China's Hong Kong Special Administrative Region and Inner Mongolia Autonomous Region have reported two similar cases of the novel coronavirus. In both, there has been more than one confirmed case from people living in the same building, even though they live on different floors.

Officials are still investigating exactly how the virus may have been transmitted inside the building. But, there are concerns because of a similar case that happened in Hong Kong in 2003 during the SARS outbreak. Back then, a patient in the Amoy Gardens housing estate infected hundreds of people through a defective sewage system.

So if the virus can actually spread through sewage pipes, how exactly does this happen?