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.     

Methodological bases for the study and the patterns of the seasonality of viral hepatitis A

On the basis of the study of the data on the incidence of viral hepatitis A in one of the districts of a big city for 20 years the authors come to the conclusion on the advisability of a comparative study of the monthly changes in the incidence of hepatitis A within individual uniform morbidity cycles covering the periods of many years and the use of average monthly data for many years for plotting the typical curve, as well as the use of the simplified for the calculation of the upper limit of annual morbidity. Similarities and differences in the monthly dynamics of morbidity in the years of high and low morbidity levels have been revealed, and the age group of the population (20-39 years) which ensures the continuity of the epidemic process all the year round has been determined. The factors contributing to the seasonal activation of the epidemic process start operating in June among schoolchildren aged 11-14 years, and later their operation spreads to other groups of the population.     

Incidence of meningococcal infection in the RSFSR]

The authors present characteristics of meningococcus infection epidemic process in case of sporadic cases and under epidemic conditions (1965--1976). A scheme of epidemiological analysis suggested by the authors permitted to differentiate and to record the incidence of various clinical forms of meningococcus infection, to present data on the age, seasonal characteristics, focality, etc. Comparison of intensive morbidity indices for 10 years, both at the individual administration territories and in the Republic as a whole demonstrated morbidity level of 1.5--2.0 to be one of prognostic signs of the beginning epidemic. The main features differentiating the sporadic and epidemic morbidity periods were revealed. The presence of group diseases, a greater percentage of children among those who fell ill, and marked signs of seasonality and territorial difference characterized the period of rise caused by meningococcus of serological group A.     

Multiyear and seasonal hepatitis A morbidity in different population age groups in certain areas

At the areas with high activity of hepatitis A (HA) epidemic process the duration of epidemic cycles was shown to differ, the intervals between the peaks of morbidity increasing in older age groups. The beginning of seasonal rises exceeding the average annual HA morbidity level in different age groups was found to depend on the activity of the epidemic process. At the areas with the highest activity of the epidemic process children aged 1-2 years were the first to be affected by the seasonal rise of HA. Stable direct correlation between HA morbidity levels at the beginning of seasonal rises and some markers indicative of unfavorable sanitary conditions (the size of the fly population, the purity of water samples deviating from the requirement of the Government Standard) during the preceding year was demonstrated.     

Prognosis of the dynamics and intensity of the epidemic process in viral hepatitis A

The article deals with approaches to the calculation of the annual morbidity rate in virus hepatitis A at the period preceding the season of maximum morbidity, necessary for planning the relevant prophylactic and antiepidemic measures in due time. The method for calculating the monthly levels of sporadic morbidity in virus hepatitis A is proposed. This method permits the detection of complications on the epidemic situation, which is necessary for the timely organization of antiepidemic measures. The proposed method for predicting annual and monthly morbidity levels can be used in the practical work of specialists at sanitary and epidemic stations.     

Several epidemiologic features of the spread of chickenpox and herpes zoster]

Epidemiological and statistical data of herpes zoster and chickenpox by such indices as morbidity level, periodicity and month-by-month changes in the incidence of these diseases were compared. The study included 2345 herpes zoster and 11116 chickenpox cases in the course of 5 years (1972--1976). In comparison with herpes zoster, the intensity of chickenpox spread among the population was on the average 4.7 times greater. Of the total number of chickenpox cases the percentage of herpes zoster contituted 21.0. Chickenpox morbidity had marked seasonal cyclic nature with the amplitude of seasonal variations of about 8; as to herpes zoster--there was no annual or seasonal cyclicity. Thus, in the development of chickenpox and herpes zoster epidemic process there was revealed a peculiar tendency inherent to each of these infections; no common epidemiological and statistical regularities in the spread intensity, annual periodicity and seasonal cyclicity were detected.     

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.     

The epidemic process of diphtheria infection in the RSFSR during the introduction of epidemiological surveillance

In this work the characterization of the epidemic process of diphtheria infection on the territory of the RSFSR under the conditions of epidemiological surveillance (1983-1986) is presented. In comparison with the period of 1979-1982, an increase in morbidity rate occurred, which accounts for more complete detection of patients with mild forms of diphtheria, including persons found to be carriers of toxigenic Corynebacterium diphtheriae. Beginning from 1983, the leveling out of seasonal morbidity rises is observed. In the total number of persons affected by this infection the prevalence of adults is noted. Among them, a decrease in the morbidity rate was registered in 1986 (the maximum decrease was observed in age and professional groups of risk), which confirms the effectiveness of measures carried out for the protection of the adult population from diphtheria. Among children, a tendency towards a decrease in morbidity rate was noted in all age groups. The existing system of epidemiological surveillance on the territory of the RSFSR is capable of stabilizing diphtheria morbidity on a sporadic level and minimizing the number of fatal outcomes. The intensification of the epidemic process in some areas of the RSFSR is due to shortcomings in the realization of different measures of epidemiological surveillance.     

Epidemiological analysis of hepatitis A morbidity

A retrospective epidemiological analysis of hepatitis A morbidity for many years among the population of two neighboring towns in the temperate climatic zone of the USSR has revealed the cyclic character of the epidemic process without a perceptible decrease in its extensiveness and has determined the high-risk groups, as well as the beginning of the seasonal rise of morbidity in these groups. The results of the study indicate that different levels of hepatitis A morbidity and risk groups can be observed in these two neighboring towns. At periods of a lower morbidity level the high-risk group embraces schoolchildren, and when morbidity is at a higher level the risk group includes schoolchildren and preschool children in organized groups. Among the latter the morbidity level is influenced by factors acting all the year round and among school children, by seasonal factors. The beginning of the seasonal rise of morbidity falls on August, while in organized groups of children of preschool age the seasonal rise of hepatitis A morbidity begins 1-1.5 months later. All prophylactic measures for controlling hepatitis A should be carried out with due regard to these features of the epidemic process.     

Intensity of the epidemic process of whooping cough under conditions of mass immunization over a period of many years

On the basis of analysis of whooping cough incidence in 1959 to 1975 in Moscow the authors present characteristics of the epidemic process under conditions of planned many-year immunization of children against this infection. Whooping cough morbidity proved to undergo significant changes-from sharp falls the first 8 years of immunization to a relative stabilization with a gradual reduction the last 5 years. Marked seasonal and periodic elevations persist against the background of reduction of morbidity. Preschool- and schoolchildren are equally involved in the epidemic process; the most frequently involved are nonvaccinated children aged 1 year and 4 to 10 years, which lost postvaccinal immunity. Further reduction of the severity of whooping cough and increase in the number of unimanifested forms of the infection was noted. This was apparently connected not only with immunization, but also with the reduction of the virulence of H. pertusis detected in studying the cultures isolated in Moscow from 1967 to 1974. The intensity indices of the epidemic process in whooping cough pointed to the necessity of using a more effective vaccine for the protection of children from whooping cough, despite the noted reduction of morbidity, and diminished severity of the course of the disease, and of the causative agent virulence.     

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.     

Cholera morbidity problems in 1 of the departments of the Democratic and Popular Republic of Algeria

A total of 1,078 cases of bacteriologically confirmed cholera were analyzed at the period of 1979-1983. In 1981 Vibrio eltor, serotype Inaba, replaced V. cholerae, serotype Ogawa, and became the prevailing infective agent. Every year young children and persons over 50 years of age were most actively involved into the epidemic process. The peak of seasonal morbidity was observed in September-October. The appearance of the foci of infection in families was found to be slightly pronounced in cholera. 85.3% of the families had only a single case of cholera. The cases of cholera with the fatal termination of the disease were registered mostly at the beginning of the seasonal rise of morbidity and at its peak.     

Manifestations of angina morbidity as a reflection of the self-regulation of the epidemic process in streptococcal infection

The data on the application of the principles of the self regulation of the epidemic process for understanding the annual dynamics of angina morbidity in organized groups of adults are presented. In this case the reservation of group A streptococci occurs in chronic (resident) carriers, whose proportion was found to be 15.8 +/- 2.6%. The epidemic manifestations of morbidity are regulated mainly by the concentration of newly arrived members in the groups, i. e. by the size of the stratum providing the optimum conditions for the parasitization of the streptococcal population. The annual morbidity levels depend essentially not only on the heterogeneity of the group members with respect to their susceptibility to streptococcal infection, but also on the conditions of their accommodation, affecting the transmission of droplet infection. The role of individual risk factors in the variation of the quantitative characteristics of the angina morbidity manifestations under study is calculated.     

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.     

Morbidity: terminology, mechanisms of formation and classification

In the 70-ies of the last century the evolution of the epidemic process doctrine resulted in developing population approach to morbidity analysis, in addition to the traditional focal approach. On the one hand, this led to the discussion on the possibility of applying such notion to non-infectious diseases and, on the other hand, to the discussion on the mechanisms of the development and formation of different manifestations in infectious diseases. In both cases the discussion was centered on the phenomenon of morbidity. The present article deals with the nature of morbidity as a phenomenon and the acceptability of general scientific approaches in the interpretation of seasonal and cyclic character of morbidity from the viewpoint of the wave process in an open system. On the basis of the data presented in this work the terms used in epidemiology in considering manifestations of the epidemic process are discussed. The improved classification of morbidity by qualitative and quantitative signs for infectious diseases is proposed.     

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.     

Trends in the development of the epidemic process in salmonellosis caused by Salmonella typhimurium and Salmonella enteritidis

The dynamics and structure of the epidemic process of Salmonella infections among the population of Perm in 1983-1988 was studied and the results of evaluation of antibiotic resistance of the dominating Salmonella species analyzed. The study revealed that a decrease in salmonellosis morbidity caused by S. typhimurium was associated with a limited circulation of anthroponotic (antibiotic-resistant) variants of Salmonellae and a relative increase in the proportion of zoonotic (antibiotic-sensitive) strains. At the period of elevated morbidity this Salmonella infection affected mainly young children in cold months, whereas in recent years seasonal morbidity rises shifted to spring-summer and summer-autumn months, affecting older age groups of the population. The study also revealed that a rise in salmonellosis morbidity caused by S. enteritidis was due to increased circulation of zoonotic variants of Salmonellae. Changes in the epidemiological situation necessitate correction of the system of epidemiological surveillance on Salmonella infections with the emphasis on sanitation measures in stock-breeding farms with unfavorable epidemiological situation.     

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.     

The characteristics of using short-term prediction methods with viral hepatitis morbidity in small areas]

The results of the approbation of the method of using the regressive equation for the short-term prognostication of viral hepatitis morbidity in limited areas (a region or a city). The specific features of the epidemic process, characteristic of limited areas, have been considered. These findings serve as the basis for proposing some methods of prognostication within the limits of an individual region or city, thus making it possible to improve the orientation of prophylactic measures aimed at decreasing viral hepatitis A morbidity.     

Problems of the epidemiology of viral hepatitis in Ryazan Province

The analysis of some features of the course of the epidemic process of viral hepatitis on the territory of the Ryazan region is presented. Periodic rises and falls in viral hepatitis morbidity, varying in their regularity (4-6 years), have been registered in the region. The general level and the seasonal distribution of viral hepatitis morbidity are determined by the morbidity rate among children, the increase in the proportion of children of senior school age being observed in recent years.