https://orcid.org/0000-0002-9926-684X
ABSTRACT
The integration of Point of Care Ultrasound (POCUS) into the care of trauma patients, specifically the E-FAST, has improved the accuracy of initial diagnoses and improved time to surgical intervention in critically ill patients. Physician assistants (PAs) are critically important members of any military trauma resuscitation team and are often team leaders in a pre-hospital setting. They may receive training in ultrasound but there are little data to support their use or evaluate their effectiveness in using POCUS. We designed a study to evaluate the image quality of an E-FAST Exam performed by Emergency Medicine Physician Assistant (EMPA) Fellows and Emergency Medicine (EM) Interns following identical training. Our hypothesis is that image quality obtained by EMPAs will be non-inferior to those images obtained by EM Interns.
This is a prospective single-blinded study comparing the image quality of E-FAST exams performed by first year EM interns and first year EMPA fellows. All participants completed standard POCUS training prior to enrollment in the study. A total of 8 EMPAs and 8 EM first year residents completed 10 recorded E-FAST exams to be used as study images. Participants also viewed a 15-question slide show containing images of positive (6) and negative (9) E-FAST exams and recorded their interpretations. Images were reviewed by expert reviewers who were blinded to which images were collected by which group. An image quality score was recorded for each view as well as an overall image quality score. Image quality was rated on a 1 to 5 image quality scale.
For overall image quality, the mean score for EMPAs was 3.6 ± 0.5 and for EM residents was 3.2 ± 0.5 with statistical significance favoring better image quality from the EMPAs. The time to completion for the EFAST exam for EMPAs was 4.8 ± 1.3 minutes and for interns it was 3.4 ± 1.4 minutes (P value = 0.02). There was no difference in image interpretation quiz scores between the groups (mean score 92% among interns and 95% among PAs).
POCUS is an imaging modality which is very portable and relatively inexpensive which makes it ideal for military medicine. PAs are essential members of military trauma teams, and often run an initial trauma resuscitation. Being able to correctly identify patients who have free fluid early in the course of treatment allows for more correct evacuation criteria to ensure the sickest patients get to care the fastest. Although there are limited data to support POCUS use by non-physicians, our data support a growing body of evidence that it is not the profession or baseline medical education that determines an individual’s ability to use and incorporate ultrasound into bedside and clinical practice. Our study shows that with training and experience PAs or other members of the military health care team can use the EFAST to better care for trauma patients.
INTRODUCTION
The integration of point of care ultrasound (POCUS) into the care of trauma patients has improved both the accuracy of initial diagnoses and the time to surgical intervention in critically ill patients. The Extended Focused Assessment in Trauma (E-FAST) exam is invaluable in the care of the critically ill trauma patient. It is used daily in emergency departments across the United States.1–3 Previous work has shown the utility of ultrasound in the field and military physicians have successfully incorporated POCUS into treatment of patients in the deployed environment.4,5 Physician assistants (PAs) are important members of any military trauma resuscitation team and are often team leaders in a pre-hospital setting. Therefore, their ability to use POCUS, including the E-FAST, was of significant interest.
Evaluation with CT or radiographs is limited in deployed settings due to the weight and size of the equipment required. The development of small, portable, ultrasound devices has allowed POCUS to be brought to deployed settings and potentially as far forward as the point of injury.6,7 In 2008, the Special Operations Clinical Level Ultrasound (SOLCUS) was conceived and debuted in 2010. The SOLCUS course included hands-on training, as well as a didactic curriculum based on the current American College of Emergency Physicians (ACEP) recommendations.8,9 Subsequently, special operations medics successfully integrated POCUS into their care in Afghanistan with the use of the E-FAST and musculoskeletal exams.10
Literature on the safety and efficacy of POCUS performed by PAs is scant. Previous work has rarely isolated PAs but has shown a trend that medics and Advanced Practice Provider (APP)s with adequate training can perform POCUS with a high degree of sensitivity and specificity.11–14 Simmons et al. showed no difference in E-FAST sensitivity and sensitivity between PAs as a secondary outcome, but were not powered to detect a small difference in image quality.15Previous studies have been limited in scope, have not attempted to isolate Emergency Medicine Physician Assistants (EMPAs), and have not included a comparison to physician-performed POCUS.
We designed a study to evaluate the image quality of an E-FAST exam performed by EMPA fellows and Emergency Medicine (EM) Interns following identical training. We believe image quality is a reasonable method to determine the ability to perform the exam correctly. Our hypothesis was that image quality obtained by EMPAs would be non-inferior to those images obtained by EM Interns.
METHODS
This was a prospective single-blinded study comparing the image quality of E-FAST exams performed by EMPA fellows and EM Interns. Both groups underwent identical training prior to enrollment in the study. Training included a 16-hour ultrasound course during orientation month. This was followed by a 4-week ultrasound rotation taking place during the first year of training that included all ACEP core ultrasound modalities. During the ultrasound rotation, participants attended weekly quality assurance (QA) sessions. This rotation included review of clinical E-FAST exams performed in the ED and completed a standardized ultrasound didactic curriculum. As a part of the rotation, they were required to record 150 ultrasound exams, of which 25 were required to be E-FAST exams. Members of the emergency medicine ultrasound fellowship faculty reviewed these studies. All students on the rotation completed between 25 and 30 E-FAST exams. Students were also required to pass an objective structured clinical exam (OSCE) at the end of the month which included the E-FAST exam.
An a priori power calculation was performed, and sample size was estimated using means equivalence in SAS, a type of statistical analysis software. Estimating a mean image quality score of 3.8 on a 1 to 5 image quality scale with an acceptable difference of 0.5 between the 2 groups, an estimated sample size of 51 studies in each group was required. The estimated mean image score was based on expert opinion by MAM who had completed an ultrasound fellowship and performed more than 5 years of Quality Assurance reviews for the Emergency Department. After completing the training listed above, 8 EMPAs and 8 EM first year residents were enrolled in the study after signing a written consent form. They each completed 10 recorded, complete E-FAST exams to be used as study images. A 6-second clip of each window (Right Upper Quadrant (RUQ), Left Upper Quadrant (LUQ), cardiac, pelvic, and lungs) was recorded. Participants were aware of the intention of the study of comparison of image quality and were supervised without intervention during image acquisition. Patients in the emergency department at a single academic location were informed of the inclusion of their images in the study and verbally consented. Institutional Review Board review determined that written consent was not required. All exams included in the study were performed for training purposes only. Exams were performed only when image acquisition did not interfere with ongoing patient care. In the event of a positive E-FAST exam, the trainee alerted the provider assigned to the patient. Participants also viewed a 15-question slideshow containing images of positive (6) and negative (9) E-FAST exams and recorded their interpretations (positive or negative exam). Percentages of positive and negative were based on the percentage of positive E-FAST exams at our facility to emulate the clinical environment.
Images were reviewed by 5 expert reviewers who had completed a 12-month advanced emergency medicine ultrasound fellowship. Reviewers were blinded to the identity and to which group of scanners the collected images belonged to. They reviewed videos from 160 complete E-FAST exams (80 done by each group). Initial study plans were for 3 expert reviewers; however, there was a higher-than-expected interobserver disagreement and a further 2 reviewers were added to strengthen the statistical analysis. An image quality score was recorded for each view including the RUQ, LUQ, pelvic, cardiac, and pulmonary views, as well as an overall image quality score. Image quality was rated on a 1 to 5 image quality scale using the guidelines published by ACEP (Fig. 1).16 This image rating scale is widely accepted and is used nationally in advanced emergency medicine ultrasound fellowships and POCUS research. A clinically usable study is defined as a score of 3 or greater in each window of the E-FAST. Data were collected using a standardized data collection form.
American College of Emergency Physician Ultrasound Imaging Guidelines Quality Assurance Grading Scale.
Image quality results and image interpretation ability based on quiz scores were pooled across the 5 reviewers. Results were compared between the 2 groups using a one-way ANOVA analysis and results were confirmed using Wilcoxon tests. The time to completion for the E-FAST exam was also compared. A repeated measures ANOVA analysis with each participant as a random effect in the model was also performed.
RESULTS
The overall mean image quality on the 1 to 5 scale for EMPAs was 3.4 ± 0.5 and for EM residents it was 3.1 ± 0.5. Mean scores ranged from 3.1 to 3.5 for the EM residents and 3.3 to 3.7 for the EMPAs for each of the quadrants (RUQ, LUQ, pelvis, cardiac, lung). Median scores ranged from 3.25 to 3.5 for each of the quadrants evaluated for the EM residents and ranged from 3.25 to 3.75 for the EMPAs. The difference between the groups was statistically significant with better image quality obtained by the EMPAs in the pelvic view, cardiac view, lung view, and overall views. For the remaining quadrants, the image quality was not statistically different between the groups when analyzed using a one-way ANOVA test or a Wilcoxon test (Table I). 75% of the images from the residents were 3 or greater while 85% of the images had a 3 or greater in the EMPA group (Table II).
Image Quality Scores
| RUQ | LUQ | Pelvic | Cardiac | Lung | Overall | ||
|---|---|---|---|---|---|---|---|
| Mean image quality | Intern | 3.3 | 3.1 | 3.2 | 3.1 | 3.5 | 3.1 |
| PA | 3.4 | 3.3 | 3.3 | 3.4 | 3.7 | 3.4 | |
| Median image quality | Intern | 3.5 | 3.25 | 3.25 | 3.25 | 3.5 | 3.25 |
| PA | 3.5 | 3.25 | 3.25 | 3.5 | 3.75 | 3.5 | |
| SD | Intern | 0.58 | 0.55 | 0.52 | 0.57 | 0.55 | 0.49 |
| PA | 0.57 | 0.52 | 0.45 | 0.61 | 0.53 | 0.47 | |
| P-value | 0.516 | 0.095 | 0.030 | 0.017* | 0.009* | 0.010* |
| RUQ | LUQ | Pelvic | Cardiac | Lung | Overall | ||
|---|---|---|---|---|---|---|---|
| Mean image quality | Intern | 3.3 | 3.1 | 3.2 | 3.1 | 3.5 | 3.1 |
| PA | 3.4 | 3.3 | 3.3 | 3.4 | 3.7 | 3.4 | |
| Median image quality | Intern | 3.5 | 3.25 | 3.25 | 3.25 | 3.5 | 3.25 |
| PA | 3.5 | 3.25 | 3.25 | 3.5 | 3.75 | 3.5 | |
| SD | Intern | 0.58 | 0.55 | 0.52 | 0.57 | 0.55 | 0.49 |
| PA | 0.57 | 0.52 | 0.45 | 0.61 | 0.53 | 0.47 | |
| P-value | 0.516 | 0.095 | 0.030 | 0.017* | 0.009* | 0.010* |
Implies significance for both one-way ANOVA and Wilcoxon’s method.
Table I contains the median and mean image quality scores, their SDs, and P values for each view for both groups.
Image Quality Scores
| RUQ | LUQ | Pelvic | Cardiac | Lung | Overall | ||
|---|---|---|---|---|---|---|---|
| Mean image quality | Intern | 3.3 | 3.1 | 3.2 | 3.1 | 3.5 | 3.1 |
| PA | 3.4 | 3.3 | 3.3 | 3.4 | 3.7 | 3.4 | |
| Median image quality | Intern | 3.5 | 3.25 | 3.25 | 3.25 | 3.5 | 3.25 |
| PA | 3.5 | 3.25 | 3.25 | 3.5 | 3.75 | 3.5 | |
| SD | Intern | 0.58 | 0.55 | 0.52 | 0.57 | 0.55 | 0.49 |
| PA | 0.57 | 0.52 | 0.45 | 0.61 | 0.53 | 0.47 | |
| P-value | 0.516 | 0.095 | 0.030 | 0.017* | 0.009* | 0.010* |
| RUQ | LUQ | Pelvic | Cardiac | Lung | Overall | ||
|---|---|---|---|---|---|---|---|
| Mean image quality | Intern | 3.3 | 3.1 | 3.2 | 3.1 | 3.5 | 3.1 |
| PA | 3.4 | 3.3 | 3.3 | 3.4 | 3.7 | 3.4 | |
| Median image quality | Intern | 3.5 | 3.25 | 3.25 | 3.25 | 3.5 | 3.25 |
| PA | 3.5 | 3.25 | 3.25 | 3.5 | 3.75 | 3.5 | |
| SD | Intern | 0.58 | 0.55 | 0.52 | 0.57 | 0.55 | 0.49 |
| PA | 0.57 | 0.52 | 0.45 | 0.61 | 0.53 | 0.47 | |
| P-value | 0.516 | 0.095 | 0.030 | 0.017* | 0.009* | 0.010* |
Implies significance for both one-way ANOVA and Wilcoxon’s method.
Table I contains the median and mean image quality scores, their SDs, and P values for each view for both groups.
Image Quality Quantiles
| Quantiles | ||||||||
|---|---|---|---|---|---|---|---|---|
| Level | Minimum | 10% | 25% | Median | 75% | 90% | Maximum | |
| Overall | Intern | 2.00 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| RUQ | Intern | 2.00 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.25 | 4.50 | |
| LUQ | Intern | 1.75 | 2.50 | 2.75 | 3.25 | 3.50 | 3.98 | 4.25 |
| PA | 1.75 | 2.50 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Pelvic | Intern | 1.25 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.25 | 2.75 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Cardiac | Intern | 2.00 | 2.28 | 2.75 | 3.25 | 3.69 | 3.75 | 4.50 |
| PA | 1.75 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| Lung | Intern | 2.00 | 2.75 | 3.00 | 3.50 | 4.00 | 4.00 | 4.25 |
| PA | 2.00 | 3.00 | 3.50 | 3.75 | 4.00 | 4.48 | 4.75 | |
| Quantiles | ||||||||
|---|---|---|---|---|---|---|---|---|
| Level | Minimum | 10% | 25% | Median | 75% | 90% | Maximum | |
| Overall | Intern | 2.00 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| RUQ | Intern | 2.00 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.25 | 4.50 | |
| LUQ | Intern | 1.75 | 2.50 | 2.75 | 3.25 | 3.50 | 3.98 | 4.25 |
| PA | 1.75 | 2.50 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Pelvic | Intern | 1.25 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.25 | 2.75 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Cardiac | Intern | 2.00 | 2.28 | 2.75 | 3.25 | 3.69 | 3.75 | 4.50 |
| PA | 1.75 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| Lung | Intern | 2.00 | 2.75 | 3.00 | 3.50 | 4.00 | 4.00 | 4.25 |
| PA | 2.00 | 3.00 | 3.50 | 3.75 | 4.00 | 4.48 | 4.75 | |
Table II contains the image quality quantiles for interns and Emergency Medicine Physician Assistants (EMPAs) with the median for both groups.
Image Quality Quantiles
| Quantiles | ||||||||
|---|---|---|---|---|---|---|---|---|
| Level | Minimum | 10% | 25% | Median | 75% | 90% | Maximum | |
| Overall | Intern | 2.00 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| RUQ | Intern | 2.00 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.25 | 4.50 | |
| LUQ | Intern | 1.75 | 2.50 | 2.75 | 3.25 | 3.50 | 3.98 | 4.25 |
| PA | 1.75 | 2.50 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Pelvic | Intern | 1.25 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.25 | 2.75 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Cardiac | Intern | 2.00 | 2.28 | 2.75 | 3.25 | 3.69 | 3.75 | 4.50 |
| PA | 1.75 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| Lung | Intern | 2.00 | 2.75 | 3.00 | 3.50 | 4.00 | 4.00 | 4.25 |
| PA | 2.00 | 3.00 | 3.50 | 3.75 | 4.00 | 4.48 | 4.75 | |
| Quantiles | ||||||||
|---|---|---|---|---|---|---|---|---|
| Level | Minimum | 10% | 25% | Median | 75% | 90% | Maximum | |
| Overall | Intern | 2.00 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| RUQ | Intern | 2.00 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 |
| PA | 2.00 | 2.75 | 3.00 | 3.50 | 3.75 | 4.25 | 4.50 | |
| LUQ | Intern | 1.75 | 2.50 | 2.75 | 3.25 | 3.50 | 3.98 | 4.25 |
| PA | 1.75 | 2.50 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Pelvic | Intern | 1.25 | 2.50 | 2.81 | 3.25 | 3.50 | 3.75 | 4.00 |
| PA | 2.25 | 2.75 | 3.00 | 3.25 | 3.75 | 4.00 | 4.50 | |
| Cardiac | Intern | 2.00 | 2.28 | 2.75 | 3.25 | 3.69 | 3.75 | 4.50 |
| PA | 1.75 | 2.50 | 3.00 | 3.50 | 3.75 | 4.00 | 4.50 | |
| Lung | Intern | 2.00 | 2.75 | 3.00 | 3.50 | 4.00 | 4.00 | 4.25 |
| PA | 2.00 | 3.00 | 3.50 | 3.75 | 4.00 | 4.48 | 4.75 | |
Table II contains the image quality quantiles for interns and Emergency Medicine Physician Assistants (EMPAs) with the median for both groups.
There was also a significant difference (P-value 0.02) between groups in time to completion of the study. EMPAs took on average 4.8 minutes and interns took on average of 3.4 minutes to complete the EFAST. 0.38 min was the SE for the RM ANOVA for time to completion.
The average image interpretation quiz score was 92% for EM Interns and 95% for EMPAs with no statistical difference between the groups (Fig. 2).
Image interpretation quiz scores.
DISCUSSION
Few studies have directly compared ultrasound image quality between EMPAs and EM interns.12 We found that the image quality was statistically different between the EMPAs and EM residents with better image quality obtained by the EMPAs. We believe that with proper training, experience, and quality feedback, EMPAs can acquire usable images and accurately interpret the E-FAST exam.
Currently there is limited exposure to POCUS during PA undergraduate medical education with less than one-third of programs including POCUS in the standard curriculum.17 Most of the experience is gained from clinical rotations which are varied and have no standardized ultrasound curriculum. If ultrasound training is incorporated into PA training, there are neither regulations nor guidelines as to the minimum number of scans nor which modalities should be covered. In 2018, 83% of PAs included in one survey reported receiving their training in POCUS on the job with minimal or no training prior to graduation.18 PAs can obtain training in ultrasound through an EMPA fellowship or an Advanced Emergency Medicine Ultrasonography (AEMUS) fellowship. The Society of Emergency Medicine Physician Assistants requires 40 hours of training in bedside ultrasound but does not further guide what training is required which leads to significant variation between programs.19 PAs may also pursue training through an ultrasound fellowship. Few ultrasound fellowships are currently open to APPs, although there are 3 Army sponsored ultrasound fellowships which accept PAs.
At our location, the EMPAs complete the ultrasound didactic course during intern orientation (about 20 hours of training in multiple modalities) as well as spend a month with the ultrasound team. During this month, they participate in quality assurance and are required to obtain at least 150 scans with 25 of those being E-FAST exams. This training is the same as the EM interns receive. This is in line with previous work showing similar outcomes with appropriate training.20 A review done in 2022 of POCUS performed by PAs found 12 studies that addressed the accuracy of PA POCUS for a variety of specific modalities. They all found PA studies to be done with a high degree of accuracy.12
Often, a PA may be the first provider to evaluate the trauma patient prior to evacuating them to higher levels of care. Being able to correctly and rapidly identify patients who have intraperitoneal free fluid allows for better triage and evacuation of the sickest patients first. Ultrasound devices have become smaller, more portable, and relatively inexpensive. These advancements make it possible to take them into the field and on missions. Having a strong background and training in ultrasound allows military medical professionals to give the best care possible to their patients.
There were several potential limitations to our study. First, the initial interventions including the intern orientation ultrasound course and our standard ultrasound rotation occurred prior to the collection of study data. The participants were aware that the intended outcome would be an image comparison between the 2 groups. This may have led to the increased scanning time in the PA group due to a desire to prove competence, although this is supposition on our part. In addition, these scans were performed in an ideal environment and not in an emergent situation. It’s possible that in a clinical setting there may be a greater difference between the 2 groups. We think that this is unlikely. PAs have been essential components of the military trauma team with proven success in the field.6 Additionally, our study does not address skill maintenance over time. It is unclear if the image quality would remain the same across the 2 groups over time.
A final significant limitation was the high inter-observer disagreement of the reviewers. We used a standard and accepted scoring system from a major ultrasound organization. This system has been used at our facility for the past 10 years. The high inter-observer disagreement was unexpected. We found that in practice different raters had different interpretations of the rating scale. We suggest that future studies provide a more detailed rating scheme for each view with the rating scale.
Although there are limited data to support POCUS use by non-physicians, our data support a growing body of evidence that it is not the profession or baseline medical education that determines an individual’s ability to use and incorporate ultrasound into bedside and clinical practice.8 We believe that with proper training and experience PAs can use the E-FAST to better care for trauma patients.
CONCLUSIONS
We conclude that EMPAs were able to obtain images for the E-FAST that were non-inferior to physician obtained images with equivalent training. We acknowledge that the EMPA fellows had a longer average time for exam completion, which will require future studies to determine the effect of the prolonged time on patient care. We suggest that using a benchmark of a least 25 E-FAST exams with expert feedback, followed by passing an OSCE, is sufficient for an EMPA to independently perform the E-FAST. Our ultrasound rotation is 1 month, and students learn multiple exams. However, the E-FAST alone could be taught over several days. This is in concordance with previous research on learning curves in POCUS and expert consensus on training on the E-FAST.21,22 We believe this study supports credentialing EMPAs for independent use of ultrasound for the E-FAST exam after appropriate training. Further studies should be conducted to evaluate EMPA use of the E-FAST in a clinical setting as well as maintenance of skill over time.
ACKNOWLEDGMENTS
The authors would like to thank Dr James Aden for his invaluable assistance with data analysis.
CLINICAL TRIAL REGISTRATION
None declared.
INSTITUTIONAL REVIEW BOARD (HUMAN SUBJECTS)
This study was approved by Regional Health Command-Atlantic (RHC-A) Institutional Review Board (IRB) (RHC-A-00-000).
INSTITUTIONAL ANIMAL CARE AND USE COMMITTEE (IACUC)
Not applicable.
INDIVIDUAL AUTHOR CONTRIBUTION STATEMENT
JB and AB collected the data. ST and RL input the data. KJ, MM, EC, NT, and JC served as expert reviewers. KJ and MM drafted the original manuscript. MM designed this research, reviewed and edited the manuscript. All authors read and approved the final manuscript.
INSTITUTIONAL CLEARANCE
Institutional clearance approved.
FUNDING
None declared.
CONFLICT OF INTEREST STATEMENT
None declared.
DATA AVAILABILITY
The data that support the findings of this study are available on request from the corresponding author.
REFERENCES
Author notes
Preliminary results presented at MHSRS August 2023.
The views expressed herein are those of the authors and do not necessarily reflect the official policy or position of the Defense Health Agency, the Department of Defense, or any agencies under the U.S. Government.
