Aerosols

Airborne Coronavirus Detected in Wuhan Hospitals

This is not really surprising.  The very efficient spread on ships suggested that the infection was spreading through ventilation systems.  In hospitals, air handing is an important issue with concentrations of infected patients shedding virus particles through their exhalations and fluids.  

The hospital standard is 6 air changes per hour (ACH), meaning that all of the air in a patient's room must be replaced six times an hour.  This standard appears to have been adopted in 2001 when it was increased from 4 to 6 ACH.  This 2014 engineering article suggests that the standard is a consensus guess rather than a research-based conclusion.  

Especially if Covid-19 patients are concentrated on a single floor, which is necessary to reduce the risk to other hospital patients and staff, the concentration of particles is almost certainly quite high.   This NYT opinion piece raised the issue of dose-response and the question of whether the severity of the illness increases with the amount of virus particles inhaled.  

These Coronavirus Exposures Might be the Most Dangerous

As with any other poison, viruses are usually deadlier in larger amounts.