The Hot Zone: Designing Hospital Units for Diseases as Infectious as COVID-19

The Hot Zone: Designing Hospital Units for Diseases as Infectious as COVID-19


Health care providers are constantly working to protect staff treating COVID-19 patients from contracting the highly contagious disease – no easy task since scientists continue to wrestle with questions about how exactly the virus propagates. Because it’s a respiratory illness, many hospital leaders’ automatic response has been to inquire about or proceed with creating more negative-pressure rooms, which have long been used in the health care industry to guard against a variety of pathogens. But negative-pressure rooms are just one component of the ideal design response to the novel coronavirus.

We must consider a combination of design strategies to mitigate both airborne and contact transmission in hospital units treating coronavirus. Architectural and engineering standards for airborne infection isolation rooms and unidirectional flow rooms with strict decontamination protocols can inform design solutions that effectively protect frontline caregivers. We detail those standards below and go a step further by presenting a design concept for a patient room that combines key features of both airborne and contact isolation environments, offering a comprehensive plan to protect against COVID-19 transmission.

What To Do First

Methods of mitigating the spread of infectious diseases vary significantly depending on the level of acuity of COVID-19 patients being treated in the unit, the current state and constraints of your facility, and the scope of the facility enhancement you’ve selected. First, take inventory of your circumstances:

  • Step 1: Determine the patient population that will be served by this facility or renovation. Is the unit for moderate-acuity COVID-19 patients or critical cases?
  • Step 2: Examine existing conditions and determine architectural and engineering constraints, including space, medical gas, ventilation, utilities and operational flows.
  • Step 3: Determine if the facility will be repurposed or renovated in place or whether new permanent or portable construction is preferred.

Protecting Against Aerosolization

COVID-19 — the illness caused by the novel coronavirus — is thought to primarily spread through large droplets issued when an infected person coughs or sneezes, exposing the eyes, mouths and noses of people nearby, or when a person touches a surface contaminated by droplets and then touches his or her face. Now evidence is emerging that the virus might also transmit through fine particles or aerosols that people exhale when they breathe and that linger in the air, unlike droplets. Research published last month in the New England Journal of Medicine showed that aerosols produced mechanically in a lab remained infectious for up to three hours. Scientists are debating the available research, and determining conclusively whether the novel coronavirus is airborne could take years, Nature science journal reports. Some scientists are advising health care workers and the public to act as if the virus is airborne unless it’s proven that it’s not.

Airborne Infection Isolation (AII) environments control the air flow in the room and reduce the level of infectious particles to avoid making other people sick. All the attributes below are necessary to ensure that an AII room serves its protective function:

  • Negative air pressure: Maintaining air pressure differentials between adjacent spaces prevents cross-contamination from room to room, allowing air flow into the isolation room and preventing escape into surrounding spaces. Negative-pressure rooms mitigate aerosolized virus transmission to other spaces by promoting air flows from clean to contaminated spaces in the facility, improving the safety of other occupants.
  • High air volume: Increasing the air changes per hour (ACH) will dilute the infectious particles in the room.
  • HEPA filtration: A HEPA (high efficiency particulate air) filter traps 99.97% of particles that are as small in size as 0.03 microns, described as “the most penetrating particle size.” This filtration removes harmful particulates and biological contaminants that enter the space.
  • 100% exhaust: Air exhausts, properly separated from external air intakes, remove contaminated particles.

Protecting Against Fomites

As noted earlier, when infected people sneeze or cough, their droplets can contaminate clothing, utensils and other objects on or around them. These inanimate items that carry disease are known as fomites. The deadly Ebola virus is a pathogen that spreads this way. 

Mitigation for this kind of transmission requires strict decontamination protocols, similar to those for chemical or biological warfare agents.

As detailed in this HKS report, national architectural and engineering guidelines recommend providing a unidirectional flow for staff to move from “warm” to “cold” or from soiled to clean.  Staff must not back-track. With this rigorous approach, all staff fastidiously follow established protocols for doffing of protective personal equipment (PPE) under observation and supervision, before showering and dressing. Unlike the AII room design, this concept incorporates separate rooms for staff to exit and for the removal of contaminated materials.

Combining Airborne and Contact Precautions

When resources allow, a patient room design concept that protects against airborne and contact transmission may be the optimal solution.  This suite for highly infectious diseases combines the attributes of both room types. This concept is an AII room with spaces for proper decontamination protocols, protecting staff from infection. As health care providers plan for or respond to a patient surge, they should consider using all available and practical spaces or rooms within the hospital or installing temporary sealed plastic partitions. These options should be discussed as part of the hospital’s overall infection control strategy.

Seattle’s UW Medical Center-Northwest has embraced a similar model in its COVID-19 unit. In a report on NBC’s the Today show, Dr. Seth Cohen showed how the hospital had “cocooned” the nurses’ station with protective plastic while providing windows that allowed clinicians to monitor the floor. An observer in a designated area watches staff to make sure they’re properly suiting up or taking off their gear when entering or leaving the “hot zone” – the area of patient care.  Caregivers moving through the “hot zone” can keep their PPE when going from patient to patient, saving scarce resources. Cohen said the hospital had also converted some floors to negative pressure to protect staff against aerosol transmission.

In addition to air flow and staff flow dynamics, other mitigation strategies include advanced surface cleaning technology.  Self-decontaminating materials such as silver and copper, antimicrobial and antiviral cleaning agents and off-the-shelf technology such as vaporized hydrogen peroxide and UV-C lighting should be considered to assist in killing pathogens.