Microbes in Air and Bioaerosols

Bioaerosols• Definition

– 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 1. pneumonia, 2. asthma, 3. rhinitis (e.g. cold, hay fever), and 4. respiratory infection.

• Some bioaerosols can also infect the eyes and via ingestion (swallowed)

Living Source Examples

Bacteria 1. Legionella,2. Actinomycetes,3. endotoxins

Fungi 1. Histoplasma,2. Alternaria,3. Pencillium,4. Aspergillus,5. Stachybotrys aflatoxins,6. aldehydes,7. alcohols

Protozoa 1. Naegleria,2. Acanthamoeba

Viruses 1. Rhinoviruses (colds), 2. Influenza (flu

Algae • Chlorococus

Green plants • Ambrosia (ragweed) pollen

Arthropods • Dermatophagoides (dust mites) feces

Mammals • horse or cat dander

Some Examples of Bioaerosols

Diseases Caused by Bioaerosols: Hypersensitivity or Allergic Diseases1. Result from exposure to antigens (of indoor bioaerosols) that stimulate an

allergic response by the body's immune system.

2. Susceptibility varies among people.

3. Diseases usually are diagnosed by a physician.

4. Once an individual has developed a hypersensitivity disease, a very small amount of the antigen may cause a severe reaction.

5. Hypersensitivity diseases account for most of the health problems due to

indoor bioaerosols.

Hypersensitivity or Allergic Diseases

1. Building-related asthma

2. Allergic rhinitis

1. Building-related asthma: Symptoms:

i. chest tightness,

ii. wheezing,

iii. coughing, and

iv. shortness of breath.

Symptoms may occur within an hour of exposure or 4-12 hours after exposure.

Can be caused by indoor bioaerosols and airborne fungi such as:i. Altamira,

ii. glycoprotein from fungi,

iii. proteases (digestive enzymes that cause the breakdown of proteins) from bacteria (indoor bioaerosols that also causes Allergic Rhinitis )

iv. the algae Clorococcus,

v. ragweed pollen,

vi. dust mites and

vii. dander from cats.

2. Allergic rhinitis: Symptoms:

i. stuffiness of the nose,

ii. clear discharge from the nose,

iii. itchy nose, and

iv. sneezing.

v. Itching eyes and

vi. puffy eyes.

All the indoor bioaerosols listed under building-related asthma except the bacteria proteases also cause rhinitis.

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 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.

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

H2O H2O H2O

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

• 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

• 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

• 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

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: Wide range, overallDepends on the microbe

– humans,– animal,– soil– dust– water– air

Amplifiers:• Places where microorganisms multiply or proliferate.• Most reservoirs are potential amplifiers.

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

Airborne Microbes and their ReservoirsViruses:• Mostly humans but some animals• Some rodent viruses are significant: ex: Lassa Fever Virus and

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

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 FeverLegionnaire'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 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:

• 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

• Discussed previously in this class.

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

• 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

• 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 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• 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• 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