Bioaerosol Basics - Airy Critters
- Bioaerosols: Airborne particles of biological origin; includes microbes (bacteria, fungi, viruses), pollen, toxins, cell fragments.
- Key Particle Sizes & Transmission:
- Droplets: >5µm; larger, settle quickly (within 1-2m); spread via direct/close contact (e.g., sneezing).
- Droplet Nuclei: <5µm (often 1-3µm); smaller, desiccated residues; remain suspended for hours, travel long distances (e.g., TB, measles).
- Formation: Generated by coughing, sneezing, talking, or aerosolizing procedures.
- Sources: Humans, animals, environment (soil, water, plants).
- Significance: Major route for respiratory infections, nosocomial infections, allergies, and sick building syndrome.
⭐ Wells's droplet nuclei hypothesis (1930s) was pivotal, explaining that evaporated respiratory droplets (<5µm) can remain airborne for extended periods, travel significant distances, and transmit infections like tuberculosis upon inhalation by susceptible individuals a considerable distance from the source. This challenged the prevailing notion that most respiratory infections spread only through large droplets or direct contact.
Key Airborne Pathogens - Sky-High Sickness
| Category | Pathogen Example (India Focus) | Key Disease(s) & Notes |
|---|---|---|
| Bacteria | Mycobacterium tuberculosis | Tuberculosis (TB): pulmonary, extrapulmonary; DOTS strategy |
| Streptococcus pneumoniae | Pneumonia (leading cause), bacteremia, meningitis | |
| Corynebacterium diphtheriae | Diphtheria: pseudomembrane, toxemia; vaccine-preventable | |
| Viruses | Influenza A, B viruses | Seasonal Influenza (Flu): epidemics, antigenic drift/shift |
| Measles virus (Morbillivirus) | Measles: Koplik's spots, rash; highly contagious, SSPE | |
| Varicella-Zoster Virus (VZV) | Chickenpox (varicella); Shingles (zoster) reactivation | |
| Fungi | Aspergillus fumigatus | Invasive Aspergillosis (immunocompromised), ABPA |
| Pneumocystis jirovecii | Pneumocystis Pneumonia (PCP): classic in HIV/AIDS |
⭐ Mycobacterium tuberculosis is a classic obligate airborne pathogen transmitted via droplet nuclei (<5 µm), making it highly infectious, especially in crowded Indian settings.
Air Sampling - Catching Air Bugs
| Method | Principle | Devices | Pros | Cons |
|---|---|---|---|---|
| Impaction | Inertial force deposits microbes onto solid agar | Andersen sampler, Slit sampler | Quantitative, Particle sizing (Andersen), Viable culturing | Agar desiccation, Particle bounce, Overloading at high counts |
| Impingement | Microbes trapped by bubbling air through liquid | All-Glass Impinger (AGI), Biosampler | High recovery for viable organisms, Can concentrate sample | Potential cell damage from shear forces, Evaporation of liquid |
| Filtration | Microbes physically retained on filter membrane | Membrane filters (MCE, PTFE), Gelatin | High collection efficiency for small particles, Versatile (culture/molecular) | Desiccation of microbes, Difficult elution of viable organisms |
| Sedimentation | Gravitational settling of microbes onto agar | Settle plates (Petri dishes) | Simple, Inexpensive, Qualitative assessment of viable fallout | Only larger particles (>5 µm), Affected by air currents, Long exposure |
Air Control Measures - Clearing the Air
- Ventilation: Dilutes/removes airborne pathogens.
- Natural: Windows, doors.
- Mechanical: HVAC systems. OTs: >15-20 ACH.
- Filtration:
- HEPA filters: 99.97% efficiency for ≥0.3 µm particles. Used in OTs, ICUs.
- HEPA filters: 99.97% efficiency for ≥0.3 µm particles. Used in OTs, ICUs.
- UVGI (Ultraviolet Germicidal Irradiation): Damages microbial DNA. Effective for TB. Upper room/in-duct.
- Laminar Airflow: Unidirectional, non-turbulent air; minimizes contamination in OTs, burn units.
- Source Control: Masks (N95), respiratory hygiene, isolation rooms (negative pressure).
⭐ Negative pressure rooms are critical for isolating patients with highly infectious airborne diseases like tuberculosis or measles to prevent nosocomial spread.
- 📌 Mnemonic: "V-F-U-L-S" (Ventilation, Filtration, UVGI, Laminar flow, Source control) for air control.
High‑Yield Points - ⚡ Biggest Takeaways
- Bioaerosols: Airborne biological particles (bacteria, fungi, viruses, pollen).
- Droplet nuclei (<5 µm): Crucial for airborne disease transmission (e.g., Tuberculosis, Measles).
- Air sampling methods: Include impaction (Andersen sampler), impingement, and filtration.
- Legionella pneumophila: Transmitted via aerosols from contaminated water systems (ACs, humidifiers).
- Aspergillus fumigatus: Common airborne fungus; causes aspergillosis in immunocompromised patients.
- Hospital air hygiene: Essential; HEPA filters & UVGI reduce nosocomial airborne infections.
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