Exactly when the coronavirus first arrived in the Bay Area has been the subject of much speculation, with people who had respiratory illnesses and pneumonia last fall and winter wondering if they had the viral disease.
Stanford researchers have come up with a preliminary answer to that question. After combing through 1,700 nasopharyngeal swabs taken from patients who had symptoms similar to COVID-19 during the last two months of 2019, they haven't found any evidence of the coronavirus, they said.
The preliminary report — which was published on medrxiv, a preprint server for health sciences, and has not been peer reviewed — only looked at samples from Stanford Health Care. It was led by Dr. Catherine A. Hogan, a Stanford Health Care Department of Pathology infectious diseases physician and medical microbiologist.
Identifying a "patient zero" within a given geographical area can help public health officers and epidemiologists understand where and how the virus was circulating and to explain any undetermined causes of death.
Speculation that the coronavirus could have circulated in the Bay Area in late 2019 was triggered after genetic analyses estimated that SARS-CoV-2, the name for this particular coronavirus, likely emerged between Oct. 6 and Dec. 11, according to the researchers. Scientists found the virus present in samples as early as mid-November in Wuhan, China, weeks or months before the World Health Organization was notified.
The earliest known case in Europe was later identified through a Dec. 29 sample in France, a month earlier than the previously thought first case, after scientists there looked back at archived samples taken from patients.
The China and France cases, coupled with the high volume of international travel to Silicon Valley and findings of previously unknown cases by the Santa Clara County Coroner-Medical Examiner's Office, added to concern that the virus may have been transmitted as early as last year.
To date, the earliest Bay Area death is known to have occurred on Feb. 6, a fact that the county medical examiner only determined by looking back at suspicious cases and sending samples to the U.S. Centers for Disease Control and Prevention for testing.
The findings spurred Gov. Gavin Newsom to call for counties to search through deaths as far back as December 2019 for possible missed COVID-19 cases.
Researchers at Stanford Health Care and the Stanford University School of Medicine — including Hogan, Natasha Garamani Malaya K. Sahoo, and Drs. ChunHong Huang, James Zehnder and Benjamin A. Pinsky — tested the 1,700 samples for the coronavirus using the polymerase chain reaction or PCR test, the type of test currently being used. They samples had been collected between Oct. 31 through Dec. 31. The patients all had symptoms consistent with COVID-19. They had been tested for other routine viruses that are prevalent in the fall and winter, such as influenza A, influenza B, respiratory syncytial virus (RSV), but they had not been tested for SARS-CoV-2, the researchers said.
COVID-19 shares many symptoms with influenza, rhinoviruses and respiratory enteroviruses, RSV and other coronaviruses.
The researchers said the study had limitations in part because the samples came from only one institution, which might contain a population that is not representative of the Bay Area as a whole.
"Further retrospective … screening using specimens collected at other institutions throughout the U.S. will be necessary to fully understand early community transmission in this country," the researchers wrote.
Find comprehensive coverage of the Midpeninsula's response to the new coronavirus by Palo Alto Online, the Mountain View Voice and the Almanac here.