Cyclicity of the Epidemic Process

An epidemic process is the process of spreading infectious diseases in a human population. It can be cyclical, that is, it naturally alternates between periods of rise and fall in morbidity. The cyclical nature of the epidemic process is one of the main mechanisms for regulating the population size of microorganisms and infections.

The cyclical nature of the epidemic is due to the natural alternation of periods of rise and fall in infectious morbidity. The rise of the epidemic is associated with an increase in the number of infected people and the spread of the disease. This may occur due to an increase in the number of sources of infection, a decrease in the level of immunity in the population, increased contact between people, or changes in environmental conditions.

The decline of the epidemic occurs as a result of a decrease in the number of infected people and the spread of the disease. This may be caused by a reduction in the number of sources of infection, an increase in the level of immunity in the population, or changes in environmental conditions that reduce the likelihood of infection spreading.

The pattern of cyclicality of the epidemic process is important for understanding the dynamics of infectious diseases and developing measures to prevent and combat them. Knowing that an epidemic can have periods of ups and downs allows us to plan strategies to combat infectious diseases and prevent their spread.

The cyclical nature of the epidemiological process ensures that the population maintains internal stability and a reserve of viability under conditions of long periods of unfavorable state of the anthropoecosystem. In changing conditions or during periods of prolonged adversity (poverty, crop failures, wars), the cyclical waves of epidemic and economic development weaken, fade, and stop altogether. This situation is called depression of periodic states of the cyclic process. At the same time, in these periods, the prerequisites are being created for resuscitation and transition to a sharp rise in the epidemic and economic situation - to the next phase transition of the system object to a new stable remission of cyclic fluctuations. As noted in the previous lecture, depression of the system during the destruction of epizootic homeostasis is accompanied by the emergence of epidemic foci - the implementation of the mechanism of co-evolution of anthropoecosystems, which, along with the deterioration of living conditions and a decrease in living standards, causes parallel demographic destruction. The consequence of what is happening is a permanent increase in the number of epidemic patients and the spread of diseases beyond the boundaries of individual local epidemic situations. *Changes in tuberculosis incidence rates.* According to statistics, the incidence rate of tuberculosis during the year has quite significant differences from one epidemic season to another. Thus, the frequency of newly diagnosed cases of tuberculosis among the permanent population of the RSFSR ranges from 30 to 65 per 1 thousand people. The lowest indicator is typical for the winter months and spring, the maximum is noted in the summer, and in the fall its level decreases, reaching the same level as the winter indicators. Following the ideas about the cyclical nature of the epidemic process discussed in the previous lecture, it should be taken into account that an increase in morbidity is observed during epidemic cycles. However, as a result of the epidemiological analysis, it was revealed that the formation of seasonal epidemic peaks has a certain delineation - most often it occurs in August-September. Several weeks before the peak, there is a significant increase in the rate of increase in the number of tuberculosis cases. The table shows that the data for 1969-1970. differ significantly from the data for an earlier period, when the peak incidence occurred in October-November (in the recovery phase). When analyzing a three-year period, a significant blurring of the incidence dynamics was already observed, the peak was noted in the middle of the rise phase, but in the middle of the month (March) the curve decreased and rose again.