--law enforcement dogs can exert tremendous bite forces. Some K-9 dogs (German shepherds) are trained to exert bite forces up to 1,500 pounds per square inch (psi), and trained Rottweilers can generate bite forces up to 2,000 psi. Compare this with the bite force exerted by untrained German shepherds, for example, who only bite with the force of maybe 200-400 psi (though still powerful enough to puncture light sheet metal). Doberman Pinschers have the highest bite force with 600 psi! A truly amazing breed. It should come to no surprise, then, that while only 1-2% of civilian dog bites require hospitalization, 50% of police dogs bites do (based on a study of the LAPD's K-9 units).
Also, police dogs are trained to bite and hold. They latch on and do not let go. The average number of bites per patient hospitalized with civilian dogs bites is one, a single bite. The average number of bites a person suffers at the jaws of police dogs is three. It seems that about 15 to 20 percent of dog bite wounds become infected. The reason there is such concern about dog bites is that there are a number of particularly nasty bugs that inhabit the mouths of some dogs, such that even innocuous looking bites can on rare occasions lead to life-threatening infections.
http://medic.wikia.com/wiki/Police_dog_bite