In Northern California, it's the season for wild chanterelle mushrooms — a highly sought-after variety — and for the amanita species of mushrooms that include what are known as "death cap" and "death angel" varieties.
Young poisonous North American amanitas often look like an edible version of a wild mushroom popular in Asia. Olson said they grow in large numbers in the San Francisco Bay area around Sacramento and in the Sierra foothills.
Investigators were quickly able to pinpoint the soup as the source of illnesses at the care home because the only person living there who did not eat dinner that night did not fall ill.
The two other people who died have been identified as Barbara Lopes, 86, and Teresa Olesniewicz, 73.
The California Department of Public Health periodically issues warnings about consumption of wild mushrooms, especially after someone eats a poisonous variety. The state recorded 1,700 cases of mushroom-related illnesses from 2009 to 2010, including two deaths.
State food regulations do not prohibit the use of foraged ingredients in food prepared at care facilities, though the rules do prevent the use of home-canned foods and unpasteurized milk.