Food Protection Trends - January/February 2021 - 165

individuals (56). Other elements contributing to aerosols,
emission include the stage of disease, speech volume, and
unknown physiological factors (3). The virus can be shed by
individuals who remain asymptomatic early during infection,
throughout the entire time while infected, or during recovery
(40). Fecal shedding of the virus raises the concern of
fecal-oral transmission due to inadequate personal hygiene.
Asymptomatic shedding of the virus poses a particular
challenge for reducing virus transmission because effective
control requires that all individuals, even those who may not
feel ill, practice virus transmission prevention strategies.
A key contributor to person-to-person transmission is the
behavior of infected individuals, especially the proximity of
infected individuals within a susceptible population, and the
precautions that are taken to prevent disease transmission.
Large gatherings are recognized as major drivers of SSEs (42,
51). This hypothesis has been supported by the reduction
of new COVID-19 cases following the prohibition of mass
gatherings (4). The food processing workplace (for meat,
poultry, fish, and vegetables) is no exception, where large
numbers of individuals work in close proximity (17, 18,
32). The longer the duration of contact with an infected
individual, such as long work shifts, the higher the risk of
transmission (42).
The primary route of SARS-CoV-2 transmission is through
the direct inhalation of contaminated droplets or aerosolized
particles. Indirect transmission acquired by touching
contaminated surfaces has been hypothesized based upon
detection of viruses on fomites, but this route of transmission
has not been documented for SARS-CoV-2 (26). The
likelihood of transmission is dependent upon sufficient
amounts of virus capable of causing an infection reaching a
susceptible host. Factors that influence the amount of virus
reaching the next host include the amount of virus (viral
load) expulsed, the distance the droplets or aerosolized
particles travel, and the viability of the virus when it reaches
a susceptible host. Some researchers have hypothesized
that individuals exposed to lower viral loads develop milder
illness (25).
When the mouth is uncovered, a cough or sneeze may
disseminate particles as far as 7 to 8 m, depending upon
airflow (8). Even speaking can disseminate particles,
and more particles are expelled when speaking loudly, as
frequently occurs in the noisy food processing environment
(3). Sampling in hospital rooms of COVID-19 patients has
revealed widespread environmental contamination, including
positive PCR assay results from air sampled 4 m from the
patient. However positive PCR test results do not necessarily
indicate that infectious virus is present; these assays may yield
positive results from inactive virus and nucleic acid fragments.
The amount of virus exposure required to result in infection
is still unknown (33), and the highly sensitive PCR tests can
detect nucleic acids at very low concentrations that may be
insufficient or unlikely to result in an infection. Proximity of

workers is important during work activities, while entering
or exiting a facility, and during breaks and meals. Covering
the mouth and nose with a mask can considerably reduce
transmission of COVID-19 (12, 13).
Environment
Environmental conditions in modern food processing
facilities are conducive to the survival and dissemination
of pathogens. Activities, temperature, and humidity impact
aerosol formation, droplet size, droplet dissemination, and
virus viability. Slaughter and food processing practices
often involve large volumes of water for carcass rinsing,
flume-based systems used to move and wash produce, and
environmental and equipment cleaning. Bioaerosols are
an important source of contamination in slaughterhouse
environments (9, 55). Airborne transmission is suspected
in the spread of avian influenza in live poultry markets
(6). Human papillomavirus 120, hepatitis B, and WU
polyomavirus (a virus believed to be involved in severe
respiratory disease of humans) have been detected in
aerosols collected from animal slaughterhouses (34). Given
the host specificity of these viruses, the source of the viral
DNA detected in the study was presumed to be workers in
these facilities. The WU polyomavirus can be aerosolized
by coughing or sneezing, but this pathogen and others may
also disseminate through splashes during hand washing and
facility and equipment (63, 69).
During coughing, sneezing, and speaking, virus are expelled
from the lungs in aerosols and droplets of various sizes (0.01
to 500 μm). Larger droplets (>170 μm) quickly drop to the
ground within 1 m and are responsible for contamination of
the environment and direct exposure to those individuals in
close proximity (28) (Fig. 2). Smaller droplets, in particular
aerosolized particles, can travel farther and be inhaled deeper
into the respiratory tract. Under experimental conditions
(21 to 23°C, 40% relative humidity), SARS-CoV-2 remained
infectious in aerosols for 3 h with only a slight decrease
in viral infectivity (70). Relative humidity affects particle
evaporation and aggregation and can thus impact both the
distance the particles can travel and their trajectory. At higher
humidity, such as often found in processing plants, particle
size is generally higher and dissemination is reduced (28). The
relative contributions of aerosols and droplets in COVID-19
transmission is not fully understood and may be influenced by
the host and the environment, but both factors are considered
important (56).
The persistence of viral RNA on surfaces is influenced by
ambient relative humidity, temperature, and the surface on
which it is deposited. Viral RNA was detectable on multiple
surfaces (e.g., floors, trash cans, handrails, and doorknobs)
in the rooms of COVID-19 patients (33). Under laboratory
conditions, predictions indicate that <1% of SARS-CoV-2
in aerosols or deposited on copper remain infectious after
8 h (21 to 23°C, 40% relative humidity), whereas on more

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