Epidemiology of bacillary dysentery in Algeria. II. The seasonality of dysentery

Morbidity rises during the period of summer and autumn are characteristic of bacterial dysentery in Algeria. During the last 18 years no essential changes in the seasonal character of bacterial dysentery were observed in the country taken as a whole. However, in different climatic and geographical zones of the country the seasonal character of dysentery greatly varies from one zone to another and essentially differs from the seasonal character of dysentery morbidity, typical of the country as a whole for many years. The most pronounced manifestations of seasonal rises are observed in the Sahara zone. The seasonal character of dysentery is formed mainly by morbidity among patients belonging to 3 age groups. The seasonal rises of dysentery can be probably explained by the complex of social and climatic factors, as well as by the biological features of the causative agents of this disease.     

Epidemiology of dysentery in Dagestan]

Analysis of material on bacterial dysentery and other acute intestinal infections morbidity in the Dagestan ASSR for a period of 15 years showed high morbidity level and its variations, with reduction and elevation in individual years, and the leading role played by Shigella flexneri among the causative agents of dysentery. The greatest incidence of dysentery was revealed among children aged under one year and between 1 and 2 years. A high bacterial dysentery incidence was recorded in Dagestan throughout the whole year. However analysis of the seasonal dysentery curve showed the beginning of elevation in July, reaching the maximum in August, and lasting four months with a decline beginning in October. The persisting activity of the water route of dysentery transmission in the Dagestan ASSR requires particular attention to the organization of good-quality water-supply to the population of the republic.     

Characteristics and trends in the development of an epidemic process of Sonne and Flexner dysentery among preschool children

The results of studies indicate that the morbidity rates of dysentery among children attending preschool institutions and children brought up at home converged in recent years. This phenomenon was most pronounced among children of the kindergarten age group. At the same time dysentery caused by Sh. sonnei and Sh. flexnery produced a higher morbidity rate among children attending nursery in comparison with that among children of the same age group brought up at home. Group infections in preschool institutions were caused by Sh. sonnei in 89.1% of cases and by Sh. flexneri in 10.9% of cases. Outbreaks due to the transfer of infection through everyday contacts were observed only in dysentery caused by Sh. sonnei, constituting 71.4% of the total number of dysentery outbreaks.     

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.     

Population migrations and the epidemic process of Flexner and Sonne dysentery

Analysis of the materials from the Khabarovsk Territory for the representative period of 25 years (1956-1980) revealed the influence of the migration of the population on the level and dynamics of morbidity in different kinds of dysentery, Flexner's dysentery shown to occur more frequently than Sonne dysentery. Intensive migrations increase the proportion of susceptible persons among the population, thus facilitating the formation and circulation of Shigella strains with pronounced virulence.     

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.     

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.     

Method for the short-term prognosis of annual morbidity indices in Sonne-type dysentery

A method for making the short-term prognosis of the annual morbidity rate in Sonne dysentery, both total and among individual groups of population, is presented. The preliminary prognosis is based on the expected data on meteorological factors, supplied by the weather forecast service, and the final prognosis, on the actual prognostic factors for June-July of the current (prognosed) year.     

Effectiveness of social hygiene and organized preventive measures in dysentery in preschool institutions]

The work presents the data on the development and realization of the complex of social and hygienic, as well as organizational and preventive measures for dysentery control at institutions for children of preschool age in one of the regions of our country. This complex comprises the improvement of "epidemiological" knowledge of the staff, preventive orientation in the work of the epidemiological section of the local Sanitary Epidemiological Station, the spread of sanitary and hygienic knowledge children and in their families, the improvement of material and technical equipment of children's institutions. The complex proved to be highly effective: at institutions for children of preschool age morbidity -ate in dysentery decrease 4--5 times, and its specific falue dropped from 40% to 5.4%, the frequency of positive results given by tests for the presence of intestinal microflora in washings from various objects decreased more than 25 times. Morbidity rate at institutions for children of preschool age decreased 4--5 times as compared with that among children not attending such institutions. The above data suggest the necessity of introducing this experience in other regions of our country.     

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.     

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.     

Analysis of the seasonality of acute intestinal diseases with regard to the detection of dysentery by antigen indication

Coincidence in the seasonal changes of the registered morbidity in dysentery and in other acute intestinal diseases is observed. The occurrence of Shigella antigens, detected with the use of erythrocyte diagnostic reagents, in the excreta of patients with the clinical diagnosis of dysentery and patients with other acute intestinal disease has a seasonal character, its peak coinciding with the period of increased morbidity in bacteriologically confirmed dysentery. The correction of monthly morbidity levels in dysentery and in other acute intestinal diseases with due regard for the proportion of Shigella antigens in the findings, made in the groups of patients with the clinical diagnosis of dysentery and with the diagnosis of other acute intestinal diseases for the corresponding month, has revealed that the actual morbidity in other acute intestinal diseases has a less pronounced seasonal character in comparison with the registered morbidity. This fact substantiates the statement that in the group of patients with other acute intestinal diseases a large proportion of such diseases is, actually, of a noninfectious nature.     

Etiologic structure of bacterial dysentery in the USSR in 1983-1985

The etiological structure of dysentery in the USSR in 1983-1985 is characterized. Sonne dysentery was found to prevail in the territories with adequate water supply, while dysentery caused by Shigella flexneri prevailed at the territories with unsatisfactory water supply. S. dysenteriae and S. boydii were found to play a limited role in the etiology of dysentery. In the presence of global pandemic, an increase in the isolation rate of S. dysenteriae I in the USSR is observed. The data on the biochemical structure of S. sonnei are presented.     

Family incidence of type B hepatitis

Family incidence of HBsAg-positive viral hepatitis was confirmed to be high. In 499 families with a type B viral hepatitis patient, type B viral hepatitis morbidity among 1116 contacts amounted to 2.24% within 6 months of the primary patients' hospitalization (being 188.2 times higher than semiannual morbidity of the population of the Czech Socialist Republic, CSR) and the prevalence of HBsAg amounted to 8.96% (being 22.4 times higher than among the population of CSR). On deducting positive findings at first blood samplings, which at least partially eliminated individuals who could themselves have been the source of infection for the first patient in each family, the rate for contact cases equalled 0.70% (58.8 times higher morbidity than among the population) and the rate for HBsAg prevalence equalled 2.50% (6.25 times higher than among the population). Among 917 members of 335 families where a case of HBsAg-negative viral hepatitis occured, 0.32% developed HBsAg-positive viral hepatitis within 6 months (26.8 times higher morbidity than population morbidity) and the HBsAg prevalence was 2.94% (7.35 greater than among the population). On deducting the first positive findings no clinical illness remained and HBsAg prevalence equalle 0.98% (2.45 times higher than among the population). The highest HBsAg prevalence was found among contacts aged 0-5 years (17.09% for the whole period, 3.41% after deducting first positive findings) and 40 years and over (10.82% and 3.39%, respectively). Type B viral hepatitis morbidity was again highest in the age groups of 0-5 years (5.12%) and 40 years and over (2.54%) for the whole period. On deducting first positive findings, the 40+ years group displayed the highest morbidity (1.27%), whereas the 0-5 years group displayed zero morbidity. Disclosure of the mechanisms of nonparenteral or inapparently parenteral transmission specific for family environments would be important for the prospect of introducing adequate measures to limit or prevent the spread of type B viral hepatitis.     

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.     

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.     

Diphtheria in the Maritime Territory

The results of the analysis of the present epidemiological situation in diphtheria in the Maritime Territory are presented. The data on absolute and intensive characteristics, death rate due to this infection, the vaccination status of diphtheria patients, as well as the results of the study of the level and intensity of antidiphtheria immunity in the healthy population of the territory. The study revealed that the defects of collective antidiphtheria immunity correlated with morbidity rate among adults and children. Adults aged 40-50 years and children aged 6-7 years were regarded as risk groups; among them the highest proportion of nonimmune persons and the highest diphtheria morbidity rate were registered. Stabilization achieved by the present moment was the result of the mass immunization of the adult population, ensuring the necessary coverage (92%) of vaccination in 1995.     

Acute intestinal diseases in Northern Africa]

Analysis of morbidity of dysentery and the rest diarrheal affections according to the books for primary recording of patients at one of the large administrative territories of the Northern Africa showed that official statistics reflected only 1/13 of dysentery patients who applied for medical aid (18.2 and 236.3 per 100 000 residents, respectively). Morbidity index of the rest of diarrheal affections constituted 2424.5 per 100 000. The mean lethality in diarrhea affections (including dysentery) was 1.7%. The fact that in the examination of 439 persons who came in contact with the patients suffering from typhoid fever the causative agents of dysentery were isolated in 19 (4.3%) indicated their wide circulation among the population.     

Risk factors in the epidemiology of dysentery

The general tendency of a decrease in the morbidity rates of dysentery induced by Shigella sonnei and Shigella flexneri (separately) from Monday to the end of the week (Saturday-Sunday) has been revealed, and at the same time the "infection risk" for both kinds of salmonellosis has been found to fall on the last days of the week (Friday-Sunday).     

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.