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Medical officials in California's Santa Clara County, in the heart of Silicon Valley, indicated late Tuesday that the first U.S. death connected to the coronavirus happened weeks earlier than previously believed.

Two deaths on Feb. 6 and Feb. 17 were not initially thought to have been COVID-19-related, but further testing has revealed that they were, the county medical examiner said Tuesday.

"Today, the Medical Examiner-Coroner received confirmation from the CDC that tissue samples from both cases are positive for SARS-CoV-2 (the virus that causes COVID-19)," the Santa Clara County Medical Examiner-Coroner said in a statement.

A fatality reported by officials in Washington state Feb. 29 was initially thought to be the earliest U.S. death from the novel coronavirus.

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News of the earlier deaths comes as the total number of U.S. fatalities from the coronavirus surpassed 44,000, among more than 800,000 confirmed cases. California now has over 35,000 cases with 1,288 deaths.

Santa Clara County officials said that the two deaths in February, and one on March 9, were not initially attributed to the coronavirus as the people died at home at a time when only very limited testing was available through the Centers for Disease Control and Prevention.

"Testing criteria set by the CDC at the time restricted testing to only individuals with a known travel history and who sought medical care for specific symptoms," the county examiner-coroner's statement said.

Testing has since greatly expanded, with the U.S. having now run 4.1 million tests, about one for every 80 people.

Antibody studies in some areas of the country are also beginning to paint a picture of the scope of the disease.

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The result of one such study that looked at the prevalence of the virus in Santa Clara County "implies that the infection is much more widespread than indicated by the number of confirmed cases." The analysis, revealed last week, estimated that 2.5 percent to 4.2 percent of area residents have antibodies.

Dr. Jeff Smith, the county's chief executive, told The Los Angeles Times this month, "The virus was freewheeling in our community and probably has been here for quite some time."