A woman with COVID-19 at a Solano County hospital — the nation’s first case from an unknown source — exposed 121 health workers to the coronavirus, yet only three got the disease, a new study of the February case reveals.
All three had been in close contact for about two hours with the patient, and two had no protective gear, according to the report published Tuesday by the Centers for Disease Control and Prevention. Those workers also examined the patient and performed treatments that involved close contact, such as placing her on a breathing machine.
The researchers tested just 43 of the 121 workers for the coronavirus because only they had developed a cough or other symptoms similar to those of COVID-19 patients within two weeks after exposure. (The study acknowledges that it is now known that even people without symptoms can test positive.) The 40 who tested negative had shorter exposure — an average of half an hour — and were farther away from the patient.
The study — which notes that “little is known about specific risk factors for (coronavirus) transmission in health care settings” — concludes that health workers should wear N95 masks and use isolation rooms in high-risk situations like putting a confirmed or suspected COVID-19 patient on a breathing machine. For other care, they recommended N95s “where available.”
“These measures are crucial to protect (health care personnel) and preserve the health care workforce in the face of an outbreak already straining the U.S. health care system,” the CDC said.
The woman at the heart of the study arrived at NorthBay VacaValley Hospital on February 15 with a respiratory illness. Health workers didn’t suspect she had COVID-19 because she hadn’t traveled recently or been in touch with someone who was sick. She remained in the hospital for four days. Some of the health workers who cared for her wore no masks, gloves, goggles or gowns — all of which are now recommended when treating COVID-19 patients.
Several days after the health staff transferred the patient to another hospital, she tested positive for the disease. That’s when the hospital, and eventually the CDC, began retracing whom she might have infected. The hospital furloughed and actively monitored health care workers at high risk and asked those at low risk to self-monitor for symptoms for two weeks.
Of 121 workers exposed, 43 developed symptoms within 14 days and were tested for COVID-19. Of those, just three had positive test results. The CDC report doesn’t explain why workers with symptoms tested negative.
Those three cases were probably the first on-the-job coronavirus infections in the country, the report says.
Today, 2,789 health workers in California have COVID-19, the state’s public health department reported Wednesday. That count includes infections not only from on-the-job exposure, but from travel and other sources — many unknown.
Across the country, more than 9,200 health workers out of an estimated 18 million have the disease, the CDC reported Tuesday in a separate paper, which notes that the number probably understates the true number of coronavirus infections.
Dr. Robert Siegel, an infectious disease expert at Stanford, called the relatively low infection rate from the Solano County patient a hopeful sign. But he added that public health officials should remain vigilant in protecting workers.
“The results are promising for health care workers. It means that the risk may be less than we thought,” Siegel said. “But the cautionary note is that by using correct (personal protective equipment), health care workers may be able to keep protected.”
Siegel cautioned against generalizing from one case, but said that a single person infecting three others in this instance was on par with estimates about infection rates without social distancing. But that rate needs to be lowered to as close to zero as possible for the pandemic to end, he said.
The case studied by the CDC proved pivotal in the fight against the coronavirus and prompted the federal agency to expand its criteria for who could get tested. Doctors had asked that the Solano County patient be tested on Feb. 19, but the CDC didn’t agree until four days later, on Feb. 23. At the time, most public health officials believed that COVID-19 was transmissable only through contact with someone known to have the disease.
Health workers are especially nervous because they often lack enough protective equipment and usually can’t remain 6 feet from their patients.
“Hospitals are like a cruise ship; it’s a petri dish,” said UCSF nurse Maureen Dugan. “We’re in the face of patients every day.”
Mallory Moench is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @mallorymoench