Anyone coming to Qatar with the intention of obtaining a residence/work permit must undergo a medical soon after arrival. They check for HIV, TB, hapatitis and maybe some other diseases.

The local press periodically prints results; all anonymous but they give figures for each disease, x number of people HIV, y number TB, etc.

While this prevents new arrivals from posing a threat to the community it doesn't preclude the very real possibility that someone might come back with something from a vacation or travel somewhere or even being infected by someone here on a visit visa who doesn't have to undergo the medical.