Airborne Infection Isolation Rooms Research Articles

Influence of human movement on the transport of airborne infectious particles in hospital

The impacts of human movement on the distribution of airborne infectious particles in hospital environment are investigated numerically. In the case of airborne infection isolation room, the influence of different walking speeds on the distribution of respiratory droplets is investigated by adopting the Lagrangian method for tracing the motion of droplets, the dynamic mesh model for describing human walking and the Eulerian unsteady Reynolds-averaged Navier–Stokes model for solving the airflow. In the case of operating theatre, the impact of surgeon bending movement on the distribution of bacteria-carrying particles (BCPs) is investigated by using a similar approach, except that the drift-flux model is used for modelling BCPs distribution. The adopted models are successfully validated against reported experimental data. The results show that both walking speed and bending posture change considerably the suspended droplets concentration in a room. The key factors regarding the simulation techniques are discussed.

Performance testing of engineering controls of airborne infection isolation rooms by tracer gas techniques

The ventilation performance of airborne infection isolation rooms (AIIRs) was assessed in three Finnish hospitals by examining the air change rate, contaminant removal efficiency and leakage of contaminants outside the isolation room by using tracer gas techniques. Results showed that infectious agents can escape from the AIIR during egress despite high ventilation rates in the AIIR and anteroom (air change rate, 4–24 h−1) and the pressure difference between the AIIR and corridor was −0.2 to −29 Pa. The control of impurities was often ineffective due to inappropriate direction of air flows and air moving from the patient towards the health care worker and anteroom. Although an anteroom reduces leakage of infectious agents to the corridor significantly, it does not prevent this completely when healthcare workers move between the AIIR and corridor. To enhance the protection of AIIRs, it is especially important to pay attention to the air distribution and removal efficiency of impurities in AIIRs and anterooms. Performance of AIIRs should be tested regularly, especially among older AIIRs.

Effective screening tool to triage recovery rooms for possible tuberculosis patients undergoing bronchoscopy

In 2005, tuberculin skin test conversions were observed following exposure to a patient with active pulmonary tuberculosis (TB) who recovered post-bronchoscopy in an open area at The Ottawa Hospital, Canada. In response, we implemented a screening tool to triage patients to an airborne infection isolation (AII) room pre- and post-bronchoscopy. To evaluate the performance of the screening tool in detecting patients with culture-confirmed TB. All bronchoscopies performed between 1 March 2006 and 31 March 2010 were retrospectively reviewed. Of 1839 patients included (55.3% of bronchoscopies), 210 screened positive, capturing 28 culture-confirmed TB cases. Three patients with positive TB cultures screened negative. The sensitivity of the screening tool was 90.3%; the negative predictive value was 99.8%. A positive screening result was strongly predictive of a positive TB culture. The screening tool is effective for identifying high-risk patients and triaging them to AII rooms. The pre-bronchoscopy screening tool is simple and inexpensive to implement and has the potential to reduce intra-institutional spread of TB.

Allocating Scarce Resources in Disasters: Emergency Department Principles

Decisions about medical resource triage during disasters require a planned structured approach, with foundational elements of goals, ethical principles, concepts of operations for reactive and proactive triage, and decision tools understood by the physicians and staff before an incident. Though emergency physicians are often on the front lines of disaster situations, too often they have not considered how they should modify their decisionmaking or use of resources to allow the "greatest good for the greatest number" to be accomplished. This article reviews key concepts from the disaster literature, providing the emergency physician with a framework of ethical and operational principles on which medical interventions provided may be adjusted according to demand and the resources available. Incidents may require a range of responses from an institution and providers, from conventional (maximal use of usual space, staff, and supplies) to contingency (use of other patient care areas and resources to provide functionally equivalent care) and crisis (adjusting care provided to the resources available when usual care cannot be provided). This continuum is defined and may be helpful when determining the scope of response and assistance necessary in an incident. A range of strategies is reviewed that can be implemented when there is a resource shortfall. The resource and staff requirements of specific incident types (trauma, burn incidents) are briefly considered, providing additional preparedness and decisionmaking tactics to the emergency provider. It is difficult to think about delivering medical care under austere conditions. Preparation and understanding of the decisions required and the objectives, strategies, and tactics available can result in better-informed decisions during an event. In turn, adherence to such a response framework can yield thoughtful stewardship of resources and improved outcomes for a larger number of patients.

Airborne Infection Isolation Rooms – A Review of Experimental Studies

Ventilation guidelines for airborne infection isolation rooms (AIIRs) are highly variable in different countries indicating lack of actual knowledge about the guidance needed. However, US guidelines for AIIRs are extensive and have been widely adopted outside the US. AIIR performance has also been evaluated in numerous studies. For a long time, the aim has mainly been to evaluate how well the existing AIIRs meet US guidelines. For historical reasons, mixing-type ventilation has been emphasised and attention has been paid to air exchange rates, although the use of auxiliary devices, such as portable room-air cleaners and ultraviolet germicidal irradiation systems, has also been examined. Recently, the scope of the investigations has been widened. The most crucial issue is to minimise the potential for disease transmission and prevent the escape of contaminated air from the AIIR. Airflow direction inside the AIIR is also important and AIIRs minimise air leakage to save energy. On the other hand, it has been observed that efficient containment can be achieved even by using simple and inexpensive construction by considering pressure differential and air flow patterns. Nevertheless, additional research is needed to assist hospitals with improving their preparedness to cope with the threat of pandemics by building and using effective AIIRs.

Numerical investigation of influence of human walking on dispersion and deposition of expiratory droplets in airborne infection isolation room

This paper introduces a numerical simulation model for investigating the influence of moving subjects on the dispersion and deposition of expiratory droplets, rather than on the dispersion of surrogate gaseous counterparts generally adopted in related research works. In our work, the Lagrangian discrete trajectory model is used for tracing the motion of droplets, the Eulerian RANS method is used for solving the airflow field, and the dynamic mesh model for describing the human movement. The model validation was performed through result comparisons with published data from literatures. A case study on the influence of human walking on the dispersion and deposition of expiratory droplets in an airborne infection isolation room (AIIR) is then presented. Our findings show that the human walking disturbs the local velocity field with wake formation. The increase of walking speed could effectively reduce the overall number of suspended droplets, which may have a positive impact on releasing the infection risk of health workers in AIIR.

Isolation Precautions

Isolation Precautions

Supplemental treatment of air in airborne infection isolation rooms using high-throughput in-room air decontamination units

Evidence has recently emerged indicating that in addition to large airborne droplets, fine aerosol particles can be an important mode of influenza transmission that may have been hitherto underestimated. Furthermore, recent performance studies evaluating airborne infection isolation (AII) rooms designed to house infectious patients have revealed major discrepancies between what is prescribed and what is actually measured. We conducted an experimental study to investigate the use of high-throughput in-room air decontamination units for supplemental protection against airborne contamination in areas that host infectious patients. The study included both intrinsic performance tests of the air-decontamination unit against biological aerosols of particular epidemiologic interest and field tests in a hospital AII room under different ventilation scenarios. The unit tested efficiently eradicated airborne H5N2 influenza and Mycobacterium bovis (a 4- to 5-log single-pass reduction) and, when implemented with a room extractor, reduced the peak contamination levels by a factor of 5, with decontamination rates at least 33% faster than those achieved with the extractor alone. High-throughput in-room air treatment units can provide supplemental control of airborne pathogen levels in patient isolation rooms.

Removal of exhaled particles by ventilation and deposition in a multibed airborne infection isolation room

Removal of airborne particles in airborne infection isolation rooms is important for infection control of airborne diseases. Previous studies showed that the downward ventilation recommended by Centers for Disease Control and Prevention (CDC) could not produce the expected 'laminar' flow for pushing down respiratory gaseous contaminants and removing them via floor-level exhausts. Instead, upper-level exhausts were more efficient in removing gaseous contaminants because of upward body plumes. The conventional wisdom in the current CDC-recommended design is that floor-level exhausts may efficiently remove large droplets/particles, but such a hypothesis has not been proven. We investigated the fate of respiratory particles in a full-scale six-bed isolation room with exhausts at different locations by both experimental and computational studies. Breathing thermal manikins were used to simulate patients, and both gaseous and large particles were used to simulate the expelled fine droplet nuclei and large droplets. Gaseous and fine particles were found to be removed more efficiently by ceiling-level exhausts than by floor-level exhausts. Large particles were mainly removed by deposition rather than by ventilation. Our results show that the existing isolation room ventilation design is not effective in removing both fine and large respiratory particles. An improved ventilation design is hence recommended. Our findings of the relatively poor performance of fine-particle removal by the existing CDC design of isolation room ventilation suggests a need for improvement, and the findings of the removal of large particles by deposition, not by ventilation, suggest that floor-level exhausts are unnecessary, and that regular surface cleaning and disinfection is necessary, thus providing evidence for maintaining isolation room surface hygiene.

Health and safety risk assessment methodology to calculate reverse airflow tolerance in a biosafety level 3 (BSL-3) or airborne infection isolation room (AII) environment

A novel methodology is proposed to calculate how much air displacement and contaminant leakage might occur during a power outage that may result in a momentary positive pressure reversal in a BSL-3 facility. Note that the ultimate goal in design and operation of a BSL-3 facility is to achieve sustained directional airflow such that under failure conditions the airflow will not be reversed. The proposed methodology should be applied when and only when all other measures to achieve zero tolerance have been ruled out. Only after determining that zero tolerance cannot be achieved for the BSL-3 facility in question should the model be employed to perform a health and safety risk assessment to determine the reverse airflow tolerance. The methodology is applicable to other room types, such as airborne infection isolation rooms, that use sustained differential air pressure as one means to prevent particle migration across a boundary.

Transport of exhaled particulate matter in airborne infection isolation rooms

The goal of this research was to examine the characteristics of the spatial velocity and concentration profiles which might result in health care workers’ exposure to a pathogenic agent in an airborne infection isolation room (AIIR). Computational fluid dynamics simulations were performed for this purpose. This investigation expanded on the work of Huang and Tsao [The influence of air motion on bacteria removal in negative pressure isolation rooms. HVAC & R Research 2005; 11: 563–85], who studied how ventilation conditions impact dispersion of pathogenic nuclei in an AIIR by investigating the airflow conditions impacting dispersion of infectious agents in the AIIR. The work included a careful quality assurance study of the computed airflow, and final simulations were performed on a fine tetrahedral mesh with approximately 1.3×10 6 cells. The 1 μm diameter particles were released from a 0.001225 m 2 area representing the nose and mouth. Two cases were investigated during the current study: continuous exhalation of pathogen-laden air from the patient and expulsion of pathogenic particles by a single cough or sneeze. Slow decay of particle concentration in the AIIR during the single cough/sneeze simulation and tendency for particle accumulation near the AIIR walls observed in the continuous breathing simulation suggest that unintended exposures are possible despite the ventilation system. Based on these findings, it is recommended that extra care be taken to assure proper functionality of personal protective equipment used in an AIIR.

A performance assessment of airborne infection isolation rooms

Airborne infection isolation rooms (AIIRs) help prevent the spread of infectious agents in hospitals. The performance of 678 AIIRs was evaluated and compared with construction design guidelines. The pressure differentials (DeltaP) between the isolation rooms and adjacent areas were measured, and ventilation and construction details were recorded for each room. Ultrafine particle concentrations were evaluated in the rooms, surrounding areas, and ventilation systems serving the rooms. Measurements were analyzed as a function of room parameters. Only 32% of the isolation rooms achieved the recommended DeltaP of -2.5 Pascals (Pa) relative to surrounding areas. AIIRs with solid ceilings had an average DeltaP of -4.4 Pa, which was significantly higher than the average DeltaP of -2.0 Pa for rooms with dropped ceilings (P = .0002). Isolation room ultrafine particle concentrations were more highly correlated with particle levels in surrounding areas (R(2) = 0.817) than in the ventilation systems serving the rooms (R(2) = 0.441). Almost all ventilation filters serving AIIRs collected fewer particles than anticipated. The results indicate that hospitals are not all maintaining AIIRs to correspond with current guidelines. The findings also support the contention that having tightly sealed rooms helps maintain appropriate pressure differentials.

Development of an Empirical Model to Aid in Designing Airborne Infection Isolation Rooms

Airborne infection isolation rooms (AIIRs) house patients with tuberculosis, severe acute respiratory syndrome (SARS), and many other airborne infectious diseases. Currently, faci-lity engineers and designers of heating, ventilation, and air-conditioning (HVAC) systems have few analytical tools to estimate a room's leakage area and establish an appropriate flow differential (ΔQ) in hospitals, shelters, and other facilities where communicable diseases are present. An accurate estimate of leakage area and selection of ΔQ is essential for ensuring that there is negative pressure (i.e., pressure differential [ΔP]) between an AIIR and adjoining areas. National Institute for Occupational Safety and Health (NIOSH) researchers evaluated the relationship between ΔQ and ΔP in 67 AIIRs across the United States and in simulated AIIR. Data gathered in the simulated AIIR was used to develop an empirical model describing the relationship between ΔQ, ΔP, and leakage area. Data collected in health care facilities showed that the model accurately predicted the leakage area 44 of 48 times. Statistical analysis of the model and experimental validation showed that the model effectively estimated the actual leakage area from −39% to +22% with 90% confidence. The NIOSH model is an effective, cost-cutting tool that can be used by HVAC engineers and designers to estimate leakage area and select an appropriate ΔQ in AIIRs to reduce the airborne transmission of disease.

Tuberculosis Prevention and Control in Large Jails: A Challenge to Tuberculosis Elimination

This study assessed the extent to which 20 large jail systems have implemented national recommendations for tuberculosis (TB) prevention and control in correctional facilities. Data were collected through questionnaires to jail medical directors and TB control directors, observation at the jails, and abstraction of medical records of inmates with TB disease and latent TB infection. Twenty percent of jail systems (4/20) had conducted an assessment of risk for TB transmission in their facilities, and 55% (11/20) monitored tuberculin skin test conversions of inmates and staff. Sixty-five percent (13/20) of jails had an aggregate record-keeping system for tracking TB status and treatment, which was usually paper based. Forty-five percent of jails (9/20) had policies to offer HIV counseling and testing to tuberculin skin test-positive patients, and 75% (15/20) screen HIV-infected inmates with chest radiographs. Three quarters of jails (15/20) had policies to always isolate patients with suspected or confirmed pulmonary TB in an airborne infection isolation room. Half of jails with airborne infection isolation rooms (6/12) conformed to Centers for Disease Control and Prevention (CDC) guidelines for monitoring negative pressure. Improvements are needed in conducting TB risk assessments and evaluations to determine priorities and reduce risk of transmission. Inadequate medical information systems are impeding TB control and evaluation efforts. Although HIV infection is the greatest cofactor for development of TB disease, jails have inadequate information on patients' HIV status to make informed decisions in screening and management of TB and latent TB infection. Jails need to improve the use of environmental controls.

Increasing isolation room surge capacity through the establishment of negative-pressure surge capacity wings/areas

ISSUE: The number of hospital airborne infection isolation (AII) rooms is limited. An outbreak of infectious disease will produce a demand for a large number of AII rooms. A multidisciplinary panel set out to provide hospitals with cost-effective options to create additional AII surge capacity rooms. PROJECT: Baseline AII capacity was obtained from general medical/surgical hospitals in the state to determine isolation capacity. The result was an emergency room (ER) AII capacity of 2.2 rooms per 100,000 population (117 rooms) and a medical/surgical (M/S) room capacity of 11.5 (617 rooms). A panel of infection control practitioners (ICPs) set minimum AII standards for all hospitals (2 ER AII, 1 AII M/S room, 1 AII intensive care unit, 1 AII room with anteroom per 100 staffed beds, 2% of all staffed beds to be AII). Federal Health Resources and Services Administration (HRSA) funds were used to support the construction of additional AII rooms, resulting in ER AII ratio of 6.1 (328 rooms) and an M/S AII ratio of 14.1 (755 rooms). Another multidisciplinary panel of ICPs, hospital plant operation managers, architects, and mechanical engineers was convened to provide options to hospitals for increasing this ratio substantially without the significant cost of constructing individual AII rooms. Criteria were established for negative-pressure surge capacity (NPSC) rooms along with the protocol for the use of these rooms as isolation rooms. RESULTS: Hospitals identified areas that could be engineered as NPSC rooms according to the criteria. This resulted in 558 additional rooms that can be used to care for 1116 cohorted patients. Combined with existing AII rooms, the total patient rooms available allow hospitals to care for a total of 2626 patients, twice the goal of 10% of staffed beds that was set by the panel. The panel developed schematics for three engineering options that hospitals can use to construct or renovate space into NPSC rooms. A metropolitan hospital added 56 NPSC rooms (112 patients) with federal HRSA funds. Funds are set aside for five additional NPSC demonstration projects so that there will be at least one hospital in each of the seven regions to serve as an isolation center. LESSONS LEARNED: 1) Synergy results from a multidisciplinary approach to problem solving. 2) Hospitals are willing to invest in AII/NPSC rooms when given cost-effective options and guidance. 3) Despite significant enhancement of physical assets, basic infection control standards remain the cornerstone for minimizing the transmission of infectious disease.

Failure mode effect analysis applied to hospital TB program

ISSUE: In 2001 the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) wrote a standard that requires healthcare organizations to conduct at least one failure mode effects analysis (FMEA) annually on a patient safety issue. The idea is to select a process that is thought to be working effectively. The FMEA is used to evaluate potential failure modes. PROJECT: This is a seven-campus hospital system. A multidisciplinary team was formed to perform an FMEA on the current TB program. The current process for identification and management of TB patients was flowcharted, as was the ideal process. Each step of the current process was then reviewed and evaluated for possible failure modes. Potential failures were then assigned a criticality score by members of the FMEA team. RESULTS: Eleven potential failure modes were identified. The failure mode that received the highest criticality score was ability to isolate. Of the seven campuses in the system, three of the emergency departments did not have airborne infection isolation (ABII) capacity. In addition, it was discovered that not all rooms thought to be suitable for ABII were. Nursing did not always activate alarms on ABII rooms or utilize portable high-efficiency particulate air (HEPA) filters correctly. Failure to screen, and thereby identify, potential TB patients was identified as the next most critical potential failure. A flaw was found in the current screening tool—weight loss as a risk factor, had been left off of the TB assessment screen when computerized charting was implemented. In addition, there is always a risk that a screen may not consistently identify the conditions being screened, in this case potential active TB. In reviewing data, we found that in one-third of confirmed pulmonary TB cases there were exposures related to failure of healthcare workers to suspect TB and isolate. Other failure modes identified were employee knowledge of size and type of PFR-95 respirator, communication of ABII status to other departments, inefficient notification system to employees when an exposure had occurred, and appropriate reporting of PPD conversions in employees. LESSONS LEARNED: FMEA is an effective tool for healthcare facilities. By using a multidisciplinary team, failure modes can be effectively identified and corrective actions put into place that improve processes and outcomes.

Containment testing of isolation rooms

Results from the tracer containment testing of four ‘state-of-the-art’ airborne infection isolation rooms, in a new hospital, are presented. A testing technician exited an isolation room several minutes after a small quantity of tracer gas was injected over the patient bed in that room. Easily measurable tracer gas concentrations were then found in the anterooms outside the patient rooms and corridor outside the isolation room suites. Containment factors for the isolation rooms and dilution factors in the anterooms and corridor were calculated, based on the measured tracer concentrations. These results indicate the desirability of evidence-based design standards and guidelines for assessing performance of airborne infection isolation rooms. The study also demonstrates that the tracer testing procedure yields comparable results for equivalent isolation room suites, suggesting good reproducibility of the testing method.

96/01894 The application of a variable-area jet pump to the external recirculation of hot flue-gases

The COVID-19 pandemic in early 2020 became a global issue and received substantial attention worldwide. In a hospital, airborne infection isolation (AII) room is significant to prevent the spread of the virus to patients and medical personnel. This research aims to improve the design of the HVAC system of AII room used for removing contaminated air by making physical changes through the addition of heat pipe heat exchanger (HPHE). Experiments were conducted with varying fresh air inlet temperature between 30 and 45 °C and velocity between 1.5 and 2.5 m/s with three configurations of HPHE to investigate the performance of the HVAC system in the AII room. To ensure the HVAC system with HPHE meets the AII room requirements, this study carried out a smoke test as well as pressure and hourly air volume measurement tests between the exhaust and supply air sides. The results showed that the design of ventilation coupled with HPHE could meet the standards for the AII room. The HPHE succeeded in reducing energy consumption through pre-cooling of fresh air before entering the cooling coil device, with the highest temperature difference of 9.4 °C. The highest energy recovery was 767 W at 0.080 m3/s air volume, which can handle 46% of the total HVAC system load at operating conditions and enhance the combined efficiency of the HVAC system. Based on the results, it can be concluded that the HPHE can be coupled in the HVAC system of the hospital AII room that is safe from cross-contamination which significantly reduces the energy consumption.