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


In this observational study of a populous US metropolitan region, encounters with patients with COVID-19 accounted for 1% of all 911 EMS responses, involving nearly 1,200 unique COVID-19 patients and several thousand patient-provider encounters during the study period. Approximately 16% of these COVID-19 patient encounters involved treatment with AGPs, typically for patients with more severe illness based on field assessment and underscored by subsequent all-cause death rates. However, risk for the first responder workforce primarily originated from nonpatient sources; 29 of 30 COVID-19 illnesses among EMS providers were not directly attributed to COVID-19 patient encounters. Collectively, the results suggest that PPE provides protection against acquiring COVID-19 during prehospital emergency patient care, which supports maintenance of established practices.

Although the results indicate that risk of transmission from patients is low, the findings also highlight potential for concern. COVID-19 patients comprised only 1% of EMS responses, but that small fraction translated to thousands of calls involving ≈55% of the region's first-responder workforce over the 6 months of our investigation. One third of COVID-19 patients did not display any common symptoms, such as fever, coughing, or shortness of breath,[2] and about one sixth of all COVID-19 patient encounters involved a prehospital AGP. Collectively, the involvement of such a large proportion of the first responder workforce, the heterogeneous nature of patient characteristics, and the time-pressured need among some patients for AGP intervention could pose major COVID-19 risk to public safety personnel and infrastructure. This reality needs to be considered not only with regard to COVID-19 but also to future infectious disease risks, including as part of pandemics.

In our study, however, we found a low overall risk of EMS provider infection from patient care; COVID-19 occurred in a single provider in 1 of 3,710 provider-patient encounters, representing an incidence of 0.28 cases/10,000 person-days at risk. The low incidence occurred under circumstances in which ample PPEs were available for EMS providers and public health management provided active oversight to support guideline-directed PPE field practices.[15,20] The low infection rate attributed to patient care covered 182 COVID-19 patient encounters when AGPs were used, including the spectrum of high-flow oxygen, advanced airway maneuvers, and attempted resuscitation. Although data from larger numbers of patient encounters with use of different AGPs could perhaps help researchers refine the overall estimate and potentially determine treatment-specific risk, the overarching inference is that PPE provides excellent protection under these prehospital circumstances. The findings should reassure first responders that emergency care in general and specifically when using AGPs can be delivered safely to treat patients as long as PPE are properly deployed and that, in general, EMS personnel and management should not change evidence-based practice solely to mitigate transmission risk.

Our results also highlight the realities of the COVID-19 pandemic. Sources of infectious risk for EMS personnel are not confined to patients. We observed that the large majority of COVID-19 illness was a consequence of encounters not with patients but in the community or occupational settings. These findings support efforts to screen workplaces for provider symptoms or initiate point-of-care provider testing to limit on-the-job exposure as well as to practice guideline-directed social distancing, masking, and hygiene recommendations outlined for the general public, acknowledging that vaccination may affect these directives.[21]

The study leveraged linking electronic records to establish EMS provider–COVID-19 patient encounters, but the data platforms or linkages may not have been comprehensive. Specifically, the registry of persons positive for COVID-19 requires a test, so we could have underestimated the risk attributable to encounters with untested patients. However, in the study methodology we attributed a priori an EMS provider's COVID-19 infection to a patient encounter if it occurred within 2–14 days after the encounter, even though the transmission could have originated from another source. Conversely, this design approach could have overestimated the risk attributable to the COVID-19 patient encounter because the study did not specifically evaluate nonpatient sources of SARS-CoV-2 provider infection (including transmission among co-workers). We defined AGP on the basis of prior research. Although the results from our study were clinically encouraging, the small number of patient encounters limited our ability to compare encounters with patients by whether AGPs were used or not and by the different types of AGPs.

This active evaluation in the context of the region's EMS operational structure and the profile of experienced EMS providers may influence the generalizability of the results. For example, each year the Seattle and King County EMS system's providers are required to review and be tested on the topic of occupational infectious diseases. As part of the standard approach to patient care before the pandemic, EMS personnel routinely wore gloves and eyewear and were regularly fit-tested for N95 masks, so PPE use was to some extent already common practice at the outset of the pandemic. Moreover, the EMS system has been able to ensure PPE supply to achieve guideline-directed practices during the pandemic. These study-specific characteristics should be considered in balance with the study's broader strengths: innovative linking across EMS records and with the SARS-CoV-2 test registry, reviewing and classifying AGP status for each COVID-19 patient encounter, and undertaking a population-based regional evaluation.

In summary, we observed a very low overall risk for COVID-19 infection among the EMS first-responder workforce attributed to COVID-19 patient encounters, although the small number of EMS provider infections prevented definitive inference regarding AGP-specific risk. These findings support clinical strategies that maintain established, evidence-based practices for emergency conditions. Future efforts should continue to evaluate care settings, patient medical characteristics, provider behaviors, specific treatments, and systemwide PPE availability and status to establish risk and refine prevention practices.