SAN FRANCISCO, Feb. 28 (Xinhua) -- The Santa Clara County Public Health Department in Northern California confirmed Friday a second COVID-19 case of unknown origin in the United States. Santa Clara health officials said a female senior with chronic health conditions was found to be infected with COVID-19 when she was treated for a respiratory illness. The county's Public Health Laboratory received the specimens Thursday and performed the testing. A final result of COVID-19 positive was confirmed Thursday night. The female patient, whose identity detail was not disclosed for protection of her privacy according to law, had no known travel history nor exposure to any other infected people.