There's no point going on a witch hunt. Ask yourself why any FL would end up with gonorrhea in the first place? It's because her clients all demand unprotected oral sex. It's a chicken and egg situation. There's a "bro" out there who passed on the infection to the FLs that sucked his unprotected dick and is probably still spreading it around. You too probably passed it to a few other girls before you were diagnosed.
Treat ALL prostitutes as high risk sexual partners. Whatever list you may come up with is only the tip of the iceberg.
Studies done in the past have shown that the gonorrhea infection rate amongst the LEGAL sex workers in Singapore was approx 10%. I have no doubt that it's even higher amongst sex workers who don't go for regular screening.
Simply put, this means that for every 10 girls you fuck, 1 of them is infected.
Use a condom for both oral sex and vaginal sex and your chances of catching the bug are reduced dramatically.