Healthcare Hygiene magazine September 2020 September 2020 | Page 12

cover story
Transmission Dynamics
and COVID-19: How the
Coronavirus is Challenging
the Hierarchy of Controls
By Kelly M. Pyrek
As
the fight against SARS-CoV-2/COVID-19 approaches
nearly three-quarters of a year, public health experts
remind us to rigorously uphold the evidence-based principles and
practices of infection prevention and control (IP&C) to mitigate
risk of acquisition and transmission.
Samuel W. Dooley, MD, and Thomas R. Frieden, MD, MPH,
advise healthcare professionals to implement the full hierarchy
of established infection controls, consisting of source control
(removal or mitigation of infection sources), engineering and
environmental controls, administrative controls, and personal
protective equipment (PPE).
As Dooley and Frieden (2020) acknowledge, “SARS-CoV-2
spreads easily, and can be transmitted by persons with asymptomatic
or pre-symptomatic infection. Infection control planning
must address all major modes of person-to-person transmission
of SARS-CoV-2: (1) large-particle respiratory droplet transmission,
when persons with COVID-19 cough; (2) contact transmission,
such as by touching persons who have surfaces or objects they
have touched or coughed on; and (3) airborne transmission during
aerosol-generating activities or procedures (e.g., bronchoscopy).
Aerosolization may be more common than previously recognized.
The dichotomy between droplet and aerosols is false; droplet
size is a continuous variable, and the combination of the volume
and size of droplet generation and ventilation will determine the
duration and distance within which transmission may occur.”
As the National Institute for Occupational Safety and Health
(NIOSH) reminds us, “The idea behind this hierarchy is that the
control methods at the top are potentially more effective and
protective than those at the bottom. Following this hierarchy
normally leads to the implementation of inherently safer systems,
where the risk of illness or injury has been substantially reduced.”
NISOH adds, “Elimination and substitution, while most
effective at reducing hazards, also tend to be the most difficult
to implement in an existing process. If the process is still at the
design or development stage, elimination and substitution of
hazards may be inexpensive and simple to implement. For an
existing process, major changes in equipment and procedures
may be required to eliminate or substitute for a hazard.”
NIOSH says that engineering controls are favored over administrative
and personal protective equipment (PPE) for controlling
existing worker exposures in the workplace because “they are
designed to remove the hazard at the source, before it comes
in contact with the worker.” The agency adds. “Well-designed
engineering controls can be highly effective in protecting workers
and will typically be independent of worker interactions to provide
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