Yes if you are conducting your research in hospital community or a single hospital community, you can do it. But, during reporting you will specify that the prevalence of this diseases at this hospital from this month to that or from this year to that is ------.
Nevertheless, it depends on your your sesearch question that what are you going to do? Are you targeting the hospital community or any other residential community
If your study is institutional based, your study participants are only patients visited to that hospital or health center, so your prevalence determines prevalence of specific diseases on that institution.
Yes depending on your study participants and the setting. One has to define the study participants and the setting. So the setting can be part of the title of the study
It is also critical to sufficiently describe the hospital (setting) and be aware of potential biases, particularly overestimation which need to be acknowledged in reporting. As such generalization of the finding would need to be done with caution.