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.     

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.     

Morbidity and prophylaxis of hemorrhagic fever with renal syndrome in the Republic of Bashkortostan

The brief retrospective analysis of morbidity, epizootological data and preventive measures with respect to haemorrhagic fever with renal syndrome (HFRS) during the whole period of its registration on the territory of the Republic of Bashkortostan along with the structure of HFRS morbidity during epidemic seasons of 1998 and 1999 is presented. The main causes of decreased HFRS morbidity in 1998, its rise in 1999 as well as prognosis for the year 2000 were detected. The level of HFRS morbidity among the population was found to be directly related to the number of rodents and their infection rate. The basic strategy of epidemic control interventions has been proposed.     

Specific prophylaxis of shigellosis

A high level of shigellosis morbidity requires new approaches to the control of bacterial dysentery. According to modern concepts, the outbreaks of Shigella infections are linked both with less intensive epidemic control measures and the objective cyclic character of the epidemic process. In this connection great importance is attached to the development of vaccines for the immunization of high risk groups in territories with unfavorable epidemic conditions and in zones of military conflicts, as well as children of school and pre-school age, who mostly determine seasonal rises of shigellosis morbidity. In this article the data describing new approaches to the creation of new live enteric vaccines on the basis of the knowledge of the genetic control of microbial pathogenicity and the regulation of its expression are presented. Attenuated Shigella mutants, created by different authors and having good prospects to be used for the development of vaccines, are characterized.     

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.     

Forecast of acute respiratory infections: expected nonepidemic morbidity in Cuba.

A forecast of nonepidemic morbidity due to acute respiratory infections were carry out by using time series analysis. The data consisted of the weekly reports of medical patient consultation from ambulatory facilities from the whole country. A version of regression model was fitted to the data. Using this approach, we were able to detect the starting data of the epidemic under routine surveillance conditions for various age groups. It will be necessary to improve the data reporting system in order to introduce these procedures at the local health center level, as well as on the provincial level.     

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.     

The epidemic spread of the influenza A and B viruses in the USSR in 1985-1986

The data on the spread of influenza A and B in the autumn and winter of 1985-1986 are given. Three epidemics caused by all presently circulating viruses, B, A (H3N2) and A (H1N1), were registered in the USSR. Of these, the greatest one was the epidemic of influenza B; morbidity rate among the adult population during this epidemic was at the level with the morbidity rate characteristic of the epidemics registered at the period of 1962-1972, and morbidity rate among children, especially school children, was even higher.     

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.     

Incidence of epidemic parotitis in different countries]

The authors analyzed the incidence of epidemic parotitis in various countries in 1960--1969 on the basis of the data published by the WHO. It can be supposed that there was no significant difference in the morbidity in various countries and that discrepancy in the official data of individual countries was apparently caused by the errors in recording. In the majority of the countries morbidity curve was fluctuating in character with a 4--5-year periodicity. In the countries of the northern hemisphere the greatest number of cases occurred in spring, and in the southern--in autumn. Monthly distribution of cases during the years with a high and low morbidity level displayed no significant changes.     

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 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.     

Basic patterns in the epidemic process of measles under conditions of massive immunization]

Observations over the measles epidemic process in Leningrad showed that the sporadic morbidity level reached in 1974--4.1 per 100 000 residents; however periodic elevation and decline of morbidity and tis seasonal variations persisted. A rise of morbidity in 1972--1973, and by preliminary data--in 1975, occurred on account of the older age groups. There was revealed no dependence of the disease incidence among the persons vaccinated on the time lapse after their vaccination. Individual batches of live measles vaccine issued in 1963--1969 were not up to the standard, this serving as one of the cases of the occurence of group incidence of the infection in some foci.     

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.     

Phase changes in the population of group A streptococci and their influence on the course of the epidemic process of tonsillitis

This work presents the data on the complex evaluation of the population of group A streptococci, studied at each of four phases (reservation, epidemic transformation, epidemic spread, reservational transformation) of the course of the epidemic process of streptococcal infection of the respiratory tracts (tonsillitis) in an organized group of adults. The characterization of the phases of the infective agent in accordance with the level of the carrier state, the size of streptococcal foci and the virulence of streptococci is given. Thus, the study shows that the heterogeneity of group A streptococci with respect to their virulence reaches its maximum level at the phases of reservation and epidemic spread and its minimum level at the phases of epidemic and reservational transformation. The size of streptococcal foci in carriers and the virulence of streptococci isolated from them are the inter-related unidirectional signs of the population of the infective agent and, at the same time, the main factors responsible for the phase character of the epidemic process and the morbidity level in tonsillitis.     

Morbidity and mortality in acute viral hepatitides in a hyperendemic region. The role of viral hepatitis E

Official annual statistical data on morbidity in acute viral hepatitides (AVH), including the number of lethal cases, for 1985-1995 were analyzed. Mortality rates per 100,000 of the population at the period of 11 years were calculated for different age groups, sex and the place of residence. 396 and 99 patients were examined for the presence of serological markers of hepatitides A, B and E, respectively, at the periods of epidemic rises in morbidity and satisfactory epidemic situation. In the course of 11 years AVH caused the death of 22,405 persons. In 1985-1987 the average mortality level (ML) reached 12.3-17.8 per 100,000 of the population (with morbidity being 1,200-1,400 and was essentially higher among the rural population in comparison with the urban population. During these years the highest ML, was registered among children aged 0-2 years (190-50 per 100,000) and, among adults, mainly among women aged 20-29 years (21.4-19.6 per 100,000). During the years when the epidemic of AVH was absent, ML among these groups was essentially lower: 40-20 among children aged 0-2 years and 4-5 among women aged 20-29 years. In 1987 in the Fergana Valley hepatitis E was detected in 72.2% of all examined patients, and in the southern areas of the country in 68.7%. A sharp rise on mortality among women of the productive age at the period of the epidemic rise of AVH morbidity in the endemic region indicated that this epidemic was linked with hepatitis E. High ML among young children may be indicative of a highly unfavorable course of hepatitis E in the group of infants, which had never been registered before. This newly established regularity may be used for the retrospective diagnostics of the outbreak of hepatitis E.     

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.     

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.     

A large-scale epidemic of diphtheria in Moscow in recent years: patterns of development

Data on the dynamics of diphtheria morbidity in Moscow in 1958-1999 are presented. The last epidemic which started at the end of the 1980s and reached its peak in 1994, giving a 59-fold rise in morbidity in comparison with the pre-epidemic period, is characterized in detail. During the epidemic 12,267 persons fell ill, 454 of them died (mortality rate was 4%). Having started in Moscow, the epidemic gradually spread not only over the territory of Russia, but also over some other republics of the former Soviet Union (Ukraine, Belarus, etc.). Possible causes of this epidemic emergency are considered. The ever increasing share of adult population among persons affected by the epidemic (75%) is noted. The infection adults is characterized by severity of clinical manifestations and increased morbidity among adults, is shown. Under complicated social and economic conditions (crisis situation) the increase of groups of high risk which included unemployed adults of working age, retirees as well as socially non-adapted persons, was registered. Mainly these groups determined tense epidemiological situation in diphtheria in Moscow.     

The epidemic process of an acute streptococcal respiratory infection in large organized collectives of children

The study of the specific features of the development of the epidemic process of scarlet fever, tonsillitis, and acute respiratory diseases (ARD) in two large organized groups of children revealed the presence of some differences which depended on the character of prophylactic measures taken in these groups. Thus, in the absence of prophylaxis with bicillin a pronounced increase in the level of carriership, accompanied by an increase in the infective capacity of carriers, was noted. This resulted in a high level and unfavorable dynamics of morbidity in scarlet fever, tonsillitis, and ARD. On the contrary, the use of prophylaxis with bicillin ensured the stability of the level of carriership, while the infective capacity of carriers was not pronounced. At the same time a rise in ARD morbidity was insignificant, and morbidity in scarlet fever and tonsillitis was reduced to nil.