Biowarfare and Bioterrorism 
Anthrax incidents occurred in the US in 2001, causing bioterrorism to attract attention on a sudden. Meanwhile, as is shown in the case of the 731 Unit of the Japanese Imperial Army in World WarU, there have been several examples of the development of biological weapons in the worldfs history. Biowarefare and bioterrorisms differ from biohazards because the former is intentional, while the latter is unintentional or accidental.  
The development of biological weapons needs to culture and stock a great amount of pathogens in facilities. Naturally there are likely to be accidental infections of laboratory workers. In addition, what will the result be if accidents causing release of pathogens happen? The worst example of these accidents was the anthrax outbreak in Sverdlovsk (now Yekaterinburg) in the old Soviet Union. 
Meanwhile, persons trying to make bioterror attacks also need to culture pathogens. So if they were to attempt to culture pathogens in places like an apartment, pathogens would leak from there, causing biohazards to neighboring people.