Strep bacteria and necrotizing fasciitis: How?

OK, I’m mostly up to speed with the subject, but some background:

A “Discovery Health” program tonight mentioned a case of a man who lost a good bit of the flesh on a leg from necrotizing fasciitis, the result of an ankle injury during a soccer game. There was no indication in the program of the skin actually having been broken.

Locally, about fifteen years ago, there were two notable cases: One in which a high-school football player suffered a bruise on his leg. A week or so later, he suddenly got sick and died.

Within a year of that, two school kids (in their teens) got into a fight, one of whom got puched in the chest and ending up with a bruise. Within a week, the kid who was punched developed “a fast spreading infection” which killed him quickly.

In that case, as well as the local football player, the diagnoses were the same: necrotizing fasciitis.

Now, not having access to the autopsy reports or their medical records, or having seen these “bruises” first-hand, I’m assuming that the bacteria was (or “were,” depending on how you look at it) able to establish a beachhead with just a bruise, and not needing the skin to be broken.

Is that plausible, and if so, why is bruised, but not broken, tissue more susceptible?

The skin would have to be broken, but not a gaping wound. I’ve cared for three children whose necrotizing fasciitis started with a chicken pox leision.
I’ve also cared for a couple over weight adults who developed a small zit under a fat roll that progressed to NF.

I’m guessing, the bruised areas had, what was thought to be, a minor abrasion. It may not even be noticed.

Atul Gawande’s book Complications has a chapter on his firsthand experience with necrotizing fasciitis. The entry point of the bacteria can be something as minor as a mild abrasion, insect bite, or blister. It doesn’t take much, and it’s scary how fast the bacteria can eat away flesh.

How common is this getting.? I thought it was very rare.