The Centers for Disease Control and Prevention reported on Tuesday that 9,282 health care professionals had contracted the coronavirus in the United States as of April 9 and that 27 had died from it.

The agency cautioned that the numbers were most likely higher than reported because of inconsistencies in data-gathering and the lack of information during the outbreak. “This is likely an underestimation,” the report said, because the occupational status of patients was available for only 16 percent of the cases in the United States reported to the C.D.C.

Health care workers are among the most vulnerable groups during the pandemic because of their proximity to infected patients, a situation made worse because some have been working with inadequate protective equipment and clothing resulting from shortages.

The report said that some health care professionals with mild or asymptomatic cases might not have been tested at all.