Biological Characteristics and Transmission
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has weak resistance. It can be inactivated by 56 ℃ for 30 minutes, 75% ethanol, chlorine containing disinfectant and peracetic acid1. SARS‐CoV‐2 spike protein uses the SARS‐coronavirus receptor, and binds angiotensin-converting enzyme 2 (ACE‐2) for entry host cells. The SARS‐CoV‐2 belongs to the subgenus sarbecovirus, and has 96.2% homology with bat coronavirus. The current view is that COVID-19 was introduced into humans through an unidentified intermediary animal.
Human to human transmission occurs mainly through the spread of respiratory droplets up to 2 meters, and may cause infection through contact on the contaminated surface. The virus is also found in fecal samples of patients, indicating that there may be a fecal oral transmission pathway; however, this route requires further investigation2. Epidemiological records in China suggest that up to 85% of human-to-human transmission has occurred in family clusters, with an absence of major nosocomial outbreaks3. Pre symptomatic infectiousness is a concern and many countries are now using 1–2 days of symptom onset as the start day for contact identification4.
Maternal-infant vertical transmission is questionable. A recent study showed no evidence of intrauterine infection of COVID-19 caused by vertical transmission from mothers who developed COVID-19 pneumonia in their third trimesters. The samples of amniotic fluid, cord blood, newborn throat swab and breast milk of 9 patients were analyzed, and 6 of them were negative for SARS-COV-25. But previous studies have shown the possibility of materno-fetal transmission of human coronavirus (HCoV) with evidence of the virus exists not only in maternal respiratory swabs, but also in vaginal swabs6.