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NIOSH Activities: Influenza Transmission Research

The Infectious Disease Transmission Program within the Health Effects Laboratory Division (HELD) at NIOSH is focused on understanding aerosol transmission of the influenza virus in healthcare settings. The amount of airborne infectious influenza virus in the environment that could potentially be inhaled by uninfected individuals is a key factor governing transmission. NIOSH research on influenza transmission develops improved methodologies to detect and determine the viability of airborne virus and then uses these methodologies to assess viable viruses in public locations such as healthcare facilities. The knowledge gained from these studies will address specific NIOSH research goals to reduce or eliminate transmission of infectious diseases in healthcare settings among workers in the Healthcare and Social Assistance sector. This research also addresses recommendations made in 2009 by the Institute of Medicine (IOM) for research to "resolve the unanswered questions regarding the relative contribution of various routes of influenza transmission...".

Bioaerosol Sampling for the Detection of Aerosolized Influenza Virus

General Description: Coughing, sneezing, talking, and breathing generate an aerosol of airborne particles with diameters that can range from a few millimeters to less than 1 µm. This study investigated the potential for influenza virus to be carried by small particles. Researchers at NIOSH developed a two-stage cyclone bioaerosol sampler that can collect air samples and separate airborne particles into three size fractions (greater than 4 µm, 1-4 µm, and less than 1 µm). Attenuated influenza virus was aerosolized in a laboratory calm-air settling chamber and airborne particles collected with the NIOSH bioaerosol sampler were assayed for the presence of influenza virus.

Relevance to Worker Safety and Health: Particles less than 10 µm in diameter can remain airborne for hours and are easily inhaled deeply into the respiratory tract. This study addressed the potential for influenza virus to be carried and potentially transmitted by viral-laden particles in a healthcare setting.

Key Findings: Airborne particles were efficiently collected by the NIOSH sampler and 2009 H1N1 influenza and H3N2 influenza virus were predominately found in the 1-4 µm and less than 1 µm size fractions. The viability of the collected virus was not determined.

Status: This peer-reviewed study has been published.

Blachere FM, Lindsley WG, Slaven JE, Green BJ, Anderson SE, Chen BT, Beezhold DH. Bioaerosol sampling for the detection of aerosolized influenza virus. Influenza and Other Respir Viruses 2007;1(3):113-120.

Point of Contact: NIOSH-INFO

Detection of Airborne Influenza in Healthcare Facilities During Influenza Seasons

General Description: We have completed two studies measuring the amount of airborne influenza viral RNA in healthcare facilities during influenza seasons. In 2008 and 2009, air samples were collected from the West Virginia University Hospital’s emergency room and Urgent Care Clinic, respectively, to determine the amount and size of airborne particles containing influenza and whether this correlated with the number and location of patients.

Relevance to Worker Safety and Health: These studies directly addressed whether influenza is present on respirable particles that could potentially place healthcare workers at risk for infection during influenza outbreaks.

Key Findings: Both studies found that the highest concentrations of influenza RNA were detected in locations where, and during times when, the number of influenza patients was highest. The studies also found that 42 to 53% of the influenza viral RNA was contained in airborne particles less than 4 µm in aerodynamic diameter (the respirable size fraction). Aerosol particles in this size range are of particular concern because they can remain airborne for an extended time and because they can be drawn down into the alveolar region of the lungs during inhalation.The viability of the collected virus was not determined.

Status: These peer-reviewed studies have been published.

Blachere FM, Lindsley WG, Pearce TA, Anderson SE, Fisher M, Khakoo R, Meade BJ, Lander O, Davis S, Thewlis RE, Celik I, Chen BT, Beezhold DH. Measurement of airborne influenza virus in a hospital emergency department. Clin Infect Dis 2009; 48:438–440. .

Lindsley WG, Blachere FM, Davis KA, Pearce TA, Fisher MA, Khakoo R, Davis SM, Rogers ME, Thewlis RE, Posada JA, Redrow JB, Celik IB, Chen BT, Beezhold DH. Distribution of airborne influenza virus and respiratory syncytial virus in an urgent care medical clinic. Clin Infect Dis 2010; 50:693–698. .

Points of Contact: Francoise M. Blachere, MS; and William G. Lindsley, PhD;

Measurements of Airborne Influenza Virus in Aerosol Particles from Human Coughs

General Description: We have completed one influenza season measuring the amount and size distribution of aerosol particles containing influenza viral RNA that were produced by influenza patients as they coughed.

Relevance to Worker Safety and Health: This study addressed whether influenza patients could potentially place healthcare workers at risk for infection during a routine examination.

Key Findings: Our results show that influenza patients produce aerosol particles containing measurable amounts of influenza virus while coughing. Further, 65% of the viral RNA was contained within particles in the respirable size fraction. Our study was also able to demonstrate that at least some influenza patients expelled airborne particles containing viable virus.

Status: This peer-reviewed study has been published.

Lindsley WG, Blachere FM, Thewlis RE, Vishnu A, Davis KA, Cao G, Palmer JE, Clark KE, Fisher MA, Khakoo R, Beezhold DH. Measurements of airborne influenza virus in aerosol particles from human coughs. PloS One 2010;5(11):1-6.

Point of Contact: William G. Lindsley, PhD;

Development of a Methodology to Detect Infectious Airborne Influenza Using the NIOSH Aerosol Sampler

General Description: In a study funded by the Environmental Protection Agency through an interagency agreement, we have characterized the efficiency of the NIOSH two-stage cyclone bioaerosol sampler for collecting and size fractionating particles containing infectious influenza virus. Influenza virus was aerosolized in a laboratory calm-air settling chamber and airborne particles collected with the NIOSH sampler were assayed for the presence of infectious virus.

Relevance to Worker Safety and Health: Aerosol transmission of influenza poses a profound threat since it has the greatest potential for widespread dissemination. The uniqueness of the NIOSH sampler to size-fractionate aerosol particles to determine whether infectious virus is present is of utmost importance in determining the magnitude of a potential epidemic.

Key Findings: The sampler’s efficiency at collecting aerosolized particles for 30 min from a calm-air chamber is essentially the same as that from the SKC BioSampler® (SKC Inc., Eighty Four, PA) that collects particles directly into a liquid media (1.2 X 104 total viral particles per liter of air (TVP/L of air) versus 1.3 X 104 TVP/L of air, respectively).The efficiency of the NIOSH air sampler is relatively constant over the collection times of 15, 30, and 60 minutes. The recovery rate for infectious viral particles with the NIOSH sampler is approximately 59% of the virus collected and, thus, it surpasses the reported infectious recovery rate of most commercial samplers with the exception of the SKC sampler. Under our experimental conditions, infectious virus was collected in all three fractions of the NIOSH sampler.

Status: This peer-reviewed study has been published.

Cao G, Blachere FM, Lindsley WG, Noti JD, Beezhold DH. Development of a methodology to detect viable airborne virus using personal aerosol samplers. Citation: Silvestri E, U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-10/127, 2010.

Access and enter "EPA/600/R-10/127" in the All EPA Search Box.

Cao G, Noti JD, Blachere FM, Lindsley WG, Beezhold. Development of an improved methodology to detect infectious airborne influenza virus using the NIOSH bioaerosol sampler. J Environ Monit 2011; 13(12):3301-3488.

Points of Contact: John D. Noti, PhD; and Donald H. Beezhold, PhD;

Development of an Enhanced Methodology for Detecting Infectious Influenza

General Description: Current screening methodologies for detecting infectious airborne influenza are limited and lack sensitivity and, therefore, we have developed an alternative and highly sensitive assay. In this assay, referred to as the viral replication assay (VRA), infectious virus within an aerosol sample is first infected into Mandin-Darby Canine Kidney cells to allow amplification of viral copy number. The amplified copies of virus are then easily detected using standard quantitative polymerase chain reaction (qPCR) analysis.

Relevance to Worker Safety and Health: The ability to detect very low levels of infectious influenza virus at the early stages of an influenza outbreak would expedite the overall response time to a potential pandemic.

Key Findings: A single virus was shown to be amplified 107 to 108 fold in the VRA. In laboratory-generated aerosol samples containing low amounts of virus, infectious virus was undetectable by the commonly-used standard plaque assay. In contrast, infectious virus was easily readily detected in all those samples.

Status: This peer-reviewed study has been published. A second generation and potentially more sensitive assay based on the development of a cell line that emits light when infected with virus is under development.

Blachere FM, Cao G, Lindsley WG, Noti JD, Beezhold DH. Enhanced detection of infectious airborne influenza virus. J Virol Methods 2011; 176:120-124.

Points of Contact: Francoise M. Blachere, MS;, John D. Noti, PhD;

Identification of Medical Procedures that Generate Aerosols

General Description: Medical procedures including bronchoscopy, tracheal suctioning, and tracheal intubation on influenza patients have the potential for producing infectious aerosols, putting healthcare workers at risk. This study will be undertaken with collaborators at the West Virginia University School of Medicine. NIOSH researchers will assess aerosols generated during representative procedures at Ruby Memorial Hospital in Morgantown, WV. Aerosols will be evaluated for the size and number of aerosol particles and for the presence of influenza virus.

Relevance to Worker Safety and Health: This study will provide information relevant to health risk created during selected medical procedures.

Status: The study is currently underway.

Points of Contact: William G. Lindsley, PhD; and Stephen B. Martin, MS, PE;

Cough Aerosol Particles Produced by Influenza Patients During and After Illness

General Description: Little is known about the quantity and size of potentially infectious airborne particles produced by people with influenza. Because respiratory infections generally increase airway mucus production, it is typically assumed that aerosol production also increases, but the actual amount of any change is unknown, and it is also unclear whether the particle size distribution of the aerosol is shifted.

The purpose of this study was to measure and compare aerosol production by influenza patients while they were ill and after they had recovered.

Relevance to Worker Safety and Health: By performing the first direct comparison of respiratory aerosol production during and after illness, these results show more clearly how influenza affects aerosol generation. A better understanding of the effects of influenza on aerosol production will help with efforts to study the potential for the airborne transmission of this illness and to devise interventions to reduce its spread.

Key Findings: Individuals with influenza produce a significantly greater volume of aerosol when ill compared to afterwards. The number of particles produced per cough was also higher when subjects had influenza compared to afterwards, although the difference did not reach statistical significance. The average number of particles expelled per cough varied widely from patient to patient. When the subjects had influenza, an average of 60% of the cough aerosol particle volume was in the respirable size fraction, indicating that these particles could reach the alveolar region of the lungs if inhaled by another person. This enhancement in aerosol generation during illness may play an important role in influenza transmission.

Status: This peer-reviewed study has been published.

Lindsley, WG, TA Pearce, JB Hudnall, KA Davis, SM Davis, MA Fisher, R Khakoo, JE Palmer, KE Clark, I Celik, CC Coffey, FM Blachere and DH Beezhold (2012). Quantity and size distribution of cough-generated aerosol particles produced by influenza patients during and after illness. J Occup Environ Hyg 9(7): 443-9.

Point of Contact: William G. Lindsley, PhD;

Factors Influencing the Transmission of Influenza

General Description: The overall purpose of this program is to develop improved methods for the collection and evaluation of virus-laden bioaerosols in order to better characterize the parameters that influence the transmission of the influenza virus. Studies are being conducted to measure and understand the parameters important for the persistence of infectivity of the influenza virus in aerosols. An environmental chamber has been built that contains a cough manikin that "coughs" influenza virus into the room to simulate a patient with influenza, and a breathing manikin to simulate a healthcare worker. The manikins can be outfitted with a mask or respirator to study how well they can protect workers. NIOSH aerosol samplers are used to collect the airborne particles containing influenza virus from the breathing manikin and at locations throughout the room. Specific questions being addressed include; how long does infectious influenza virus remain airborne, what is the distance over which infectious virus can be transmitted, and what is the effect of room temperature and humidity on infectivity of the virus?

Relevance to Worker Safety and Health: These studies will better our understanding of the mechanisms of transmission of influenza in occupational settings and directly assess the risk of infection when workers are exposed for short periods to infected individuals in a confined environment.

Key Findings: Extensive testing in the environmental chamber using potassium chloride aerosols indicate that the immediate exposure to aerosol particles from a cough depends on the location of the simulated healthcare worker, but within 5–10 minutes the particles are dispersed throughout the room and the worker is exposed regardless of location. As expected, N95 respirators reduced exposure levels to negligible levels, while surgical masks typically admitted 20% of the airborne particles even when the mask was sealed to the breathing machine head. This work has now been expanded to include testing using influenza virus. We have demonstrated that viable influenza was present in all three aerosol fractions collected and that surgical masks sealed to the manikin head admitted approximately 15% of viable virus while N95 respirators further significantly reduced exposure.

Status: Two peer-reviewed manuscripts have been published.

Lindsley, WG, WP King, RE Thewlis, JS Reynolds, K Panday, G Cao and JV Szalajda (2012). Dispersion and exposure to a cough-generated aerosol in a simulated medical examination room. J Occup Environ Hyg 9(12): 681-90.

Noti, JD, WG Lindsley, FM Blachere, G Cao, ML Kashon, RE Thewlis, CM McMillen, WP King, JV Szalajda and DH Beezhold (2012). Detection of infectious influenza virus in cough aerosols generated in a simulated patient examination room. Clin Infect Dis 54(11): 1569-77.

Points of Contact: John D. Noti, PhD;, William G. Lindsley, PhD;, and Donald H. Beezhold, PhD;