My son's mosquito bites repeatedly end in bad infections (staph and mrsa). what could be causing this?

Mrsa: It appears that his skin is colonized by MRSA. A 10-14 day course of an effective antibiotic may clear the bacteria living on his skin. However, this should be discussed with a specialist in infectious diseases.

Dirty fingernails: Young boys invariably have dirt under their fingernails. When your son gets a bite, it itches. When he scratches it, the bacteria in the dirt under his nails get into the skin and cause the infection. The cure is to keep his nails cut short and keep him from scratching. You can use Hibicleanse wash to scrub his nails a couple of times a week too.