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A patient with respiratory issues arrived Feb. 15 at a hospital in Solano County, Calif. It was a different time — before social distancing, masks and lockdowns. During a four-day hospital stay, doctors, nurses and other workers interacted with the person and performed multiple aerosol-generating procedures without special protective gear.

Eleven days later, they discovered the patient had covid-19, and 121 staff had been exposed to the virus, according to a Centers for Disease Control and Prevention report on the case. Of the 43 staffers who subsequently experienced flu-like symptoms and were tested with nasal swabs, three had confirmed infections — making them among the first known cases of occupational transmission in a hospital. While two of those three workers were involved in higher-risk procedures that tend to kick the virus into the air, the third was not.

The number of American health-care workers with covid-19 has spiraled upward ever since. About 9,000 have had positive coronavirus tests as of April 9, according to a separate CDC analysis released Tuesday that provides an early snapshot of infections in health-care workers across the country. They are mostly white, female and in their 40s, the report found. Although most were not sick enough to be hospitalized, 27 died, the CDC said. As with the rest of the U.S. population, most of the deaths occurred among those age 65 or older.

These numbers are believed to be a gross undercount of infections due to the continuing lack of available tests in many areas. Some regions and institutions are no longer testing health-care workers, reserving kits for the sickest patients.

The Solano patient’s story shows the sheer number of people involved in a single patient’s care and the web of interactions in a hospital that makes social distancing all but impossible. In this case, those tested included 22 nurses, four respiratory therapists, four phlebotomists, three nursing assistants, three physicians, three environmental service workers, two nutrition services workers and one pharmacist.

The CDC noted that of the three who became infected, two had “frequent, close contact with the index patient.” These two were considered at high risk. One was present for three hours while the patient was on a breathing machine. The other participated in placing the machine and in intubating the patient.

“Neither wore a facemask, respirator, eye protection, or gown,” according to the report. The third staff member, considered to be at medium risk, had close contact with the patient for two hours and wore a face mask and gloves but removed the mask sometimes to speak.

The report does not offer any hypotheses for why the 38 other staffers considered high or medium risk were not infected.

The patient was subsequently transferred to another hospital for care, where she was on a ventilator until receiving a positive test result for covid-19. None of the 146 health-care workers who interacted with the person at the second hospital were infected at the time.

“These findings underscore the heightened covid-19 transmission risk associated with prolonged, unprotected patient contact,” wrote the CDC, which also called for early recognition and prompt isolation of patients who are infected.

These measures are crucial to protect and “preserve the health care workforce in the face of an outbreak already straining the U.S. health care system,” the CDC report said.

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