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Man Sneezing into tissue

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…”.

NIOSH Influenza-related Transmission Activities

Bioaerosol Sampling for the Detection of Aerosolized Influenza Virus

General Description: Coughing, sneezing, talking, and breathing produce an aerosol of airborne particles with diameters ranging from a few millimeters to less than 1 micron (µm). This study focuses on how small particles could carry the influenza virus. NIOSH researchers 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 sample( were assayed for the presence of the 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 focused on how the influenza virus can be carried and transmitted by viral-laden particles in a healthcare setting.

Key Findings: The NIOSH sampler efficiently collected airborne particles, and the 2009 H1N1 influenza and H3N2 influenza viruses were most often 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 [2007]. Bioaerosol sampling for the detection of aerosolized influenza virus. Influenza Other Respir Viruses 1(3):113-120,

Point of Contact: CDC-INFO

Detection of Airborne Influenza in Healthcare Facilities During Influenza Seasons

General Description: NIOSH researchers completed two studies measuring how much airborne influenza viral Ribonucleic acid (RNA) was present 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. These samples were studied to find the amount and size of airborne particles containing influenza and determine whether this related to the number and location of patients.

Relevance to Worker Safety and Health: These studies addressed whether influenza is present on respirable particles that could 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 places 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 cause more concern because they can remain airborne for more time and because they can be drawn down into the alveolar region of the lungs during when inhaled. 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 [2009]. Measurement of airborne influenza virus in a hospital emergency department. Clin Infect Dis 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 [2010]. Distribution of airborne influenza virus and respiratory syncytial virus in an urgent care medical clinic. Clin Infect Dis 50:693-698,

Point of Contact: CDC-INFO

Measurements of Airborne Influenza Virus in Aerosol Particles from Human Coughs

General Description: NIOSH, during the seasonal influenza seasons, completed three clinical studies that measured the amount and size distribution of aerosol particles containing influenza viral ribonucleic acid (RNA) that influenza patients produced as they coughed.

Relevance to Worker Safety and Health: The studies focused on whether influenza patients could place healthcare workers at risk for infection during routine examinations.

Key Findings: The results showed that influenza patients while coughing produced aerosol particles containing measurable amounts of influenza. Further, 65% of the viral RNA was contained within particles in the respirable size fraction. The latest study revealed that of 58 confirmed influenza positive test subjects, 54 produced viable virus in either their coughs, breaths, or both.

Status: These peer-reviewed studies have been published or are in review.

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

Lindsley WG, Noti JD, Blachere F, Thewlis RE, Martin SB, Othumpangat S, Noorbakhsh B, Goldsmith WT, Vishnu A, Palmer JE, Clark KE, Beezhold D [2015]. Viable Influenza A Virus in airborne particles from human coughs. J Occup Environ Hyg 12(2):107-113,

Lindsley WG, Blachere FM, Beezhold DH, Thewlis R, Noorbakhsh B, Othumpangat S, Goldsmith TW, McMillen CM, Burrell CN, Noti JD [2016]. Viable influenza A virus in airborne particles expelled during coughs versus exhalations. Influenza Other Respir Viruses 10(5): 404-413,

Point of Contact: CDC-INFO

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 (EPA) through an interagency agreement, researchers measured the efficiency of the NIOSH two-stage cyclone bioaerosol sampler for collecting and dividing into fractions particles that contain 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: Airborne influenza poses a threat because it is the most likely route for the virus to spread widely from a single person or point source. The NIOSH sampler’s ability to divide aerosol particles by size fractions and to find whether infectious virus is present is important for determining the transmissibility of a potential epidemic.

Key Findings: The sampler’s efficiency at collecting aerosolized particles for 30 minutes from a calm-air chamber is essentially the same as that from the SKC BioSampler® (SKC Inc., Eighty Four, PA). The SKC biosampler 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 the experimental conditions, the NIOSH sampler collected particles and found infectious virus in of all three size fractions.

Status: These peer-reviewed study has been published.

Cao G, Blachere FM, Lindsley WG, Noti JD, Beezhold DH [2010]. 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,

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

Point of Contact: CDC-INFO

Identification of Medical Procedures that Generate Aerosols

General Description: Medical procedures on influenza patients, including bronchoscopy, tracheal suctioning, and tracheal intubation, can produce infectious aerosols, putting healthcare workers at risk. NIOSH researchers collaborated with research at the West Virginia University School of Medicine. NIOSH researchers assessed aerosols produced during representative procedures at Ruby Memorial Hospital in Morgantown, WV. Aerosols were evaluated for the size and number of aerosol particles and for the presence of influenza virus.

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

Status: This peer-reviewed study has been published.

Cummings KJ, Martin SB Jr., Lindsley WG, Othumpangat S, Blachere FM, Noti JD, Beezhold DH, Roidad N, Parker JE, Weissman DN [2014]. Exposure to influenza virus aerosols in the hospital setting: is routine patient care an aerosol generating procedure? Letter to editor. J Infect Dis 210(3): 504-505,

Point of Contact: CDC-INFO

Development of an Enhanced Methodology for Detecting Infectious Influenza

General Description: Current screening methods for detecting infectious airborne influenza are limited and lack sensitivity. For this reason, NIOSH developed an alternative and highly sensitive assay. In the viral replication assay, infectious virus within an aerosol sample was first infected into Madin-Darby canine kidney cells to allow amplification of viral copy number. The amplified copies of virus were 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 can speed the response to a potential pandemic.

Key Findings: The research showed that a single virus was amplified by the viral replication assay 107 to 108 fold. 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 is being developed based on making a cell line that emits light when infected with virus.

Blachere FM, Cao G, Lindsley WG, Noti JD, Beezhold DH [2011]. Enhanced detection of infectious airborne influenza virus. J Virol Methods 176(1-2):120-124,

Point of Contact: CDC-INFO

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 how this illness spreads through the air and how to reduce its spread.

Key Findings: Individuals with influenza produce much more aerosol when ill compared to afterwards. More particles were produced per cough 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 particle volume of the cough aerosol was in the respirable size fraction. This indicates that these particles could reach the alveolar region of the lungs if inhaled by another person. More aerosol produced during illness may play an important role in the spread of influenza.

Status: This peer-reviewed study has been published.

Lindsley WG, Pearce TA, Hudnall JB, Davis KA, Davis SM, Fisher MA, Khakoo R, Palmer JE, Clark KE, Celik I, Coffey CC, Blachere FM, Beezhold DH [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: CDC-INFO

Factors Influencing the Transmission of Influenza

General Description: This program developed improved ways to collect and evaluate virus-laden bioaerosols to better understand what influences the spread of influenza. Studies sought to measure and understand how the influenza virus in aerosols maintains its ability to infect. Researchers built an environmental chamber with two manikins inside. A cough manikin “coughs” influenza virus into the room to simulate a patient with influenza, and a breathing manikin simulates a healthcare worker. The manikins were outfitted with a mask or respirator to study how well they can protect workers. NIOSH aerosol samplers were used to collect the airborne particles containing influenza virus from the breathing manikin and at places throughout the room. The study addressed factors such as how long infectious influenza virus can remain airborne, the distance an infectious virus can be transmitted, and how room temperature and humidity affect the ability of a virus to infect a healthcare worker.

Relevance to Worker Safety and Health: These studies help us understand how influenza spreads in workplace settings, and they assess the risk of infection when workers are exposed for short periods to infected individuals in a confined environment.

Key Findings: Researchers did extensive testing in an environmental chamber using potassium chloride aerosols. The results indicate that the immediate exposure to aerosol particles from a cough depends on where the simulated healthcare worker is located, but within 5–10 minutes the particles are dispersed throughout the room, exposing the worker in any location. As expected, N95 respirators reduced exposure levels to negligible levels. Surgical masks typically admitted 20% of the airborne particles even when the mask was sealed to the breathing machine head. Researchers expanded this work to include testing using influenza virus and found viable influenza was present in all three aerosol fractions collected. Surgical masks sealed to the manikin head admitted about 15% of viable virus, but N95 respirators reduced significantly more exposure compared to surgical masks. Researchers found that a faceshield can effectively block large droplets of coughed influenza particles from infecting a healthcare worker wearing this faceshield. Also, high humidity (40%–45%) can inactivate virus coughed from the cough manikin. The virus survives significantly better at low humidity (20%–25%).

Status: These peer-reviewed manuscripts have been published.

Lindsley WG, King WP, Thewlis RE, Reynolds JS, Panday K, Cao G, Szalajda JV [2012]. Dispersion and exposure to a cough-generated aerosol in a simulated medical examination room. J Occup Environ Hyg 9(12): 681-690,

Noti JD, Lindsley WG, Blachere FM, Cao G, Kashon ML, Thewlis RE, McMillen CM, King WP, Szalajda JV, Beezhold DH [2012]. Detection of infectious influenza virus in cough aerosols generated in a simulated patient examination room. Clin Infect Dis 54(11):1569-1577,

Lindsley WG, Noti JD, Blachere FM, Szalajda JV, Beezhold DH [2014]. Efficacy of face shields against cough aerosol droplets from a cough simulator. J Occup Environ Hyg. 11(8): 509-518,

Noti JD, Blachere FM, McMillen CM, Lindsley WG, Kashon ML, Slaughter DR, Beezhold DH [2013]. High humidity leads to loss of infectious influenza virus from simulated coughs. PLoS One 8(2):e57485,

Point of Contact: CDC-INFO