An analysis of the dysentery epidemic process in Blagoveshchensk

The retrospective analysis of dysentery morbidity in Blagoveshchensk for the period of 1960-1987 was made. The regularities linking general natural and biological factors triggering the epidemic process with dysentery morbidity among the population are emphasized. The study revealed that under the conditions of Blagoveshchensk dairy products were of major epidemic importance among factors contributing to the transmission of dysentery. Such a factor as flies also had a definite influence on the epidemic process of dysentery. Another risk factor was drinking water which influenced the epidemic process both directly and indirectly through dairy products and, probably, other foodstuffs. Reliable correlation between dysentery morbidity among the population and the quality of dairy products, tap water and the number of flies was established.     

Nature of the epidemic process in Sonne and Flexner dysenteries and the causes of its induction

A comparative study of the epidemic process in Sh. sonnei and Sh. flexneri dysentery in different regions of the USSR revealed that the morbidity level of Sh. sonnei dysentery changed simultaneously in the regions under study at intervals of 2-3 years. Sh. flexneri dysentery showed morbidity rises occurring at intervals 6-8 years, and their occurrence did not coincide with the periods of elevated morbidity in Sh. sonnei dysentery. The data obtained in the cohort analysis and in the study of recurrent morbidity suggest that Sh. flexneri dysentery produces more pronounced postinfection immunity than Sh. sonnei dysentery, and the immunological factor probably affects the dynamics of the epidemic of these Shigella infections.     

The mechanism of the development of the epidemic process in Sonne dysentery

An epidemic outbreak of Sonne dysentery has been studied. The data of epidemiological monitoring before and after the epidemic have been analyzed. The real prognostication value of controlling the biological properties of Shigella sonnei and the increase of their intrapopulation heterogeneity at the period of the activation of the epidemic process of Sonne dysentery has been established.     

The definition of the forms of the epidemic process in intestinal infections]

A method for the identification of the forms of the epidemic process in dysentery (annual, seasonal and outbreak forms) has been worked out. The method is based on the calculation of the upper limits of annual and seasonal morbidity from the data on the period of several years with the use of the formulae of binomial distribution, serving as the mathematical model of alternative random values, such as morbidity. The comparison of actual morbidity for each year of the analyzed period with the upper limits of annual and seasonal morbidity helps identify the form of the epidemic process.     

The results of a seroepidemiologic study of Newcastle dysentery

Differences in the monthly distribution in the number of seropositive individuals among children and adults in years with different intensity of the epidemic process have been revealed. Immunity in cases of dysentery caused by S. newcastle reflects the yearly and seasonal activation of the epidemic process in this Shigella infection both in children and adults, the seroconversion characteristics observed in the year of a high morbidity level being a more objective criterion indicating the beginning of the activation of the epidemic process in dysentery caused by S. newcastle in comparison with the commonly registered morbidity level.     

The formulation of epidemiological hypotheses by using the methods of multivariate statistical analysis

The work demonstrates the main approaches to the use of the methods of multidimensional analysis for the creation of a hypothesis on the mechanism of the epidemiological process of dysentery in organized groups. The main risk factors have been established, and their role in the formation of annual, all-the-year-round and seasonal dysentery morbidity has been quantitatively evaluated. The results of analysis show the existence of diverse variants of the alimentary route of the transmission of infection, maintaining the epidemic process of dysentery, and the necessity of differentiating measures for the prophylaxis of all-the-year-round and seasonal morbidity.     

Manifestations of the cyclic nature of the epidemic process in dysentery

Different forms of dysentery, especially those caused by Sh. sonnei and Sh. flexneri, have been found to differ considerably in their cyclic recurrence. The development cycles of the epidemic processes of dysentery have an objective character, occur in the presence of any tendencies in the morbidity rate, and depend on the natural factors. Thus, the cycles of increase and decrease in morbidity are 3, 6, 9, 12 years for dysentery caused by Sh. sonnei and 6, 7, 8 years for dysentery caused by Sh. flexneri.     

The manifestations of the epidemic process in shigellosis and their theoretical interpretation]

This work, based on the retrospective analysis of shigellosis morbidity among organized groups of adults, as well as the whole population of the city, demonstrates the manifestations of the epidemic process. Water supply was common in the city, while water consumption was autonomous. The organized groups of adults did not use the products of the local milk-processing factory. The following facts were established. The dynamics of morbidity in Flexner's dysentery showed the change of dominating variants of the infective agent, which reflected the action of internal mechanisms of the development of the epidemic process. The role of Sonne dysentery in the total structure of shigellosis morbidity did not correlate with the consumption of milk and milk products. The theory of the self-regulation of the parasitic system and the theory of correspondence served as the basis for the theoretical interpretation of the manifestations of the epidemic process of Shigella infections. To ascertain the real correspondence of individual Shigella species to concrete transmission factors, further investigation are necessary.     

Seeding efficiency of the causative agent of dysentery as an index of the intensity of the epidemiologic process]

A study was made of the character and extent of interrelationship between the indices of dysentery morbidity and the indices of the seeding efficiency of dysentery bacilli persons who did not apply for medical aid. Establishment of such interrelationship permitted the authors to suggest the use of a more objective index of the seeding efficiency of dysentery bacilli, along with morbidity indices, for the assessment of the intensity of the epidemic process in this infection. On the basis of investigations carried out the authors came to the conclusion that a tendency to the increase of dysentery incidence the last few years chiefly bore a "statistical" character and was due to the improved detection of patients and carriers.     

The possibility of using the demonstration of Shigella antigens in the study of the epidemic process in dysentery

The detection of Shigella antigens in feces in accordance with the results of the passive hemagglutination test is more effective than the bacteriological method for finding out persons infected with Shigella, especially in the absence of pronounced clinical manifestations of dysentery, and can be used in the study of the mechanism of the epidemic process. The examination of two groups, each consisting of permanent and temporary members, has revealed that the use of this method for detection of the antigen makes it possible to perform the epidemiological analysis of morbidity and, in particular, to determine the source(s) of infection.     

The structure of the population morbidity with specific intestinal infections in areas with different intensities in the development of the epidemic process and an evaluation of its manifestations]

The authors analyze the morbidity structure in five enteric infections (typhoid fever, dysentery caused by Shigella flexneri and Shigella sonnei, hepatitis A, and hepatitis E (non A, non B) with the fecal/oral mechanism of the agent transmission) in three towns of Turkmenia and in the town of Novomoskovsk, Tula Province. The incidence of S. sonnei dysentery was found higher in Novomoskovsk and that of the rest enteric infections under study in Turkmenia. The incidence of typhoid fever and hepatitis E was the highest among schoolchildren and adults, whereas preschool children suffered mostly from hepatitis A and S. sonnei dysentery. The authors discuss the specific features of the epidemic process manifestation in enteric infections.     

Relation of the epidemiological characteristics of dysentery to the biological properties of the causative agents

The main forms of the epidemic manifestation of dysentery induced by different causative agents in 1975-1980 were revealed. During these years the cases of dysentery induced by Shigella sonnei, biovar II, were found to prevail (82.0-90.1%) both at the periods between epidemics and at the periods of the seasonal rise of morbidity. The experimental infection of white mice by intraperitoneal inoculation revealed no relationship between the seasonal rise of morbidity in dysentery and the virulence of its causative agents.     

Quantitative research on the cyclic fluctuations of the epidemic process in a number of infectious diseases in Bulgaria

The cyclic nature of the epidemic process in Bulgaria was studied by various methods (spectral analysis, etc.), forming a system. The morbidity dynamics in 10 infectious diseases (scarlet fever, rubella, measles, epidemic parotitis, whooping cough, diphtheria, typhoid fever, enterocolitis, bacterial dysentery, viral hepatitis) over the years of 1909-1983 were studied and cycles covering the periods of 3-4, 5-6, 10-11 and over 16 years were established. The data on the relative part of cyclic processes in the registered morbidity of infectious diseases, as well as information on the prognostication of the spread of infections in the absence of vaccinal prophylaxis, are presented.     

Formation of the dysentery epidemic process in three small towns]

Data are presented concerning the epidemiological analysis of Sonnei dysentery outbreaks in three towns connected by common nutrition and water supply. The epidemic processes in these populated localites were strongly interrelated. Possibilities of the effect of the water factor on the extent of Sonnei dysentery incidence were studied as well. The results of studies led to the conclusion on the presence of numerous action forms of the water factor which should be taken into consideration in carrying out prophylactic and antiepidemic measures in Sonnei dysentery.     

Ways of determination of the intensity of the epidemic process in Shigella sonnei dysentery]

Proper view on the true prevalence of Sonne dysentery characterised by polymorphous clinical picture in which many cases coursed in subclinical form could be reached only by using additional active methods for detecting the infection rate of the population. For this purpose the authors applied passive hemagglutination test which permitted to reveal the response of the organism to the antigenic stimulation in the course of two months after the sustained sickness. Over 12 000 persons were examined. According to the results of passive hemagglutination test seasonal activization of the epidemic process occurred one month earlier than it was revealed by recording of the incidence of the disease. The results of the mentioned test also showed infection rate of the population with Sonne dysentery to be as a rule greater than established by the official statistics.     

Experience in the study of the epidemiology and prevention of intestinal infections under conditions of the extreme north of western Siberia]

A study was made of peculiarities of typhoid and dysentery and of conditions promoting the spread of these infections in the Yamalo-Nenetsk National Area. The efficacy of antiepidemic measures conducted against these infections under conditions of the extreme north was assessed. A sharp fall of typhoid incidence was reached. As to dysentery-the complex of measures carried out could not significantly influence the direction of the epidemic process (for this purpose elaboration of special prophylactic measures is required).     

Natural population migration and the dysentery epidemic process

The complex analysis of materials obtained in different regions and territories of the Far East makes it possible to establish that the natural migration of population affects dysentery morbidity by enhancing the susceptibility of human population to this infection. The internal mechanisms of the influence exerted on morbidity by the natural migration of population is disclosed from the viewpoint of the theory of the self regulation of the epidemic process.     

Changes in the etiologic structure of Sonne shigellosis in its multiyear dynamics

The dynamics of Sonne dysentery morbidity in connection with changes in the structure of S. sonnei circulating among the population of Leningrad for the period of 1959-1984 was studied. Considering such sign as the leading fermentovar, three smaller periods were established in this stretch of time. Changes in the structure of circulating shigellae were accompanied by changes in the intensity and direction of tendencies or decrease in the manifest and asymptomatic forms of infection, as well as in annual morbidity levels and seasonal rises. A slow decrease in morbidity, which started in 1974, occurs in the presence of the predominant circulation of S. sonnei, fermentovar II, among the population; this fermentovar showed greater virulence and immunogenicity than other biovars. One of the decisive moments characterizing the dynamics of the epidemic process of Sonne dysentery is the intensity of the circulation of shigellae in the S-form, and the intensity of the population immunity of the host, linked with this fact, is subject to phasic fluctuations during each annual epidemic cycle.     

Modern methods of intraspecies typing of Sonne shigellae. II. Spread of Sonne shigellae of different biochemical types]

The paper presents the results of studying peculiarities of the Sh. sonnei of different biochemical types spread established by their typing scheme suggested by the authors earlier according to rhamnose, xylose and maltose. The epidemic process in dysentery both during the years of the rise and of the decline of its incidence at various territories of the countries proved to be maintained on account of circulation of Sh. sonnei of various biochemical types. The results of studying their dissociative and virulent properties confirmed the biological separation of individual biochemical types. An interrelationship between the character of the biochemical pattern of Shigellae sonnei at the individual territories and the persisting activity of different ways of dysentery transmission was determined. The results of studying the biochemical pattern could be used as an indicator of the degree of activity of individual ways of dysentery spread at various territories.     

Use of data on Shigella contamination and immunity indices for studying the activity of the epidemic process in dysentery

The comparative study of the monthly distribution of characteristics indicating the levels of contamination with Sh. sonnei and Sh. flexneri separately, as well as the seasonal dynamics of the corresponding antibodies, in the years with high and low morbidity levels has been made with the use the indirect hemagglutination test. The possibility of using these characteristics for the evaluation of the activity of the epidemic process in dysentery caused by Sh. sonnei is shown.