AUTHOR=Trifonova I. , Korsun N. , Levterova V. , Pavlova D. , Simeonovski I. , Ivanova M. , Velikov P. , Voleva S. , Ivanov I. , Ivanov D. , Dakov T. , Tcherveniakova T. , Angelova S. , Christova I. 

TITLE=Respiratory infections in the post-COVID-19 era: impact, prevalence, and clinical characteristics of bacterial and viral co-infections

JOURNAL=Frontiers in Medicine

VOLUME=Volume 12 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2025.1597782

DOI=10.3389/fmed.2025.1597782

ISSN=2296-858X

ABSTRACT=IntroductionHumans are affected by respiratory infections globally, originating from both bacterial and viral agents. However, the pathogens responsible for respiratory tract infections and the specific effects of viral-viral, viral-bacterial, and bacterial-bacterial co-infections on disease progression and clinical outcomes remain unclear. Тhis study aimed to determine the prevalence, estimate the age burden, and provide clinical characteristics of mono- and co-infections involving various bacterial and viral co-pathogens.MethodsA total of 609 nasopharyngeal specimens were collected from outpatients and hospitalized patients with respiratory symptoms between April and December 2024. The specimens were analyzed using an in-house multiplex real-time polymerase chain reaction method. Six separate primer and probe mixtures were prepared to detect 15 respiratory viruses and 5 common bacterial respiratory pathogens.ResultsThis study, conducted over an 8-month period, found that 65.7% of the patients (400) had at least one respiratory pathogen, with viral infections (49.2%) being more common than bacterial infections (16.5%). Infections were categorized as follows: Viral mono-infections: 217 cases (35.6%); Bacterial-bacterial co-infections: 6 cases (1%); Viral-viral co-infections: 39 cases (6.4%); and Bacterial-viral co-infections: 87 cases (34.3%). Common pathogens causing mono- and co-infections included SARS-CoV-2, rhinovirus, influenza A/B, bocavirus, adenovirus, Streptococcus pneumoniae, and Streptococcus pyogenes. Mixed infections were more common in children aged <5 years (p < 0.05). The disease resulted in a fatal outcome in four patients (1.3%). Notably, one patient with confirmed Streptococcus pneumoniae serotype 11A/D had a fatal outcome. Analysis of age as a factor in infection severity revealed that infants aged 7–11 months and patients aged >65 years with bacterial-viral co-infections had mean saturations of 89.6 ± 10.4% and 90 ± 5%, respectively. Moreover, hospitalized patients aged >65 with viral-viral co-infections exhibited significantly higher C-reactive protein levels (150.8 ± 14.3 mg/L) compared to children aged < 15 (p < 0.05).ConclusionThis study identified SARS-CoV-2, rhinoviruses, adenoviruses, and Streptococcus pneumoniae as key respiratory pathogens associated with mono- and co-infections. Mixed infections with SARS-CoV-2 were associated with progressively worsening symptoms, particularly in patients aged >65 years. This study highlights the need for preventive measures, including vaccination and revaccination of older adults with vaccines covering a broader range of S. pneumoniae serotypes.