Detection of influenza virus and Streptococcus pneumoniae in air sampled from co-infected ferrets and analysis of their influence on pathogen stability

Abstract

Secondary infection with Streptococcus pneumoniae has contributed significantly to morbidity and mortality during multiple influenza virus pandemics and remains a common threat today. During a concurrent infection, both pathogens can influence the transmission of each other, but the mechanisms behind this are unclear. In this study, condensation air sampling and cyclone bioaerosol sampling were performed using ferrets first infected with the 2009 H1N1 pandemic influenza virus (H1N1pdm09) and secondarily infected with S. pneumoniae strain D39 (Spn). We detected viable pathogens and microbial nucleic acid in expelled aerosols from co-infected ferrets, suggesting that these microbes could be present in the same respiratory expulsions. To assess whether microbial communities impact pathogen stability within an expelled droplet, we performed experiments measuring viral and bacterial persistence in 1 µL droplets. We observed that H1N1pdm09 stability was unchanged in the presence of Spn. Further, Spn stability was moderately increased in the presence of H1N1pdm09, although the degree of stabilization differed between airway surface liquid collected from individual patient cultures. These findings are the first to collect both pathogens from the air and in doing so, they provide insight into the interplay between these pathogens and their hosts. IMPORTANCE The impact of microbial communities on transmission fitness and environmental persistence is under-studied. Environmental stability of microbes is crucial to identifying transmission risks and mitigation strategies, such as removal of contaminated aerosols and decontamination of surfaces. Co-infection with S. pneumoniae is very common during influenza virus infection, but little work has been done to understand whether S. pneumoniae alters stability of influenza virus, or vice versa, in a relevant system. Here, we demonstrate that influenza virus and S. pneumoniae are expelled by co-infected hosts. Our stability assays did not reveal any impact of S. pneumoniae on influenza virus stability, but did show a trend towards increased stability of S. pneumoniae in the presence of influenza viruses. Future work characterizing environmental persistence of viruses and bacteria should include microbially complex solutions to better mimic physiologically relevant conditions.

Stability of influenza A virus in droplets and aerosols is heightened by the presence of commensal respiratory bacteria

“…Specifically, airborne particles between 0.65 µm and 3.3 µm dry size were enriched for both pathogens when they were co-aerosolized, though it is possible that particles outside of the tested size range (i.e., <0.65 µm) could also contain high levels of IAV. An animal study previously identified both S. pneumoniae and IAV within the same expelled aerosol fraction from co-infected ferrets ( 35 ), and it is promising that the mechanical system utilized in our study could reproduce these animal-based findings. Stabilization of IAV by co-aerosolized bacteria was also observed in our data, with IAV retaining higher infectivity for at least 45 min in indoor air conditions (40% RH) when bacteria were co-aerosolized ( Fig.…”

“…6B ) mediated by S. pneumoniae . An unrelated study investigating S. pneumoniae and IAV in small droplets of respiratory matrix conversely found that bacterial presence did not improve viral stability ( 35 ). However, this study used complex airway surface liquid collected from cultures of human lung bronchial epithelial cells, and in this fluid, IAV alone was suitably stable already (authors measured 1-log 10 decay total over multiple hours).…”