The number of confirmed Covid-19 cases has more than tripled in Marin over the past week, and that likely represents just a tiny fraction of the actual cases. Around 1 percent—or 3,000 residents—have been infected with the coronavirus, Dr. Lisa Santora, the deputy health officer, estimated on Tuesday. “Some have recovered, some are asymptomatic, and some think they just have allergies,” she said. Testing capacity is limited. Out of 527 tests administered at Marin’s drive-through…