It was not surprising when three-quarters of the house tested positive. There were 12 people in three bedrooms, with a bathroom whose door frequently required a knock and a kitchen where dinnertime shifts extended from 5 p.m. well into the evening.
Karla Lorenzo, a Guatemalan immigrant who cleaned houses in San Francisco and Silicon Valley, lived in the big room along the driveway. Big is a relative term when a room has five people in it. She and her partner, Abel, slept in a queen-size bed along the wall. There was a crib for the baby at the foot, with