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)