Stanford’s study should give us more info soon. They recently screened a decent sized group in Santa Clara County to get a sense of how widespread it is, using their newly developed finger-prick test which looks for both antigens and antibodies (whether you have it / had it and recovered). Currently the test is being prioritized for frontline healthcare workers while they work on scaling up:
https://www.stanforddaily.com/2020/04/04/stanford-researcher...