When the workers at a pistachio packing plant in California’s Central Valley started falling ill last spring, they turned to Veronica Perez with questions. Ms. Perez is not a doctor or public health official — she’s a trained outreach volunteer from the nonprofit Líderes Campesinas. In the past, her neighbors and coworkers might have asked her for help locating a food pantry, applying for social services, or understanding where they could get affordable medical care. This time, their questions were about COVID-19.