In the current scientific literature, the problem of "frequently ill children" (FIC) is considered primarily from the point of view of transient physiological immunodeficiency inherent in certain stages of a child’s growing up, accompanied by an inadequate or paradoxical immune response [1,2]. The selection of a separate dispensary group for observation did not lead to the solution of the problem, unfortunately, and the incidence of acute respiratory diseases (ARDs) among children for decades has remained 3–4 times higher than in the adult population1. The main reasons for the unresolved issue are the heterogeneity of recurrent respiratory infections, the lack of timely laboratory and nosological verification, as well as a high percentage of late diagnosis of various pathological processes occurring under the mask of FIC [3]. So, one of the clinical masks of FIC may be a previously undiagnosed allergic pathology of the respiratory tract. According to modern concepts, the frequency of respiratory allergy patients among FIC can reach 60–80% [4].

The problem of diagnosing allergic diseases and pollinosis, the epidemiological growth of which has been growing rapidly over the past decades, is currently acute in the Russian Federation [5]. According to official data, the allergy prevalence rate ranges from 5 to 20.5% in our country. According to the results of epidemiological studies conducted at the Institute of Immunology of the FMBA of Russia, the range of fluctuations can be from 17.5 to 30% [6]. Moreover, the prevalence of allergopathology among children is almost 50% according to various data [7].

Climatogeographic features of various regions of our country should be taken into account by doctors of various specialties in their daily practice. In particular, in the Rostov Region, more than 80% of adult patients are sensitized to ragweed according to the results of skin testing [8]. Fungal and household allergens identified by various laboratory methods are in second place [9].

The study of sensitization prevalence is of great importance for understanding the formation mechanisms of symptoms of allergic diseases and the development of allergy prevention programs [10–12]. At the same time, the prevalence and structure of sensitization in Russia in children of different age groups have not been fully studied [13]. The purpose of our study was to identify the frequency and etiology of latent sensitization among frequently ill preschool children living in Rostov-on-Don.

The study was conducted in 2022 at the Research Institute of Clinical Immunology, the pediatric department of the Rostov State Medical University clinic, and the children's polyclinic department of Semashko City Hospital No. 1. Preschool age, the frequency of ARD episodes from 5 to 9 times a year, and the absence of family heredity allergopathology were the criteria for inclusion in the examination group. Forty preschool children (5.3 ± 1.2 years old) who were under dispensary supervision for frequent protracted respiratory diseases were examined. By the nature of the clinical course, the following groups were distinguished: group I – often sick children with recurrent pathology of the respiratory tract (adenoiditis, bronchial obstructive syndrome, n = 19), group II – often sick children with different durations of ARD episodes (from 3 to 5 days and from 5 to 10 days). Complaints, medical history, the hereditary burden of allergic diseases, and the presence of concomitant nosologies were collected. The absence of a hereditary burden due to allergic pathology was a mandatory criterion for inclusion in the group. All patients underwent an allergological examination, which included determination of specific blood IgE to the antigens of meadow timothy, rPh1 p1, Phl p 5; Altenaria alternata antigens, rAlt a1; ragweed high antigens, nAmb a1; to sagebrush antigens, nArt v1 using an automatic immunochemiluminescence analyzer (Immuno CAP 100 Phadia AB, Switzerland). A patient is considered sensitized to an allergen if the concentration of antibodies exceeds 0.35 kU/L. The lower detection limit of the device is less than 0.01 kU/l [14]. The study underwent preliminary ethical review and was approved by the local ethical committee, performed with the written consent of patients in accordance with the Helsinki Declaration of the World Medical Association "Ethical Principles for Medical Research with Human Participation" amended in 2000, WMA Declaration of Helsinki – Ethical Principles for Medical Research Involving Human Subjects (2013), "Rules of Clinical Practice in the Russian Federation", approved by Order of Russian Ministry of Health dated June 19, 2003 No. 266. Inclusion in the study was carried out upon receipt of a signed informed voluntary consent to the examination from the parent or legal representative of the child. Statistical data processing was performed using the STATISTICA 12 software package (StatSoft Inc., USA).

The clinical characteristics of the examined patients are presented in Table 1. The average age of the subjects was 5.3 ± 1.2 years, with prevalence of boys (55%). Most of the patients were aged 3 to 5 years. At the time of the survey, 35 children attended preschool institutions. History of frequent acute respiratory infections in the subjects was complicated by otitis media in 10 children, sore throats – in 10, bronchial obstructive syndrome – in 10, adenoiditis – in 9 children; according to clinical and laboratory examination, persistent herpes virus infection was detected in 12 children, 11 had hypertrophied tonsils. Additionally, 9 children were registered at the dispensary accounting with a neurologist and 10 – with an otolaryngologist. Medical history: atopic dermatitis and food allergy in the first year of life were diagnosed in 3 and 11 children, respectively. Characteristics of living conditions: pets lived in 16 families, indoor plants were in 15 families, and the presence of mold in residential premises was indicated in 3 cases. None of the patients had undergone allergy testing before.

More than a third of the subjects (16 patients) revealed latent sensitization; 8 patients had polysensitization according to the content of specific IgE to the main cause-significant allergens for the Rostov region in preschool children often suffering from ARDs. The main cause-significant allergen, sensitization to which was detected in all cases, was Ambrosia wormwood high, its major fraction (nAmb a1). All cases of diagnosable sensitization to the major fraction of the common wormwood allergen (nArt v1) always accompanied sensitization to Ambrosia wormwood high. The results are shown in Table 2.

Among the examined patients, FIC with a clinical picture of predominant respiratory tract damage (recurrent bronchial obstructive syndrome, adenoiditis, and recurrent otitis media) were identified as a separate subgroup. In total, 19 children were included in this observation group; the average age of children was 5.8 ± 1.1 years. In this group of patients, sensitization to the main cause-significant allergens for the Rostov Region was detected in 14 cases, of which monosensitization was detected in 5 children, and polysensitization in 9 children. As in the general group of FIC, the main cause-significant allergen, sensitization to which was detected in all diagnosed situations, was the major fraction of Ambrosia wormwood high (nAmb a1). The results are shown in Table 3.

In addition, FIC were divided into subgroups depending on the duration of acute respiratory infections: up to 5 days (3.5 ± 0.9 days), n = 12 (3A), and more than 5 days (7.8 ± 2.1 days), n = 28 (3B). During the laboratory examination in the subgroup of 3A, sensitization to the main cause-significant allergens for the Rostov Region was diagnosed in every third patient (4 cases); the variant of polyvalent sensitization was detected only in 2 cases. In the 3B subgroup, sensitization was recorded in 11 patients, of which the polyvalent form was documented in 6 cases. Regardless of the duration of ARD episodes, the dominant causal allergen was the major fraction of Ambrosia wormwood high (nAmb a1). In the subgroup of children with a protracted course of ARDs, specific IgE were detected for all the desired allergens. The results of the laboratory examination are presented in Table 4.

The study of sensitization profile variants is important for obtaining information about the general picture of the course of allergic diseases, understanding their mechanism, and developing methods of helping patients [15][16]. Based on the examination results of frequently ill preschool children, we present summary data on the variants of hypersensitivity development in the examined patients, depending on the nature of the recurrent respiratory pathology course (Table 5).

According to the study, in frequently ill preschool children living in Rostov-on-Don, depending on the variant of the course of recurrent pathology of the respiratory tract, sensitization to the main cause-significant for the region allergens is formed in 33–74% of cases. The most frequently causally significant allergen, sensitization to which is diagnosed in the majority of the examined patients, is the major fraction of Ambrosia wormwood high (nAmb a1). Sensitization to the major fraction of the Wormwood common allergen (nArt v1) is not diagnosed in the monovariate but always accompanies hypersensitivity to Ambrosia wormwood high. In frequently ill preschool children living in Rostov-on-Don, the presence of concomitant pathology of the respiratory tract in the form of adenoiditis, bronchial obstructive syndrome, as well as a long (more than 5 days) course of often recurrent ARDs is a factor indicating a high probability of latent sensitization.

For FIC with symptoms of recurrent respiratory tract pathology living on the territory of Rostov-on-Don, allergodiagnostic screening with the detection of specific IgE to the main cause-significant for the region allergens is recommended.

1. Infectious morbidity in the Russian Federation in January-December 2014/Rospotrebnadzor, 2015. URL: http://rospotrebnadzor.ru/ activities/statistical-materials/statictic_details. php? ELEMENT _ ID = 10049 (Accessed: 19.09.2023).