Abstract

The COVID-19 pandemic left an unprecedented impact on the general public health, resulting in hundreds of thousands of deaths in the U.S. alone. Nationwide testing plans were initiated with drive-through being the currently dominant testing approach, which, however, exhausts personal protective equipment supplies, and is unfriendly to individuals not owning a vehicle. Walkup positive pressure testing booths are a safe alternative, whereby a health care provider situated on the inside of an enclosed and positively pressurized booth swabs a patient on the outside through chemical resistant gloves. The booths, however, are too prohibitively priced on the market to allow for nationwide deployment. To mitigate this, we present in this paper a safe, accessible, mobile, and affordable design of positive-pressure COVID-19 testing booths. The booths have successfully passed the Centers for Disease Control and Prevention and Health care Infection Control Practices Advisory Committee pressure, air exchange, and air quality requirements for positive-pressure rooms, following the guidelines for environmental infection control in health care facilities. The booths are manufactured using primarily off-the-shelf components from U.S. vendors with minimized customization, and the final bill of materials does not surpass USD 3,900. Since August 2019, five booths were deployed and used at the Johns Hopkins University School of Nursing, Baltimore City Health Department, and two community health centers in Baltimore. No health care provider was infected when using our booths, which have shown to facilitate walkup testing with decreased personal protective equipment consumption, reduced risk of infection, and enhanced accessibility to lower-income communities and nondrivers.

1 Introduction

As of January 2021, a novel coronavirus (SARS-CoV-2) emerging in December 2019 (commonly known as COVID-19) has resulted in a total of 21,100,000 confirmed cases in the U.S., with over 371,000 deaths across age groups [1]. The virus is believed to spread from person to person through respiratory droplets and aerosols [2], with the primary morbidity and mortality linked to pulmonary involvement. The substantial spread and significant impact of the COVID-19 pandemic are ongoing as reports in the U.S. have frequently surpassed 20,000 daily new cases since July 2020 [1]. With effective vaccines only recently developed, and expected distribution to be limited in the coming months to a year, the importance of diagnostic testing and contact tracing remains paramount for protecting the population. Upper respiratory swab specimens, particularly nasopharyngeal and nasal swab specimens, are generally collected for COVID-19 testing. During the collection, a cotton swab is gently inserted through a nostril to the nasopharynx or anterior nares, rotated a few times, and withdrawn. The swab is then placed in a sterile transparent vial, and transported for viral tests (Fig. 1).

Fig. 1
Representative images of the anterior nasal swab procedures: (a) preparing for swab sample collection; (b) insert the swab into nostril; (c) gently twist the swab while rubbing the anterior nares multiple times; and (d) replacing the swab in a vial, and then in a biohazard bag for analysis. Source from cdc.gov/coronavirus.
Fig. 1
Representative images of the anterior nasal swab procedures: (a) preparing for swab sample collection; (b) insert the swab into nostril; (c) gently twist the swab while rubbing the anterior nares multiple times; and (d) replacing the swab in a vial, and then in a biohazard bag for analysis. Source from cdc.gov/coronavirus.
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The U.S. successfully initiated nationwide COVID-19 testing programs, among which are drive-through tests designed to mitigate potential cross-infection at hospitals and clinics, whereby testing sites are commonly setup in parking lots near health centers and select pharmacies [3]. During specimens' collection, healthcare providers are required to wear disinfected personal protective equipment (PPE), while the patient remains safely seated inside a vehicle. As of January 2020, more than 250 million tests were administered nationwide [1]. However, drive-through tests impose several limitations. First, the need for replacing all PPE after each test can quickly turn into a burden considering its increasing cost and scarcity. Second, although creating a safe environment for patients, drive-through testing facilities can compromise the healthcare providers' protection. Working in outdoor conditions in uncomfortable positions while wearing multiple layers of PPE can induce fatigue and sample handling errors, and increase the risk of self-contamination during PPE donning and doffing procedures between every patient [4]. Third, drive-through tests are only accessible to a limited portion of the population, namely, consisting of people who own vehicles. For instance, multiple studies have shown that African Americans form the highest percentage of COVID-19 cases and deaths [59]. The reasons behind such disparities are linked to the long-standing health and social inequities, as explained by the Centers for Disease Control and Prevention (CDC) [10]. Factors such as absence of insurance coverage, placement of testing locations in more affluent areas, and social stigma act as a deterrent for equal testing opportunities. These elements drive the need to propose a solution that allows expansion of testing to areas where underrepresented communities can receive convenient access to tests, while offering protection to both medical personnel and patients with limited PPE consumption.

H Plus Yangji Hospital in Seoul, South Korea, pioneered the concept of walkup testing facilities to accommodate nondrivers [11,12], and mitigate the absence of space for car queues in dense urban regions. The first testing facilities consisted of a row of depressurized plastic booths the size of a phone booth, with an intercom system and gloves protruding into the booth to allow medical personnel to collect swab samples from patients. Although daily testing capacity increased from 10 to more than 70 patients, disinfecting internal surfaces while allowing sufficient time for ventilation between each patient proved to be time consuming [11]. An upgraded variant was introduced, whereby the healthcare provider stands inside the booth to test the patient on the outside [10,13]. The booths are positively pressurized using filtered air, with glove ports providing access to collect specimens outside the booth. Such setup allows the health care provider to stay inside the booth in between sample collection, avoid regular PPE replacement, and save time on ventilating the booth between usages. With a positive pressure booth, only the outer surface of the booth needs to be disinfected after every patient testing. The cost of purchasing these positive pressure booths in the U.S. amounted to USD 7,500, excluding shipping rates. Such expensive prices can extend beyond the financial capacity of numerous institutions in the U.S., especially with the incurred increasing costs and decreasing revenues during the COVID-19 pandemic [14]. A simplified and affordable booth was subsequently designed by the Brigham and Women's Hospital (Boston, MA) [15], yet without making it fully enclosed by leaving the backside of the booth exposed to open air, thus putting the tester at a theoretical risk of infection. A few manufacturing facilities in the U.S. followed in South Korea's footsteps and designed their own positive pressure testing booths (e.g., Garmat, Englewood, CO), but their products are within the same price range as the Korean booths.

In this paper, we hypothesize that our low-cost, do-it-yourself, positive-pressure testing booth is safe and easy to use for collecting COVID-19 specimens. To test this hypothesis, we demonstrated that the booths meet the safety requirements set forth by the CDC and the Health care Infection Control Practices Advisory Committee (HICPAC) for the environmental infection control in health care facilities. In particular, we validated that the booths are capable of (a) maintaining a constant internal pressure that exceeds the minimum requirement of +8.0 Pa by a safety factor of 2.5, (b) supplying enough airflow to secure at least 12 air exchanges per hour, (c) eliminating airborne respirable particles through a high-efficiency particulate air (HEPA) filter, and (d) are easy to use by providers. Although the CDC and HICPAC only recommend using a HEPA filter without specifying numerical limits to particulate matter concentration, we conducted experiments to better assess the filtering capabilities of our setup. Our main contributions are attributed to the booth's simple “DIY” (do-it-yourself) design, and the successful clinical deployment and usage around testing facilities in Baltimore, MD. The booth is affordable for local governments, is designed in a way that facilitates transportation across multiple communities, and can be manufactured using exclusively off-the-shelf components from vendors such as McMaster Carr, Home Depot, and 80/20. Any research institution or local manufacturer is capable of producing a similar booth within one week, guided by our installation instructions.

2 Materials and Methods

The booth's design needs to meet a set of requirements, the most crucial of which relate to the safety of medical personnel and patients. One safety factor in this case corresponds to maintaining a minimum of +8.0 Pa (0.82 mm H2O) pressure differential within the booth set by the CDC and HICPAC for positive pressure rooms [16]. Additional CDC and HICPAC requirements include a minimum of 12 air exchanges per hour, as well as the usage of a HEPA filter. Continuous monitoring of the pressure within the booth relayed to a simple visual indicator is desired as an additional layer of safety for the occupant.

From a practical standpoint, the booths should be first of all affordable to enable different testing facilities to acquire them, especially charities and facilities in lower income communities whose resources are often more constrained. Additionally, raw materials need to be locally available to reduce shipping time and associated costs. Lastly, manufacturing the booths should not require overly expensive equipment, advanced manufacturing facilities and profuse amounts of custom-made parts, which would negatively impact their affordability and public access.

From a mechanical standpoint, the gloves—the only physical medium through which healthcare providers can interact with patients—need to offer sufficient dexterity for handling sample collection and packaging. The gloves should also be comfortably reachable for medical staff with varying height, and the overall dimensions of the booth should accommodate individuals across different heights and body composition. Disinfecting the booth is imperative; therefore its constitutive materials (particularly the gloves and surface they are attached to) must be resistant to cleaning chemicals, most commonly containing ethanol, hydrogen peroxide, and quaternary ammonium [17].

Additional desirable specifications involve the integration of a communication system between healthcare personnel and patients, and a secure and comfortable setup for the patient outside the booth, since swab sample collection is a fairly uncomfortable procedure that can trigger an abrupt and undesirable physical response. Enabling the patient to visualize the healthcare worker's face can also enhance the patient's comfort. Lastly, the booths should be easily transportable to expand testing to multiple locations, and generally provide sufficient flexibility for repositioning them when needed.

These requirements are summarized in the first column of Table 1, which is also used to oversee the final product's degree of compliance with them. The booth design was thus broken down into three major elements: (a) the mechanical aspect of the design, (b) the ventilation and air conditioning setup, and (c) the electrical and circuitry integration, details of which are provided in the subsequent subsections.

Table 1

Summary of the design requirements for the booths and details on the final specifications

Design requirementsNotes and comments
Minimum +8.0 Pa internal pressureThe effective pressure inside the booth surpasses +19.6 Pa, corresponding to a safety factor of 2.5.
Continuous monitoring of pressureA pressure sensor was installed inside the booth to monitor all pressure changes and alert medical personnel in the event of a drastic pressure drop.
Filtered air inflowAir is channeled inside the booth through a HEPA filter, which was shown to filter out particulate matter of diameter smaller than 10 μm.
✓ Minimum 12 air exchanges per hourThe air conditioning and fan system offer 50 air exchanges per hour.
AffordabilityThe total cost of the booth (excluding labor cost) amounted to USD 3,900, almost twice as cheap as commercially available booths.
Locally available raw materialsAll raw material can be purchased from local vendors.
ManufacturabilityNo special equipment is needed to manufacture the booth. Any machine shop would suffice.
Materials resistant to decontamination chemicalsAll materials are resistant to the most common decontaminants.
Dexterity of glovesGloves allow medical personnel to comfortably open a vial, collect a swab sample, and replace it in a vial without additional assistance.
Comfort for various body height and habitusThe booth offers sufficient space for all body types, and a height-adjustable stepper can make the glove ports more reachable to those in need.
Communication system between medical personnel and patientAn intercom system ensures a clear communication between medical personnel and patients.
Tip-proof setup for patientsA chair for patients was designed to prevent any tipping during swabbing.
TransportabilityThe booths are easily transportable using either four triangular dollies or a pallet jack.
Design requirementsNotes and comments
Minimum +8.0 Pa internal pressureThe effective pressure inside the booth surpasses +19.6 Pa, corresponding to a safety factor of 2.5.
Continuous monitoring of pressureA pressure sensor was installed inside the booth to monitor all pressure changes and alert medical personnel in the event of a drastic pressure drop.
Filtered air inflowAir is channeled inside the booth through a HEPA filter, which was shown to filter out particulate matter of diameter smaller than 10 μm.
✓ Minimum 12 air exchanges per hourThe air conditioning and fan system offer 50 air exchanges per hour.
AffordabilityThe total cost of the booth (excluding labor cost) amounted to USD 3,900, almost twice as cheap as commercially available booths.
Locally available raw materialsAll raw material can be purchased from local vendors.
ManufacturabilityNo special equipment is needed to manufacture the booth. Any machine shop would suffice.
Materials resistant to decontamination chemicalsAll materials are resistant to the most common decontaminants.
Dexterity of glovesGloves allow medical personnel to comfortably open a vial, collect a swab sample, and replace it in a vial without additional assistance.
Comfort for various body height and habitusThe booth offers sufficient space for all body types, and a height-adjustable stepper can make the glove ports more reachable to those in need.
Communication system between medical personnel and patientAn intercom system ensures a clear communication between medical personnel and patients.
Tip-proof setup for patientsA chair for patients was designed to prevent any tipping during swabbing.
TransportabilityThe booths are easily transportable using either four triangular dollies or a pallet jack.

2.1 Mechanical Design.

The proposed testing booth was designed to accommodate a single healthcare provider at a time, as demonstrated in Fig. 2. The overall exterior dimensions of the booth are 1.00 m × 1.19 m × 2.05 m (width × depth × height), providing ample space for the provider on the inside to feel comfortable and at ease. The frame was constructed using aluminum extrusions due to their lightweight properties, and structural brackets along with concealed anchors were used to reinforce the structure and hold it together. Extrusions were added around the middle of the booth, connecting adjacent vertical members for strengthening purposes. Depending on the environment in which the booths need to be deployed, a steel tread plate or a plastic solid deck pallet was used as flooring. The steel tread plate is more suited for flat terrains, whereas the pallet can be used for deploying the booth in more rugged areas. The pallet platform raised the booth's overall height to 2.22 m. Handles were added to the external extrusions to assist with the transportation.

Fig. 2
Computer-aided design model of the positive-pressure testing booth design
Fig. 2
Computer-aided design model of the positive-pressure testing booth design
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The roof, lower front, and lower side panels were made of white opaque high-density polyethylene (HDPE), whereas the upper side, upper front, and door panels were made of clear acrylic. HDPE provided sufficient protection from direct sunlight, whereas acrylic offered healthcare providers the convenience of observing their surroundings. To reduce the potential heating up of the booth from sunlight, and possible visual discomfort from sun rays during the swabbing procedure, the upper side panels and door panels were tinted using an adhesive window tint film. The tint also offers additional privacy to the medical staff, adding an extra layer of comfort working inside the booth.

To ensure the booth is properly sealed to meet the minimum requirement for medical positive pressure of 8.0 Pa [16], the roof was tightly clamped along its perimeter to the aluminum extrusions using L-shaped steel rails, and the door was taped with weatherseal foam to close off any gaps. A heavy duty rubber mat was also clamped in between the floor and base frame of the booth for a better seal, which also added comfort to the medical personnel.

A pair of Hypalon gloves (8Y1532/9Q, Honeywell, Charlotte, NC) was attached to two flange ports, with a specimen collection tray mounted on the outside beneath them. The gloves are resistant to chemical contamination, as well as standard chemical disinfecting procedures. A height adjustable platform (0.100, 0.150, and 0.200 m) was placed inside the booth to allow healthcare providers of different heights to comfortably reach the glove ports. Since healthcare providers usually work with tablet computers or laptops, a side table was mounted on the inside of the booth for their convenience. Patients are tested while sitting on a chair to offer better control and maneuverability to the medical staff. Since nasopharyngeal swab collection can be somewhat uncomfortable, and patients tend to lean backward during the procedure, a tip-proof chair setup was designed to avoid possible injuries. The chairs were clamped onto a wooden platform covered by an HDPE sheet for easier cleaning, some of which were elevated using raisers to compensate for the added height from the pallets.

2.2 Ventilation and Air Conditioning Design.

Generating a positive pressure environment inside the booth requires a forced air system capable of delivering air at a specific flow rate with expected backpressure. To this end, a portable air conditioning (AC) and filtering system were installed. The AC (T9F796000, Global Industrial, Port Washington, NY) was integrated with a booster fan (OA172AP-11-1TB, DigiKey, Thief River Falls, MN), concurrently supplying a maximum of 899 m3/h of airflow. The fans can be turned on independently, or in combination with the cooling option. The cooling option only serves the purpose of moderating the temperature and reducing humidity levels inside the booth during summers, as the fan by itself is capable of providing sufficient airflow to create a positive pressure. To ensure a safe environment, the airflow was channeled through a HEPA filter (HEPA 500 F321, Dri-Eaz, Burlington, WA) that was mounted inside the booth. The filter, listed to block 99.97% of 0.3 μm oily aerosol particles, was mounted on the booth, and sealed using silicone on its periphery to prevent unfiltered air leakage. A differential pressure sensor (SDP810-125PA, Sensirion AG, Stäfa, Switzerland) measuring the pressure difference between the outside and inside of the booth is controlled by an Arduino Nano-Every board (Arduino, Somerville, MA), mounted inside the booth. The board was placed inside an electrical box, and connected to a light emitting diode (LED) (PML50RGFVW, Visual Communications Company, Carlsbad, CA) indicator to warn healthcare providers about an unexpected pressure drop, which can result from an improperly sealed door, dirty filter, or an air leak from mechanical damage to the booth. The accuracy of the pressure sensor is listed as ±3%. The CDC requirement for a safe positive pressure environment is 8.0 Pa; therefore, the readings of said pressure can range between 7.76 and 8.24 Pa. A conservative safety factor of 2.5 was considered for the measurements; therefore, a cutoff pressure of +19.6 Pa was used to account for sensor inaccuracies, below which the booth is deemed to be unsafe for regular operation. The LED light will turn green if the pressure reading exceeds aforementioned cutoff of +19.6 Pa, and red otherwise. The booth is intended to be used exclusively under positive pressure conditions.

2.3 Electrical Design.

The booth requires 120 V AC power to operate as designed. A single hospital-grade plug is used to make the connection to main power. The booth is equipped with receptacles to provide additional convenience to the healthcare providers. A weatherproof external outlet is used to supply power connection for external items such as the ventilation system. A dimmable LED light (FP2X2/4WY/WH/HD, Commercial Electric Products, Cleveland, OH) was installed on the ceiling to allow testing even at later times of the day. The pressure sensor was also powered from the booth, and an additional charging outlet was installed on the inside. To ensure a clear communication between the medical personnel and patients, a hands-free two-way intercom system was installed. The intercom (TW102, Retekess Technology Co., Shenzhen, China) consists of a base speaker/microphone placed inside the booth, from which the medical staff has full control over the powering of the device and volume of the outputs, and a substation speaker/microphone placed outside the booth, closer to the patient. The substation was positioned inside a three dimensional-printed cradle, attached to one of the vertical aluminum extrusions.

2.4 Experimental Setup.

To evaluate the adherence of the booths to the CDC and HICPAC guidelines for environmental infection control in health care facilities for positive pressure rooms, pressure tests, air flow measurements, and particle filtration analyses were conducted on the booths. The air supply to the booths can be at ambient temperature (fan only mode), or at a colder temperature (fan and cooling mode). All experiments were conducted in both modes.

The pressure test was repeated 10 times for each booth using an inclined manometer (Dwyer Mark II, Michigan City, IN). The booth is first properly ventilated before closing the door. The tubing coming out of the manometer is placed inside the booth through the hole used for the internal pressure differential sensor, while the manometer is stationed outside. The reading on the manometer is set at 0 for calibration. The start time of the fan is recorded, as well as the time at which the pressure reading stabilizes.

To obtain the air exchange rate, the airflow was measured using a digital anemometer (Holdpeak, Zhuhai, China). The wind velocity sensor is placed at the outlet of the fan hose, which is tightly sealed to the booth through a cloth to minimize air leakage. The values are recorded over 1 min to account for variations and noise. The airflow is divided by the internal volume of the booth to obtain the air exchange rate.

A particle detection sensor (SPS30, Sensirion AG, Stäfa, Switzerland) was used to analyze the filtration capacity of the booth. Inhalable respiratory droplets that carry the COVID-19 virus are greater than 5 μm and less than 10 μm in diameter, whereas aerosols and droplet nuclei have a diameter smaller than 5 μm [18,19]. Therefore, the mass concentration of particulate matter smaller than 10 μm in diameter (PM10) and number concentration for particulate matter smaller than 10 μm in diameter (NC10) evaluation metrics were chosen to assess each booth's safety in both fan only and fan with cooling modes. The mass concentration of particulate matter smaller than 2.5 μm in diameter (PM2.5) and number concentration for particulate matter smaller than 2.5 μm in diameter (NC2.5) were reported for a more accurate measurement of the fine inhalable particles, since transmission of COVID-19 through aerosol has been shown in Ref. [2]. The experiments were repeated 20 times for each booth—10 with fan only, and 10 with fan and cooling. The particle sensor was placed inside each booth, which was ventilated for different amounts of time to vary the initial conditions of the experiments; in 5 out of 10 tests the booths were fully ventilated, and in the remaining 5 tests the booths were only partially ventilated. Measurements began when the air conditioning and/or fan system was turned on.

Nasopharyngeal swabs were collected using our first booth prototype to receive feedback from medical personnel for finalizing our design. Eight patients were tested by a nurse practitioner and a physician using the prototype booth. The swab procedure can be divided into five steps, which include an inquiry step during which the health care provider communicates with the patient to inform them about the procedure; sample collection using a swab, patient leaving, specimen packaging, and decontamination. The duration of each step was recorded, and subsequently used to compare the throughput of the testing booths to that of drive-through testing.

3 Results

A total of five booths were successfully manufactured and deployed at various testing facilities across Baltimore, MD (Fig. 3): (a) Two community health centers; (b) Baltimore VA Medical Center; and (c) Johns Hopkins University School of Nursing. In the first column of Table 1, a check mark indicates that the requirements set in the Materials and Methods section have been met. Additional details on how each specification was met are presented in the second column. The specifications that were fulfilled as well as additional testing results are more thoroughly analyzed in the following subsections.

Fig. 3
(a) Overview of the five manufactured testing booths. (b) A picture of our team members demonstrating the booth usage to healthcare providers at Total Health Care, Baltimore, MD.
Fig. 3
(a) Overview of the five manufactured testing booths. (b) A picture of our team members demonstrating the booth usage to healthcare providers at Total Health Care, Baltimore, MD.
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3.1 Booth Design and Mobility.

Two main designs were adopted for the manufacturing process, with the major difference being in the platform on which they were constructed, namely, a steel tread platform and a deck pallet. The steel platform facilitates the placement of four triangular dollies at the corners of the booths for easy transportation, whereas the pallet platform allows to move the booth using a pallet jack. All booths can be transported by one person of average body composition, however two people are recommended to ensure the stability of the booth and raise the steel tread plate once for positioning the dollies beneath them.

3.2 Safety.

Positive pressure is a critical factor in ensuring medical personnel's safety, since it prevents contaminants and droplets from infiltrating into the booth. The pressure of the booths amounted to an average of 23.7 ± 0.7 Pa in 8.7 ± 2.2 s during fan only mode, and in 7.7 ± 2.4 s when cooling is turned on. The obtained pressure readings for all booths surpassed the minimum threshold of 8.0 Pa set by the CDC and HICPAC safety requirements for positive pressure rooms by over 2.5 times [16]. The air flow rate was measured as 302 ± 44.1 m3/h during fan only mode, and 332 ± 41.6 m3/h when cooling is turned on. The air exchange is subsequently estimated at 123 ± 18.0 per hour during fan only mode, and 136 ± 17.0 when cooling is turned on. The obtained ventilation rate satisfies the CDC recommendations of 12 air exchanges per hour [16].

The average results of the particle filtering tests are shown in Fig. 4, whereby it can be observed that after a certain period of time, the sensor reported no particulate matter in its vicinity. The percentage decrease is reported instead of numerical values due to the different initial concentration of particles across different experiments. Particulate matter for all booths and all modes reached a constant zero reading after 4.3 ± 1.4 min using fan only, and 2.7 ± 1.0 min with the cooling. The number concentration of particles exhibited the same behavior, decaying to a steady zero within 4.6 ± 1.4 min with a fan, and 3.1 ± 1.0 min with fan and cooling. For both pressure and particle tests, the experiments reached a favorable outcome faster with the cooling function on, since it provides additional airflow to that of the fan, resulting in a faster air exchange rate.

Fig. 4
PM10, PM2.5, NC10, and NC2.5 inside the booth when only the fan is operating, and when both fan and cooling are operating
Fig. 4
PM10, PM2.5, NC10, and NC2.5 inside the booth when only the fan is operating, and when both fan and cooling are operating
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3.3 Cost and Manufacturability.

The final bill of materials did not exceed USD 3,900 for any of the booths, which is substantially lower than that of the commercially available ones. Mass production could, of course, significantly reduce the per booth material costs. Additionally, the booths are entirely made of off-the-shelf materials and components with the exception of the three dimensional-printed speaker/microphone substation holder, which can nonetheless be substituted with an equivalent product from local vendors. The ease of procurability of the manufacturing components facilitates the manufacturing process, and gives opportunity to various local institutions and organizations for developing their own. The availability of certain products, however, can depend on the market demand; a temporary shortage of acrylic sheets, for instance, occurred due to the deployment of sneeze guards across the nation, yet replacement materials (such as polycarbonate sheets) can usually be purchased from local plastic vendors. Some components had to be modified, such as mechanically and electrically integrating the booster fan with the air conditioner. The intercom wiring connecting the substation speaker to the base one also had to be divided into two parts to add an adapter for tightly sealing the corresponding opening on the booths.

3.4 Prototype Test.

The median swab times required for each step are listed in Fig. 5 in a boxplot. The average times required for each of the aforementioned steps are, respectively: 75.0 ± 24.6 s; 27.4 ± 5.8 s; 8.5 ± 10.2 s; 46.0 ± 18.6 s; 96.5 ± 6.8 s. It hence takes an average of 4 min and 23 s for one patient to get swabbed. Moreover, after collecting specimens from all eight patients, we collected multiple swab samples from the booth's interior surfaces, the results of which were shown to be negative for COVID-19.

Fig. 5
Box plots of nasopharyngeal swab times for eight volunteer patients throughout the different stages of the swab test
Fig. 5
Box plots of nasopharyngeal swab times for eight volunteer patients throughout the different stages of the swab test
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3.5 Usability Test.

We compiled a set of 9 questions sent out to the health care providers who have been using our booths to collect COVID-19 specimens since August 2019. The answers were based on a Likert-scaled evaluation, ranging from 1 (extremely dissatisfied) to 10 (extremely satisfied). The average of eight health care providers are reported in Table 2, demonstrating the overall satisfaction and approval of the medical staff. None of the used booths have suffered damage or deterioration, and are still being utilized for COVID-19 testing at select locations.

Table 2

Usability questionnaire results reported on a Likert-scaled evaluation ranging from 1 (extremely dissatisfied) to 10 (extremely satisfied)

Average of eight health providers responses
Comfort7.9 ± 2.2
Dexterity6.4 ± 2.1
Safety10 ± 0.0
Communication6.7 ± 1.8
Temperature comfort8.1 ± 2.2
Air quality9.5 ± 1.4
Patient's response8.5 ± 1.7
Booth dimension8.5 ± 1.4
Overall impression8.5 ± 2.0
Average of eight health providers responses
Comfort7.9 ± 2.2
Dexterity6.4 ± 2.1
Safety10 ± 0.0
Communication6.7 ± 1.8
Temperature comfort8.1 ± 2.2
Air quality9.5 ± 1.4
Patient's response8.5 ± 1.7
Booth dimension8.5 ± 1.4
Overall impression8.5 ± 2.0

3.6 Clinical Approval.

PPE in the U.S. is generally evaluated and regulated by the Food and Drug Administration (FDA) prior to clinical usage. Due to the COVID-19 public health emergency, some PPE (such as medical gloves), whereby its intended usage is not expected to assist in preventing the transmission of infectious disease, may not require the manufacturer to submit a notice to the FDA prior to marketing their products. Face masks are subject to FDA regulation; however, regulatory flexibility was introduced for such products, such as eliminating the 510(k) premarket notification and Quality System Regulations. Respirators, on the other hand, still require the National Institute for Occupational Safety and Health's approval. The testing booths do fall under the umbrella of devices that prevent a disease's transmission, as well as under the Emergency Use Authorization provided by the FDA, in particular for Face Shields and Barriers. The booths are used at the medical personnel's discretion.

4 Discussion

The proposed booths have shown to be a feasible solution for collecting samples from patients in a safer and more cost-effective way. As a walkup testing means, they are accessible to all communities, especially minorities. They are also affordable, and easy to manufacture and assemble using readily available products from local vendors. This speeds up the manufacturing process, allowing facilities to quickly meet any rising demand for such testing booths. They are also mobile, which means that they can service more communities depending on the need. Lastly and most importantly, the booths offer a safe working environment to medical personnel, since our results show that inhalable particles of diameter smaller than 10 μm are eliminated through the HEPA filter.

The booths were well received by the medical staff at the five deployment sites, three of which are located in facilities serving lower income communities. The low cost and ease of manufacturability are encouraging factors, and should help local governments deploy the booths in clinics facing challenges in procuring appropriate PPE. These booths have the opportunity to address testing deserts, or areas with low testing access, which are concentrated in lower income communities. As such, this initiative provides an opportunity to increase testing among those with disparate risk to greater morbidity and mortality.

Additionally, walkup booths offer a range of advantages over the prevalent drive-through testing, among which is enhanced testing throughput, with the testing time per patient using the walkup booth amounting to an average of 4 min, as compared to 15 min using drive-through facilities [10]. The 4-min testing time during the pilot study is expected to further decrease as clinical teams get into routine workflow. Walkup booths may offer a more comfortable and air-conditioned working environment to the healthcare providers, reducing handling errors, uncomfortable postures, and mental stress. Positively pressured testing booths are also a better alternative to negatively pressured ones, since they require less time and effort to decontaminate and ventilate the workspace, and are safer for patients as they would be tested in a more open environment.

Another advantage of our booths is the design’s flexibility, which leaves room for modification and personalization; the dimensions of the booth, materials used, and additional accessories can be altered depending on the need or preference of the users. With any possible design change, however, it is crucial to maintain an acceptable internal positive pressure; hence, special care needs to be taken with the choice of fan and air conditioning units in order to supply suitable airflow. The booths are also designed in a way that allows for easy replacement of components. The HEPA filter, which is susceptible to collecting dust and particles, especially when deployed outdoors in a city, can be easily taken out for cleaning or replacement. The gloves can be replaced, as they are held by a quick-release clamp to the ports. The HDPE and acrylic sheets can also be substituted; however, it would involve a more demanding disassembly procedure. Such interchangeability extends the longevity of the booths, allowing to salvage components, and thus reduce costs in the long run.

Major limitations of the design include the lack of robustness against adverse weather conditions (such as rain and strong wind) and poor overnight outdoor security, as we recommend to place the booths inside protective sheds for storage. Purchasing a large enough shed to house a booth will, however, incur additional costs. Alternatively, due to the ease of transportation of the booths, they can be stored in enclosed garage areas, in a facility basement, or even outdoors if properly secured and shielded from precipitation. A waterproof design can offer additional protection to the booths from the weather, yet at an additional cost. Moreover, labor cost has not been factored into the final cost of the product as it can vary from one facility to another, meaning that the final price of a booth might exceed USD 3,900, which can, nonetheless, be mitigated by a reduction in material cost when ordered in bulk for larger production runs. Some level of customization is still required (e.g., setting up the electrical connections for the AC and fan), which might appear to be challenging for inexperienced users. Future research directions would involve a clinical analysis of the booth's safety and efficacy in a larger experiment, and over an extended period of time. Samples can be collected from the booth's interior and exterior surfaces on a continuous basis to analyze whether infected patients impose any risk on the medical staff, as well as other noninfected patients. The number of infected medical personnel through the booths (if any) should also be compared to drive-through and other testing methods.

5 Conclusion

This paper presents the details of the design and implementation of five positive pressure testing booths for COVID-19 sample collection. The booths are equipped with an external fan and air conditioning system, channeling airflow through a HEPA filter for added safety. The pressure and air exchange rate for all booths meet the standard minimum for medical applications specified by the CDC and HICPAC for positive pressure rooms following the guidelines for environmental infection control in health care facilities, and particle detection tests demonstrated the efficiency of the filter at eliminating particles of sizes smaller than 2.5 and 10 μm. The booths were positively reviewed by eight healthcare professionals, and are currently in use at five different testing facilities across Baltimore, MD.

Funding Data

  • University of Maryland, College Park, the Johns Hopkins Malone Center for Engineering in Healthcare, and the REACH Initiative of the Johns Hopkins University School of Nursing (Funder ID: 10.13039/100007880).

Nomenclature

     
  • NC2.5 =

    particulate number concentration. Number per cubic meter of air of particles with a diameter generally less than 2.5 μm

  •  
  • NC10 =

    particulate number concentration. Number per cubic meter of air of particles with a diameter generally less than 10 μm

  •  
  • PM2.5 =

    particulate matter concentration. Mass per cubic meter of air of particles with a diameter generally less than 2.5 μm

  •  
  • PM10 =

    particulate matter concentration. Mass per cubic meter of air of particles with a diameter generally less than 10 μm

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