Cockroaches... Fastest way to eradicate?

[David Bardwell]

4 unit apartment building, 100 years old, have been using professional exterminator monthly for last 3 months but not seeing improvement. I'm on the verge of losing tenants over the problem.

I know sanitation is key and I'm working to keep tenants on top of things in this regard. But I'm hoping someone can provide a suggestion that I can act on immediately.

Instead of baiting or trapping, is there a good reason my exterminator wouldn't recommend fumigation?