ASHRAE Journal - September 2020 - 22

TECHNICAL FEATURE

Well Ventilated Cruise Ship. Epidemiological investigation of the 696 COVID-19 cases aboard the Diamond
Princess provided an opportunity to evaluate the role
of a recirculating HVAC system that was reported to
be operating with ventilation rates consistent with
ASHRAE standards. Infection cases were classified
into three categories: (a) individuals interacting without restriction (i.e., passengers prior to quarantine);
(b) passengers quarantined in their cabin with no
COVID-positive individuals present; and (c) passengers quarantined in their cabins where they were
directly exposed to an infected person. Infections only
occurred in categories (a) and (c). Passengers quarantined in cabins free of infected individuals continued
to be exposed to recirculated air from spaces with
infection. The lack of cases in category (b) suggests that
circulation and dilution of air through the HVAC system did not cause infection.7
Korean Call Center. All 1,145 occupants of an office/
apartment building were tested for COVID-19, and a
cluster of cases was found on one floor, a densely occupied call center. There, 44% of the employees tested
positive, and 94% of those were located on one side of
the building. Only five cases were found on the rest of
the floor, where the majority of employees worked. Any
contact between occupants of the affected side of the
floor with the other employees was very brief. Uniform
spread throughout the affected area suggests there was
airborne transmission beyond direct contact. No information was provided to determine the relationship
between case location and HVAC zoning.8
Other COVID-19 studies sampled SARS-CoV-2 in air
and on surfaces but did not correlate this with infection
patterns. While measured contaminant concentrations
established airborne exposure away from the infected
individual, it was not determined if this exposure transmitted the infection to others.
Oregon Hospital. Surfaces were tested for SARS-CoV-2
inside a recirculating HVAC system with COVID-19
patients in some rooms. Sites with positive samples
included the prefilter receiving mixed air (return and
outside) and supply air dampers after filtration. These
recently reported results establish, for the first time,
that the virus can be transmitted through the HVAC
system. Analysis did not determine if the virus was still
infectious (airborne virus inactivates over time), and air
quality was not tested.9
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SEPTEM BER 2020

Two Wuhan Hospitals. Airborne SARS-CoV-2 was
sampled at two Chinese hospitals and nearby outdoor
locations. Investigators classified some samples by particle size and estimated surface deposition rates. Findings
included:
* Virus was detected in the air at most sites with patients present.
* Concentrations were lower in the temporary
hospital, where air infiltration was greater than in the
permanent hospital.
* Elevated airborne concentrations were found in a
bathroom (potential fecal contribution).
* Deposition tests associated particle settling with
fomite contamination.
* Airborne virus settled on surfaces beyond the immediate area surrounding the source and subsequently
resuspended, contributing to airborne exposure.
* Elevated air concentrations were measured in a
staff changing area with used personal protective equipment (PPE) (suggesting resuspension of settled virus).
* Concentrations were lower in the staff changing
area after more rigorous sanitizing was instituted.
* Particle size distribution varied, with >1 micron
(droplets) dominating at one site, <1 micron (airborne)
dominating at another, and a third site equally divided
between droplets and small particles.
Investigators concluded that their findings supported
airborne transmission.10
Nebraska Hospital. This study also detected
SARS-CoV-2 in the air more than 2 m (7 ft) from the
patient, including in the adjacent hall.11 SARS-CoV-2
was not detected in the air around infected patients in
Singapore and Iranian hospitals. Insufficient information was provided to determine if negative results were
due to methodological limitations.12,13
A similar virus to SARS-CoV-2 was artificially generated and measured for infectivity. Infectious virus was
detected after three hours in the air and three days on
surfaces.14 Another study found airborne virus infectious after 12 hours.15
Sampling studies represent occupant exposure, but
not necessarily disease transmission. Most analyses cited
above were by polymerase chain reaction (PCR), which
measures total SARS-CoV-2 RNA, including viruses that
have been inactivated and can no longer cause infection.
Methods are also available that measure only infectious
virus.

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ASHRAE Journal - September 2020

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