The following is a timeline of the COVID-19 pandemic in California.
2020 January–February On January 26, the Centers for Disease Control and Prevention (CDC) confirmed the first case in California, the third case in the U.S. The person, a man in his 50s, who had returned from travel to Wuhan, China, was released from the hospital in Orange County on February 1 in good condition to in-home isolation. On January 31, the CDC confirmed the seventh case in the U.S., a man in Santa Clara County, who had recently traveled to Wuhan. The man recovered at home and was released from in-home isolation on February 20.
On January 29, the U.S. Department of State evacuated 195 of its employees, their families, and other U.S. citizens from Hubei Province aboard a chartered flight to March Air Reserve Base in Riverside County.
On February 2, the CDC confirmed the U.S.'s ninth case in a woman in Santa Clara County, California, who had recently traveled to Wuhan. This case was unrelated to the first case in Santa Clara. On the same day, the CDC reported the tenth and eleventh cases in San Benito County, including the second instance of human-to-human transmission.
On February 5, the U.S. evacuated 345 citizens from Hubei Province and took them to two air bases in California, Travis Air Force Base in Solano County and Marine Corps Air Station Miramar, San Diego, to be quarantined for 14 days. The evacuees from one more government evacuation flight on February 6 were also taken to bases in Nebraska and Texas.
On February 6, 57-year-old Patricia Dowd of San Jose, California became the first COVID-19 death in the United States discovered by April 2020. She died at home without any known recent foreign travel, after being unusually sick from flu in late January, then recovering, remote working, and suddenly dying on February 6. A February 7 autopsy was completed in April (after virus tests on tissue samples) and attributed the death to Transmural Myocardial Ischemia (Infarction) with a Minor Component of Myocarditis due to COVID-19 Infection. Her case indicates that community transmission was happening undetected in the US, most likely since December.
On February 15, the government evacuated 338 U.S. nationals stranded aboard the cruise ship Diamond Princess, which had been held in quarantine in Yokohama, Japan. Fourteen of those repatriated people were infected with the virus. Five more nationals who were also reported as being infected were evacuated from the ship the following week, and were quarantined at Travis Air Force Base; several more cases among the evacuees were later confirmed.
On February 26, a case of unknown origin was confirmed in a resident of Solano County. The UC Davis Medical Center in Sacramento said that when the person was transferred there on February 19, the medical team suspected it was COVID-19 and asked the CDC to test for SARS-CoV-2. The CDC initially refused since the person, who had no known exposure to the virus through travel or close contact with a known infected individual, did not meet the criteria for testing. The person was ultimately tested on February 23; the test results returned positive on February 26.
After this first case of community transmission in the U.S., a case with no known origin recognized in Solano County, California, the CDC revised its criteria for testing patients for SARS-CoV-2, and on February 28 began sending out the new guidelines for healthcare workers.
March
March 1: Two cases were reported in Alameda and Solano Counties, in health care workers at the NorthBay VacaValley Hospital. The workers were exposed to the patient in the case reported February 26 in Solano County.
March 2: An adult resident of San Mateo County tested presumptively positive; they were placed in isolation in a hospital. The source of exposure was reported as unknown.
March 4: California public health officials in Placer County reported a second confirmed case in an "older adult" resident with underlying health conditions who was aboard the Princess Cruises cruise ship on a cruise to Mexico that departed San Francisco on February 11 and returned on February 21. Although initial reports indicated that the new case had been hospitalized in "critically ill" condition, public health officials in Placer County subsequently reported the new case's death later on the same day. This marked the eleventh death in the United States attributable to coronavirus, the first death in the U.S. attributable to coronavirus outside Washington state, and the first death in California attributable to coronavirus. The source of the new case's infection appears to be the same as that of a resident of Sonoma County who tested positive on March 2 and who was also aboard the cruise ship Grand Princess on the same dates. In relation to this, Governor Gavin Newsom declared a State of Emergency in California. Consequently, Princess Cruises, the owner and operator of the cruise ship Grand Princess, working with the CDC, the state of California, and public health officials in San Francisco, terminated a port call in Ensenada, Mexico planned for March 5 and ordered the cruise ship to return to San Francisco over concerns about the potential for an outbreak of coronavirus aboard the cruise ship. Sixty-two passengers still aboard Grand Princess who may have made contact with the Placer County case that died earlier in the day were quarantined aboard the cruise ship at the request of the CDC. In addition, eleven passengers and ten crew members were exhibiting potential symptoms of coronavirus, and Grand Princess was ordered by the state of California to remain offshore while test kits were being airlifted to the cruise ship.
March 5: The San Francisco Department of Public Health reported two community spread cases within the city. The two cases were unrelated and hospitalized at different hospitals in San Francisco. Yolo County reported its first case, through community transmission.
Press reports in April indicated that Santa Clara County began a community surveillance test from March 5 to 14, finding that 11% of patients reporting non-flu respiratory symptoms were infected with coronavirus. As a result of those findings, the county began issuing increasingly aggressive social-distancing policies, starting on March 9.
March 7: Eight new cases were reported in Santa Clara County, bringing the total number of cases in the county to 32. A faculty member of the Stanford University School of Medicine tested positive for coronavirus. The faculty member stopped attending work after symptoms had appeared, and the member's place of work was closed for terminal cleaning.
In Santa Cruz County, officials confirmed the county's first case, a former passenger of Grand Princess. Six presumptive positive cases were reported in San Francisco. All were reported as isolated at home in good condition. Each patient had contact with a confirmed case. In Elk Grove, a family tested positive and was quarantined, resulting in the closure of Elk Grove Unified School District for the week of March 7–13, including student activities and events. In a letter to families, the school district announced no students or employees had tested positive.
In Madera County, officials confirmed the county's first coronavirus case from a person who had been aboard Grand Princess. Their spouse, whom they were with on the cruise, was also being monitored. Both were taken to the Madera Community Hospital and were reported as in monitored isolation. In Fresno County, two people returning from Grand Princess were quarantined and tested for the virus, with one person testing positive, making them the county's first confirmed case.
March 8: Contra Costa County reported 5 new cases. Four of the patients did not travel or have known contact with a coronavirus case and were treated at hospitals around the county. The fifth person had contact with a previous case and was being isolated at home. This brings the total number of confirmed cases in the county to nine. Santa Clara County reported 5 new cases, bringing the total number of known cases in the county to 37. In Rocklin, Sierra College announced all classes and lectures would be moved online by March 18 after two office staff members were quarantined following exposure to COVID-19, with students being tested. In addition, the campus announced it would be limiting student activities, including continuing sporting events with no spectators. Shasta County reported its first presumptive case. A 50-year-old man with a history of recent travel was reported to be recovering in isolation at home.
March 9: Three people tested positive in Sacramento County. Santa Clara County announced the state's second COVID-19 death. A woman in her 60s was in the hospital for several weeks, she was the first confirmed case of COVID-19 in the county who had not traveled internationally or had contact with an already infected patient, which suggests it was a 'community spread' case. The patient was also the third confirmed case reported in the county on February 28. San Francisco reported five new cases, who each had known contact with an existing case. The patients are isolated at home and are in good condition. This brings the number of cases in San Francisco to 13. An Elementary aged child attending grammar school in Elk Grove tested positive for COVID-19.
March 10: Newsom announced 24 new cases of COVID-19 for a total of 157 confirmed cases in the state. Alameda County reported its third confirmed case in the county. The new case is the spouse of the second case, who was a passenger aboard Grand Princess. The new patient had already been quarantined at home and remains isolated. San Francisco reports a new case in a patient who had known contact with a confirmed case, bringing the total number of confirmed cases of COVID-19 in the city to 14 with 89 confirmed cases in the Bay Area. The patient of the new case is currently hospitalized. The city announces a ban on large gatherings and relief for small businesses A resident of an assisted living home in Elk Grove in Sacramento County tested positive from complications of the virus. County health officials said they have the capacity to only test 20 people per day and would be focusing all their efforts on the other residents of the retirement home. That resident died from complications of the virus on the same day. Ventura County confirms its first case of COVID-19.
March 11: Marin County reported two new cases, bringing the total number of confirmed cases in the county to three. The two cases lived with the first confirmed case, who was a passenger on Grand Princess. The pair have been isolated in their home and are experiencing mild symptoms that do not require hospitalization. A woman who was in her 60s and had underlying medical conditions died in Los Angeles County. She was not a resident of Los Angeles and had traveled extensively, including a long layover in South Korea. Her death is the first in Los Angeles County and the fourth in California. San Jose International Airport reported that three of its TSA agents have tested positive. All three agents worked in Terminal B, and 42 TSA agents have been quarantined. A firefighter in the city of Alameda tested positive for coronavirus and was being quarantined.