Ventilation Improvements Among K-12 Public School Districts - United States, August-December 2022.

Improving ventilation has been one of several COVID-19 prevention strategies implemented by kindergarten through grade 12 (K-12) schools to stay open for safe in-person learning. Because transmission of SARS-CoV-2 occurs through inhalation of infectious viral particles, it is important to reduce the concentration of and exposure time to infectious aerosols (1-3). CDC examined reported ventilation improvement strategies among U.S. K-12 public school districts using telephone survey data collected during August-December 2022. Maintaining continuous airflow through school buildings during active hours was the most frequently reported strategy by school districts (50.7%); 33.9% of school districts reported replacement or upgrade of heating, ventilation, and air conditioning (HVAC) systems; 28.0% reported installation or use of in-room air cleaners with high-efficiency particulate air (HEPA) filters; and 8.2% reported installation of ultraviolet (UV) germicidal irradiation (UVGI) devices, which use UV light to kill airborne pathogens, including bacteria and viruses. School districts in National Center for Education Statistics (NCES) city locales, the West U.S. Census Bureau region, and those designated by U.S. Census Bureau Small Area Income Poverty Estimates (SAIPE) as high-poverty districts reported the highest percentages of HVAC system upgrades and HEPA-filtered in-room air cleaner use, although 28%-60% of all responses were unknown or missing. Federal funding remains available to school districts to support ventilation improvements. Public health departments can encourage K-12 school officials to use available funding to improve ventilation and help reduce transmission of respiratory diseases in K-12 settings.

Use of a Negative Pressure Containment Pod Within Ambulance-Workspace During Pandemic Response.

Emergency medical service (EMS) providers have a higher potential exposure to infectious agents than the general public (Nguyen et al., 2020, "Risk of COVID-19 Among Frontline Healthcare Workers and the General Community: A Prospective Cohort Study," Lancet Pub. Health, 5(9), pp. e475-e483; Brown et al., 2021, "Risk for Acquiring Coronavirus Disease Illness Among Emergency Medical Service Personnel Exposed to Aerosol-Generating Procedures," Emer. Infect. Disease J., 27(9), p. 2340). The use of protective equipment may reduce, but does not eliminate their risk of becoming infected as a result of these exposures. Prehospital environments have a high risk of disease transmission exposing EMS providers to bioaerosols and droplets from infectious patients. Field intubation procedures may be performed causing the generation of bioaerosols, thereby increasing the exposure of EMS workers to pathogens. Additionally, ambulances have a reduced volume compared to a hospital treatment space, often without an air filtration system, and no control mechanism to reduce exposure. This study evaluated a containment plus filtration intervention for reducing aerosol concentrations in the patient module of an ambulance. Aerosol concentration measurements were taken in an unoccupied research ambulance at National Institute for Occupational Safety and Health (NIOSH) Cincinnati using a tracer aerosol and optical particle counters (OPCs). The evaluated filtration intervention was a containment pod with a high efficiency particulate air (HEPA)-filtered extraction system that was developed and tested based on its ability to contain, capture, and remove aerosols during the intubation procedure. Three conditions were tested (1) baseline (without intervention), (2) containment pod with HEPA-1, and (3) containment pod with HEPA-2. The containment pod with HEPA-filtered extraction intervention provided containment of 95% of the total generated particle concentration during aerosol generation relative to the baseline condition, followed by rapid air cleaning within the containment pod. This intervention can help reduce aerosol concentrations within ambulance patient modules while performing aerosol-generating procedures.

Efficacy of Do-It-Yourself air filtration units in reducing exposure to simulated respiratory aerosols.

Many respiratory diseases, including COVID-19, can be spread by aerosols expelled by infected people when they cough, talk, sing, or exhale. Exposure to these aerosols indoors can be reduced by portable air filtration units (air cleaners). Homemade or Do-It-Yourself (DIY) air filtration units are a popular alternative to commercially produced devices, but performance data is limited. Our study used a speaker-audience model to examine the efficacy of two popular types of DIY air filtration units, the Corsi-Rosenthal cube and a modified Ford air filtration unit, in reducing exposure to simulated respiratory aerosols within a mock classroom. Experiments were conducted using four breathing simulators at different locations in the room, one acting as the respiratory aerosol source and three as recipients. Optical particle spectrometers monitored simulated respiratory aerosol particles (0.3-3 µm) as they dispersed throughout the room. Using two DIY cubes (in the front and back of the room) increased the air change rate as much as 12.4 over room ventilation, depending on filter thickness and fan airflow. Using multiple linear regression, each unit increase of air change reduced exposure by 10%. Increasing the number of filters, filter thickness, and fan airflow significantly enhanced the air change rate, which resulted in exposure reductions of up to 73%. Our results show DIY air filtration units can be an effective means of reducing aerosol exposure. However, they also show performance of DIY units can vary considerably depending upon their design, construction, and positioning, and users should be mindful of these limitations.

Ventilation Improvement Strategies Among K-12 Public Schools - The National School COVID-19 Prevention Study, United States, February 14-March 27, 2022.

Effective COVID-19 prevention in kindergarten through grade 12 (K-12) schools requires multicomponent prevention strategies in school buildings and school-based transportation, including improving ventilation (1). Improved ventilation can reduce the concentration of infectious aerosols and duration of potential exposures (2,3), is linked to lower COVID-19 incidence (4), and can offer other health-related benefits (e.g., better measures of respiratory health, such as reduced allergy symptoms) (5). Whereas ambient wind currents effectively dissipate SARS-CoV-2 (the virus that causes COVID-19) outdoors,* ventilation systems provide protective airflow and filtration indoors (6). CDC examined reported ventilation improvement strategies among a nationally representative sample of K-12 public schools in the United States using wave 4 (February 14-March 27, 2022) data from the National School COVID-19 Prevention Study (NSCPS) (420 schools), a web-based survey administered to school-level administrators beginning in summer 2021.† The most frequently reported ventilation improvement strategies were lower-cost strategies, including relocating activities outdoors (73.6%), inspecting and validating existing heating, ventilation and air conditioning (HVAC) systems (70.5%), and opening doors (67.3%) or windows (67.2%) when safe to do so. A smaller proportion of schools reported more resource-intensive strategies such as replacing or upgrading HVAC systems (38.5%) or using high-efficiency particulate air (HEPA) filtration systems in classrooms (28.2%) or eating areas (29.8%). Rural and mid-poverty-level schools were less likely to report several resource-intensive strategies. For example, rural schools were less likely to use portable HEPA filtration systems in classrooms (15.6%) than were city (37.7%) and suburban schools (32.9%), and mid-poverty-level schools were less likely than were high-poverty-level schools to have replaced or upgraded HVAC systems (32.4% versus 48.8%). Substantial federal resources to improve ventilation in schools are available.§ Ensuring their use might reduce SARS-CoV-2 transmission in schools. Focusing support on schools least likely to have resource-intensive ventilation strategies might facilitate equitable implementation of ventilation improvements.

Surveillance practices and air-sampling strategies to address healthcare-associated invasive mold infections in Society for Healthcare Epidemiology of America (SHEA) Research Network hospitals-United States, 2020.

With this survey, we investigated healthcare-associated invasive mold infection (HA-IMI) surveillance and air sampling practices in US acute-care hospitals. More than half of surveyed facilities performed HA-IMI surveillance and air sampling. HA-IMI surveillance was more commonly performed in academic versus nonacademic facilities. HA-IMI case definitions and sampling strategies varied widely among respondents.

Efficacy of Ventilation, HEPA Air Cleaners, Universal Masking, and Physical Distancing for Reducing Exposure to Simulated Exhaled Aerosols in a Meeting Room.

There is strong evidence associating the indoor environment with transmission of SARS-CoV-2, the virus that causes COVID-19. SARS-CoV-2 can spread by exposure to droplets and very fine aerosol particles from respiratory fluids that are released by infected persons. Layered mitigation strategies, including but not limited to maintaining physical distancing, adequate ventilation, universal masking, avoiding overcrowding, and vaccination, have shown to be effective in reducing the spread of SARS-CoV-2 within the indoor environment. Here, we examine the effect of mitigation strategies on reducing the risk of exposure to simulated respiratory aerosol particles within a classroom-style meeting room. To quantify exposure of uninfected individuals (Recipients), surrogate respiratory aerosol particles were generated by a breathing simulator with a headform (Source) that mimicked breath exhalations. Recipients, represented by three breathing simulators with manikin headforms, were placed in a meeting room and affixed with optical particle counters to measure 0.3-3 µm aerosol particles. Universal masking of all breathing simulators with a 3-ply cotton mask reduced aerosol exposure by 50% or more compared to scenarios with simulators unmasked. While evaluating the effect of Source placement, Recipients had the highest exposure at 0.9 m in a face-to-face orientation. Ventilation reduced exposure by approximately 5% per unit increase in air change per hour (ACH), irrespective of whether increases in ACH were by the HVAC system or portable HEPA air cleaners. The results demonstrate that mitigation strategies, such as universal masking and increasing ventilation, reduce personal exposure to respiratory aerosols within a meeting room. While universal masking remains a key component of a layered mitigation strategy of exposure reduction, increasing ventilation via system HVAC or portable HEPA air cleaners further reduces exposure.

Efficacy of Portable Air Cleaners and Masking for Reducing Indoor Exposure to Simulated Exhaled SARS-CoV-2 Aerosols - United States, 2021.

SARS-CoV-2, the virus that causes COVID-19, can be spread by exposure to droplets and aerosols of respiratory fluids that are released by infected persons when they cough, sing, talk, or exhale. To reduce indoor transmission of SARS-CoV-2 between persons, CDC recommends measures including physical distancing, universal masking (the use of face masks in public places by everyone who is not fully vaccinated), and increased room ventilation (1). Ventilation systems can be supplemented with portable high efficiency particulate air (HEPA) cleaners* to reduce the number of infectious particles in the air and provide enhanced protection from transmission between persons (2); two recent reports found that HEPA air cleaners in classrooms could reduce overall aerosol particle concentrations by ≥80% within 30 minutes (3,4). To investigate the effectiveness of portable HEPA air cleaners and universal masking at reducing exposure to exhaled aerosol particles, the investigation team used respiratory simulators to mimic a person with COVID-19 and other, uninfected persons in a conference room. The addition of two HEPA air cleaners that met the Environmental Protection Agency (EPA)-recommended clean air delivery rate (CADR) (5) reduced overall exposure to simulated exhaled aerosol particles by up to 65% without universal masking. Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%. The HEPA air cleaners were most effective when they were close to the aerosol source. These findings suggest that portable HEPA air cleaners can reduce exposure to SARS-CoV-2 aerosols in indoor environments, with greater reductions in exposure occurring when used in combination with universal masking.

Surface Dosimetry of Ultraviolet Germicidal Irradiation Using a Colorimetric Technique.

Ultraviolet germicidal irradiation uses ultraviolet C (UV-C) energy to disinfect surfaces in clinical settings. Verifying that the doses of UV-C energy received by surfaces are adequate for proper disinfection levels can be difficult and expensive. Our study aimed to test commercially available colorimetric labels, sensitive to UV-C energy, and compare their precision with an accepted radiometric technique. The color-changing labels were found to predictably change color in a dose-dependent manner that would allow them to act as a qualitative alternative to radiometry when determining the minimum UV-C energy dosage received at surfaces. If deployed using careful protective techniques to avoid unintentional exposure to sunlight or other light sources, the use of colorimetric labels could provide inexpensive, easy, and accurate verification of effective UV-C dosing in clinical spaces.

Aerosol agitation: Quantifying the hydrodynamic stressors on particulates encapsulated in small droplets.

Lower respiratory tract infections originate from multiple aerosol sources, varying from droplets erupting from bursting bubbles in a toilet or those produced by human speech. A key component of the aerosol-based infection pathway-from source to potential host-is the survival of the pathogen during aerosolization. Due to their finite-time instability, pinch-off processes occurring during aerosolization have the potential to rapidly accelerate the fluid into focused regions of these droplets, stress objects therein, and if powerful enough, disrupt biological life. However, the extent that a pathogen will be exposed to damaging hydrodynamic stressors during the aerosolization process is unknown. Here we compute the probability that particulates will be exposed to a hydrodynamic stressor during the generation of droplets that range in size from one to 100 microns. For example, particulates in water droplets less than 5 µm have a 50% chance of being subjected to an energy dissipation rate in excess of 1011 W/m3, hydrodynamic stresses in excess of 104 Pa, and strain rates in excess of 107 s-1, values known to damage certain biological cells. Using a combination of numerical simulations and self-similar dynamics, we show how the exposure within a droplet can be generally predicted from its size, surface tension, and density, even across different aerosolization mechanisms. Collectively, these results introduce aerosol agitation as a potential factor in pathogen transmission and implicate the pinch-off singularity flow as setting the distribution of hydrodynamic stressors experienced within the droplet.

Efficacy of an ambulance ventilation system in reducing EMS worker exposure to airborne particles from a patient cough aerosol simulator.

The protection of emergency medical service (EMS) workers from airborne disease transmission is important during routine transport of patients with infectious respiratory illnesses and would be critical during a pandemic of a disease such as influenza. However, few studies have examined the effectiveness of ambulance ventilation systems at reducing EMS worker exposure to airborne particles (aerosols). In our study, a cough aerosol simulator mimicking a coughing patient with an infectious respiratory illness was placed on a patient cot in an ambulance. The concentration and dispersion of cough aerosol particles were measured for 15 min at locations corresponding to likely positions of an EMS worker treating the patient. Experiments were performed with the patient cot at an angle of 0° (horizontal), 30°, and 60°, and with the ambulance ventilation system set to 0, 5, and 12 air changes/hour (ACH). Our results showed that increasing the air change rate significantly reduced the airborne particle concentration (p < 0.001). Increasing the air change rate from 0 to 5 ACH reduced the mean aerosol concentration by 34% (SD = 19%) overall, while increasing it from 0 to 12 ACH reduced the concentration by 68% (SD = 9%). Changing the cot angle also affected the concentration (p < 0.001), but the effect was more modest, especially at 5 and 12 ACH. Contrary to our expectations, the aerosol concentrations at the different worker positions were not significantly different (p < 0.556). Flow visualization experiments showed that the ventilation system created a recirculation pattern which helped disperse the aerosol particles throughout the compartment, reducing the effectiveness of the system. Our findings indicate that the ambulance ventilation system reduced but did not eliminate worker exposure to infectious aerosol particles. Aerosol exposures were not significantly different at different locations within the compartment, including locations behind and beside the patient. Improved ventilation system designs with smoother and more unidirectional airflows could provide better worker protection.

Case Report: Imported Case of Lassa Fever - New Jersey, May 2015.

We report a fatal case of Lassa fever diagnosed in the United States in a Liberian traveler. We describe infection control protocols and public health response. One contact at high risk became symptomatic, but her samples tested negative for Lassa virus; no secondary cases occurred among health care, family, and community contacts.

Detection of an avian lineage influenza A(H7N2) virus in air and surface samples at a New York City feline quarantine facility.

BACKGROUND: In December 2016, an outbreak of low pathogenicity avian influenza (LPAI) A(H7N2) occurred in cats at a New York City animal shelter and quickly spread to other shelters in New York and Pennsylvania. The A(H7N2) virus also spread to an attending veterinarian. In response, 500 cats were transferred from these shelters to a temporary quarantine facility for continued monitoring and treatment. OBJECTIVES: The objective of this study was to assess the occupational risk of A(H7N2) exposure among emergency response workers at the feline quarantine facility. METHODS: Aerosol and surface samples were collected from inside and outside the isolation zones of the quarantine facility. Samples were screened for A(H7N2) by quantitative RT-PCR and analyzed in embryonated chicken eggs for infectious virus. RESULTS: H7N2 virus was detected by RT-PCR in 28 of 29 aerosol samples collected in the high-risk isolation (hot) zone with 70.9% on particles with aerodynamic diameters >4 µm, 27.7% in 1-4 µm, and 1.4% in <1 µm. Seventeen of 22 surface samples from the high-risk isolation zone were also H7N2 positive with an average M1 copy number of 1.3 × 103 . Passage of aerosol and surface samples in eggs confirmed that infectious virus was present throughout the high-risk zones in the quarantine facility. CONCLUSIONS: By measuring particle size, distribution, and infectivity, our study suggests that the A(H7N2) virus had the potential to spread by airborne transmission and/or direct contact with viral-laden fomites. These results warranted continued A(H7N2) surveillance and transmission-based precautions during the treatment and care of infected cats.

Ambulance disinfection using Ultraviolet Germicidal Irradiation (UVGI): Effects of fixture location and surface reflectivity.

Ambulances are frequently contaminated with infectious microorganisms shed by patients during transport that can be transferred to subsequent patients and emergency medical service workers. Manual decontamination is tedious and time-consuming, and persistent contamination is common even after cleaning. Ultraviolet germicidal irradiation (UVGI) has been proposed as a terminal disinfection method for ambulance patient compartments. However, no published studies have tested the use of UVGI in ambulances. The objectives of this study were to investigate the efficacy of a UVGI system in an ambulance patient compartment and to examine the impact of UVGI fixture position and the UV reflectivity of interior surfaces on the time required for disinfection. A UVGI fixture was placed in the front, middle, or back of an ambulance patient compartment, and the UV irradiance was measured at 49 locations. Aluminum sheets and UV-reflective paint were added to examine the effects of increasing surface reflectivity on disinfection time. Disinfection tests were conducted using Bacillus subtilis spores as a surrogate for pathogens. Our results showed that the UV irradiance varied considerably depending upon the surface location. For example, with the UVGI fixture in the back position and without the addition of UV-reflective surfaces, the most irradiated location received a dose of UVGI sufficient for disinfection in 16 s, but the least irradiated location required 15 hr. Because the overall time required to disinfect all of the interior surfaces is determined by the time required to disinfect the surfaces receiving the lowest irradiation levels, the patient compartment disinfection times for different UVGI configurations ranged from 16.5 hr to 59 min depending upon the UVGI fixture position and the interior surface reflectivity. These results indicate that UVGI systems can reduce microbial surface contamination in ambulance compartments, but the systems must be rigorously validated before deployment. Optimizing the UVGI fixture position and increasing the UV reflectivity of the interior surfaces can substantially improve the performance of a UVGI system and reduce the time required for disinfection.

Persistence of Bowl Water Contamination during Sequential Flushes of Contaminated Toilets.

Toilets contaminated with infectious organisms are a recognized contact disease transmission hazard. Previous studies indicate that toilet bowl water can remain contaminated for several flushes after the contamination occurs. This study characterized contamination persistence over an extended series of flushes using both indicator particles and viable bacteria. For this study, toilets were seeded with microbe-size microbial surrogates and with Pseudomonas fluorescens or Clostridium difficile bacteria and flushed up to 24 times. Bowl water samples collected after seeding and after each flush indicated the clearance per flush and residual bowl water contaminant concentration. Toilets exhibited 3 + log10 contaminant reductions with the first flush, only 1-2 logs with the second flush, and less than 1 log thereafter. Contamination still was present 24 flushes post contamination. Clearance was modeled accurately by a two-stage exponential decay process. This study shows that toilet bowl water will remain contaminated many flushes after initial contamination, posing a risk of recurring environmental contamination and associated infection incidence.

Effective dust control systems on concrete dowel drilling machinery.

Rotary-type percussion dowel drilling machines, which drill horizontal holes in concrete pavement, have been documented to produce respirable crystalline silica concentrations above recommended exposure criteria. This places operators at potential risk for developing health effects from exposure. United States manufacturers of these machines offer optional dust control systems. The effectiveness of the dust control systems to reduce respirable dust concentrations on two types of drilling machines was evaluated under controlled conditions with the machines operating inside large tent structures in an effort to eliminate secondary exposure sources not related to the dowel-drilling operation. Area air samples were collected at breathing zone height at three locations around each machine. Through equal numbers of sampling rounds with the control systems randomly selected to be on or off, the control systems were found to significantly reduce respirable dust concentrations from a geometric mean of 54 mg per cubic meter to 3.0 mg per cubic meter on one machine and 57 mg per cubic meter to 5.3 mg per cubic meter on the other machine. This research shows that the dust control systems can dramatically reduce respirable dust concentrations by over 90% under controlled conditions. However, these systems need to be evaluated under actual work conditions to determine their effectiveness in reducing worker exposures to crystalline silica below hazardous levels.

Assessing Effectiveness of Ceiling-Ventilated Mock Airborne Infection Isolation Room in Preventing Hospital-Acquired Influenza Transmission to Health Care Workers.

Exposure to airborne influenza (or flu) from a patient's cough and exhaled air causes potential flu virus transmission to the persons located nearby. Hospital-acquired influenza is a major airborne disease that occurs to health care workers (HCW). This paper examines the airflow patterns and influenza-infected cough aerosol transport behavior in a ceiling-ventilated mock airborne infection isolation room (AIIR) and its effectiveness in mitigating HCW's exposure to airborne infection. The computational fluid dynamics (CFD) analysis of the airflow patterns and the flu virus dispersal behavior in a mock AIIR is conducted using the room geometries and layout (room dimensions, bathroom dimensions and details, placement of vents and furniture), ventilation parameters (flow rates at the inlet and outlet vents, diffuser design, thermal sources, etc.), and pressurization corresponding to that of a traditional ceiling-mounted ventilation arrangement observed in existing hospitals. The measured data shows that ventilation rates for the AIIR are about 12 air changes per hour(ach). However, the numerical results reveals incomplete air mixing and that not all of the room air is changed 12 times per hour. Two life-sized breathing human models are used to simulate a source patient and a receiving HCW. A patient cough cycle is introduced into the simulation and the airborne infection dispersal is tracked in time using a multiphase flow simulation approach. The results reveal air recirculation regions that diminished the effect of air filtration and prolong the presence of flu-contaminated air at the HCW's zone. Immediately after the patient coughs (0.51 s), the cough velocity from the patient's mouth drives the cough aerosols toward the HCW standing next to patient's bed. Within 0.7 s, the HCW is at risk of acquiring the infectious influenza disease, as a portion of these aerosols are inhaled by the HCW. As time progresses (5 s), the aerosols eventually spread throughout the entire room, as they are carried by the AIIR airflow patterns. Subsequently, a portion of these aerosols are removed by the exhaust ventilation. However, the remaining cough aerosols reenter and recirculate in the HCW's zone until they are removed by the exhaust ventilation. The infectious aerosols become diluted in the HCW's region over a period of 10 s because of the fresh air supplied into the HCW's zone. The overall duration of influenza infection in the room (until the aerosol count is reduced to less than 0.16% of the total number of aerosols ejected from the patient's mouth) is recorded as approximately 20 s. With successive coughing events, a near-continuous exposure would be possible. Hence, the ceiling-ventilation arrangement of the mock AIIR creats an unfavorable environment to the HCW throughout his stay in the room, and the modeled AIIR ventilation is not effective in protecting the HCW from infectious cough aerosols. The CFD results suggest that the AIIR ceiling ventilation arrangement has a significant role in influencing the flu virus transmission to the HCW.

Computational fluid dynamics study on the influence of an alternate ventilation configuration on the possible flow path of infectious cough aerosols in a mock airborne infection isolation room.

When infectious epidemics occur, they can be perpetuated within health care settings, potentially resulting in severe health care workforce absenteeism, morbidity, mortality, and economic losses. The ventilation system configuration of an airborne infection isolation room is one factor that can play a role in protecting health care workers from infectious patient bioaerosols. Though commonly associated with airborne infectious diseases, the airborne infection isolation room design can also impact other transmission routes such as short-range airborne as well as fomite and contact transmission routes that are impacted by contagion concentration and recirculation. This article presents a computational fluid dynamics study on the influence of the ventilation configuration on the possible flow path of bioaerosol dispersal behavior in a mock airborne infection isolation room. At first, a mock airborne infection isolation room was modeled that has the room geometry and layout, ventilation parameters, and pressurization corresponding to that of a traditional ceiling-mounted ventilation arrangement observed in existing hospitals. An alternate ventilation configuration was then modeled to retain the linear supply diffuser in the original mock airborne infection isolation room but interchanging the square supply and exhaust locations to place the exhaust closer to the patient source and allow clean air from supply vents to flow in clean-to-dirty flow paths, originating in uncontaminated parts of the room prior to entering the contaminated patient's air space. The modeled alternate airborne infection isolation room ventilation rate was 12 air changes per hour. Two human breathing models were used to simulate a source patient and a receiving health care worker. A patient cough cycle was introduced into the simulation, and the airborne infection dispersal was tracked in time using a multi-phase flow simulation approach. The results from the alternate configuration revealed that the cough aerosols were pulled by the exhaust vent without encountering the health care worker by 0.93 s after patient coughs and the particles were controlled as the aerosols' flow path was uninterrupted by an air particle streamline from patient to the ceiling exhaust venting out cough aerosols. However, not all the aerosols were vented out of the room. The remaining cough aerosols entered the health care worker's breathing zone by 0.98 s. This resulted in one of the critical stages in terms of the health care worker's exposure to airborne virus and presented the opportunity for the health care worker to suffer adverse health effects from the inhalation of cough aerosols. Within 2 s, the cough aerosols reentered and recirculated within the patient and health care worker's surroundings resulting in pockets of old contaminated air. By this time, coalescence losses decreased as the aerosol were no longer in very close proximity and their movement was primarily influenced by the airborne infection isolation room airflow patterns. In the patient and health care worker's area away from the supply, the fresh air supply failed to reach this part of the room to quickly dilute the cough aerosol concentration. The exhaust was also found to have minimal effect upon cough aerosol removal, except for those areas with high exhaust velocities, very close to the exhaust grill. Within 5-20 s after a patient's cough, the aerosols tended to break up to form smaller sized aerosols of less than one micron diameter. They remained airborne and entrained back into the supply air stream, spreading into the entire room. The suspended aerosols resulted in the floating time of more than 21 s in the room due to one cough cycle. The duration of airborne contagion in the room and its prolonged exposure to the health care worker is likely to happen due to successive coughing cycles. Hence, the evaluated alternate airborne infection isolation room is not effective in removing at least 38% particles exposed to health care worker within the first second of a patient's cough.

Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity.

The ability to disinfect and reuse disposable N95 filtering facepiece respirators (FFRs) may be needed during a pandemic of an infectious respiratory disease such as influenza. Ultraviolet germicidal irradiation (UVGI) is one possible method for respirator disinfection. However, UV radiation degrades polymers, which presents the possibility that UVGI exposure could degrade the ability of a disposable respirator to protect the worker. To study this, we exposed both sides of material coupons and respirator straps from four models of N95 FFRs to UVGI doses from 120-950 J/cm(2). We then tested the particle penetration, flow resistance, and bursting strengths of the individual respirator coupon layers, and the breaking strength of the respirator straps. We found that UVGI exposure led to a small increase in particle penetration (up to 1.25%) and had little effect on the flow resistance. UVGI exposure had a more pronounced effect on the strengths of the respirator materials. At the higher UVGI doses, the strength of the layers of respirator material was substantially reduced (in some cases, by >90%). The changes in the strengths of the respirator materials varied considerably among the different models of respirators. UVGI had less of an effect on the respirator straps; a dose of 2360 J/cm(2) reduced the breaking strength of the straps by 20-51%. Our results suggest that UVGI could be used to effectively disinfect disposable respirators for reuse, but the maximum number of disinfection cycles will be limited by the respirator model and the UVGI dose required to inactivate the pathogen.