Causes of pneumonia in children

Causes of community-acquired (domestic) pneumonia in children

Etiology of community-acquired pneumonia is represented by mixed microflora in 50% of cases, and in most cases (in 30% of cases) community-acquired pneumonia is caused by a virus-bacterial association. This reason is more often observed in children of early and preschool age. In a small percentage of cases (5-7%), the etiology is represented by a virus-virus mixed microflora and in 13-15% by a bacterial-bacterial association, for example, the association of Streptococcus pneumoniae with noncapsular Haemophilus influenzae. In the remaining 50% of cases, the etiology of community-acquired pneumonia is only bacterial. The type of bacterium-pathogen depends on the age of the child.

In the first 6 months of life the etiologic role of pneumococcus and hemophilic rod is negligible, since antibodies to these pathogens are transmitted from the mother in utero. The leading role in this age is played by E. Coli, K. Pneumoniae and S. Aureus and epidermidis. The etiologic significance of each of them is small and does not exceed 15-20%, but they determine the most severe forms of the disease in children, complicated by the development of infectious-toxic shock and destruction of the lungs. In 3% of cases, Moraxella catarrhalis occurs . Another group of pneumonia at this age is pneumonia caused by atypical pathogens, mostly Chlamydia trachomatis, which infants get infected from the mother, or intranatally (less often antenatal), or in the early days of life. In addition, Pneumocystis carinii infection is possible (especially in prematurity).

From 6 months of age and up to 6-7 years of age, pneumonia is mainly caused by Streptococcus pneumoniae, which accounts for up to 60% of all cases of pneumonia. Often, as already mentioned, seedless hemophilic rod is also sown. Haemophilus influenzae type b are less common (in 7-10% of cases). This causative agent, as a rule, causes severe pneumonia, complicated by the destruction of the lungs and pleurisy. Diseases caused by S. Aureus, S. Epidermidis and S. Pyogenes usually develop as a complication of severe viral infections, such as influenza, chicken pox, measles, and herpetic infection, and do not exceed 2-3% in frequency. Pneumonia caused by atypical pathogens in children of this age is due mainly to M. Pneumoniae and C. Pneumoniae. It should be noted that the role of M. Pneumoniae as a cause of pneumonia in children has clearly increased in recent years. Mycoplasma infection begins to be diagnosed more often in the second-third years of life. C. Pneumoniae is detected, as a rule, in children older than 5 years.

The etiology of pneumonia in children older than 7 years practically does not differ from that of adults. More often pneumonia is caused by S. Pneumoniae (up to 35-40% of all cases), M. Pneumoniae (23-44%), S. Pneumoniae (15-30%). Such pathogens as H. influenzae type b, Enterobacteriaceae (K. Pneumoniae, E. Coli, etc.), S. Aureus and S. Epidermidis, practically do not reveal.

Viruses can also cause community-acquired pneumonia. They can be both an independent cause of the disease, and (much more often) create viral-bacterial associations. The most important is the PC virus, which occurs in approximately 50% of cases of viral and viral-bacterial diseases; in 25% of cases, the cause of the disease is parainfluenza viruses of the 3rd and 1st types. Influenza A and B viruses and adenoviruses play a small role. Rhinoviruses, enteroviruses, coronaviruses are detected less often. It should be noted. That the pneumonia caused by viruses of measles, rubella, chickenpox are described.

[1], [2], [3], [4], [5], [6], [7]

Hospital-acquired (hospital, nosocomial) pneumonia in children

Hospital pneumonia significantly differs from community-acquired pneumonia in the spectrum of pathogens and their resistance to antibiotics. The spectrum of bacterial and fungal pathogens of the hospital fan-non-associated pneumonia is in a certain dependence on the profile of the hospital where the patient is. Thus, in patients with a therapeutic department, hospital pneumonia may be caused by pneumococcus, but more often - S. Aureus, or S. Epidermidis, or K. Pneumonia. Preterm in the hospital of the second stage of nursing - S. Aureus, or S. Epidermidis, or K. Pneumoniae, or (in more rare cases) Pneumocystis carinii.

Bacterial etiology of ventilator-associated hospitalized pneumonia, depending on the patient's stay

Character of separation	Pathogens of pneumonia
Resuscitation, intensive care	Ps. aeruginosa S. Aureus et epidermidis E. coli K. Pneumoniae Acinetobacter spp. Candida spp.
Surgery, burn department	Ps. Aeruginosa K. Pneumoniae E. Coli Acinetobacter spp. S. Aureus et epidermidis Anaerobes
Oncohematology	Ps. Aeruginosa K. Pneumoniae E. Coli and other enterobacteria S. aureus et epidermidis Aspergillus spp
Therapeutic departments	S. Aureus et epidermidis K. Pneumonia S. Pneumoniae
Divisions of the second stage of nursing preterm	S. Aureus et epidermidis K. Pneumonia Pneumocystis carinii

In the etiology of hospital pneumonia (as well as in the etiology of community-acquired), respiratory viruses occupy a significant place in children (up to 20% of cases). These pathogens cause the disease independently or more often in the form of a virus-bacterial association, in 7% of cases - in the form of association of fungi of the genus Candida with viruses or viruses and bacteria. Among the viruses that caused hospital pneumonia, influenza A viruses predominate, and less often influenza B. Parainfluenza viruses, adenoviruses and Coxsackie viruses B are even less common, and PC viruses and Coxsackie A viruses are detected in single observations.

Among the fan-associated hospital pneumonia, early and late pneumonia are isolated. Their etiology is different. Pneumonia, which developed in the first 72 hours after intubation, usually have the same etiology as community-acquired pneumonia in patients of the same age. This is due primarily to the fact that in their pathogenesis the microaspiration of the contents of the oropharynx and, correspondingly, the microflora, which is contaminated and colonized by the mucous membranes of the upper respiratory tract, is of primary importance. Thus, in children aged 2 weeks to 6-7 months of age, early VAP are usually caused by E. Coli, K. Pneumoniae, S. Aureus et epidermidis. In children aged 6-7 months to 6-7 years - S. Pneumoniae, although there may be pneumonia caused by H. Influenzae. In children and adolescents older than 7 years of pneumonia, M. Pneumonia and, more rarely, S pneumoniae are usually caused .

With late VAP (when pneumonia develops after 72 hours of ventilation), etiology of hospital pneumonia is dominated by pathogens such as Ps. Aeruginosa, S. Marcescens, Acinetobacter spp, as well as S. Aureus, K. Pneumoniae, E. Coli, Candida, etc. The reason for this is that late VAP are caused by hospital microflora colonizing the respiratory apparatus, and therefore non-fermenting Gram-negative bacteria and, above all, Pseudomonas aeruginosa. The etiology of the ventilator of associated pneumonia is presented in Table. 76-2.

Causes of fan-associated hospitalized pneumonia in children

Ventilator-associated pneumonia	Pathogens of pneumonia
Early	The etiology corresponds to the age-related aetiological structure of community-acquired pneumonia
Late	Ps. aeruginosa Acinetooacter spp S. Marsensens S. Aureus K. Pneumoniae E. Coli Candida spp

Especially it is necessary to say about etiology of pneumonia in patients with immunodeficiency. In children with primary cellular immunodeficiencies, HIV-infected and AIDS patients, pneumonia is more often caused by Pneumocystis carinii and Candida fungi , as well as M. Avium-intracellulare and herpes virus, cytomegalovirus. With humoral immunodeficiency pneumonia is more often caused by S. Pneumoniae, as well as by staphylococci and enterobacteria, with neutropenia caused by gram-negative enterobacteria and fungi.

[8], [9], [10],

Causes of pneumonia in immunocompromised patients

Groups of patients	Pathogens of pneumonia
Patients with primary cellular immunodeficiency	Pneumocystis Mushrooms of the genus Candida
Patients with primary humoral immunodeficiency	Pneumococcus Staphylococci Enterobacteria
Patients with acquired immunodeficiency (HIV-infected, AIDS patients)	Pneumocysts Cytomegaloviruses Viruses of herpes Mycobacterium tuberculosis Fungi of the genus Candida
Patients with neutropenia	Gram-negative enterobacteria Fungi of the genus Candida, Aspergillus, Fusarium

[11], [12], [13], [14], [15], [16], [17]

Pathogenesis of pneumonia in children

In the pathogenesis of pneumonia, a low level of anti-infective protection in children (in comparison with adults) plays a certain role. Especially it is peculiar to children of early age, therefore the propensity to develop pneumonia is higher. In addition, the relative insufficiency of mucociliary clearance is important, especially with the development of respiratory viral infection. With which, as a rule, and begins pneumonia in the child, especially the early age. It should also be noted the propensity of the mucous membrane of the respiratory tract to edema and the formation of viscous sputum in the development of inflammation, which also violates the mucociliary clearance in the child.

There are 4 main pathogenetic mechanisms of the development of pneumonia: microspiration of the secretion of the oropharynx, inhalation of an aerosol containing microorganisms, hematogenous spread of microorganisms from the extrapulmonary focus of infection and direct spread of infection from neighboring affected organs.

Of these mechanisms in children, the most important is the microaspiration of the secretion of the oropharynx. It plays a major role in pathogenesis as a community-acquired pathway. And hospital pneumonia. Especially in cases of bronchial obstructive syndrome, which is so frequent in children of early and preschool age, airway obstruction also plays a significant role in microaspiration. Often observe a combination of these mechanisms. Aspiration of a large amount of contents of the upper respiratory tract and / or stomach is characteristic of newborns and children of the first months of life and occurs during feeding and / or when vomiting, as well as when regurgitation.

When microaspiration (or aspiration, or inhalation of an aerosol containing microorganisms) coincides with a violation of the mechanisms of nonspecific resistance of the child's organism, for example, in ARVI, favorable conditions for the development of pneumonia are created. The hematogenous spread of microorganisms from the extrapulmonary focus of infection and the direct spread of infection from neighboring injured organs is also of great importance for pathogenesis. However, more often these mechanisms play an important role in the development of secondary pneumonia.

Factors predisposing to microaspiration, and consequently, to the development of pneumonia:

• age up to 6 months, especially premature babies;
• encephalopathy of various genesis (posthypoxic, with malformations of the brain and hereditary diseases, convulsive syndrome);
• Dysphagia (vomiting and regurgitation, esophageal tracheal fistulas, achalasia, gastroesophageal reflux);
• bronchoobstructive syndrome with respiratory, including viral, infection;
• mechanical damage to protective barriers (nasogastric tube, endotracheal intubation, tracheostomy, gastroduodenoscopy);
• repeated vomiting during intestinal paresis, severe infectious and somatic diseases;
• carrying out mechanical ventilation; o development of a critical condition due to the underlying disease;
• the presence of malformations (especially heart and lung defects);
• neuromuscular blockade.