytosis or lymphocytosis) is revealed. The purpose of the study of the material from non-sterile loci - sputum, BAL, separated from the ear or paranasal sinuses - is to determine its suitability for bacteriological inoculation and determine the nature of the inflammation. The criterion for the suitability of sputum is the presence of less than 10 epithelial cells and more than 25 neutrophilic leukocytes in the field of view. Bacterioscopy of swabs from the nasal and oropharynx is not informative, therefore it is not carried out.
The culture method is used to isolate and identify a pure pathogen culture. In clinical practice, the method is used to detect bacterial pathogens of acute respiratory infections (Streptococcus pneumoniae, Haemophilus influenzae, etc.) with the exception of Mycoplasma pneumoniae and Chlamydophila pneumoniae. Bacteriological culture of the clinical material is carried out for the purpose of further cultural and biochemical identification of the pathogen, determination of antibiotic susceptibility. Indication for the study of blood is pneumonia, septic states, meningitis. The method allows to detect the pathogen in no more than 10-20% of hospitalized patients with community-acquired pneumonia.
Among viral pathogens ORZ, cultivation is possible for influenza A and B viruses, respiratory syncytial virus, 1-3 types of parainfluenza viruses, human metapneumovirus and adenoviruses, however, as a routine procedure, this method is used only for influenza viruses. The study is characterized by a sufficiently long duration, but it is indispensable in the case of a detailed study of pathogenicity, sensitivity to antimicrobial agents, antigenic and other properties of microbial isolates. The analytical characteristics of cultural studies largely depend on the quality of media used, as well as immunological and biochemical identification tests.