In adults older than 30 years old, the most frequent pathogens of pneumonia are bacteria, and in all age groups, under all socio-economic conditions and in all geographical areas, Streptococcus pneumoniae dominates. However, pneumonia can cause any disease-causing organisms, from viruses to parasites.
The respiratory tract and lungs are constantly exposed to disease-causing organisms in the environment; the upper respiratory tract and oropharynx are especially colonized by the so-called normal flora, which is safe thanks to the body’s immune defenses. If disease-causing organisms overcome numerous protective barriers, infection develops.
See also: Inflammation of the lungs
Protective factors of the upper respiratory tract include salivary IgA, proteolytic enzymes and lysozyme, as well as growth inhibitors produced by normal flora and fibronectin, which covers the mucosa and inhibits adhesion. Nonspecific protection of the lower respiratory tract includes coughing, clearance of ciliated epithelium and the angular structure of the respiratory tract, which prevents airspace infection. Specific protection of the lower respiratory tract is provided by pathogen-specific immune mechanisms, including opsonization of IgA and IgG, anti-inflammatory effects of surfactant, phagocytosis by alveolar macrophages and T-cell immune responses. These mechanisms protect most people from infection. But in many conditions (for example, in case of systemic diseases, malnutrition, hospitalization or stay in a nursing home, antibiotic therapy), the normal flora changes, its virulence increases (for example, when exposed to antibiotics) or the protective mechanisms are violated (for example, when smoking cigarettes, nasogastric or endotracheal intubation). Pathogens that in these cases reach the alveolar spaces by inhalation, due to contact or hematogenous spread or aspiration, can multiply and cause inflammation of the lung tissue.
Specific pathogens that cause inflammation of the lung tissue are not released in more than half of the patients, even with a comprehensive diagnostic study. But, since under similar conditions and risk factors there are certain tendencies in the nature of the pathogen and the outcome of the disease, pneumonia is classified into community-acquired (acquired outside the hospital), hospital-acquired (including postoperative and associated with artificial ventilation of the lungs), acquired in nursing homes, and in immunocompromised persons; This allows you to prescribe empirical treatment.
The term “interstitial pneumonia” refers to a variety of conditions with an unknown etiology characterized by inflammation and fibrosis of the pulmonary interstitium.
Community-acquired pneumonia develops in people with limited or no contact with medical institutions. Usually identified Streptococcus pneumoniae, Haemophilus influenzae and atypical microorganisms (ie. E. Chlamydia pneumoniae, Mycoplasma Legionella sp pneumoniae ). Symptoms - fever, cough, shortness of breath, tachypnea and tachycardia. The diagnosis is based on clinical manifestations and chest X-ray. Treatment is carried out empirically selected antibiotics. The prognosis is favorable for relatively young and / or healthy patients, but many pneumonia, especially caused by S. Pneumoniae and the influenza virus, are fatal in the elderly and debilitated patients.
Many microorganisms cause community-acquired pneumonia, including bacteria, viruses, and fungi. Different pathogens prevail in the etiological structure depending on the patient's age and other factors, but the relative importance of each as a cause of community-acquired pneumonia is doubtful, since most patients do not undergo a complete examination, but even with the examination specific agents are detected in less than 50% of cases.
S. Pneumoniae, H. Influenzae, S. Pneumoniae, and M. Pneumoniae are the most common bacterial pathogens. Chlamydia and mycoplasma are clinically indistinguishable from other causes. Frequent viral pathogens are respiratory syncytial virus (RSV)., Adenovirus., Influenza virus, metapneumovirus and parainfluenza virus in children and influenza in the elderly. Bacterial superinfection may complicate viral differentiation from bacterial infection.
C. Pneumoniae causes 5–10% of community-acquired pneumonia and is the second leading cause of lung infections in healthy people aged 5–35 years. C. Pneumoniae is usually responsible for outbreaks of respiratory tract infections in families, educational institutions and military training camps. It causes a relatively benign form that does not often require hospitalization. Pneumonia caused by Chlamydia psittaci (ornithosis) occurs in patients with birds.
The reproduction of other organisms causes an infection in the lungs in immunocompetent patients, although the term community-acquired pneumonia is commonly used for more frequent bacterial and viral etiologies.
Qu fever, tularemia, anthrax and plague are rare bacterial infections for which there may be marked pneumonia; The last three infectious diseases should raise suspicion of bioterrorism.
Adenovirus, Virus and virus is a widespread virus that rarely causes pneumonia. The varicella zoster virus and hantavirus cause lung infection in adults with chickenpox and gantavirus pulmonary syndrome; A new coronavirus causes severe acute respiratory syndrome.
The most common fungal pathogens are Histoplasma (histoplasmosis) and Coccidioides immitis (coccidioidomycosis). Blastomyces dermatitidis (blastomycosis) and Paracoccidioides braziliensis (paracoccidioidomycosis) are less common.
Parasites that cause lung damage in patients in developed countries include Plasmodium sp. (malaria) Tokhocara canis or catis (migration of larvae to internal organs), Dirofilaria immitis (dirofipariosis) and Paragonimus westermani (paragonimiaz).
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