The results of epidemiological analysis of salmonellosis incidence in the Rostov region under current conditions

Introduction

Salmonellosis takes one of the leading places among intestinal bacterial infections. Annually worldwide, salmonella causes 153 million cases of diarrhea and 57 thousand deaths [1][2]. According to the World Health Organization (WHO) experts, salmonellosis as a zoonotic infection has no equal in the complexity of the development of both epizootic and epidemic processes and in the difficulty of combating it [1][2].

Salmonella causes human and animal diseases; salmonellosis is a global problem in the world. Pathogens are transmitted, as a rule, with various food products of animal origin. Salmonella infection plays an important role among foodborne infectious diseases due to the possible development of severe forms of the course of diseases in humans and the occurrence of various complications [3].

According to WHO, the incidence of salmonellosis has not decreased in recent decades and is ubiquitous. Currently in Russia, as in many countries of the world, Salmonella enteritidis plays a leading role in the etiology of infections. Salmonellosis pathogens are able to form a high level of sporadic morbidity and outbreak among the population [4].

In the Russian Federation, the long-term dynamics of the salmonellosis incidence are characterized by a general downward trend. In 2022, the incidence rate of salmonellosis was 17.1 per 100 thousand of the population, which is lower than the long-term average, which for the period of 2010–2019 was 29.1.¹

In the etiological structure, salmonellosis caused by salmonella of group D dominates (72.5%). Salmonellosis remains relevant in the formation of outbreak morbidity and ranks third (after acute intestinal infections (AIIs) of viral etiology) in the structure of foci of group morbidity with a fecal-oral mechanism of transmission of infection. In 2022, 27 foci of group incidence of salmonellosis (in 2021 – 24) were registered in 22 subjects of the country with a total number of 1204 (in 2021 – 659). Etiological interpretation revealed that Salmonella enteritidis1 was isolated in most foci.

The main sources of salmonella infection are farm animals and birds. The most epidemically significant sources of the pathogen are currently chickens, cattle, and pigs. The main mechanism of transmission of the pathogen is fecal-oral, realized mainly by food (alimentation). The factors of transmission of the pathogen are food products: meat and meat products, eggs and cream products, mayonnaise, and dry egg powder.

In the Rostov Region, salmonellosis is a relevant infection, which is manifested by sporadic and group morbidity.

The purpose of the study is to analyze the incidence of salmonellosis in the population of the Rostov Region and to identify the epidemiological features of the formation of an outbreak incidence for further adjustment of preventive and anti-epidemic measures.

Materials and methods

To assess the intensity, dynamics, and structure of the epidemic process of salmonella infection, the database of the Unified Information and Analytical System of Rospotrebnadzor in the Rostov Region was used, as well as forms of Federal Statistical Surveillance No. 2 “Information on Infectious and Parasitic Diseases” for 2018–2022, No. 23-21 “Information on Outbreaks of Infectious Diseases for the Period 2012–2022” in the Rostov Region, data of the Report “On the State of Sanitary and Epidemiological Well-Being of the Population of the Rostov Region”, the results of surveys, studies at a catering enterprise, questionnaires of patients with AIIs of the branch of the Federal Budgetary Healthcare Institution “Center for Hygiene and Epidemiology in the Rostov Region” in Rostov-on-Don, and conclusions of the reference centers for salmonellosis monitoring – the Central Research Institute of Epidemiology of Rospotrebnadzor and the Research Institute of Epidemiology and Microbiology named after Pasteur. In order to identify the causative agent of the infection, bacteriological, serological, and molecular genetics methods were used.

Results

Analysis of the dynamics of salmonellosis incidence in the Rostov Region over the past 5 years showed that its level fluctuated. The maximum values were recorded in 2018–2019, in 2020–2021, the indicator decreased by 2 times or more (the minimum value was in 2020), and in 2022, the value of the indicator was 15.2, that is, there was an increase of 1.5 times compared to 2021, but at the same time, it remained below the national average, including in 2022 by 11.7%. In Rostov-on-Don, the dynamics were the same, but the incidence rate was constantly higher in Rostov-on-Don than the regional incidence rate and periodically than the average Russian level of incidence rate; the most significant excess over the regional level was detected in 2018 (1.7 times) and especially in 2022 (2.1 times). Not so pronounced (1.4–1.3–1.2 times) excess of the average Russian incidence rate was registered in 2018, 2019, and 2021; the average Russian level was maximally exceeded in 2022 by 1.8 times.

Over the analyzed 5 years, 10.2% of the total number of cases was group morbidity. Outbreaks of salmonellosis were reported in 2019, amounting to 5.02% of the number of registered cases, in 2021 amounting to 33.9%, and in 2022 amounting to 20.8%. In 2022, the proportion of cases in the group salmonellosis incidence in the Rostov Region accounted for 11.0% of the total number of cases in the foci of group salmonellosis incidence in the Russian Federation.

In the etiological structure of salmonellosis during these years in the Rostov Region, salmonella of group D dominated (in 2021 – 86.0%, 2020 – 71.2%, 2019 – 68.2%, from 60.3% in 2018 to 68.9% in 2022).

It is of interest that in all these years and previous ones, Salmonella enteritidis prevailed in group morbidity. So, for 2012–2022 in the Rostov Region, 17 episodes of group morbidity were registered, the etiological agent of which was Salmonella, and in 11 of them (65.0%), it was Salmonella enteritidis, in three foci – Salmonella typhimurium, one focus – Salmonella seegefeld, Salmonellae muenchen, Salmonellae isangi, and also DNA of Salmonella spp. was detected.

In organized teams, when forming foci of group morbidity among the population of the Rostov Region, the occurrence of salmonella infection was facilitated by flagrant violations of the requirements of sanitary legislation mainly in the manufacture of finished culinary products during the implementation of the disinfection regime due to non-compliance with personal hygiene rules by employees. Sources of salmonella infection caused by S. enteritidis, as a rule, were chickens, and factors for the transmission of infection were semi-finished products from poultry and eggs. It should be noted that in recent years in many countries, there has been an increase in the incidence of salmonellosis associated with the spread of the pathogen through poultry and eggs [5].

In recent years, in the city of Rostov-on-Don and in the Rostov Region, the manufacture and delivery of finished culinary products, including dishes from dietary and sports nutrition rations, has been widely practiced as part of remote ordering.

In 2023, from February 13 to February 27, 189 cases of AIIs were registered (of which 24 were children), in persons who consumed finished products, including diet products manufactured at the “GF” catering enterprise (individual entrepreneur K.). The analysis of questionnaires showed that the sick consumed a wide range of finished products: rice with chicken, the complex menu “Sushka”; complex lunch “Fitness”; complex menu “Balance”; cheesecakes; lettuce with pink salmon and lettuce leaves; tomato omelet; omelet; chicken in teriyaki sauce; salad with vegetables; chicken roll; orange pie; chicken cutlet; salad (chicken, cheese, eggs); chicken liver; spaghetti; beef cutlet; bulgur; pancakes filled with “Caesar”, etc.

To localize the group morbidity, specialists of the Rospotrebnadzor Office in the Rostov Region (hereinafter referred to as the Office) organized a sanitary and epidemiological investigation and a set of anti-epidemic and preventive measures together with the Center for Hygiene and Epidemiology in the Rostov Region.

Investigation findings

The first 5 people fell ill on February 11, 2023, in total, 167 people (88.4%) fell ill in the first 3 days; moreover, in 85.7% of cases, the victims fell ill on February 12 and 13, 2023.

In patients, the predominant symptoms were fever from 38.0 °C to 39.5 °C (in 78.8% of patients), vomiting (75.1%), and multiple loose stools (5–10 times in 95.8%). One hundred eighty-five people (98.9%) had moderate disease severity. Four people (2.1%) had no clinical manifestations.

Clinical manifestations in the majority of patients were observed on the first day after the use of finished culinary products (57.7% – 109 people), on the second day – in 37.0% of cases (70 victims), and on the third day – in 5.3% (10 victims).

Among the identified patients, adults prevailed (87.3%, slightly more than half were women (55.0%).

Among the cases, the bulk were 147 residents of Rostov-on-Don (77.8%), 21 residents of Bataysk (11.1%), 12 residents of Novocherkassk (6.3%), 7 residents of the Aksai District (3.7%), and 2 residents of the Myasnikovsky District (1.1%).

One hundred thirty-eight people were hospitalized (73.0% of the total number of cases), of which 21 were children. Eighty-six people (including 18 children) were hospitalized in the City Hospital No. 1 named after N.A. Semashko in Rostov-on-Don, 12 people were hospitalized in Don Infectious Disease Center, 11 people were hospitalized in the Specialized Infectious Diseases Hospital in Novocherkassk, 12 people were hospitalized in the infectious diseases department of the Central City Hospital in Bataysk, 7 people were hospitalized in the infectious diseases department of the Central District Hospital of the Aksai District, and 2 people were hospitalized in the infectious diseases department of the Central District Hospital of the Myasnikovsky District. The condition of the hospitalized patients was moderate. Fifty-one people (27.0%) were treated on an outpatient basis, of which 3 were children.

The bulk of hospitalized patients (93 people – 67.4%) were admitted to the hospital from February 12, 2023 to February 14, 2023 (on days 2–4 of the outbreak), which was 52% in relation to the number of all cases from February 11, 2023 to February 14, 2023 (179 people). On February 15, 2023, on the fifth day of the outbreak, 31 people were hospitalized (22.5%), and the remaining 12 (8.7%) of those hospitalized were admitted to the hospital from the 6th to the 9th day of the outbreak.

In order to determine the etiological agent in 18 first identified patients and 23 “GF” employees, material for examination by PCR to identify pathogens of enteropathogenic microorganisms of bacterial and viral nature was selected. The study was carried out in the virological laboratory of the Center for Hygiene and Epidemiology in the Rostov Region. Salmonella spp. DNA was found in 9 patients and 1 employee during a PCR study. During bacteriological examination, a culture of Salmonella enteritidis gr. O:9 (D1) was identified in 121 patients and 3 employees of “GF” who used the manufactured culinary products.

A serological study of material from 18 “GF” employees, who were directly related to the technological process, was also carried out; the results were negative.

In addition, 55 family members who had contact with the sick were examined by the bacteriological method, primarily children and workers of the decreed professions. As a result, in 6 sick, a culture of Salmonella enteritidis gr. O:9 (D1) was found.

The manufacturing of “GF” culinary products is located at two addresses in Rostov-on-Don, the first is located in K. Avenue, and the second is located in Zh. Alley. Notification of the start of entrepreneurial activity at Rostov-on-Don, K. Avenue for the manufacture of culinary products and delivery to consumers under the brand name “GF” was not submitted. In both branches, the following gross violations of the requirements of the current legislation were revealed:

- there were no conditions for processing raw materials, including raw eggs, poultry meat, fish, fruits and vegetables (in the procurement workshop of the 1st branch, there was a washing bath with only cold water, in the 2nd – only 2 washing baths);

- cutting equipment and tables were not marked according to the type of processed products;

- no in-process control, including laboratory control, no in-process control program with laboratory test reports. Procedures based on the principles of HACCP (Hazard Analysis and Critical Control Points – food production and catering quality system) were not developed and maintained;

- there were no conditions for compliance with the rules of personal hygiene;

- there were no personal medical records of employees (in the 1st branch – for all employees, in the 2nd branch – for some employees, and for some, the deadlines for medical examination and hygienic certification were overdue);

- the necessary information (shelf life, storage conditions, etc.) was missing on the labels of finished culinary products.

In addition, in the production located in K. Avenue, the commodity neighborhood was not observed in the refrigeration equipment: dairy products, vegetables, fruits, semi-finished products, and raw materials were stored in one refrigerator chamber, and poultry fillets were defrosted; refrigeration equipment was not equipped with thermometers, and in the bulk product warehouse – with a psychrometer; there were no process documentation and shipping documents ensuring product traceability.

At the production facility located in Zh. Alley, part of the production and storage facilities was in unsatisfactory sanitary and technical condition (there was no coating on the walls that was resistant to detergents and disinfectants) and there was no instruction for the preparation of disinfectant solutions.

In addition, there was an underestimation of the concentration of the active substance in the disinfectant by 1.3 times.

According to the explanation given by the individual entrepreneur K. (February 13, 2023), the production workshop located in K. Avenue received chilled meat products (chicken fillet, chicken thigh, and beef) weekly from the supplier without the manufacturer's labeling and without documents confirming their quality and safety. Products were ordered by phone.

During the sanitary and epidemiological investigation and control (supervisory) measures, samples of food products and finished semi-finished products were taken: food raw materials, culinary products (pancakes with custard, salmon salad with poached eggs, cottage cheese casserole with pear, chicken fillet with boiled potatoes, chicken coops, curd pudding with lemon sponge with seasonal berry, torn veal in honey-tomato sauce with hummus, salad with smoked chicken with pickled carrots and Caesar sauce, wheat porridge with a mix of nuts and berries, vegetable soup, tea with lemon), food products (canned green peas), washes from environmental objects, drinking water; disinfectants, as well as culinary products from home foci (“Pancakes with Caesar filling”).

During a laboratory study of samples taken at the “GF” manufacturing, Salmonella enteritidis gr. O:9 (D1) was found in washes from the surface of “Raw meat” and “Cooked meat” boards, in “Green garnish”, “Torn veal in honey-tomato sauce with hummus”, and “Semi-finished chicken fillet chilled” samples.

The same pathogen was isolated from the finished culinary products of “Pancakes with Caesar filling” in two home foci. Moreover, in two cases there was contamination of CMAFAnM and BHKP (coliforms).

In addition, the presence of BHKP on the surface of the slicer, “Boiled vegetables” cutting board, salad containers, the surface of the scales in the hot shop and in the “Salad with salmon and poached egg” culinary product was found; in the latter, also S. aureus was found.

Thus, the putative etiological agent Salmonella enteritidis, gr. O:9 (D1) was determined both during the bacteriological examination of people (121 patients) who consumed the products of the “GF” catering enterprise, 6 family members who had contact with the sick, and in three employees of “GF”, and during the study of the material of washes taken in production, semi-finished and finished products.

Isolated cultures from patients, from raw materials, finished products, and from the external environment (washes) were sent to the Research Institute of Epidemiology and Microbiology named after Pasteur (39 cultures) and Central Research Institute of Epidemiology of Rospotrebnadzor (20 cultures).

According to the reference center for monitoring salmonellosis of the Central Research Institute of Epidemiology of Rospotrebnadzor and the Research Institute of Epidemiology and Microbiology named after Pasteur, salmonellas of the S. enteritidis serotype, genetically identical to each other, which phylogenetically formed a unique clade with statistical support of 100%, were isolated by the molecular typing method from the obtained isolates. The specified strain was isolated from material taken from 6 victims, from the “Chilled chicken fillet” semi-finished product, food products selected in the shop for production of culinary products, such as “Green garnish”, “Torn veal in honey-tomato sauce with hummus”; in home foci (two samples of “Pancakes with Caesar filling” culinary products) and washings from environmental objects in the shop (from the surfaces of “Raw meat” and “Boiled meat” boards). Thus, data from phenotypic and genetic analyses suggest a common source of origin for all strains of Salmonella enteritidis.

On February 15, 2023, an order was sent to the individual entrepreneur K. to carry out sanitary and anti-epidemic (preventive) measures, including requirements for the withdrawal of low-quality hazardous food products and food raw materials from circulation, and the organization of periodic medical examinations of employees.

In the course of the investigation organized by the Office, not only examinations of employees and contact persons were carried out, including from the decreed groups of the population, with a decision on the temporary suspension of employees from work, in which the pathogen was isolated, sampling of food products and finished semi-finished products, washes on the enteropathogenic group of bacteria, but as part of a set of anti-epidemic and preventive measures, final disinfection and phage in the foci were carried out.

The employees of the Office carried out interdepartmental interaction with the Rosselkhoznadzor Office for the Rostov, Volgograd and Astrakhan Regions and the Republic of Kalmykia and the Veterinary Office for the Rostov Region.

In relation to “GF”, administrative proceedings were initiated under Art. 6.6 of the Code of Administrative Offenses of the Russian Federation, protocols were drawn up on the temporary prohibition of activities at both addresses of the proceedings, and the materials were sent to the judicial authorities. By the decisions of the Soviet and Zheleznodorozhny District Courts of Rostov-on-Don, the activities of “GF” at two addresses: K. Avenue and Zh. Alley were suspended for 90 and 60 days, respectively.

The information was sent to the investigative committee, the Prosecutor's Office of the Rostov region, the Ministry of Internal Affairs of Russia in Rostov-on-Don, and a criminal case was initiated against the individual entrepreneur K.

On the basis of the Department of Consumer Market of the Rostov Region and in the Administration of the Proletarsky District of Rostov-on-Don, a training seminar was held with the involvement of specialists from municipalities and business entities of the consumer sphere of the Rostov Region on compliance with sanitary and epidemiological legislation, as well as preventive measures aimed at preventing the occurrence and spread of infectious diseases.

Information was widely covered in the media, comments were given, including to federal channels; it was also published on the website of the Office.

In connection with the provision of catering services not meeting the requirements of the current legislation, giving to the consumers on the Internet on the “GF” website inaccurate information (in terms of indicating a balanced diet and proper, healthy nutrition), misleading consumers regarding the properties of the food sold, the Office filed a lawsuit in court to declare the actions of the individual entrepreneur illegal in relation to an indefinite number of consumers and provided legal assistance to 147 consumers in the preparation of a draft claim that caused property and moral damage.

The outbreak was localized and eliminated.

In the future, constant hygienic training of personnel and unconditional fulfillment of the requirements of sanitary legislation, preventive measures in relation to business entities engaged in the provision of catering services, timely notification of the start of activities (conducting preventive visits, training seminars, informing, consulting) are required. It is necessary to ensure the routing of patients with AIIs, develop (adjust) a plan for re-profiling medical organizations in case of mass receipts, constant training of primary care, create a database on the presence of salmonella bacteriophage in the pharmacy network (with constant updating), etc.

Discussion

The results of the epidemiological analysis of the salmonellosis incidence among the population of the Rostov Region indicate the relevance of continuing and improving epidemiological surveillance of this infection, since the epidemic process of salmonellosis can manifest itself not only in the form of sporadic morbidity, but, which is especially important to take into account, in the form of outbreaks. This situation was clearly confirmed by the epidemic situation among the population of Rostov-on-Don, who used the culinary products of the “GF” catering enterprise. During the epidemiological investigation, an acute multiple focus of salmonellosis was revealed, which was due to food transmission of the pathogen. There is a commonality of power sources: all involved in the outbreak consumed “GF” products. The explosive nature of the outbreak, the predominance of moderate forms in the clinical structure and the strict monoetiology of the outbreak: isolation of an identical strain of Salmonella enteritidis gr. O:9 (D1) in 121 patients, in five contacts, and in three “GF” employees also indicate the effect of the food factor.

The probable source of infection was chickens, from the meat of which “Semi-finished chilled chicken fillet” was prepared, which is confirmed by the discovery of Salmonella enteritidis gr. O:9 (D1).

The transfer factor was the finished culinary products produced by “GF” and contaminated with the pathogen during the preparation process, which was confirmed by the isolation of Salmonella enteritidis gr. O:9 (D1) in two samples of culinary products “Pancakes with Caesar filling” from home foci, in samples taken in the workshop for the production of culinary products “Green side dish”, “Torn veal in honey-tomato sauce with hummus”.

Conditions contributing to the transmission of infection were gross violations in the organization of the work of the catering enterprise (violation of the flow of the technological process, lack of conditions for the processing of food raw materials, lack of documents confirming the quality, safety, traceability of food raw materials, lack of labeling on the technological inventory, non-compliance with the commodity neighborhood in the refrigeration equipment of the procurement workshop and in the stationary refrigerator and violation of the disinfection regime, as well as lack of instructions for the preparation of disinfectant solutions, etc.). Due to the violations, contamination with the pathogen originally contained in the raw materials of finished culinary products was realized, which is directly confirmed by the results of laboratory studies: Salmonella enteritidis gr. O:9 (D1) was found in two washes from the surface of the “Raw meat” board.

A feature of the spread of salmonellosis in the group of consumers of catering products in this case was the expansion of the borders of the focus of infection (several municipalities adjacent to the metropolis) and an increase in the number of infected persons by the availability of ready-made culinary products by remote order.

Conclusion

Thus, as the results of the investigation of this outbreak have shown, the epidemic potential of salmonella infection, which can form group morbidity, can be realized in case of gross violations of sanitary rules at catering establishments, within the boundaries of the availability of ready-made culinary products through orders, including the Internet.