On April 14, 2020, this report was posted online as an MMWR Early Release.

Unprotected, prolonged patient contact, as well as certain exposures, including some aerosol-generating procedures, were associated with SARS-CoV-2 infection in HCP. Early recognition and isolation of patients with possible infection and recommended PPE use can help minimize unprotected, high-risk HCP exposures and protect the health care workforce.

Among 121 HCP exposed to a patient with unrecognized COVID-19, 43 became symptomatic and were tested for SARS-CoV-2, of whom three had positive test results; all three had unprotected patient contact. Exposures while performing physical examinations or during nebulizer treatments were more common among HCP with COVID-19.

On February 26, 2020, the first U.S. case of community-acquired coronavirus disease 2019 (COVID-19) was confirmed in a patient hospitalized in Solano County, California (1). The patient was initially evaluated at hospital A on February 15; at that time, COVID-19 was not suspected, as the patient denied travel or contact with symptomatic persons. During a 4-day hospitalization, the patient was managed with standard precautions and underwent multiple aerosol-generating procedures (AGPs), including nebulizer treatments, bilevel positive airway pressure (BiPAP) ventilation, endotracheal intubation, and bronchoscopy. Several days after the patient’s transfer to hospital B, a real-time reverse transcription–polymerase chain reaction (real-time RT-PCR) test for SARS-CoV-2 returned positive. Among 121 hospital A health care personnel (HCP) who were exposed to the patient, 43 (35.5%) developed symptoms during the 14 days after exposure and were tested for SARS-CoV-2; three had positive test results and were among the first known cases of probable occupational transmission of SARS-CoV-2 to HCP in the United States. Little is known about specific risk factors for SARS-CoV-2 transmission in health care settings. To better characterize and compare exposures among HCP who did and did not develop COVID-19, standardized interviews were conducted with 37 hospital A HCP who were tested for SARS-CoV-2, including the three who had positive test results. Performing physical examinations and exposure to the patient during nebulizer treatments were more common among HCP with laboratory-confirmed COVID-19 than among those without COVID-19; HCP with COVID-19 also had exposures of longer duration to the patient. Because transmission-based precautions were not in use, no HCP wore personal protective equipment (PPE) recommended for COVID-19 patient care during contact with the index patient. Health care facilities should emphasize early recognition and isolation of patients with possible COVID-19 and use of recommended PPE to minimize unprotected, high-risk HCP exposures and protect the health care workforce.

HCP with potential exposures to the index patient at hospital A were identified through medical record review. Hospital and health department staff members contacted HCP for initial risk stratification and classified HCP into categories of high, medium, low, and no identifiable risk, according to CDC guidance.* HCP at high or medium risk were furloughed and actively monitored; those at low risk were asked to self-monitor for symptoms for 14 days from their last exposure.† Nasopharyngeal and oropharyngeal specimens were collected once from HCP who developed symptoms consistent with COVID-19§ during their 14-day monitoring period, and specimens were tested for SARS-CoV-2 using real-time RT-PCR at the California Department of Public Health. Serologic testing and testing for other respiratory viruses was not performed.

The investigation team, including hospital, local and state health departments, and CDC staff members, attempted to contact all 43 tested HCP by phone to conducted interviews regarding index patient exposures using a standardized exposure assessment tool. Two-sided p-values were calculated using Fisher’s exact test for categorical variables and Wilcoxon rank-sum test for continuous variables; p-values <0.05 were considered statistically significant. Analyses were conducted using SAS (version 9.4; SAS Institute). The California Health and Human Services Agency’s Committee for the Protection of Human Subjects and CDC determined this investigation to be public health practice.

Hospital A identified 145 HCP with potential exposure to the index patient. After the initial interview, 24 (17%) HCP were classified as having no identifiable risk; the remaining 121 were classified as having high (14), medium (80), or low (27) risk. Over the course of their monitoring periods, 43 (36%) of these HCP became symptomatic and underwent testing for SARS-CoV-2, with a median of 10 days from last exposure to specimen collection (Table 1); SARS-CoV-2 was detected in three (7%) HCP. Thirty-seven of 43 (86%) HCP who were tested were interviewed, including all three HCP with positive test results.¶

Among 43 HCP who were tested, 84% were female, 51% were registered nurses, and 95% were at high or medium risk (Table 1). Among the three HCP with COVID-19, two had high-risk and one had medium-risk exposures. Both HCP at high risk who developed COVID-19 had frequent, close contact with the index patient; one reported being present for a total of 3 hours while the patient was on BiPAP, and the other participated in BiPAP placement and intubation. Neither wore a facemask, respirator, eye protection, or gown. The third staff member with COVID-19, who was at medium risk, reported close contact with the patient for a total of 2 hours but not during AGPs. This staff member reported wearing a facemask and gloves most of the time but removed the mask occasionally to speak and did not wear eye protection.

Seventeen (46%) of 37 interviewed HCP reported exposure to the patient during at least one AGP (Table 2).** Being present for or assisting with nebulizer treatments was more common among HCP who developed COVID-19 (67%) than among those who did not (9%) (p = 0.04); being present for or assisting with BiPAP was also more common among HCP with COVID-19, although the difference was not statistically significant (p = 0.06). The median estimated duration of overall exposure to the patient was higher among HCP with COVID-19 (120 minutes) than among those without COVID-19 (25 minutes) (p = 0.06). Similarly, the median duration of exposure during AGPs†† was higher among HCP with COVID-19 (95 minutes) than among those without COVID-19 (0 minutes) (p = 0.13) (Table 3). Among non-AGP clinical activities, performing a physical examination was more common among HCP with COVID-19 (p = 0.02) (Table 2). Some HCP reported wearing gloves or facemasks during index patient care activities (Table 3); however, none reported use of eye protection, gowns, N95 respirators, or powered air-purifying respirators (PAPRs). At hospital B, 146 HCP had high-, medium-, or low-risk exposures; eight became symptomatic and were tested, none of whom had SARS-CoV-2 detected (CS Martin, MSN, personal communication, 2020).