Fourth persons are died after eating soup made with poisonous mushrooms at a retirement home in northern California, local officials say.It is thought the member of staff at Gold Age Villa home in the town of Loomis who prepared the soup did not know the mushrooms were poisonous.The caregiver was among those who fell ill after eating the soup.The name of the fourth person to die after eating the soup has not been made public.The first three fatalities were identified in US media as 86-year-old Barbara Lopes, 73-year-old Teresa Olesniewicz and 90-year-old Frank Warren Blodgett.The home remains open with one resident pending the outcome of an official investigation, local media reports say.A poisonous variety of the amanita species of mushroom which grows in California can resemble an edible mushroom found in Asia, according to experts.California recorded 1,700 cases of mushroom-related illnesses from 2009 to 2010, including two deaths, the Associated Press reports.