Risk for Acquiring COVID-19 Illness Among Emergency Medical Service Personnel Exposed to Aerosol-Generating Procedures

Aubrey Brown; Leilani Schwarcz; Catherine R. Counts; Leslie M. Barnard; Betty Y. Yang; Jamie M. Emert; Andrew Latimer; Christopher Drucker; John Lynch; Peter J. Kudenchuk; Michael R. Sayre; Thomas Rea


Emerging Infectious Diseases. 2021;27(9):2340-2348. 

In This Article


Encounters With COVID-19 Patients

During the February 16–July 31, 2020, study period, 1,592 different EMS providers cared for 946 unique COVID-19 patients as part of 1,115 EMS responses, resulting in 3,710 provider-patient COVID-19 encounters. Over that period, 1,328 EMS providers did not care for any patients in whom COVID-19 had been diagnosed. Cohorts 1–3 encompassed a total of 287,032 person-days in which there were COVID-19 patient encounters, and cohort 4 encompassed a total of 240,245 person-days in which there were no COVID-19 patient encounters (Figure 2). Among the 1,592 EMS providers with ≥1 COVID-19 patient encounter, 655 (41%) had 1 encounter, 417 (26%) had 2, and 520 (33%) had ≥3.

Figure 2.

Flow diagram of emergency medical service provider encounters with COVID-19 patients and person-days at risk for transmission, King County, Washington, February 16–July 31, 2020. Individual provider's person-days may transition among cohorts 1–3. AGP, aerosol generating procedure; COVID-19, coronavirus disease; EMS, emergency medical services.

We recorded details from the 1,115 encounters involving ≥1 provider and ≥1 COVID-19 patient, overall and stratified by AGP status (Table 1). An AGP was performed in 182 (16%) patient encounters involving 787 EMS providers (567 different providers). Overall, half of the EMS responses were for female patients; the average patient age was 68 years. About half of EMS responses were to private residences and 41% to long-term care or assisted living facilities. Responders reported ≥1 clinical signs of shortness of breath (42%), cough (36%), or fever (42%) in 67% of patients. In the cohort of provider person-days when using AGPs (cohort 1) compared with the cohort of person-days when not using AGPs (cohort 2), patient encounters were more often characterized by tachypnea (63% vs. 28%), hypoxemia (70% vs. 18%), abnormal heart rate (48% vs. 38%), systolic blood pressure <90 mm Hg (17% vs. 4%), and Glasgow coma scale ≤12 (25% vs. 6%). The most common EMS provider-recorded impression of patient illness overall among the 1,115 responses was respiratory distress (n = 417, 37%), 24% (n = 101) of those among patients needing AGPs and 76% (n = 316) among patients not needing AGPs. Twenty-two patients had out-of-hospital cardiac arrests, comprising 12.1% of the provider person-days in cohort 1 (Table 1). The most common AGP provided was nonrebreather mask oxygen (n = 139) (Table 2). Other common AGPs included BVM ventilation (n = 42) and endotracheal intubation (n = 29). Among patient encounters grouped in the first cohort, 44 (24%) involved >1 AGP during a single encounter, most often nonrebreather oxygen followed by BVM ventilation, then intubation. Overall, 34% of COVID-19 patients, 57% of those receiving AGPs and 29% of those not receiving AGPs, died during follow-up from the time of encounter through December 31, 2020.

EMS Provider Risk

The 2,920 EMS providers followed over the 181-day study period produced 525,154 person-days at risk: 8,582 person-days from 705 providers treating COVID-19 patients using AGP within the incubation period (cohort 1); 26,583 person-days from 1,389 providers treating COVID-19 patients without AGP within the incubation period (cohort 2); 252,867 person-days from 1,592 providers treating COVID-19 patients outside the incubation period (cohort 3); and 240,245 person-days from 1,328 providers who never treated a COVID-19 patient during the study period (cohort 4). Thirty EMS providers had positive rRT-PCR COVID-19 test results (Table 3). The median interval between COVID-19 patient encounter and EMS provider positive rRT-PCR test was 73 days (IQR 30–105 days). Only 1 infection occurred within the 2–14-d window after an encounter with a COVID-19 patient; during that period, the provider encountered >1 COVID-19 patient with ≥1 involving AGP use, so transmission was attributed to a patient encounter in which an AGP was provided. An additional 18 EMS providers cared for COVID-19 patients and acquired COVID-19. However, their COVID-19–positive tests were outside the 2–14-d incubation period after caring for a patient with COVID-19. Eleven EMS providers who never cared for a patient with COVID-19 tested positive for COVID-19.

Overall, the incidence of rRT-PCR positive tests among EMS providers was 0.57/10,000 person-days (30 positive tests in 525,154 person-days). The relative risk associated with COVID-19 patient encounters, with or without AGP use, did not differ compared with those without any COVID-19 patient encounters (Table 3). Finally, we found no difference in incidence between aggregated person-days attributed to COVID-19 patient encounters, 0.28/10,000 person-days (1 positive test in 35,165 person-days), and person-days not attributed to COVID-19 patient encounters, 0.59/10,000 person-days (29 positive tests in 489,989 person-days; p>0.05).