1.2 Droplets & Aerosols
Viral transmission via eye contamination is very low but it exists. The
first reported hepatitis B case via conjunctiva was reported in 1973.(6)
In 1982, herpesvirus 1 (B virus) was inoculated directly on the
conjunctival mucosa in a chimpanzee resulted in its transmission.(39) In
Bischoff WE et al’s model, high rates of transocular transmission of
live attenuated influenza virus was found in patients, likely via the
nasolacrimal duct.(40) Aerosolised virus in surgical plume has been
reported to cause iatrogenic infections. Human papillomavirus has been
detected in laser plume, and has been reported to cause laryngeal
papillomatosis in surgeons.(41) Aerosolised blood generated by high
speed rotating instruments and electric coagulator has been found to
travel according to the anticipated aerial current generated by the
central air conditioning system in the operating room.(42)
Shoham S et al’s modelling found that surgical mask with visor, as well
as safety eyeglasses with respirator resulted in eye contamination with
oil-based fluorescent dye, whereas the full face shield did not.(43)
Loveridge JM et al demonstrated that the mask visor in the inverted
position conferred better protection to the face.(44) Weber RT et al’s
study of PPE contamination found PPE contamination, including the face
shield during simulated AGPs and close contact with patients.(5) The
mask under the face shield was contaminated in 4% of the trials.(5)
They also found that generation of infectious aerosol was not limited to
AGPs but during routine care.(5) Lindsley WG et al’s simulation has
found that the use of face shield, and increasing the distance between
the coughing source significantly reduced the amount of cough aerosol
inhaled (p <0.001). It also reduced the amount of viable virus
on the respirator by 70%.(25) The amount of virus deposited on the
outer layer of respirator was significantly less (p
<0.001).(25) Use of face shield only caused a modest decrease
in the inhalation of airborne particles over the long term.(25) In the
first 5 minutes after a cough, the amount of virus on the respirator was
96% lower when a face shield was worn.(25) After 30 minutes, the amount
of virus collected when the face shield was worn was reduced by 81%,
likely because smaller particles are able to float around it and
accumulate over time.(25) It was also less effective against the
small-particle cough aerosol with 68% reduction of virus deposition as
small particles are better able to travel around the face shield and be
inhaled.(25)
The use of goggles in addition to gown and mask has resulted in a
reduction of nosocomial RSV infection from 43% to 6% in admitted
children, and 38% to 5% in staff.(45)
Inconsistent use of gown, cap and goggles were strongly associated with
SARS transmission.(46) Suboptimal adherence to wearing a face shield
during aerosol generating procedures (AGP) was significantly (p
<0.001) and independently (OR 3.56, 95% CI 1.18-10.69)
associated with acquiring an influenza-like illness while working on a
ward with influenza A and B patients during peak influenza season.(47)
This was significant even after adjusting for possible household
contacts.
One of the expert taskforce who visited Wuhan developed COVID-19 despite
fully gowned with protective suit and the N95 respirator.(12) His first
symptom was unilateral conjunctivitis.(12) In addition, van Doremalen N
et al’s modelling reported viability of SARS-CoV-2 in aerosols.(26) Some
authors reported the lack of its presence in air samples obtained from
rooms of hospitalised patients with COVID-19 may provide contradictory
evidence regarding the extent of aerosol transmission.(48, 49) However,
another study contradicted this by finding environmental contamination a
metre away from a COVID-19 positive 6-month old patient whose only
contact is HCW in full PPE.(50)