ETIOLOGY, CLINICAL MANIFESTATIONS, AND AGE CHARACTERISTICS OF MIXED VIRAL RESPIRATORY INFECTIONS WITHIN 2024-2025

Authors

  • Dyana Pavlova National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria , Center of Competence “ImmunoPathogen”, Sofia, Bulgaria Author
  • Ivelina Trifonova National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria , Center of Competence “ImmunoPathogen”, Sofia, Bulgaria Author
  • Neli Korsun National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria , Center of Competence “ImmunoPathogen”, Sofia, Bulgaria Author
  • Petar Velikov National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria , Center of Competence “ImmunoPathogen”, Sofia, Bulgaria Author
  • Ivan Ivanov Infectious Disease Hospital “Prof. Ivan Kirov” , Medical University of Sofia, Bulgaria Author
  • Daniel Ivanov Infectious Disease Hospital “Prof. Ivan Kirov” , Medical University of Sofia, Bulgaria Author
  • Trifon Valkov Infectious Disease Hospital “Prof. Ivan Kirov” , Medical University of Sofia, Bulgaria Author
  • Iva Christova National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria , Center of Competence “ImmunoPathogen”, Sofia, Bulgaria Author

DOI:

https://doi.org/10.58395/peq4mg59

Keywords:

acute respiratory infections, respiratory viruses, co-pathogens, lower respiratory tract infections

Abstract

Introduction: This study aims to investigate mixed viral respiratory infections, examining their causes, age patterns, and the involvement of co-pathogens in the lower respiratory tract infections (LRTIs).

Materials and methods: A total of 2825 nasopharyngeal samples were collected from April 2024 to March 2025. Multiplex real-time PCR assays were used to test for 13 respiratory viruses, while capillary electrophoresis was used to determine viral load.

Results: This study identified 180 (6.4%) cases of coinfections with respiratory viruses, predominantly involving bocaviruses (BoVs) (51%), rhinoviruses (RVs) (38.8%), and influenza A viruses (34.4%). Children under 5 had the highest mixed infection rate (13.5%), especially involving respiratory-syncytial virus (RSV), rhinoviruses (RVs), adenoviruses (AdV), and bocaviruses (BoVs). The co-infection rate in patients with bronchiolitis was significantly higher than that in patients with infections restricted to the nose, sinuses, and pharynx (p=0.0006). RSV was most commonly associated with bronchiolitis cases (54%). Children under 2 years with mixed infections faced a greater risk of developing lower (58%) versus upper respiratory tract infections (URTIs) (39%) (p = 0.0276). Additionally, in co-infected patients with lower respiratory tract complications (LRTCs), SARS-CoV-2 had higher viral loads compared to those of other co-pathogens.

Conclusion: This study found a relatively low rate of mixed respiratory viral infections, with BoVs RVs, and influenza A viruses being the main causative agents. Children under two years of age are particularly vulnerable and are at higher risk of severe complications such as bronchiolitis. Understanding the interactions of these viruses is essential for developing effective treatments and prevention strategies for this at-risk group.

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Author Biographies

  • Dyana Pavlova, National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria, Center of Competence “ImmunoPathogen”, Sofia, Bulgaria

    National Laboratory “Influenza and ARD”, Department of Virology

  • Ivelina Trifonova, National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria, Center of Competence “ImmunoPathogen”, Sofia, Bulgaria

    National Laboratory “Influenza and ARD”, Department of Virology

  • Neli Korsun, National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria, Center of Competence “ImmunoPathogen”, Sofia, Bulgaria

    Head of National Laboratory “Influenza and ARD”, Department of Virology

  • Petar Velikov, National Centre of Infectious and Parasitic Diseases, Sofia, Bulgaria, Center of Competence “ImmunoPathogen”, Sofia, Bulgaria

    National Laboratory “Influenza and ARD”, Department of Virology

  • Ivan Ivanov, Infectious Disease Hospital “Prof. Ivan Kirov”, Medical University of Sofia, Bulgaria

    Department for Infectious Diseases, Parasitology and Tropical Medicine

  • Daniel Ivanov, Infectious Disease Hospital “Prof. Ivan Kirov”, Medical University of Sofia, Bulgaria

    Department for Infectious Diseases, Parasitology and Tropical Medicine, 

  • Trifon Valkov, Infectious Disease Hospital “Prof. Ivan Kirov”, Medical University of Sofia, Bulgaria

    Department for Infectious Diseases, Parasitology and Tropical Medicine, 

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2026-05-11

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Vol. 54 No. 1 (2026)

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Pavlova, D.; Trifonova, I.; Korsun, N.; Velikov, P.; Ivanov, I.; Ivanov, D.; Valkov, T.; Christova, I. ETIOLOGY, CLINICAL MANIFESTATIONS, AND AGE CHARACTERISTICS OF MIXED VIRAL RESPIRATORY INFECTIONS WITHIN 2024-2025. Probl Infect Parasit Dis 2026, 54 (1), 5-15. https://doi.org/10.58395/peq4mg59.

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