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Do the varying drying rates influence rhinovirus infectivity?

Pourjam Alavijeh, Zhaleh LU ; Ralevska, Natalia ; Menzel, Mandy LU ; Uller, Lena LU ; Medstrand, Patrik LU orcid and Alsved, Malin LU orcid (2025) 6th Workplace and Indoor Aerosols Conference (WIAC 2025) p.59-60
Abstract

Objective: Humanrhinovirus is the most common cause of the common cold worldwide (1). It hasbeen shown that a substantial part of the airborne viruses is found in aerosolparticles in the range of 1-4 µm (2). Studying the infectivity of aerosolparticles in this range is, however, challenging; therefore, not many studieshave been conducted on their infectivity. The aim of this work is toinvestigate the infectivity of aerosolized rhinovirus in particles <5 µmunder varying levels of relative humidity (7%, 50%, and 80%-90%).
Methods: We performed aerosolization and collection of rhinovirus in alaboratory setup previously described by Alsved et al. (3). A flow tube wasplaced... (More)

Objective: Humanrhinovirus is the most common cause of the common cold worldwide (1). It hasbeen shown that a substantial part of the airborne viruses is found in aerosolparticles in the range of 1-4 µm (2). Studying the infectivity of aerosolparticles in this range is, however, challenging; therefore, not many studieshave been conducted on their infectivity. The aim of this work is toinvestigate the infectivity of aerosolized rhinovirus in particles <5 µmunder varying levels of relative humidity (7%, 50%, and 80%-90%).
Methods: We performed aerosolization and collection of rhinovirus in alaboratory setup previously described by Alsved et al. (3). A flow tube wasplaced inside a laminar flow (LAF) cabinet to avoid any contamination duringthe experiment. The BioAerosol Nebulizing Generator (BANG) was used to generatethe aerosol of rhinovirus, which was introduced into either a long or shortexposure tube under different levels of relative humidity (RH). At the otherend of the exposure tube, the bioaerosol was collected by impaction in threedifferent size fractions using the BioCascade (Aerosol Dynamics Inc.): >10µm, 4-10 µm and 1.5-4 µm. The remaining particles <1.5 µm continued to theBioSpotVIVAS (Aerosol Devices) where they were grown to larger droplets bywater condensation before impaction into liquid. In addition, an aerodynamicParticle Sizer (APS, Model 3321, TSI Inc.) and a Scanning Mobility ParticleSizer (SMPS, TSI Inc.) were used for analyzing the size distribution of thebioaerosol. To ensure that we were measuring the dry size of the particles, asilica drier was connected before the APS and SMPS. Additionally, the viralload of the collected bioaerosol samples was determined by quantitativepolymerase chain reaction (qPCR). Since qPCR only detects the total presence ofcDNA in a solution and does not assess the infectivity of the virus, theinfectivity of rhinovirus was assessed by measuring the cytopathic effect inHeLa cells, using the 50% Tissue Culture Infectious Dose (TCID50) and the MostProbable Number (MPN) method. To minimize the influence of small variations inaerosol concentration on virus infectivity results, MPN values were normalizedby the total aerosol mass measured by the APS during the sampling time.
Result: In the experiment when all particle sizes were collected withthe BioSpot, our results suggest that airborne rhinovirus infectivity was about50% higher at RH above 80% compared to a 7% RH, however, it was notstatistically significant. When collecting the aerosol in different sizefractions using the BioCascade and the BioSpot, the smallest particle sizefraction (<1.5 µm) was significantlymore infectious than the two larger sizefractions (1.5-4 and 4-10 µm) when aerosolized at 7% RH (t-test, p<0.05). Nodifference in infectivity was found when comparing larger particles to eachother (4-10 μm vs 1.5-4 μm). The infectivity of the largest particle sizefraction (>10 µm) was below the detection limit of the MPN assay.
Conclusion: Based on the experimental results, aerosol at high humidityand particles smaller than 1.5 µm contained more infectious rhinovirus peraerosol mass than aerosol in low humidity and in particles >1.5 µm. There isa possibility that the collection methods, direct impaction for particles>1.5 µm versus condensational growth prior to impaction for <1.5 µm,influenced the result. So far, experiments have only been conducted once, sorepeating the experiment is essential to be able to draw any firm conclusions.In addition, we will develop a copy standard for the qPCR to be able tonormalize the infectivity by the virus copy number.

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organization
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Contribution to conference
publication status
published
subject
pages
59 - 60
conference name
6th Workplace and Indoor Aerosols Conference (WIAC 2025)
conference location
GAETA, Italy
conference dates
2025-05-06 - 2025-05-08
language
English
LU publication?
yes
id
db9de725-8cb9-4213-b2cb-8da387dc3794
date added to LUP
2025-07-02 13:42:22
date last changed
2026-04-17 09:18:57
@misc{db9de725-8cb9-4213-b2cb-8da387dc3794,
  abstract     = {{<p class="MsoNormal" style="text-align:justify"><b>Objective</b>: Humanrhinovirus is the most common cause of the common cold worldwide (1). It hasbeen shown that a substantial part of the airborne viruses is found in aerosolparticles in the range of 1-4 µm (2). Studying the infectivity of aerosolparticles in this range is, however, challenging; therefore, not many studieshave been conducted on their infectivity. The aim of this work is toinvestigate the infectivity of aerosolized rhinovirus in particles &lt;5 µmunder varying levels of relative humidity (7%, 50%, and 80%-90%).<br/><b>Methods</b>: We performed aerosolization and collection of rhinovirus in alaboratory setup previously described by Alsved et al. (3). A flow tube wasplaced inside a laminar flow (LAF) cabinet to avoid any contamination duringthe experiment. The BioAerosol Nebulizing Generator (BANG) was used to generatethe aerosol of rhinovirus, which was introduced into either a long or shortexposure tube under different levels of relative humidity (RH). At the otherend of the exposure tube, the bioaerosol was collected by impaction in threedifferent size fractions using the BioCascade (Aerosol Dynamics Inc.): &gt;10µm, 4-10 µm and 1.5-4 µm. The remaining particles &lt;1.5 µm continued to theBioSpotVIVAS (Aerosol Devices) where they were grown to larger droplets bywater condensation before impaction into liquid. In addition, an aerodynamicParticle Sizer (APS, Model 3321, TSI Inc.) and a Scanning Mobility ParticleSizer (SMPS, TSI Inc.) were used for analyzing the size distribution of thebioaerosol. To ensure that we were measuring the dry size of the particles, asilica drier was connected before the APS and SMPS. Additionally, the viralload of the collected bioaerosol samples was determined by quantitativepolymerase chain reaction (qPCR). Since qPCR only detects the total presence ofcDNA in a solution and does not assess the infectivity of the virus, theinfectivity of rhinovirus was assessed by measuring the cytopathic effect inHeLa cells, using the 50% Tissue Culture Infectious Dose (TCID50) and the MostProbable Number (MPN) method. To minimize the influence of small variations inaerosol concentration on virus infectivity results, MPN values were normalizedby the total aerosol mass measured by the APS during the sampling time.<br/><b>Result</b>: In the experiment when all particle sizes were collected withthe BioSpot, our results suggest that airborne rhinovirus infectivity was about50% higher at RH above 80% compared to a 7% RH, however, it was notstatistically significant. When collecting the aerosol in different sizefractions using the BioCascade and the BioSpot, the smallest particle sizefraction (&lt;1.5 µm) was significantlymore infectious than the two larger sizefractions (1.5-4 and 4-10 µm) when aerosolized at 7% RH (t-test, p&lt;0.05). Nodifference in infectivity was found when comparing larger particles to eachother (4-10 μm vs 1.5-4 μm). The infectivity of the largest particle sizefraction (&gt;10 µm) was below the detection limit of the MPN assay.<br/><b>Conclusion</b>: Based on the experimental results, aerosol at high humidityand particles smaller than 1.5 µm contained more infectious rhinovirus peraerosol mass than aerosol in low humidity and in particles &gt;1.5 µm. There isa possibility that the collection methods, direct impaction for particles&gt;1.5 µm versus condensational growth prior to impaction for &lt;1.5 µm,influenced the result. So far, experiments have only been conducted once, sorepeating the experiment is essential to be able to draw any firm conclusions.In addition, we will develop a copy standard for the qPCR to be able tonormalize the infectivity by the virus copy number.</p>}},
  author       = {{Pourjam Alavijeh, Zhaleh and Ralevska, Natalia and Menzel, Mandy and Uller, Lena and Medstrand, Patrik and Alsved, Malin}},
  language     = {{eng}},
  month        = {{05}},
  pages        = {{59--60}},
  title        = {{Do the varying drying rates influence rhinovirus infectivity?}},
  url          = {{https://lup.lub.lu.se/search/files/224721469/Pourjam-Alavijeh_-Z._et-al._Conference-abstract_WIAC2025.pdf}},
  year         = {{2025}},
}