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Lidia Morawska
Queensland University of
Technology
World Health
Organization
Collaborating
Centre for
Air Pollution
and
Health
The airborne infection spread in
buildings:
it’s time to stop it!
By “time” I mean now, during the time of this pandemic!
By buildings I mean indoor environment in general
In this presentation
• Airborne spread of infection - scientific basis
• Focus on ventilation: is air exchange
rate all what we need to know?
• Focus on the direction of the air flow: do
we ever talk about this?
• What can we do to make the world listen?
• Engineering controls
Morawska and Cao. Environment International, 139: 105730, 2020
How are infections transmitted?
Transmission routes:
• By close contact: in the range of larger droplets, or touching
surfaces where they were deposited
• Inhaling small airborne droplets, somewhere in the room
What is the role of
one against the
other transmission
routes?
Airborne spread of infection-
scientific basis
We all have expiratory fluids
The fluids are aerosolised during all
expiratory activities
The mouth and nose are the
sources of expiratory droplets
Droplet atomization in
expiratory activities
….results from the passage of an
air-stream at a sufficiently high
speed over the surface of a liquid
0.0001
0.01
1
0.1 1 10 100 1000
dC
n/
dL
og
D (
cm
-3)
Diameter (µm)
Bronchiolar Fluid Film Burst (BFFB Mode); Johnson & Morawska; JAMPDD. 2009.Laryngial Vibration (LV Mode); Morawska et al.; JAS 2009.Oral Speech Articulation Movements (OSAM Mode); Morawska et al.; JAS 2009.Bronchiole Lanyngial Oral Trimodal (BLOT) Model
Size distribution of droplets from
human expiration: speech
Small
droplets
After 10 steps!
Bronchial Fluid Film Burst
Mode (BFFB)
Fluid blockages form in
respiratory bronchioles
during exhalation
0.0001
0.01
1
0.1 1 10 100 1000
dC
n/
dL
og
D (
cm
-3)
Diameter (µm)
Bronchiolar Fluid Film Burst (BFFB Mode); Johnson & Morawska; JAMPDD. 2009.Laryngial Vibration (LV Mode); Morawska et al.; JAS 2009.Oral Speech Articulation Movements (OSAM Mode); Morawska et al.; JAS 2009.Bronchiole Lanyngial Oral Trimodal (BLOT) Model
These burst during
subsequent inhalation
produce the aerosol
H5N1
Laryngeal Vibration (LV) Mode
Fluid bathing the larynx
is aerosolised during
voicing due to vocal
fold vibrations
0.0001
0.01
1
0.1 1 10 100 1000
dC
n/
dL
og
D (
cm
-3)
Diameter (µm)
Bronchiolar Fluid Film Burst (BFFB Mode); Johnson & Morawska; JAMPDD. 2009.Laryngial Vibration (LV Mode); Morawska et al.; JAS 2009.Oral Speech Articulation Movements (OSAM Mode); Morawska et al.; JAS 2009.Bronchiole Lanyngial Oral Trimodal (BLOT) Model
Oral Speech Articulation
Movement (OSAM) Mode
Saliva in the mouth is
aerosolised during
interaction of the
tongue, teeth palate and
lips during speech
articulation.
0.0001
0.01
1
0.1 1 10 100 1000
dC
n/
dL
og
D (
cm
-3)
Diameter (µm)
Bronchiolar Fluid Film Burst (BFFB Mode); Johnson & Morawska; JAMPDD. 2009.Laryngial Vibration (LV Mode); Morawska et al.; JAS 2009.Oral Speech Articulation Movements (OSAM Mode); Morawska et al.; JAS 2009.Bronchiole Lanyngial Oral Trimodal (BLOT) Model
H1N1
Droplets from human
expiration
b – breathing
n- nose
m – mouth
c- counting
v- voice
w- whisper
Average concentrations during each expiratory activity
How do
we know
all this?
Distinct physiological processes → distinct modes
Speech: BFFB (1 µm), LV (2 µm), OSAM (50 µm)
Morawska, L., Johnson, G.R., Ristovski, Z.D., Hargreaves, M., Mengersen, K., Corbett, S., Chao, C.Y.H., Li, Y. and Katoshevski, D.
Size distribution and sites of origin of droplets expelled during expiratory activities. Journal of Aerosol Science, 40: 256-269, 2009.
Study on generation and transport
of droplets from human expiration
APS
transparent
modules
flow straightener
flexible ducting
air speed
sensor
HEPA filter speed controlled fan
butterfly
valve
RH
flow direction
inflow
for overpressure
UV-APSIMI
Glass slides
Particle size
0.5 ≤ d ≤ 20 µm
20 - 2000 µm
2 - 2000 µm
Johnson & Morawska 2009; Morawska et al 2009
APS and IMI measurements
DDA measurements
The rig - distance
HEPA
BlowerRotator
ACI
The rig -
duration
The study continues: bioaerosols
in expiratory activities
Modifications to
the rig and
the method!
Johnson, G., Knibbs, L.D., Kidd, T.J., Wainwright, C., Wood, C.E., Ramsay, K.A., Bell, S. and Morawska, L et al, A novel method and its
application to measuring pathogen decay in bioaerosols from patients with respiratory disease; PLOS ONE, 2016
,
Expansion of
the project
team!
How far infectious aerosols travel?
Easily the whole length of the tunnel – over 4 m!
Clinical dogma: an arm length!
Wrong!
Knibbs et al., Thorax, 69: 740-745, 2014
Study of Pseudomonas
aeruginosa bacteria in cough
aerosols from 19 infected CF
patients
How long cough aerosols remain
infectious in the air?
Clinical dogma: seconds!
Up to 45 min
Knibbs et al., Thorax, 69: 740-745, 2014
Wrong!
The study continues…
Using the whole genome analysis of a global collection of
clinical isolates majority were acquired through
transmission
Bryant et al, Science, 354 (6313):751-756, 2016
How are
nontuberculous mycobacterium
infections acquired?
Until recently acquired independently by individuals
through exposure to soil or water.
Mechanism: airborne transmission (detection of viable M
abscessus in cough bioaerosols and droplets generated by an
individual with CF
Which means by which route of transmission?
Is it easy to find out HOW a
person was infected?
• It is easier to find out from whom…
• But not “how”, by which transmission route
• Such studies are by nature retrospective,
with incomplete data
There were no investigators during these events
to study the infection transmission routes!
By CHRIS EPP, SENIOR REPORTER
“They followed all the rules and did nothing
wrong. "
By RICHARD READ, SEATTLE BUREAU
CHIEF MARCH 29, 2020 7:34 PM
May 10, 2020
Does it make a difference which
transmission route?
To limit the airborne transmission:
It does, in terms of mitigations!
“Appropriate building engineering controls
include sufficient and effective ventilation,
possibly enhanced by particle filtration and air
disinfection, avoiding air recirculation and
avoiding overcrowding”
Environment International,
Accepted 22/05/2020
Ventilation is the process of providing outdoor air to a space
or building by natural or mechanical means (ISO 2017)
Can use the existing ventilation guidelines for
controlling infection transmission?
Focus on ventilation
Example: control of CO2
Concentrations easy to predict – we all
exhale it, and it is well known how much
The meetings starts…
CO2
One hour later…
A quantum is the dose of airborne droplet nuclei
required to cause infection in 63% of susceptible persons
Emitted quanta depend on:
• Location of the pathogen in the respiratory tract
• Physiology of the respiratory tract
• Stage of the disease
• Type of respiratory activity
• THE VIRUS
Infection transmission:
infectious quanta
Traditional steady-state Wells-Riley model (W-R)
Where:
I - the number of infectious source cases
q - the number of infectious quanta produced per source case (quanta/h),
p - the average respiratory ventilation rate of susceptible persons (m3/h),
t - the duration of exposure (h)
Q - the volume of infection-free (i.e. outdoor) air supplied to the room (m3/h)
Risk of infection transmission
Knibbs et al. American Journal of Infection Control, 39: 866-872, 2011
Lung function laboratory: infection risk for 15 and 45 min occupancy
The Prince Charles Hospital,
Brisbane: ventilation and infection risk
Quanta generation
rates from literature
(quanta/hour):
Influenza - 67
Tuberculosis - 12.7
Rhinovirus – 5
Knibbs et al. Epidemiology and Infection, 9: 1-5, 2011
The risk of airborne
influenza
transmission in
passenger cars
• Influenza: 67 (quanta/hour)
high
medium (ventilation)
low
• Wells & Riley’s equation
• Car characteristics and ventilation
rate measurements
cv - the viral load in the sputum (RNA copies mL-1)
ci - a conversion factor defined as the ratio between one infectious quantum and the
infectious dose expressed in viral RNA copies,
Vbr - the volume of exhaled air per breath (cm3; also known as tidal volume),
Nbr - the breathing rate (breath h-1),
Nd - the droplet number concentration (part. cm-3),
Vd(D) - the volume of a single droplet (mL) as a function of the droplet diameter (D).
(determined based of experimental data by (Morawska et al., 2009))
The viral load emitted:ERq, quanta h-1
Buonanno et al. Environment International, 141: 105794, 2020
Buonanno et al. Environment International, 141: 105794, 2020
Quanta concentrations and infection risks in a
pharmacy for exposure scenarios before
lockdown (B) in Italy
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
3.5%
4.0%
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 10 20 30 40 50 60 70 80 90 100
R (
%)
n(t)
(q
ua
nta
m-3
)
t (min)
n(t) - B, NV
n(t) - B, MV
R - B, NV
R - B, MV
Customer’s risk, R=2.8%
Customer’s risk, R=1.2%
Infe
cte
d in
div
idu
al r
em
ain
s 1
0 m
in in
sid
e
Customer inside from min 26 to min 36
An infected
individual enters
The risk for a customer entering at
min 26 and remaining for 10 min
NV- natural ventilation
MV -mechanical ventilation
Buonanno et al. Environment International, 141: 105794, 2020
Before lockdown After lockdown
Natural ventilation Mechanical ventilation Natural ventilation Mechanical ventilation
R0 derived from the
quanta concentration
and the infection risk
Reproduction number (R0) simulated
for Italian exposure scenarios
R0 - the average number
of infected people from
one contagious person
Focus on air flow distribution
and direction
Xian et al. 2017, Role of fomites in SARS transmission during
the largest hospital outbreak in Hong Kong, PloS One, 12(7)
(A) Reported attack
rates distribution
(B) Predicted average
infection risk distribution
Price of Wales Hospital
Focus on air flow distribution
and direction
Posted April 22, 2020 doi:
https://doi.org/10.1101/2020.04.16.2
0067728. medRxiv preprint
More advance guidelines will be developed taking into
account knowledge about airborne infection transmission
For mechanical systems ASHRAE, REHVA and others
have already:• recommended ventilation and other control measures based on
the existing evidence that airborne transmission is possible
• have provided guidelines on their implementation
New guidelines for engineering
controls
https://www.thejakartapost.com/life/202
0/04/27/perspex-screens-fever-checks-
offer-spain-cafes-route-to-reopen.html
https://www.tmj4.com/rebound/bay-view-restaurant-owner-installs-
partitions-between-tables-in-anticipation-of-reopening
Will barriers help to control
airborne transmission?
Obstruction to air
movement, potentially
contributing to a build
up of virus-laden
droplets
“Airborne infection transmission
is not possible”
Anonymous Australian Research
Council grant application reviewer June
2014
“One of the main reasons why nosocomial infection is
such a major problem, is widespread failure to
recognize that the transmission of infection in
hospitals involves complex systems …”Beggs et al, Indoor Air, 25(5): 462-474, 2015.
Recognition
“Airborne transmission over longer distances,
such as from one patient room to another has
not been documented and is thought not
to occur.” http://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm
The US CDC updated COVID-19 transmission messages:https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-covid-spreads.html
The virus is thought to spread mainly from person-to-person
• Between people who are in close contact with one another (within
about 6 feet).
• Through respiratory droplets produced when an infected person
coughs, sneezes, or talks.
• These droplets can land in the mouths or noses of people who are
nearby or possibly be inhaled into the lungs.
“The disease spreads primarily from person to person through
small droplets from the nose or mouth, which are expelled when
a person with COVID-19 coughs, sneezes, or speaks.”
https://www.who.int/emergencies/diseases/novel-coronavirus-2019/question-and-answers-hub/q-a-detail/q-a-coronaviruses
The critical role of WHO
“These droplets are relatively heavy, do not travel far and quickly
sink to the ground. … This is why it is important to stay at least
1 meter away from others.”
How does COVID-19 spread?
What can we do to make the world listen?
Beyond COVID-19
To keep in mind:
• The next pandemic will not be caused by SARS2-CoV-19, but by
a virus of different characteristics
• Resilience should apply to all types of airborne infections (eg
seasonal flu)
• The measures should be adaptable, in a flexible manner, to the
specific risks and demands (energy conservation is one of them)
To all the colleagues around the world who have
been part of this journey over the years
To the Group of 36
To Junji Cao and Giorgio Buonanno who motivated
me to act now
Thank you
Thank you!
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