Morbidity and Mortality Weekly Report
Early Release / Vol. 69 April 14, 2020
Transmission of COVID-19 to Health Care Personnel During Exposures to a
Hospitalized Patient — Solano County, California, February 2020
Amy Heinzerling, MD1,2; Matthew J. Stuckey, PhD3; Tara Scheuer, MPH4; Kerui Xu, PhD2,3; Kiran M. Perkins, MD3; Heather Resseger, MSN5;
Shelley Magill, MD, PhD3; Jennifer R. Verani, MD3; Seema Jain, MD1; Meileen Acosta, MPH4; Erin Epson, MD1
On February 26, 2020, the first U.S. case of community- recognition and isolation of patients with possible COVID-19
acquired coronavirus disease 2019 (COVID-19) was confirmed and use of recommended PPE to minimize unprotected, high-
in a patient hospitalized in Solano County, California (1). The risk HCP exposures and protect the health care workforce.
patient was initially evaluated at hospital A on February 15; HCP with potential exposures to the index patient at
at that time, COVID-19 was not suspected, as the patient hospital A were identified through medical record review.
denied travel or contact with symptomatic persons. During a Hospital and health department staff members contacted HCP
4-day hospitalization, the patient was managed with standard for initial risk stratification and classified HCP into categories
precautions and underwent multiple aerosol-generating proce- of high, medium, low, and no identifiable risk, according to
dures (AGPs), including nebulizer treatments, bilevel positive CDC guidance.* HCP at high or medium risk were furloughed
airway pressure (BiPAP) ventilation, endotracheal intubation, and actively monitored; those at low risk were asked to self-
and bronchoscopy. Several days after the patient’s transfer to monitor for symptoms for 14 days from their last exposure.†
hospital B, a real-time reverse transcription–polymerase chain Nasopharyngeal and oropharyngeal specimens were collected
reaction (real-time RT-PCR) test for SARS-CoV-2 returned once from HCP who developed symptoms consistent with
positive. Among 121 hospital A health care personnel (HCP) COVID-19§ during their 14-day monitoring period, and spec-
who were exposed to the patient, 43 (35.5%) developed symp- imens were tested for SARS-CoV-2 using real-time RT-PCR at
toms during the 14 days after exposure and were tested for the California Department of Public Health. Serologic testing
SARS-CoV-2; three had positive test results and were among and testing for other respiratory viruses was not performed.
the first known cases of proabable occupational transmission The investigation team, including hospital, local and state
of SARS-CoV-2 to HCP in the United States. Little is known health departments, and CDC staff members, attempted
about specific risk factors for SARS-CoV-2 transmission in to contact all 43 tested HCP by phone to conducted inter-
health care settings. To better characterize and compare expo- views regarding index patient exposures using a standardized
sures among HCP who did and did not develop COVID-19, exposure assessment tool. Two-sided p-values were calculated
standardized interviews were conducted with 37 hospital A using Fisher’s exact test for categorical variables and Wilcoxon
HCP who were tested for SARS-CoV-2, including the three rank-sum test for continuous variables; p-values <0.05 were
who had positive test results. Performing physical examina-
tions and exposure to the patient during nebulizer treatments * Exposure was defined according to CDC guidance for HCP with potential
were more common among HCP with laboratory-confirmed exposure to COVID-19, which categorizes exposures based on factors such as
COVID-19 than among those without COVID-19; HCP exposure to the patient during AGPs, personal protective equipment use, and
source control (e.g., patient wearing a facemask) during exposure. https://www.
with COVID-19 also had exposures of longer duration to the cdc.gov/coronavirus/2019-ncov/hcp/guidance-risk-assesment-hcp.html.
patient. Because transmission-based precautions were not in † HCP categorized as being at low risk were allowed to continue to report to
use, no HCP wore personal protective equipment (PPE) rec- work but were checked for symptoms before the start of each shift; no additional
follow-up was conducted for HCP categorized as having no identifiable risk.
ommended for COVID-19 patient care during contact with § Including fever (subjective or measured at ≥100.4°F [38°C]), cough, shortness
the index patient. Health care facilities should emphasize early of breath, or sore throat.
U.S. Department of Health and Human Services
Centers for Disease Control and Prevention
Early Release
considered statistically significant. Analyses were conducted TABLE 1. Demographic characteristics, exposure risk categories, and
using SAS (version 9.4; SAS Institute). The California Health job titles of 43 health care personnel (HCP) who were exposed to a
hospitalized patient with COVID-19, became symptomatic, and were
and Human Services Agency’s Committee for the Protection tested for SARS-CoV-2 — Solano County, California, February 2020
of Human Subjects and CDC determined this investigation Characteristic No. (%)
to be public health practice.
Total HCP 43 (100)
Hospital A identified 145 HCP with potential exposure to
the index patient. After the initial interview, 24 (17%) HCP Age in yrs, median (range) 39 (27–60)
were classified as having no identifiable risk; the remaining Sex
Female 36 (84)
121 were classified as having high (14), medium (80), or low Male 7 (16)
(27) risk. Over the course of their monitoring periods, 43 Risk category*
(36%) of these HCP became symptomatic and underwent High 5 (12)
Medium 36 (84)
testing for SARS-CoV-2, with a median of 10 days from last Low 2 (5)
exposure to specimen collection (Table 1); SARS-CoV-2 was Days from last contact with index patient to 10 (8–14)
detected in three (7%) HCP. Thirty-seven of 43 (86%) HCP SARS-CoV-2 specimen collection, median (range)
who were tested were interviewed, including all three HCP Job title
Registered nurse 22 (51)
with positive test results.¶ Respiratory therapist 4 (9)
Among 43 HCP who were tested, 84% were female, 51% Phlebotomist 4 (9)
were registered nurses, and 95% were at high or medium risk Certified nursing assistant 3 (7)
Physician 3 (7)
(Table 1). Among the three HCP with COVID-19, two had Environmental services worker 3 (7)
high-risk and one had medium-risk exposures. Both HCP at Nutrition services worker 2 (5)
Pharmacist 1 (2)
high risk who developed COVID-19 had frequent, close con- Other 1 (2)
tact with the index patient; one reported being present for a
Abbreviation: COVID-19 = coronavirus disease 2019.
total of 3 hours while the patient was on BiPAP, and the other * According to initial risk stratification by hospital and public health
participated in BiPAP placement and intubation. Neither wore staff members.
a facemask, respirator, eye protection, or gown. The third staff
member with COVID-19, who was at medium risk, reported duration of exposure during AGPs†† was higher among HCP
close contact with the patient for a total of 2 hours but not with COVID-19 (95 minutes) than among those without
during AGPs. This staff member reported wearing a facemask COVID-19 (0 minutes) (p = 0.13) (Table 3). Among non-AGP
and gloves most of the time but removed the mask occasionally clinical activities, performing a physical examination was more
to speak and did not wear eye protection. common among HCP with COVID-19 (p = 0.02) (Table 2).
Seventeen (46%) of 37 interviewed HCP reported exposure Some HCP reported wearing gloves or facemasks during index
to the patient during at least one AGP (Table 2).** Being patient care activities (Table 3); however, none reported use of
present for or assisting with nebulizer treatments was more eye protection, gowns, N95 respirators, or powered air-puri-
common among HCP who developed COVID-19 (67%) than fying respirators (PAPRs). At hospital B, 146 HCP had high-,
among those who did not (9%) (p = 0.04); being present for medium-, or low-risk exposures; eight became symptomatic
or assisting with BiPAP was also more common among HCP and were tested, none of whom had SARS-CoV-2 detected
with COVID-19, although the difference was not statisti- (CS Martin, MSN, personal communication, 2020).
cally significant (p = 0.06). The median estimated duration Discussion
of overall exposure to the patient was higher among HCP
with COVID-19 (120 minutes) than among those without HCP are at high risk for acquiring infections during novel
COVID-19 (25 minutes) (p = 0.06). Similarly, the median disease outbreaks, especially before transmission dynamics are
fully characterized. The cases reported here are among the first
¶ One of the remaining six HCP declined to participate; the other five could known reports of occupational transmission of SARS-CoV-2
not be reached after at least three attempted phone calls.
** For the purposes of this report, the following procedures during the patient’s †† This was estimated by asking interviewed HCP to report the number and
hospitalization were considered AGPs: airway suctioning, noninvasive positive average duration of each exposure to the patient during each AGP. Total
pressure ventilation including BiPAP, manual ventilation, nebulizer treatments, estimated duration for each AGP was calculated by multiplying the number
breaking the ventilator circuit, sputum induction, intubation, and of exposures by average duration of exposure during that AGP. Total estimated
bronchoscopy. Exposure during an AGP included both direct participation exposure time for all AGPs was calculated by adding total duration of exposures
in AGP (i.e., performing or assisting with intubation), as well as presence in across all AGPs.
the patient’s room while AGP was being performed.
2 MMWR / April 14, 2020 / Vol. 69
Early Release
TABLE 2. Reported patient care activities, including aerosol-
generating procedures (AGPs), conducted by 37 health care Summary
personnel (HCP) who were tested for SARS-CoV-2 and participated What is already known about this topic?
in interviews — Solano County, California, February 2020
Health care personnel (HCP) are at heightened risk of acquiring
No. (%) COVID-19 infection, but limited information exists about
HCP with HCP without transmission in health care settings.
Exposures COVID-19 COVID-19 p-value
What is added by this report?
Total HCP 3 34 N/A Among 121 HCP exposed to a patient with unrecognized
Non-AGP activities* COVID-19, 43 became symptomatic and were tested for
Taking vital signs 2 (67) 7 (21) 0.14 SARS-CoV-2, of whom three had positive test results; all three
Taking medical history 1 (33) 7 (21) 0.53 had unprotected patient contact. Exposures while performing
Performing physical exam 3 (100) 8 (24) 0.02 physical examinations or during nebulizer treatments were
Providing medication 1 (33) 10 (29) 1.00 more common among HCP with COVID-19.
Bathing or cleaning patient 0 (0) 4 (12) 1.00
Lifting or positioning patient 1 (33) 12 (35) 1.00 What are the implications for public health practice?
Emptying bedpan 1 (33) 2 (6) 0.23 Unprotected, prolonged patient contact, as well as certain
Changing linens 0 (0) 5 (14) 1.00
Cleaning patient room 0 (0) 4 (12) 1.00
exposures, including some aerosol-generating procedures, were
Peripheral line insertion 0 (0) 1 (3) 1.00 associated with SARS-CoV-2 infection in HCP. Early recognition
Central line insertion 0 (0) 1 (3) 1.00 and isolation of patients with possible infection and recom-
Drawing arterial blood gas 1 (33) 1 (3) 0.16 mended PPE use can help minimize unprotected, high-risk HCP
Drawing blood 0 (0) 5 (15) 1.00 exposures and protect the health care workforce.
Manipulation of oxygen mask or 2 (67) 5 (15) 0.09
tubing
Manipulation of ventilator or 0 (0) 7 (21) 1.00 or airborne precautions.§§ As community transmission of
tubing
In room while high-flow oxygen 1 (33) 9 (26) 1.00 COVID-19 increases, determining whether HCP infections are
being delivered acquired in the workplace or in the community becomes more
Collecting respiratory specimen 0 (0) 3 (9) 1.00
difficult. This investigation presented a unique opportunity
AGPs*,†
Airway suctioning 0 (0) 7 (21) 1.00 to analyze exposures associated with COVID-19 transmis-
Noninvasive ventilation (BiPAP, CPAP) 2 (67) 4 (12) 0.06 sion in a health care setting without recognized community
Manual (bag) ventilation 1 (33) 2 (6) 0.23 exposures. Describing exposures among HCP who did and
Nebulizer treatments 2 (67) 3 (9) 0.04
Breaking ventilation circuit 0 (0) 5 (15) 1.00 did not develop COVID-19 can inform guidance on how to
Sputum induction 0 (0) 1 (3) 1.00 best protect HCP.
Intubation 1 (33) 2 (6) 0.23
Performed or assisted 1 (33) 1 (3) 0.16
Among a cohort of 121 exposed HCP, 43 of whom
Present in room 0 (0) 1 (3) 1.00 were symptomatic and tested, three developed confirmed
Bronchoscopy 0 (0) 3 (9) 1.00 COVID-19, despite multiple unprotected exposures among
Performed or assisted 0 (0) 1 (3) 1.00
Present in room 0 (0) 3 (9) 1.00 HCP. HCP who developed COVID-19 had longer durations
Any AGP 2 (67) 15 (44) 0.58 of exposure to the index patient; exposures during nebulizer
Abbreviations: BiPAP = bilevel positive airway pressure; COVID-19 = coronavirus treatments and BiPAP were also more common among HCP
disease 2019; CPAP = continuous positive airway pressure; N/A = not applicable. who developed COVID-19. These findings underscore the
* Other patient care activities addressed in the exposure assessment tool but
not listed here were not reported by any interviewed HCP. heightened COVID-19 transmission risk associated with
† For all AGPs listed here except intubation and bronchoscopy, exposure to AGP
prolonged, unprotected patient contact and the importance
includes either performing or assisting with the procedure or being present
in the patient’s room while the procedure was being performed. For intubation of ensuring that HCP exposed to patients with confirmed or
and bronchoscopy, performing or assisting with the procedure and being suspected COVID-19 are protected. CDC recommends use of
present in the room are presented separately.
N95 or higher-level respirators and airborne infection isolation
rooms when performing AGPs for patients with suspected or
to HCP in the United States, although more cases have since confirmed COVID-19; for care that does not include AGPs,
been identified (2). Little is known to date about SARS-CoV-2 CDC recommends use of respirators where available.¶¶ In
transmission in health care settings. Reports from Illinois, §§ Additional detail on recommended transmission-based precautions
Singapore, and Hong Kong have described cohorts of HCP recommended for patients with suspected or confirmed COVID-19. https://
exposed to patients with COVID-19 without any documented www.cdc.gov/coronavirus/2019-ncov/infection-control/control-
HCP transmission (3–5); most HCP exposures in these cases recommendations.html.
¶ ¶ https://www.cdc.gov/coronavirus/2019-ncov/infection-control/control-
occurred with patients while HCP were using contact, droplet, recommendations.html.
MMWR / April 14, 2020 / Vol. 69 3
Early Release
TABLE 3. Reported personal protective equipment (PPE) use and exposure characteristics among 37 health care personnel (HCP) who were
tested for SARS-CoV-2 and participated in interviews — Solano County, California, February 2020
No./Total no. (%)
Exposures HCP with COVID-19 HCP without COVID-19 p-value
Reported always* using specified PPE during AGPs†,§ with index patient
Gloves 2/2 (100) 10/16 (63) 0.53
Facemask 0/2 (0) 3/16 (19) 1.00
Reported always* using specified PPE during non-AGP activities† with index patient
Gloves 3/3 (100) 21/34 (62) 0.54
Facemask 0/3 (0) 3/34 (9) 1.00
Duration of exposure to index patient
Longest single duration of time in room (mins)
<2 0/3 (0) 2/34 (6) 0.70
2–30 2/3 (67) 23/34 (68)
31–60 0/3 (0) 4/34 (12)
>60 1/3 (33) 3/34 (9)
Median (IQR) total estimated time in patient room, mins 120 (120–420) 25 (10–50) 0.06
Median (IQR) total estimated time in patient room during AGPs, mins¶ 95 (0–160) 0 (0–3) 0.13
Came within 6 ft of index patient 3/3 (100) 30/34 (91) 1.00
Reported direct skin-to-skin contact with index patient 0/3 (0) 8/34 (24) 1.00
Index patient either masked or on closed-system ventilator when contact occurred
Always 0/3 (0) 7/34 (23) 0.58
Sometimes 2/3 (67) 10/34 (32)
Never 1/3 (33) 14/34 (45)
Abbreviations: AGPs = aerosol-generating procedures; COVID-19 = coronavirus disease 2019; IQR = interquartile range.
* Versus sometimes or never.
† No HCP reported use of gowns, N95 respirators, powered air-purifying respirators (PAPRs), or eye protection during any patient care activities for index patient.
§ Denominators for PPE use during AGPs are numbers of HCP exposed to AGPs.
¶ This was estimated by asking each interviewed staff member to report the number and average duration of each exposure to the patient during AGPs. Total estimated
duration for each AGP was calculated by multiplying the number of exposures by average duration of exposure during that AGP. Total estimated exposure time for
all AGPs was calculated by adding total duration of exposures across all AGPs.
California, the Division of Occupational Safety and Health procedures and the protectiveness of different types of PPE,
Aerosol Transmissible Diseases standard requires respirators as well as the extent of short-range aerosol transmission of
for HCP exposed to potentially airborne pathogens such as SARS-CoV-2, is needed.
SARS-CoV-2; PAPRs are required during AGPs.*** Patient source control (e.g., patient wearing a mask or con-
Studies of other respiratory pathogens have documented nected to a closed-system ventilator during HCP exposures)
increased transmission risk associated with AGPs, many of might also reduce risk of SARS-CoV-2 transmission. Although
which can generate large droplets as well as small particle the index patient was not masked or ventilated for the major-
aerosols (6). A recent study found that SARS-CoV-2 generated ity of hospital A admission, at hospital B, where the patient
through nebulization can remain viable in aerosols <5 μm for remained on a closed system ventilator from arrival to receiv-
hours, suggesting that SARS-CoV-2 could be transmitted at ing a positive test result, none of the 146 HCP identified as
least in part through small particle aerosols (7). Among the exposed developed known COVID-19 infection (8). Source
three HCP with COVID-19 at hospital A, two had index control strategies, such as masking of patients, visitors, and
patient exposures during AGPs; one did not and reported HCP, should be considered by health care facilities to reduce
wearing a facemask but no eye protection for most of the risk of SARS-CoV-2 transmission.
contact time with the patient. Given multiple unprotected This findings in this report are subject to at least three
exposures among HCP in this investigation, separating risks limitations. First, exposures among HCP were self-reported
associated with specific procedures from those associated with and are subject to recall bias. Second, the low number of cases
duration of exposure and lack of recommended PPE is difficult. limits the ability to detect statistically significant differences
More research to determine the risks associated with specific in exposures and does not allow for multivariable analyses to
adjust for potential confounding. Finally, additional infections
*** Aerosol Transmissible Diseases. California Code of Regulations, Section 5199 might have occurred among asymptomatic exposed HCP who
(2009). https://www.dir.ca.gov/title8/5199.html. were not tested, or among HCP who were tested as a result of
4 MMWR / April 14, 2020 / Vol. 69
Early Release
timing and limitations of nasopharyngeal and oropharyngeal All authors have completed and submitted the International
specimen testing; serologic testing was not performed. Committee of Medical Journal Editors form for disclosure of potential
To protect HCP caring for patients with suspected or conflicts of interest. No potential conflicts of interest were disclosed.
confirmed COVID-19, health care facilities should continue References
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