Microbes in Air and Microbes in Air and BioaerosolsBioaerosols

BioaerosolsBioaerosols

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 pneumonia, asthma, rhinitis (e.g. cold, hay fever), and respiratory infection.

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

Airborne Microbes and AerosolsAirborne 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.

Some Examples of BioaerosolsSome Examples of Bioaerosols

Living Source Examples Microorganisms (microbes): Bacteria Legionella, Actinomycetes, endotoxinsFungi Histoplasma, Alternaria, Pencillium,

Aspergillus, Stachybotrys aflatoxins, aldehydes, alcohols

Protozoa Naegleria, Acanthamoeba Viruses Rhinoviruses (colds), Influenza (flu) Algae ChlorococusGreen plants Ambrosia (ragweed) pollenArthropods Dermatophagoides (dust mites) feces

Mammals horse or cat dander

Diseases Caused by Bioaerosols:Diseases Caused by Bioaerosols:

Diseases Caused by Bioaerosols:

Hypersensitivity or Allergic DiseasesHypersensitivity 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.

1. Hypersensitivity or Allergic Diseases1. Hypersensitivity or Allergic Diseases

Building-related asthma:◦symptoms -an hour of exposure or 4-12 hours after exposure. ◦by airborne fungi such as Altemaria, glycoproteins from fungi,

proteases from bacteria, the algae Chlorococus, 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 also cause rhinitis.

1. 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. ◦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

Legionella: Legionellosis and Pontiac FeverLegionella: 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….

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

Legionnaire’s Disease and Pontiac FeverLegionnaire’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 exposureFrequently requires hospitalization Aerosol exposure from contaminated cooling towers, evaporative

condensers, whirlpools, shower heads, faucets, & hot water tanks.

Hydroscopicity and Aerosol Deposition in Hydroscopicity and Aerosol Deposition in the Respiratory Tractthe 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

Agents of Respiratory Infectious DiseasesAgents 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 of Airborne MicrobesReservoirs of Airborne Microbes

Reservoirs: sources of air microbesWide range, overallDepends on the microbe

◦humans,◦animal,◦soil◦dust◦water◦air

Airborne Microbes and their ReservoirsAirborne Microbes and their Reservoirs

Viruses:Mostly humans but some animalsSome 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.).

Amplifiers of air microbesAmplifiers of air microbes

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

DisseminatorsDisseminators

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)

DisseminatorsDisseminators

◦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

Factors Influencing Airborne Factors Influencing Airborne InfectionInfection

Factors Influencing Airborne InfectionFactors Influencing Airborne InfectionAerosol FactorsAerosol 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 microbesFactors 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

Microbe Factors: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 pollutionProtective forms:

◦spores ◦cysts◦growth phase◦moisture content

Host FactorsHost Factors

Discussed previously in this class.

Sampling the air microbesSampling the air microbes

Active sampling methodsPassive sampling method

Air Samplers - Sedimentation and Slit SamplersAir 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) SamplerAir 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 MethodsAir 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 PrecipitationAir 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 ImpingersAir Samplers - Liquid ImpingersCollects 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 SamplersAir 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