the airborne infection spread in buildings€¦ · “airborne infection transmission is not...

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

http://images.google.com.au/imgres?imgurl=http://www.geeksontime.com/venusimages/computervirusredCOMPRESSED.jpg&imgrefurl=http://www.geeksontime.com/computer-virus-removal.html&h=336&w=336&sz=16&hl=en&start=7&tbnid=cmvA2uXJhRnRYM:&tbnh=119&tbnw=119&prev=/images%3Fq%3Dvirus%2Bcall%26gbv%3D2%26svnum%3D10%26hl%3Den

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)


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)


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)


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


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


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!

the airborne infection spread in buildings€¦ · “airborne infection transmission is not...

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