Gov. Gavin Newsom’s director of the California Department of Public Health resigned on Sunday, an abrupt departure of a key advisor in the state’s coronavirus battle just days after the discovery of a computer system failure that resulted in the undercounting of COVID-19 cases.

Dr. Sonia Angell, who held the position for less than a year, announced her resignation in an email sent to department staff that was released by the California Health and Human Services Agency.

“Since January, when we got word of repatriation flights arriving from Wuhan, China, our department has been front and center in what has become an all-of-government response of unprecedented proportions to COVID-19,” Angell wrote in the email to public health staff members. “In the final calculation, all of our work, in aggregate, makes the difference.”

Angell’s decision to step aside comes at a crucial moment in California’s battle against the spread of the virus. More than 10,000 Californians have died from the disease and 38 of the state’s 58 counties are on a watchlist that has required the closure of businesses that had briefly reopened in the early summer and K-12 schools as the academic year begins. Angell, who frequently has appeared alongside Newsom in his public briefings on the state’s efforts to combat the pandemic, was considered a key player in the coordination with local public health departments across the state.

“I want to thank Dr. Angell for her service to the state and her work to help steer our public health system during this global pandemic, while never losing sight of the importance of health equity,” the governor said in a written statement Sunday night.

Last week, state officials confirmed that as many as 300,000 records had not been processed by the computer clearinghouse system relied upon to provide to local officials the COVID-19 test results reported by labs on a daily basis. Two separate errors were identified — one related to a computer server outage, the other to the expiration of an electronic certificate for data to be transferred from Quest Laboratories.

Administration officials insisted they did not know the extent of the problem until after Newsom’s public event on Aug. 3 in which he expressed optimism that current case numbers — lower than some had expected — meant some progress in the state’s efforts. But some local officials were sent communications the week before from the state Department of Public Health acknowledging a problem with the CalREDIE computer system.

Dr. Mark Ghaly, the secretary of the California Health and Human Services Agency, said on Friday that a full investigation was underway to determine what happened. And although he said that he had become aware of the “magnitude” of the problem only after Newsom’s public statements, some state officials had information on the problem earlier.

“We are aware that individuals there were knowledgeable of some of these challenges,” Ghaly said in discussing both the state Public Health Department and his agency, which oversees those operations.

A spokeswoman for the state health agency would not comment Sunday on whether Angell’s sudden resignation was related to, or prompted by, the database errors.

“I am grateful to Dr. Angell for her service to the people of California during this unprecedented public health crisis,” Ghaly said in a written statement Sunday night. “She has worked tirelessly for all Californians, always keeping health equity in mind. Her leadership was instrumental as Californians flattened the curve once and in setting us on a path to do so again.”

Angell served both as the director of the state Department of Public Health and as the state’s public health officer. Those duties will now be split between two women, state officials said. Sandra Shewry, a vice president at the nonprofit California Health Care Foundation who oversaw the state’s Medi-Cal program under then-Gov. Arnold Schwarzenegger, will serve as acting director of the Department of Public Health. Dr. Erica Pan, recently brought into the Newsom administration after serving as public health officer in Alameda County, will take over as acting state public health officer.

Newsom is expected to provide an update on the state’s coronavirus efforts Monday afternoon.