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Fundamentals of Aerobiology
Aerosol Mechanics • What is an aerosol?
– A suspension of tiny particles or droplets in the air, such as dusts, mists, or fumes.
• The movement of aerosols is influenced by: – Gravity – Brownian motion – Electric charge – Vapors – Temperature – Inertial precipitation and impaction
The Chain Model of Airborne Diseases
• Infectious agent • Reservoirs and/or sources • Portals of exit • Modes of transmission • Portals of entry • Susceptible hosts
The Aerobiological Pathway Source Factors • Reservoirs • Organisms
Types Concentrations Prevalence
Aerosol Factors • Release • Composition • Dispersion • Decay
Biological Physical
Exposure Factors • Time • Activity • Inhalation • Deposition • Removal
Response Factors • Cellular • Systemic
Risk Assessment And Exposure Guidelines
Examples of Bioaerosols Living Source Examples
Bacteria
Legionella, Actinomycetes, endotoxins
Fungi
Histoplasma, Alternaria, Penicillium, Aspergillus
Protozoa Naegleria, Acanthamoeba
Viruses
Rhinoviruses, Influenza
Green Plants
Ragweed Pollen
Arthopods Dermatophagoides (dust mite) feces
Mammals Horse or cat dander
Approximate Size Ranges of Various Bioaerosols
Particles Diameters (microns)
Smoke 0.001 – 0.1
Viruses 0.015 – 0.45
Bacteria 0.3 – 5
Fungal spores 2 – 50
Algae cells/clusters 1 – 100+
Protozoa 2 – 100+
Dermatophagoides fecal pellets
~20
Fern Spores 20 – 60
Pollen 10 -100
Regions of the Respiratory System Nasopharynx Region: the head region, including the nose, mouth, pharynx, and larynx.
Tracheobronchial Region: includes the trachea, bronchi, and bronchioles.
Pulmonary (Alveolar) Region: comprised of the alveoli; the exchange of oxygen and carbon dioxide through the process of respiration occurs in the alveolar region.
Aerosols and Respiratory Deposition
• Aerosols >5 microns in diameter are removed in the upper respiratory tract, especially the nose. – Particles are brought to the pharynx by mucociliary
activity of the upper respiratory epithelial mucosa, where they are expectorated or swallowed. Swallowed particles containing enteric microbes can initiate enteric infections.
Aerosols and Respiratory Deposition
• Particles <5 microns in diameter, esp. 1-3 microns diameter, penetrate to the lower respiratory tract – Can be deposited in the bronchioles, alveolar ducts and alveoli. – Deposition efficiency in lower respiratory tract is ~50% for
particles 1-2 microns diameter. – Particles <0.5 microns dia. can also be deposited in the lower
respiratory tract, especially particles <0.25 microns dia. – Particles deposited in the lower respiratory tract can be
phagocytized by respiratory (alveolar) macrophages • Can be destroyed or • Carried to the mucociliary escalator, where they are transported
upward to the pharynx.
Infectious Aerosols
Photo Credit: Department of Medical Microbiology, Edinburgh University
Transmission of Infections by Respiratory Aerosols
Photo Credit: Medical Supplies & Equipment Company
1-5 microns > 10 microns 5-10 microns
Aerosol & Droplet Basics • May require up to 1 hour or longer to settle-dependent on
many factors • Procedures that impart energy to a microbial suspension
produce aerosols • Ubiquitous in laboratory procedures • Often undetected • Extremely pervasive, putting all at risk, or exposing staff to
hazardous conditions • Splashes can cause airborne droplets which settle faster • Aerosols and droplets contain suspensions of pathogens, may
not be seen or smelled, but can be inhaled
Risk Assessment of Aerosol Work
• size of particle • concentration of pathogen • Risk Group of agent (RG1-4) • amount of aerosol produced by the procedure • dilution of aerosol in air • survival of agent
Aerosol Disseminators • Devices causing microbes to enter airborne state or be aerosolized; often
the reservoir or amplifier. • Any device able to produce droplets and aerosols:
– Humans and other animals: coughs and sneezes, esp. – Mechanical ventilation systems – Nebulizers and vaporizers – Toilets (by flushing) – Showers, whirlpools baths, Jacuzzi, etc. – Wet or moist, colonized surfaces (wet walls and other structures in buildings) – Environments that are dry and from which small particles can become
airborne by scouring or other mechanisms: • Vacuuming or walking on carpets and rugs • Excavation of contaminated soil • Demolition of buildings
Commonly Acquired Lab Infections
.
Aerosol-generating Procedures • Pipetting (vigorous mixing) • Mixing • Centrifugation • Inoculating culture bottles • Vortexing • Pouring off specimens • Loading syringes • Flaming loops • Open bench subculturing
• Hot loop into broth or media • Grinding • Opening lyophilized cultures • Entering or opening vessels at
non-ambient pressures, fermenters, freezer vials
• Bone saw at autopsy • Homogenizing • Sonication • Flow cytometry
Prevention and Control Measures
Protects only the wearer
Protects most
people
• Elimination of Potential Exposures
• Engineering Controls
• Administrative Controls
• PPE
Risk Assessment is conducted to determine what control measures should be in place
Aerosol Exposure Prevention
Engineering and Administrative Controls
Laboratory Air Changes Air changes per hour (ACH) and time required for removal efficiencies of 99% and 99.9% of airborne contaminants* Minutes required for removal efficiency† ACH 99% 99.9% 2 138 207 4 69 104 6 46 69 12 23 35 15 18 28 20 7 14 50 3 6 400 <1 1 † Time in minutes to reduce the airborne concentration by 99% or 99.9%.
HEPA Filter
• High Efficiency Air Particulate (HEPA) Filter – Particles at 0.3 microns are captured with an efficiency of
99.97% – Particles larger than 0.3 microns and particles smaller
than 0.3 microns are captured with a greater efficiency than 99.97%
Classifications of BSCs • Class I • Class II (four configurations)
– Type A1 – Type A2 – Type B1 – Type B2
• Class III
Biosafety Cabinet Types Class, Type
BSL Airflow Pattern
Volatile Chemicals
II, A1 BSL1-3
70% recirculated to the cabinet work area through HEPA; 30% balance can be exhausted through HEPA back into the room or to the outside through a thimble unit
NO
II, A2 BSL1-3
Same as II, A1, but plenums are under negative pressure to room; exhaust air is thimble-ducted to the outside through a HEPA filter
Minute Amounts
II, B1 BSL1-3
30% recirculated to the cabinet work area through HEPA. Exhaust cabinet air must pass through a dedicated duct to the outside through a HEPA filter
Minute amounts
II, B2 BSL1-3
No recirculation; total exhaust to the outside through hard-duct and a HEPA filter
YES [small amounts]
Working in the BSC
• Do not block front or rear grilles. • The sash must be adjusted to the appropriate level • Check and record your airflow gauge reading to verify proper airflows
before using the BSC. • The BSC should only contain those items needed to perform the specific
function. Upon completion all items should be decontaminated and removed.
• Work should be conducted 4-6 inches inside the BSC. • Minimize traffic flow past the BSC when in use. • Avoid sweeping motions • Do not use volatile chemicals in recirculating BSCs. Be aware some
chemicals may damage the HEPA filtration system. Use a fume hood for volatile chemicals.
Using a Loop
• Use a cooled loop for insertion into a culture.
• Ensure the loop is completely closed.
• Use short loops: the shank should be no more than 6 cm long to avoid vibrations.
• Use a micro-incinerator or pre-sterilized plastic loops rather than flaming a loop in an open flame.
Pipetting • Use “to deliver” pipettes to avoid blowing out
the last drop.
• Drain pipettes gently with the tip against the inner wall of the receiving vessel.
• Use pipettes with plugs to reduce contamination of the pipetting device.
• Work over an absorbent, plastic-backed pad to avoid aerosol dispersion from drops falling on hard surfaces.
• Do not mix materials by alternate suction and expulsion through a pipette (use vortex mixer).
Centrifuging
• Use sealed safety cups and sealed rotors.
• Open cups inside a biosafety cabinet.
• Allow cups to sit prior to opening to allow aerosols to settle if no biosafety cabinet available.
Photo credit: ehs.columbia.edu
Blending and Homogenizing
• Use a laboratory blender with a tight-fitting gasketed lid and leak-proof bearings (domestic kitchen blenders leak and release aerosols).
Using Needles and Syringes
• Use syringes with a Luer lock connector.
• Dispose of needles directly into sharps container without further manipulation (needle-cutting devices release aerosols).
Opening Tubes
• Avoid using tubes with push-in closures (when opened, the film of liquid trapped between tube and closure breaks and releases aerosols).
• Use a vortex mixer instead of inverting tubes. • Wait 30 seconds after shaking a tube before
opening to allow aerosols to settle.
Breakage
• Use plastic labware rather than glass. • Less likely to break which generates aerosols.
Adapted from http://www.superstock.com
Personal Protection
Personal Protective Equipment
Personal Protective Equipment (PPE) • Eye and Face Protection • Protective Clothing • Gloves • Scrubs • Booties
Respiratory Protection
Surgical Mask Dust Mask N-95 Mask
Half face mask & Full face mask Chemical and or biological
protection
Powered Air purifying respirators
(PAPR)