Salmonellosis remains an important problem in Russia. We have analysed surveillance data on salmonellosis from Leningrad oblast in 1995-2007. The incidence has decreased since 1995 to 30 cases per 100 000 population in 2006. Group D Salmonella (usually S. Enteritidis) made up some 70% of cases. Data from epidemiological investigations of sporadic and clustered cases show that patients may be infected by poultry meat, eggs and egg-products. Education of the population in prevention of diseases transmitted by food products is an important element in the combat against salmonellosis.
To date, salmonellosis has been an important problem for the Russian regions. The epidemiological situation has been characterized by rises in sporadic cases and clustered cases linked to poultry products. Despite decreasing morbidity since 1993, the causative agents of salmonellosis (in particular S. Enteritidis) are widely spread among farm animals, wild birds and in other environmental sites. Hence salmonellosis has become one of the most important problems not only from a medical and veterinary but also from an ecological point of view in several parts of the Russian Federation (RF) and internationally (9).
Leningrad oblast is situated in the Northwestern Federal district and consists of 17 administrative areas with a population of more than 1.5 million people. Despite decreasing morbidity, salmonellosis presents a significant problem for all areas of the region. Sporadic and clustered cases are seen all-year-round. The vehicle of transmission may be commercially produced poultry products (meat, eggs, and egg products), including locally produced items.
The purpose of the investigation was to characterize the epidemiological situation and the etiology of salmonellosis in Leningrad oblast between 1995 and 2007.
Materials and methods
We analysed data from official reports using descriptive and graphic methods.
Case detection of infectious diseases is carried out by all physicians and paramedical personnel in patient care institutions and prophylactic institutions in the Russian Federation.
For every confirmed or suspected case of infectious disease or carrier state a notification form is sent to the regional office of the state sanitary epidemiological service (until 2005) or the Rospotrebnadzor (from 2005). Patients with severe disease forms are admitted to hospital, whereas patients with light and mild disease forms are treated at home. Monthly and annual reports about infectious diseases are compiled according to a standard form (7).
All cases of salmonellosis confirmed by bacteriological and/or serological methods are notifiable in the Russian Federation. Cases are classified as salmonellosis caused by Salmonella group B, C or D and also reported as total number of salmonellosis cases. Typhoid fever and paratyphoid fever, as well as typhoid and paratyphoid fever carriers, are registered separately. Diarrhoeal diseases with missing or negative laboratory examination are notifiable as acute enteric infections of unknown etiology.
The classic bacteriological method of laboratory diagnostics is used. For Salmonella culture and typing, bismuth-sulfite agar, Endo culture medium, and selenite broth are used; followed by enzymatic characteristics of strains. Antigen characteristics are detected in agglutination reaction with monovalent O and H sera. Then antibiotic resistance is determined. The results of identification of Salmonella serovars are sent to the consulting doctor and epidemiologist.
Results and discussion
According to statistical data, the incidence of salmonellosis disease in Leningrad oblast, as well as in the Russian Federation, decreased steadily from 1995 (Figure 1). The highest incidence 46.5 per 100 000, was observed in 1995. Then the rates decreased and fluctuated from 23.8 in 2002 to 30.0 in 2006.
Figure 1. Incidence of salmonellosis in Leningrad oblast and Russia in 1995-2007
The secular trend of salmonellosis in Leningrad oblast and in the Russian Federation seemed similar with the same lows and peaks. Both in Leningrad oblast and in the Russian Federation, the peak incidence was observed in 1995. The incidence used to be lower in Leningrad oblast. In 1996, the Russian rates were 2.4 times higher, but in 2006 the rates were similar. The reasons for these changes are currently unknown.
Salmonellosis remains one of the major enteric infections with fecal-oral transmission route in Leningrad oblast, constituing 2.8 % of notified cases in 2001 and 6.1 % in 2007 (Table 1). Shigellosis made up 2.9 % of cases in 2007, while 81.2 % were acute enteric infections of unknown etiology. This tendency was seen in different age groups.
Table 1. Structure of enteric infections registered in Leningrad oblast in 2007
Nosologic forms/ Нозологические формы
No.ofpatients / Число заболевших
Acute enteric infections of unknown etiology / Острыекишечныеинфекциинеустановленнойэтиологии
Typhoid fever / Брюшной тиф
Rotavirus infection / Ротавирусная инфекция
Enteropathogenic Escherichia coli/ ЭПКП
Otheracuteentericinfectionsof knownetiology / Прочие острые кишечные инфекции установленной этиологии
Enterovirus infection / Энтеровирусная инфекция
Acute hepatitis A/ Острый гепатит А
Total / Всего
Group D Salmonella predominated, with between 63% (in 1997) and 83% (in 1995) of cases. S. Enteritidis constituted more than 90 % of group D. The proportions of Salmonella groups B, C and other did not exceed 10% (Figure 2).
Figure 2. Proportion of salmonellosis by serotype in Leningrad oblast in 1995-2007
The etiological structure of salmonellosis in the Leningrad oblast did not change significantly during the last 15 years. Altogether more than 20 Salmonella serovars were isolated from patients in the region. S. Enteritidis made up more than 70 % of all identified Salmonella strains.
Both in the Leningrad oblast as a whole and in the administrative areas and in the whole period under review the highest incidence were registered in young children. Of the 17 areas, four (Vsevolozhsky, Gatchinsky, Lomonosovsky and Tikhvinsky areas) had higher than average rates for all years. Two additional areas joined this list for the last five years (Kirishsky and Podporozhsky areas). Some areas had large changes in incidence. For example, the incidence increased more than 10 times in the Kirovsky area from 2000 to 2001 (from 4.0 to 44.0), but then decreased fourfold in 2002 (to 11.3 per 100 000 population). During the last 9 years, salmonellosis incidence was lower than average for the region in three areas only (Luzhsky, Vyborgsky, and Volhovsky areas). In 2007, the difference between the peak and minimum rates in the areas was 21-fold (88.4 for the Kirishsky area versus 4.2 for the Vyborgsky area).
Data from epidemiological investigations of sporadic and clustered cases show that patients may be infected by poultry meat, eggs and egg-products. This is supported by frequent findings of Salmonella in products produced by poultry farms that supply the population of Leningrad oblast. Unscheduled checks at one of the farms revealed Salmonella in 7.7% to 60% of poultry, convenience foods and by-products.
In 2006, S. Enteritidis infections linked to publicly served food were registered in the Leningrad region. Egg omelettes, poultry meat-pies and other poultry food products were implicated.
We have described the epidemiological situation of Salmonella infection in one of the territories of the Northwestern district of the Russian Federation. Evidence shows that salmonellosis remains a current problem in the Leningrad oblast. According to the Northwestern Regional Salmonellosis Centre (Pasteur Institute, Saint-Petersburg) the situation is rather similar in all Northwestern territories.
During the period under review, some directives aimed at preventing salmonellosis (2-5) were implemented. This may have contributed to the decreasing incidence. Nevertheless, the continuing challenges affirm the necessity of developing further measures to restrict the circulation of Salmonella and the creation of an integrated surveillance system for salmonellosis in Leningrad oblast.
Education of the population in prevention of diseases transmitted by food products is an important element in decreasing sporadic cases of salmonellosis.
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