Measurement and filtration of virus aerosols

Details

• Personal Author:
  Zuo Z
• Description:
  The potential involvement of virus aerosols (i.e., airborne virus-carrying particles) in the transmission of human respiratory diseases has led to increased public concern. This dissertation focuses on 1) measurement of laboratory generated virus aerosols as a function of particle size, virus type, and composition of nebulizer suspensions (Chapter 2 and 3) and 2) performance evaluation of filtering facepiece respirators against virus aerosols (Chapter 4 and 5) with the long term goal to better understand and better control the airborne transmission of viral diseases. Although laboratory generated virus aerosols have been widely studied in terms of infectivity and survivability, how they are related to particle size, especially in the submicron size range, is little understood. In the first study (Chapter 2), four viruses (MS2 bacteriophage, transmissible gastroenteritis virus, swine influenza virus, and avian influenza virus) were aerosolized, size classified (100-450 nm) using a differential mobility analyzer (DMA), and collected onto gelatin filters. Uranine dye was also nebulized with the virus, serving as a particle tracer. Virus infectivity assay and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) were then used to quantify the amount of infectious virus and total virus present in the samples, respectively. The virus distribution was found to be better represented by the particle volume distribution rather than the particle number distribution. The capacity for a particle to carry virus increased with the particle size and the relationship could be described by a power law. Virus survivability was dependent on virus type and particle size. Survivability of the three animal viruses at large particle size (300-450 nm) was significantly higher than at particle size close to the size of the virion (100-200 nm), which could be due to the shielding effect. The data suggest that particle size plays an important role in infectivity and survivability of airborne viruses and may, therefore, have an impact on the airborne transmission of viral illness and disease. The data do not support the use of MS2 bacteriophage as a general surrogate for animal and human viruses. Laboratory studies of virus aerosols have been criticized for generating airborne viruses from artificial nebulizer suspensions (e.g., cell culture media), which do not mimic the natural release of viruses (e.g., from human saliva). Therefore, the objectives of the second study (Chapter 3) were to determine the effect of human saliva on the survival of airborne virus and to compare it with those of artificial saliva and cell culture medium (i.e., 3% tryptic soy broth). A stock of MS2 bacteriophage was diluted in one of the three nebulizer suspensions, aerosolized, size selected (100 to 450 nm) using a differential mobility analyzer, and collected onto gelatin filters. Uranine was used as a particle tracer. The resulting particle size distribution was measured using a scanning mobility particle sizer. The amounts of infectious virus, total virus, and fluorescence in the collected samples were determined by infectivity assays, qRT-PCR, and spectrofluorometry, respectively. For all the nebulizer suspensions tested, the virus content generally followed a particle volume distribution rather than a number distribution. The survival of airborne MS2 was independent of particle size but was strongly affected by the type of nebulizer suspension. Human saliva was found to be much less protective than cell culture medium and artificial saliva. These results indicate the need for caution when extrapolating laboratory results, which often use artificial nebulizer suspensions. To better assess the risk of airborne transmission of viral diseases in real-life situations, the use of natural suspensions such as saliva or respiratory mucus is recommended. In the third study (Chapter 4), particle number penetration (one form of physical penetration) and infectivity penetration of human adenovirus and swine influenza virus aerosols through respirators were measured to better characterize the effectiveness of filtering facepiece respirators against airborne viruses. Particle number penetration was found to range from 2% to 5%. However, aerosol loading and large sample-to-sample variation made it difficult to quantify the difference in particle number penetration caused by the different virus aerosols. Infectivity penetration of human adenovirus was much lower than particle number penetration, indicating that the latter provides a conservative estimate for respirator performance against airborne viruses. In the fourth study (Chapter 5), infectivity, viral RNA, photometric, fluorescence (particle volume), and particle number penetration of MS2 bacteriophage through three different models of respirators were compared to better understand the correlation between infectivity and physical penetration. Although infectivity and viral RNA penetration were better represented by particle volume penetration than particle number penetration, they were several-fold lower than photometric penetration, which was partially due to the difference in virus survival between upstream and downstream aerosol samples. Results suggest that the current NIOSH (photometer-based) certification method may be used to prescreen respirators for infection control applications. These four studies comprise the main body of this dissertation and have been published or currently under review. [Description provided by NIOSH]
• Subjects:
  Aerosols Air Pollutants, Occupational Irritants Laboratories Lung Occupational Health Particulate Matter Respiratory Protective Devices Respiratory System Respiratory Tract Diseases Safety Viral Diseases

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• Keywords:
  Airborne-particles Laboratory-testing Particulates Pulmonary-function Pulmonary-system Pulmonary-system-disorders Respirators Respiratory-equipment Respiratory-infections Respiratory-irritants Respiratory-system-disorders Viral-diseases Viral-infections

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• Publisher:
  University of Minnesota
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Dissertation
• Place as Subject:
  Minnesota ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-127
• NIOSHTIC Number:
  nn:20046474
• Citation:
  Minneapolis, MN: University of Minnesota, 2014 Jun; :1-127
• Federal Fiscal Year:
  2014
• Performing Organization:
  University of Minnesota, Schools of Veterinary Medicine, Minneapolis, Minnesota
• Peer Reviewed:
  False
• Start Date:
  20080901
• Source Full Name:
  Measurement and filtration of virus aerosols
• End Date:
  20130831
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:3f0e0e765ae95733c7a06665a86f9c657cc7abf231b74972aca3e37b7a1afb455a5e02010785283eacf1d24ea3f1fc77254dfce0a49dd09b324e318c312abef5
• Download URL:
  https://stacks.cdc.gov/view/cdc/201522/cdc_201522_DS1.pdf
• File Type:
  [PDF - 1.37 MB ]