How common are cases of chagas disease originating from bites in the usa?

Not very common: As your question suggests, most cases in the United States originated in Latin America with individuals having become infected as children. The parasitic infection is transmitted by the kissing bug, Triatomine, biting near the eyes or mouth. Chagas is a reportable disease in only 4 states in the US, including Texas. A very small number, 10 or fewer, of cases have been reported as locally acquired.

Not common: About 300,000 people in the US have been infected with Chaga's disease but most are old cases in people who have migrated from endemic areas.