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The influence of various factors on the development of the epidemic process
The epidemic process of respiratory infections is constantly influenced by various social, natural and biological factors of human life. So, in schools and preschool institutions with well-established ventilation and heating, the incidence of acute respiratory infections (ceteris paribus) is always lower than among children living in similar rooms with poor ventilation and irregular heating. According to foreign researchers, PC infection is especially common in large families with many children with low living standards. A direct correlation was found between the degree of crowding of people and the frequency of PC-virus isolation. It is known that outbreaks of mycoplasmal pneumonia most often begin in closed groups, with especially close and prolonged contacts of people among themselves. Poorly organized laboratory monitoring of convalescents returning to organized children's groups, and for staff working in such groups, often leads to the emergence of new foci of acute respiratory infections, primarily parainfluenza and MS infection.
Speaking about the influence of natural factors on the spread of acute respiratory infections, most often they mean the influence of climatic conditions. Special studies on this issue are extremely few, and the data cited are often contradictory. When studying the specific gravity of acute respiratory infections in northern and southern cities, no differences were found in the intensity of spread of PC infection; a higher incidence of parainfluenza in Leningrad, and adenovirus infection in Yerevan. In another observation, a different distribution was found: a significantly higher incidence (1.5-3.3 times higher) of adenovirus infection was observed in northern cities (Perm, Arkhangelsk) and approximately the same frequency of parainfluenza diseases was recorded in both northern and southern (Astrakhan, Dnepropetrovsk) cities. Most publications by foreign researchers indicate a lack of connection between outbreaks of PC infection with temperature, humidity, solar radiation intensity, rainfall and other climatic factors. Other observations revealed a definite relationship between the average monthly air temperature and the incidence of MS infection. We have already mentioned the pronounced "seasonality" in the spread of acute respiratory infections of a viral nature.
Of course, biological factors have the greatest influence on the level of acute respiratory infections - the pathogen property, the degree of susceptibility of people, gender, age, etc.
An increase in the virulence of respiratory virus strains circulating among the population increases the incidence, the number of group outbreaks, and the percentage of recurrent diseases. An analysis of the incidence carried out by employees of the epidemiology laboratory of the Research Institute of Influenza of the Russian Academy of Medical Sciences for 10 years shows that during the circulation of weakly virulent strains of the PC virus, the incidence per 100 people averaged 3.6, 3 outbreaks occurred, 17% of children were infected, no cases of reinfection have been reported; during the circulation of highly virulent strains, these indicators were significantly higher: the incidence rate per 100 people was 8.3, the number of outbreaks was 13, the infection rate of children was over 69%, and repeated diseases (reinfection) - 5.7%.
When respiratory viruses enter the body, the outcome of the infection is largely determined by the degree of susceptibility of people to the causative agent of this infection. So, with the infection of often ill (highly susceptible) young children with adenoviruses, clinically pronounced and severe diseases were noted 5 times more often; and when infected with PC viruses and Mycoplasma pneumoniae, it is 10-14 times more often than children who are rarely ill.
Of particular interest are data on the incidence of acute respiratory infections during influenza epidemics. A comparison of the incidence of ARI of viral etiology by year (1976-1985) showed that the highest rates were observed during the years of intense influenza A epidemics. First of all, this refers to adenovirus, parainfluenza, and PC-viral infections.
Most experts believe that the level of infection with pathogens of acute respiratory infections does not depend on the gender of the diseased. However, in some works it is noted that, for example, boys are more likely to suffer from PC infection than girls. Women are more likely to have a parainfluenza infection than men, although parainfluenza pathogens are more likely to be excreted from boys than from girls. As for age, a clear pattern is manifested here: with increasing age, the incidence of acute respiratory infections of viral etiology decreases; the severity of the clinical forms of the disease decreases, mainly due to an increase in the number of asymptomatic forms; the number of serious complications decreases.
In recent years, studies are increasingly being conducted to study the influence of environmental factors on the development of the epidemic process in influenza and other acute respiratory infections.
As an example, we give a generalization of the data from three observations. During 1980 - 1996 in territories with different levels of xenobiotic contamination (complex of harmful chemicals) and radionuclides, we studied the level, structure, dynamics of morbidity and mortality in long-term collectives and among hospitalized patients. A pronounced intensification of the epidemic process in all groups of acute respiratory infections was revealed - an increase (1.5-2 times) in the average annual and epidemic indicators of morbidity; an increase (1.5-2.5 times) in cases of a more severe course of diseases in hospitalized patients; significantly more often managed to isolate respiratory viruses from healthy individuals. Frequently ill children showed higher levels of highly toxic metals (mercury, cadmium) and autoantibodies to lung tissues in the blood.
Approximately similar data were obtained when studying the manifestations of the epidemic process and antiviral immunity in influenza and other acute respiratory infections among residents of areas affected by radionuclides as a result of accidents at the Chernobyl nuclear power plant. Soil contamination in areas contaminated with radionuclides was 137Cs at 1-5 Ci / km2. It was found that the incidence of children with influenza and acute respiratory infections in contaminated areas after the accident was 3 times higher than in unpolluted ones. Serological and virological studies indicated the activation of adenovirus infection in areas contaminated with radionuclides. The percentage of clinically healthy virus carriers in these areas was 35.1 among children 3-6 years old and 16.7 among children 7-14 years old, which was 1.5-2 times higher than in St. Petersburg and Vyborg. Herpes simplex viruses and latent strains of adenoviruses were most often identified. Children from areas contaminated with radionuclides showed a decrease in the number of total and active T-lymphocytes and the migration activity of leukocytes. A correlation was observed between the degree of soil contamination and the incidence rate.
The intensification of the infectious process is confirmed by the study of the clinical course of acute respiratory infections in children hospitalized for 10 years in infectious hospitals in St. Petersburg from two regions polar in industrial (chemical) pollution. In children living in an ecologically unfavorable area, more severe forms of the disease were more often detected - 13.6% of cases against 9% among children from the “clean” area; in a larger percentage of cases, the disease progressed against a fever of 39 ° C and above (41.2% versus 28.1% of cases); deeper1 respiratory tract lesions (bronchitis, pneumonia) developed 1.6 times more often. and at the peak of the rise of the RS-infsktsnn these differences were even more significant.
Thus, the intensity of the epidemic process with the same infection can vary under the influence of various factors. Therefore, the implementation of anti-epidemic, preventive and therapeutic measures must be approached differentially, taking into account climatic hydrographic, environmental, social conditions, age, biological characteristics of pathogens circulating in a given period and the epidemiological situation of influenza.
Using the IFM in Leningrad (1976-1985), the tendency of the spread of acute respiratory infections of various etiologies in three main age groups (children 0-6 years old, 7-14 years old and adults) and among all residents of the city as a whole was determined. Over 65 thousand patients were examined. An analysis of the data showed that the incidence of parainfluenza over the years has been steadily declining mainly due to the incidence of children 0-6 years old and adults; among children 7-14 years old, the incidence was slowly growing. On the contrary, the incidence of PC-infection increased markedly, especially among children 0-6 years old (2.5-3 times). The tendency for the spread of adenovirus infection turned out to be somewhat different: among all residents as a whole, the incidence rate gradually decreased, mainly due to a noticeable decrease among adults; among children aged 7-14 years and especially 0-6 years, the incidence over these years gradually increased. The incidence of mycoplasma pneumonia has markedly increased. But while in preschool children (0-6 years old) growth was pronounced, in schoolchildren (7-14 years old) it was slowed down, and in adults it was practically absent.
Thus, the IFM made it possible for the first time to establish the long-term dynamics of changes in the intensity of the epidemic process of the main etiological forms of acute respiratory infections in a large city, in various population groups.
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The influence of various factors on the development of the epidemic process
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