Although there is a risk of disease to spread, it is slim. Wild birds will not go after feed bought for your fowl, they prefer seeds. I have kept hens outside in the daytime just feet from feeders and now they have lived outside almost a year and fine and I now also have 3 month old chicks out in a hutch and allow them to free range. They of course go near the feeders for seed, but are also fine. Although it would be best not to have THAT close contact with wild birds, probably, living in the city doesn't give you much choice :)