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.