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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: Human
rhinovirus is the most common cause of the common cold worldwide (1). It has
been shown that a substantial part of the airborne viruses is found in aerosol
particles in the range of 1-4 µm (2). Studying the infectivity of aerosol
particles in this range is, however, challenging; therefore, not many studies
have been conducted on their infectivity. The aim of this work is to
investigate the infectivity of aerosolized rhinovirus in particles <5 µm
under varying levels of relative humidity (7%, 50%, and 80%-90%).

Methods: We performed aerosolization and collection of rhinovirus in a
laboratory setup previously described... (More)

Objective: Human
rhinovirus is the most common cause of the common cold worldwide (1). It has
been shown that a substantial part of the airborne viruses is found in aerosol
particles in the range of 1-4 µm (2). Studying the infectivity of aerosol
particles in this range is, however, challenging; therefore, not many studies
have been conducted on their infectivity. The aim of this work is to
investigate the infectivity of aerosolized rhinovirus in particles <5 µm
under varying levels of relative humidity (7%, 50%, and 80%-90%).

Methods: We performed aerosolization and collection of rhinovirus in a
laboratory setup previously described by Alsved et al. (3). A flow tube was
placed inside a laminar flow (LAF) cabinet to avoid any contamination during
the experiment. The BioAerosol Nebulizing Generator (BANG) was used to generate
the aerosol of rhinovirus, which was introduced into either a long or short
exposure tube under different levels of relative humidity (RH). At the other
end of the exposure tube, the bioaerosol was collected by impaction in three
different size fractions using the BioCascade (Aerosol Dynamics Inc.): >10
µm, 4-10 µm and 1.5-4 µm. The remaining particles <1.5 µm continued to the
BioSpotVIVAS (Aerosol Devices) where they were grown to larger droplets by
water condensation before impaction into liquid. In addition, an aerodynamic
Particle Sizer (APS, Model 3321, TSI Inc.) and a Scanning Mobility Particle
Sizer (SMPS, TSI Inc.) were used for analyzing the size distribution of the
bioaerosol. To ensure that we were measuring the dry size of the particles, a
silica drier was connected before the APS and SMPS. Additionally, the viral
load of the collected bioaerosol samples was determined by quantitative
polymerase chain reaction (qPCR). Since qPCR only detects the total presence of
cDNA in a solution and does not assess the infectivity of the virus, the
infectivity of rhinovirus was assessed by measuring the cytopathic effect in
HeLa cells, using the 50% Tissue Culture Infectious Dose (TCID50) and the Most
Probable Number (MPN) method. To minimize the influence of small variations in
aerosol concentration on virus infectivity results, MPN values were normalized
by the total aerosol mass measured by the APS during the sampling time.

Result: In the experiment when all particle sizes were collected with
the BioSpot, our results suggest that airborne rhinovirus infectivity was about
50% higher at RH above 80% compared to a 7% RH, however, it was not
statistically significant. When collecting the aerosol in different size
fractions using the BioCascade and the BioSpot, the smallest particle size
fraction (<1.5 µm) was significantlymore infectious than the two larger size
fractions (1.5-4 and 4-10 µm) when aerosolized at 7% RH (t-test, p<0.05). No
difference in infectivity was found when comparing larger particles to each
other (4-10 μm vs 1.5-4 μm). The infectivity of the largest particle size
fraction (>10 µm) was below the detection limit of the MPN assay.

Conclusion: Based on the experimental results, aerosol at high humidity
and particles smaller than 1.5 µm contained more infectious rhinovirus per
aerosol mass than aerosol in low humidity and in particles >1.5 µm. There is
a 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, so
repeating 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 to
normalize the infectivity by the virus copy number.

(Less)
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author
; ; ; ; and
organization
publishing date
type
Contribution to conference
publication status
published
subject
pages
2 pages
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
2025-09-03 11:34:47
@misc{db9de725-8cb9-4213-b2cb-8da387dc3794,
  abstract     = {{<p class="MsoNormal" style="text-align:justify"><b>Objective</b>: Human<br>
rhinovirus is the most common cause of the common cold worldwide (1). It has<br>
been shown that a substantial part of the airborne viruses is found in aerosol<br>
particles in the range of 1-4 µm (2). Studying the infectivity of aerosol<br>
particles in this range is, however, challenging; therefore, not many studies<br>
have been conducted on their infectivity. The aim of this work is to<br>
investigate the infectivity of aerosolized rhinovirus in particles &lt;5 µm<br>
under varying levels of relative humidity (7%, 50%, and 80%-90%).<br/><br>
<b>Methods</b>: We performed aerosolization and collection of rhinovirus in a<br>
laboratory setup previously described by Alsved et al. (3). A flow tube was<br>
placed inside a laminar flow (LAF) cabinet to avoid any contamination during<br>
the experiment. The BioAerosol Nebulizing Generator (BANG) was used to generate<br>
the aerosol of rhinovirus, which was introduced into either a long or short<br>
exposure tube under different levels of relative humidity (RH). At the other<br>
end of the exposure tube, the bioaerosol was collected by impaction in three<br>
different size fractions using the BioCascade (Aerosol Dynamics Inc.): &gt;10<br>
µm, 4-10 µm and 1.5-4 µm. The remaining particles &lt;1.5 µm continued to the<br>
BioSpotVIVAS (Aerosol Devices) where they were grown to larger droplets by<br>
water condensation before impaction into liquid. In addition, an aerodynamic<br>
Particle Sizer (APS, Model 3321, TSI Inc.) and a Scanning Mobility Particle<br>
Sizer (SMPS, TSI Inc.) were used for analyzing the size distribution of the<br>
bioaerosol. To ensure that we were measuring the dry size of the particles, a<br>
silica drier was connected before the APS and SMPS. Additionally, the viral<br>
load of the collected bioaerosol samples was determined by quantitative<br>
polymerase chain reaction (qPCR). Since qPCR only detects the total presence of<br>
cDNA in a solution and does not assess the infectivity of the virus, the<br>
infectivity of rhinovirus was assessed by measuring the cytopathic effect in<br>
HeLa cells, using the 50% Tissue Culture Infectious Dose (TCID50) and the Most<br>
Probable Number (MPN) method. To minimize the influence of small variations in<br>
aerosol concentration on virus infectivity results, MPN values were normalized<br>
by the total aerosol mass measured by the APS during the sampling time.<br/><br>
<b>Result</b>: In the experiment when all particle sizes were collected with<br>
the BioSpot, our results suggest that airborne rhinovirus infectivity was about<br>
50% higher at RH above 80% compared to a 7% RH, however, it was not<br>
statistically significant. When collecting the aerosol in different size<br>
fractions using the BioCascade and the BioSpot, the smallest particle size<br>
fraction (&lt;1.5 µm) was significantlymore infectious than the two larger size<br>
fractions (1.5-4 and 4-10 µm) when aerosolized at 7% RH (t-test, p&lt;0.05). No<br>
difference in infectivity was found when comparing larger particles to each<br>
other (4-10 μm vs 1.5-4 μm). The infectivity of the largest particle size<br>
fraction (&gt;10 µm) was below the detection limit of the MPN assay.<br/><br>
<b>Conclusion</b>: Based on the experimental results, aerosol at high humidity<br>
and particles smaller than 1.5 µm contained more infectious rhinovirus per<br>
aerosol mass than aerosol in low humidity and in particles &gt;1.5 µm. There is<br>
a possibility that the collection methods, direct impaction for particles<br>
&gt;1.5 µm versus condensational growth prior to impaction for &lt;1.5 µm,<br>
influenced the result. So far, experiments have only been conducted once, so<br>
repeating the experiment is essential to be able to draw any firm conclusions.<br>
In addition, we will develop a copy standard for the qPCR to be able to<br>
normalize 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}},
}