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Microbes in Air and Bioaerosols. ENVR 133 Mark D. Sobsey. Bioaerosols. Microorganisms or particles, gases, vapors, or fragments of biological origin (i.e., alive or released from a living organism) that are in the air. Bioaerosols are everywhere in the environment.

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microbes in air and bioaerosols

Microbes in Air and Bioaerosols

ENVR 133

Mark D. Sobsey

  • Microorganisms or particles, gases, vapors, or fragments of biological origin (i.e., alive or released from a living organism) that are in the air.
  • Bioaerosols are everywhere in the environment.
  • Some bioaerosols, when breathed in, can cause diseases including pneumonia, asthma, rhinitis (e.g. cold, hay fever), and respiratory infection.
  • Some bioaerosols can also infect the eyes and vai ingestion (swallowed)
some examples of bioaerosols
Some Examples of Bioaerosols

Living Source Examples

Microorganisms (microbes):

  • Bacteria Legionella, Actinomycetes, endotoxins
  • Fungi Histoplasma, Alternaria, Pencillium, Aspergillus, Stachybotrys aflatoxins, aldehydes, alcohols
  • Protozoa Naegleria, Acanthamoeba
  • Viruses Rhinoviruses (colds), Influenza (flu
  • Algae Chlorococus

Green plants Ambrosia (ragweed) pollen

Arthropods Dermatophagoides (dust mites) feces

Mammals horse or cat dander

diseases caused by bioaerosols hypersensitivity or allergic diseases
Diseases Caused by Bioaerosols: Hypersensitivity or Allergic Diseases
  • Result from exposure to antigens (of indoor bioaerosols) that stimulate an allergic response by the body's immune system.
  • Susceptiblity varies among people.
  • Diseases usually are diagnosed by a physician.
  • Once an individual has developed a hypersensitivity disease, a very small amount of the antigen may cause a severe reaction.
  • Hypersensitivity diseases account for most of the health problems due to indoor bioaerosols.
hypersensitivity or allergic diseases
Hypersensitivity or Allergic Diseases
  • Building-related asthma: result in complaints of chest tightness, wheezing, coughing, and shortness of breath.
    • symptoms may occur within an hour of exposure or 4-12 hours after exposure.
    • Can be caused by airborne fungi such as Altemaria, glycoproteins from fungi, proteases (digestive enzymes that cause thebreakdown of proteins) from bacteria, the algae Clorococus, ragweed pollen, dust mites, and dander from cats.
  • Allergic rhinitis: stuffiness of the nose, clear discharge from the nose, itchy nose, and sneezing. Itching and puffy eyes.
    • All the indoor bioaerosols listed under building-related asthma except the bacteria proteases alsocause rhinitis.
hypersensitivity or allergic diseases1
Hypersensitivity or Allergic Diseases
  • Hypersensitivity pneumonitis (extrinsic allergic alveolitis):
    • Can be an acute, recurrent pneumonia with fever, cough, chest tightness, and fluids entering the lungs.
    • Or, can be a cough that progresses to shortness of breath, fatigue, weight loss and thickening and scarring of the lungs.
    • microorganisms associated with hypersensitivity pneumonitis: fungi such as Penicillium and Sporobolomyces, bacteria such as Thermoactinomyces, and protozoa such as Acanthamoeba.
  • Humidifier fever: fever, chills, muscle aches, and malaise (general feeling of being unwell), but no lung symptoms.
    • The symptoms usually start within 4-8 hours of exposure and end within 24 hours without long-term effects.
airborne microbes and aerosols
Airborne Microbes and Aerosols
  • Airborne transmission is possible for essentially all classes of microbes: viruses, bacteria, fungi and protozoans.
  • Any respiratory pathogen able to survive aerosolization and air transport is considered a potential cause of airborne disease.
  • Aerosols: Airborne particles, either solid or liquid, about 0.5 to 20 microns in diameter, that remain airborne for extended periods of time.
  • Droplets: >20 (usually 100+) microns in diameter; settle rapidly or evaporate to form droplet nuclei in the aerosol size range.
regions of the respiratory system
Regions of the Respiratory System
  • The cellular composition as well as geometry of the respiratory system influence particle deposition.
  • 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
lung anatomy and physiology and particle deposition
Lung Anatomy and Physiology and Particle Deposition


  • largest airway; lined by a ciliated epithelium covered by mucus and serous secretions produced by the cells and glands of the epithelium.
  • The secretions may trap and/or dissolve some inhaled particles
  • Beating of the cilia tends to drive secretions upward toward the mouth where they are ingested or expectorated.
  • Particles deposited in this portion of the lung will also be expelled in this manner.
lung anatomy and physiology and particle deposition1
Lung Anatomy and Physiology and Particle Deposition

Tracheobronchial Region:

  • As the airways divide and become smaller in diameter, the composition of the epithelium also changes
  • Becomes thinner with less ciliated cells and increasing numbers of Clara or non-ciliated bronchiolar cells.
  • Clearance via the mucociliary escalator is less likely than in the trachea.
  • The Clara cells do produce secretions and have metabolic capabilities.
    • Can detoxify locally absorbed chemicals
lung anatomy and physiology and particle deposition2
Lung Anatomy and Physiology and Particle Deposition

Pulmonary (Alveolar) Region:

  • Airways become even smaller in diameter (respiratory and terminal bronchioles) and open into the alveolar region.
  • Lined primarily by very thin Type I epithelial cells.
  • Other epithelial cell type found less frequency: pulmonary macrophage.
    • Specifically recruited (by migration or cell division) to the alveolar region when there is a local particle burden.
    • Engulf the particles and either migrate into the lung interstitium or move up the airways to be caught and removed by the mucociliary escalator.
  • Region of primary lung function: gas exchange.
  • Only a layer of surfactant, the Type I cell layer, and a thin interstitium containing fibroblasts and endothelial cells separate air from blood.
aerosols and respiratory deposition
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 deposition1
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 ciliary escalator, where they are transported upward to the pharynx.
hydroscopicity and aerosol deposition in the respiratory tract
Hydroscopicity and Aerosol Deposition in the Respiratory Tract

When inhaled, aerosol particles derived from aqueous fluids pick up moisture (water) while traveling in the respiratory passageways, thereby increasing in size.

  • Increased size changes deposition site




respiratory deposition impaction
Respiratory Deposition - Impaction
  • Each time airflow changes due to a bifurcation in the airways, suspended particles tend to travel along their original path due to inertia and may impact on an airway surface.
  • This mechanism is highly dependent on aerodynamic diameter, since the stopping distance for very small particles is quite low.
  • Occurs mostly for larger particles that are very close to airway walls, near the first airway bifurcations.
  • Therefore, deposition by impaction is greatest in the bronchial region.
  • Impaction accounts for the majority of particle deposition on a mass basis.
respiratory deposition sedimentation
Respiratory Deposition - Sedimentation
  • Settling out of particles in the smaller airways of the bronchioles and alveoli, where air flow is low and airway dimensions are small.
  • Rate of sedimentation is dependent on the terminal settling velocity of the particles
  • Sedimentation plays a greater role in the deposition of particles with larger aerodynamic diameters.
  • Hygroscopic particles may grow in size as they pass through the warm, humid air passages, thus increasing the probability of deposition by sedimentation.
respiratory deposition interception
Respiratory Deposition - Interception
  • Occurs when a particle contacts an airway surface due to its physical size or shape.
  • Unlike impaction, particles that are deposited by interception do not deviate from their air streamlines.
  • Most likely to occur in small airways or when the air streamline is close to an airway wall.
  • Interception is most significant for fibers, which easily contact airway surfaces do to their length.
    • Furthermore, fibers have small aerodynamic diameters relative to their size, so they can often reach the smallest airways.
respiratory deposition diffusion
Respiratory Deposition - Diffusion
  • Primary mechanism for particles <0.5 microns in diameter
  • Governed by geometric rather than aerodynamic size
  • Net transport of particles from a region of higher to lower concentration due to Brownian motion.
    • Brownian motion: random wiggling motion of a particle due to the constant bombardment of air molecules.
  • Occurs mostly when particles have just entered the nasopharynx
  • Also most likely to occur in the smaller airways of the pulmonary (alveolar) region, where air flow is low.
agents of respiratory infectious diseases
Agents of Respiratory Infectious Diseases

Viruses: influenza, measles (rubeola), chickenpox (herpes varicella‑zoster) and rhinoviruses (colds); Hantavirus (from a rodent; mouse)

Bacteria: Legionella spp., tuberculosis and other mycobacteria (Mycobacterium spp.), anthrax (Bacillus anthracis), and brucellosis (Brucella spp.).

Fungi: diseases: histoplasmosis, cryptococcosis, blastomycosis, coccidiodomycosis, and aspergillosis

Protozoans: Pneumocystis carinii pneumonia; prevalent in immunodeficient hosts such as AIDS patients.

Acanthamoeba encephalitis; primary amebic meningoencephalitis (PAM)

reservoirs and amplifiers of airborne microbes
Reservoirs and Amplifiers of Airborne Microbes


Wide range, overall

Depends on the microbe

    • humans,
    • animal,
    • soil
    • dust
    • water
    • air


  • Places where microorganisms multiply or proliferate.
  • Most reservoirs are potential amplifiers.
  • 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
airborne microbes and their reservoirs
Airborne Microbes and their Reservoirs


  • Mostly humans but some animals
  • Some rodent viruses are significant: ex: Lassa Fever Virus and Hantavirus.


  • Humans (TB & staphylococci),
  • other animals (brucella and anthrax),
  • water (Legionella)
  • soil (clostridia).


  • soil and birds (Cryptococcus and Histoplasma)
  • dead plant material
  • wet surfaces (wood and other building materials)
  • indoor air (mycotic air pollution)
  • stagnant water for the opportunistic fungi (e.g., Aspergillus sp.).
legionella legionellosis and pontiac fever
Legionella: Legionellosis and Pontiac Fever

Reservoirs and amplifiers:

  • Hot water systems
  • circulating water ventilation systems (cooling towers)
  • Plumbing (e.g., shower heads).
  • Hot tubs, whirlpools, etc.
  • Produce fresheners

Cleveland Auto plant outbreak, March, 2001:

  • Plant cooling tower is considered a possible source of the outbreak.
  • But, more than 100 other internal water sources -- favorite breeding grounds for the Legionella bacteria -- were also under investigation….
legionnaire s disease and pontiac fever
Legionnaire’s Disease and Pontiac Fever

Legionnaire's disease:

  • Bacterial pneumonia caused by Legionella pneumophila.
  • A type of pneumonia that affects the lungs and may also affect the stomach and intestines, kidneys, and central nervous system.
  • Incubation period: 2-10 days after exposure
  • Frequently requires hospitalization
  • Aerosol exposure from contaminated cooling towers, evaporative condensers, whirlpools, shower heads, faucets, & hot water tanks.

Pontiac fever: also caused by Legionella.

  • A "flu-like" illness with fever, chills, headache, myalgia (pain in the muscles), cough, nausea, and breathlessness.
  • Pneumonia does not occur.
  • Usually lasts 2-5 days.
  • Same sources as for Legionnaires' disease
factors influencing airborne infection aerosol factors
Factors Influencing Airborne InfectionAerosol Factors
  • Particle size; <5 um dia.; "droplet nuclei" from coughing & sneezing
    • Deposition site: depends on particle size and hygroscopicity
    • Chemical composition of the aerosol particle
  • Relative humidity (RH); dessication (loss of moisture)
  • Temperature: generally greater inactivation at higher temperature
  • Sunlight: UV inactivation of microbes
  • Factors influencing air movement: winds, currents, mechanical air handlers, etc.
  • Seasonal factors: precipitation, air currents, pollen sources, etc.
  • Air pollution:
    • chemicals inactivating airborne microbes (OAF= Open Air Factor)
    • enhancing their ability to cause infection in a host
factors influencing airborne infection microbe factors
Factors Influencing Airborne Infection Microbe Factors:
  • Size of microbe and of aerosol particle
    • influences air transport
    • influences deposition site: in environment and in host
  • Composition:
    • lipids, proteins (structural, enzymes), amino acids, etc.
    • enveloped and non-enveloped viruses respond differently to air pollution
  • Protective forms:
    • spores
    • cysts
    • growth phase
    • moisture content
host factors
Host Factors
  • Discussed previously in this class.
air samplers sedimentation and slit samplers
Air Samplers - Sedimentation and Slit Samplers
  • Sedimentation methods: collection of aerosol particles on a sticky surface; e.g., a petri dish containing agar or glycerol.
  • Slit samplers: Sampled of air is directed through a slit against a rotating collection surface. For bacteria, this could be an agar medium petri plate. Rotation is intermittent so that each impaction area represents a specific volume of sampled air and a time series of samples can be collected.

Sedimentation - Agar Medium Plate

Slit Sampler

air samplers stacked sieve anderson type sampler
Air Samplers - Stacked Sieve (Anderson type) Sampler
  • Six stages, each a perforated plate located above a petri dish.
  • Diameter of air passageway is smaller at each successive level, collecting progressively smaller particles.
  • Classifies and collects particles according to size
  • Used mostly for bacteria.
  • Can be used for virus sampling by collecting onto a sticky surface in the petri dish.
air sampling filtration methods
Air Sampling - Filtration Methods
  • Pass air through a membrane filter of small enough pore size to trap aerosol particles.
  • After collection, the filter can be plated or particles can be washed off.
  • Dessication and inefficient washing/recovery of collected particles can be problems.

Open Face Air Filter Cassette with Cap

air samplers electrostatic precipitation
Air Samplers - Electrostatic Precipitation
  • Air is drawn over electrically charged collection plates so that charged particles are attracted to and collected on either a positively or negatively charged, wetted surface.
  • Collected particles are washed off into the circulating collection fluid on the charged plate surface.
air samplers liquid impingers
Air Samplers - Liquid Impingers
  • Collects particles from sampled air into a liquid medium.
  • All glass impinger (AGI).
  • Particles are drawn through a small orifice that increases their velocity, thereby causing them to impinge on the bottom surface of the container and be "scrubbed" into the collection fluid.
  • Excessive cooling and evaporation and leakage (particles not being retained) can be a problem.
air samplers
Air Samplers
  • High volume liquid (cyclone) scrubber: Particles in air traveling at high speeds through a progressively smaller, helical passageway impinge against the container walls and are collected into a recirculating collection fluid supplied by a pump