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)