This study assesses the effectiveness of Polyvalent Mechanical Bacterial Lysate (PMBL-Ismigen) in reducing nasal methicillin-resistant Staphylococcus aureus (MRSA) colony growth in children with pollen allergic rhinitis (AR) aged 5 to 17. Half of the participants received PMBL and the other half received a placebo.

Seasonal allergic rhinitis (SAR) is caused by the allergens of wind-pollinated plants, and in Poland mainly by grass pollen allergens. During the grass pollen season, patients may suffer from fatigue, weakness, lack of fitness, difficulty in sleeping and reduced performance at school. In people allergic to the above-mentioned pollen, the disease significantly reduces the quality of life and requires intensive treatment in the pollen period.

MRSA colonizing the nasal cavity has the ability to actively modulate the immune response in children suffering from SAR. Many studies have shown a greater severity of AR symptoms in patients with a MRSA-positive nasal swab compared to patients with normal nasal flora.

Due to the high incidence of AR, the negative impact of the disease on the quality of life, and incomplete effectiveness of previously available therapeutic methods, new methods of treatment are being developed. Recent research highlights the immunoregulatory potential of bacterial lysates, indicating the possibility of their future use in the prevention and treatment of allergic diseases, including atopic dermatitis, AR, and asthma.

Based on the above considerations, it can be hypothesized that bacterial lysates reduce the severity of AR symptoms by eradicating MRSA from the nasal cavity. However, so far no randomized, double-blind, placebo-controlled study has been conducted to evaluate the effect of bacterial lysates on nasal Staphylococcus aureus carriage in children with SAR.

The main aim of this study was to evaluate nasal colonization by MRSA among children with SAR and the effect of PMBL on the reduction of MRSA colony growth in these children.

70 children with SAR were enrolled to this study and were randomly assigned to the PMBL group (n=35) and placebo group (n=35). Two visits took place as part of the study: at the beginning of the grass pollen season and at the end of the season. The time frame of the grass pollen season for south-eastern Poland was determined using the "95%" method on the basis of measurements of grass pollen concentration in the atmospheric air, which were obtained from the Environmental Allergy Research Centre in Warsaw. Nasal swabs for bacteriological cultures were taken at each visit and were transferred to the hospital laboratory.

Inclusion Criteria:

• Children of both genders aged 5 to 17 years.
• Children with grass pollen-induced allergic rhinitis recognized and treated according to current ARIA (Allergic Rhinitis and its Impact on Asthma) recommendations.
• Positive skin prick test to grass pollen allergens or positive specific IgE (defined as ≥ class 2, ≥ 0,70 kU/l) against timothy grass pollen allergens.
• Presentation of clinical symptoms of the allergic rhinitis (rhinorrhea, nasal congestion, nasal itching, sneezing) in at least two recent grass pollen seasons in Poland before inclusion in the study.
• Proper use of polyvalent mechanical bacterial lysate sublingual tablets.
• Written informed consent obtained from parents/guardians before any study related procedures are performed.

Exclusion Criteria:

• Patient received mechanical or any other polyvalent bacterial lysate immunostimulation within the previous 12 months before randomisation visit.
• Patient received oral/subcutaneous allergen-immunotherapy within the previous 3 years before the start of the study.
• Vaccination performed within 3 months before the beginning of the study.
• Deficiencies in cellular and humoral immunity.
• Treatment with antibiotics within the last 1 month before the start of the study.
• Treatment with systemic corticosteroids within the last 6 months before the start of the study.
• Pregnant or breastfeeding woman.
• Other chronic conditions of the nose or nasal sinuses.