Transmission
Respiratory droplet (5-50 µm) is the main route of transmission, and may
cause direct transmission via close contact (including the eye), or
surface contamination.(1, 11-18) SARS-nCoV-2 can be transmitted via
smaller aerosols with a droplet nuclei ≤5µm, which can travel long
distances and remain airborne for 2 – 4 hours, depending on the ambient
conditions.(19-21)
Certain events (eg coughing or sneezing, cardiopulmonary resuscitation)
and aerosol generating procedures (AGP) (eg intubation, tracheostomy)
can generate aerosols composed of smaller virus containing particles
suspended in air.(17) SARS-nCoV-2 has been reported to remain infectious
on inanimate surfaces at room temperature for up to 9 days.(22)
SARS-CoV-2 is more stable on plastic and stainless steel than copper and
cardboard.(21) It is detected up to 72 hours after application onto
plastic, though the viral titre decayed exponentially.(21) The viral
half-life was 6.8 hours on plastic, 5.6 hours on stainless steel.(21)
SARS-nCoV-2 is contagious during the latency period.(14, 15, 20, 23-27)
Viral loads are highest in the first week (peaks at 3 to 5 days) after
symptoms began and decline over the second week, especially in the nose
than throat.(12, 15, 28-31) The viral loads in asymptomatic patients has
been found to be similar to symptomatic patients.(14, 28) As such, when
the COVID-19 status of patients is unknown, they are treated as if they
are COVID-19 positive.(32) Prolonged viral shedding after recovery has
also been reported.(26)
The transmission is reported to be between 2.1 and 4 cases per
exposure.(1, 12, 20, 33-35) Systematic effort is required to reduce the
transmission, which is influenced by various factors like: Pathogens,
ventilation, air filtration, sterilization and PPE.(36) Respiratory
protection is one of the key strategy for pandemic control, and to
sustaining the HCW.