The Air Between Us
How We Forgot (Then Remembered) That Disease Travels Through Air
With every article and podcast episode, we provide comprehensive study materials: References, Executive Summary, Briefing Document, Quiz, Essay Questions, Glossary, Timeline, Cast, FAQ, Table of Contents, Index, Polls, 3k Image, and Fact Check.
The history of medicine isn't a straight line of progress. It's a winding path of discoveries, forgotten wisdom, and blind spots that have shaped how we handle disease—sometimes for the worse.
The pandemic forced us to relearn an inconvenient truth: the air we share can kill us. But this wasn't new knowledge. We'd known it before. We just chose to forget.
The Wisdom We Left Behind
In the 1850s, Florence Nightingale transformed battlefield hospitals not with advanced medicine or surgical techniques, but with something far simpler—she opened the windows.
Without microscopes or germ theory to guide her, Nightingale observed something that modern medicine would later overlook: cramped, stuffy rooms made people sicker. Fresh air made them better.
She didn't need to understand microbes or viral particles. She saw the results. Open windows saved lives. Ventilation worked.
This was revolutionary healthcare with nothing but observation and common sense. No million-dollar research grants. No pharmaceutical patents. Just windows, flung wide open.
But somewhere along the way, we forgot her wisdom. We closed the windows, sealed our buildings, and created the perfect incubators for airborne pathogens.
How Hand Washing Made Us Forget About Air
In the late 1800s, Ignaz Semmelweis and Joseph Lister revolutionized medicine by proving that doctors were spreading disease on their unwashed hands. This was the birth of modern infection control.
It was a crucial discovery that saved countless lives. But it also created a mental blind spot that would persist for over a century.
The medical establishment became fixated on contact transmission—things you could touch and see. Wash your hands. Sterilize your instruments. Wipe down surfaces.
This fixation was so powerful that it overshadowed what Nightingale had already demonstrated: disease travels through air.
The problem wasn't that hand washing was wrong—it wasn't. The problem was that it was incomplete. It addressed only one route of transmission while letting another route flourish unchecked.
The Technology Trap
After World War II, medical research took a fateful turn. The technology of the era could easily detect bacteria but struggled to identify viruses.
This technological limitation shaped our entire understanding of disease transmission. Researchers found bacteria primarily in larger droplets that fell quickly to surfaces—reinforcing the belief that hand washing and surface cleaning were the main solutions.
There was just one exception: tuberculosis. TB bacteria were found lingering in tiny aerosols that hung in the air for hours. This should have been a clue that airborne transmission was important, but TB was considered exceptional rather than instructive.
The medical establishment looked at the evidence and drew exactly the wrong conclusion. They decided TB was the outlier, not the canary in the coal mine.
This mistake was compounded when they applied what they knew about bacterial transmission to viruses, despite having limited ability to study viruses directly. It was like developing traffic laws based solely on studying trucks while ignoring cars.
The Era of Sealed Buildings
As the droplet theory took hold, our built environment changed to reflect it. Windows that once opened were replaced with sealed panes. Natural ventilation gave way to recirculated air.
The energy crisis of the 1970s accelerated this trend. Buildings became more energy-efficient but also more airtight. We prioritized keeping warm air in and cold air out over keeping fresh air flowing.
HEPA filters, developed during World War II, could have helped, but they were largely forgotten in civilian applications. The technology existed, but the perceived need didn't.
Meanwhile, vaccines and treatments created a false sense of security. We thought we had infectious disease under control, so why worry about something as intangible as air quality?
The Evidence We Couldn't Ignore
By the early 2000s, new technology finally allowed scientists to see what had been invisible before. Viruses like influenza were far more prevalent in tiny aerosols than in larger droplets.
This shouldn't have been surprising. Many respiratory viruses prefer the deep lung tissue where aerosols originate, while bacteria often colonize the upper respiratory tract where droplets form.
The evidence was clear: different pathogens prefer different parts of the respiratory system, creating different transmission patterns.
But institutional inertia is powerful. Despite mounting evidence, healthcare systems and public health agencies remained anchored to outdated models of disease transmission.
It took a global pandemic to finally force a reckoning with the science that had been accumulating for decades.
Seeing the World Through New Eyes
Understanding airborne transmission changes how we see everyday spaces:
A crowded bus isn't just a place where you might touch a contaminated surface; it's a shared air environment that needs proper ventilation.
A restaurant isn't just about clean tables; it's about airflow patterns that can carry viral particles from one table to another.
An office building isn't just a collection of desks and computers; it's a complex air system that can either protect or endanger its occupants.
This knowledge empowers us to make better choices. Is that conference room stuffy? Are there windows that could be opened? Does the building have adequate filtration?
The pandemic forced us to ask these questions. The challenge is making sure we continue to ask them after the immediate crisis passes.
The Simplicity of the Solution
The most powerful solutions are often the simplest.
Florence Nightingale didn't need to understand the molecular structure of pathogens to know that fresh air helped her patients heal. She observed, she acted, and she saved lives.
Today, we have the scientific understanding she lacked. We know why ventilation works: it dilutes and removes airborne pathogens, reducing infection risk.
But knowledge isn't enough if we don't apply it. We need to redesign our buildings, update our HVAC systems, and rethink our approach to shared indoor spaces.
And yes, sometimes we just need to open a window.
The Lessons We Can't Afford to Forget Again
This history of forgetting and remembering carries important lessons:
Simple solutions matter. Sometimes the most effective interventions aren't the most complex or profitable.
Technological limitations shape our understanding. What we can measure influences what we think is important.
Different pathogens behave differently. A one-size-fits-all approach to disease control is bound to have major blind spots.
Institutional knowledge can be lost. Without conscious effort to preserve it, crucial wisdom can disappear between generations.
Changing established practices is difficult. Even with solid evidence, institutional inertia can delay necessary changes for decades.
The story of airborne transmission isn't just about germs and ventilation. It's about how societies learn, forget, and sometimes have to relearn critical knowledge.
As we move forward, we have a choice: We can integrate this rediscovered wisdom into our buildings, our policies, and our daily habits, or we can risk forgetting again once the immediate danger passes.
The air we share has always mattered. The question is whether we'll remember that it does.
Link References
A Fight About Viruses in the Air Is Finally Over. Now It’s Time for Healthy Venting
The 60-Year-Old Scientific Screwup That Helped Covid Kill
All pandemic long, scientists brawled over how the virus spreads. Droplets! No, aerosols! At the heart of the fight was a teensy error with huge consequences.
Links to this Episode
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Links to Heliox
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https://www.youtube.com/channel/UCd5BbCEeC3Z6dp-nNjWRbBw
https://helioxpodcast.substack.com/archive?sort=new
https://episodes.fm/1769969487
https://www.patreon.com/c/HelioxPodcast
STUDY MATERIALS
1. Briefing Document
Airborne Transmission: A Historical Re-evaluation of Healthcare Practices
Briefing Document: Re-evaluating Airborne Transmission in Healthcare
Source: Thread by @1goodtern on Thread Reader App
Main Themes:
Historical Context: From Nightingale to Droplet Theory: The thread traces a historical arc, starting with Florence Nightingale's practical understanding of ventilation in preventing respiratory illnesses, moving through Semmelweis and Lister's focus on contact transmission and hygiene, and culminating in the dominance of droplet theory in modern healthcare.
The Rise and Fall of Aerosol Understanding: Pre-WWII scientists understood that some diseases could spread through airborne particles (aerosols). Post-WWII, research focused on bacteria, which were found predominantly in larger droplets. This led to the widespread adoption of droplet theory, neglecting the significance of aerosol transmission.
The Droplet vs. Aerosol Dichotomy: The thread highlights a critical distinction between droplets and aerosols, emphasizing that they originate in different parts of the respiratory system and carry different types of pathogens. Droplets are produced mainly in the throat and mouth and upper airway, and aerosols are produced mainly in the deep lungs.
Consequences of Neglecting Aerosol Transmission: The dominance of droplet theory has led to inadequate ventilation in healthcare settings, a lack of emphasis on aerosol-intercepting masks, and a general misunderstanding of how viruses like influenza and COVID-19 spread.
The Role of Management vs. Innovation: The thread criticizes the managerial approach to infection control, arguing that a focus on checklists and adherence to outdated guidelines has stifled innovation and prevented the adoption of new scientific findings.
Ignoring Scientific Reality: The author argues that, despite the science around aerosol transmission being ignored, reality will eventually catch up, emphasizing the importance of understanding airborne transmission and implementing effective mitigation measures like masks and ventilation.
Key Ideas and Facts:
Nightingale's Observational Success: Florence Nightingale recognized the importance of ventilation without understanding the underlying science: "She could see with her own eyes that windows closed meant increased risk of infection and windows open meant decreased risk."
Semmelweis and Lister: Hygiene Pioneers: They introduced the concept that doctors themselves could be sources of infection, revolutionizing healthcare through handwashing and surface hygiene.
Pre-WWII Understanding of Aerosols: Scientists demonstrated that diseases could spread through "whatever was floating on its breath," proving airborne transmission.
The Bacteria vs. Virus Misconception: Initial post-WWII research focused on bacterial transmission because it was easier to detect bacteria in droplets than viruses: "At the time, you could have someone cough onto a petri dish, and you could watch the bacteria grow. But you couldn't have someone cough onto a petri dish and watch viruses grow."
TB as an Exception: While bacteria like Scarlet Fever were found mainly in droplets, TB was found in aerosols. However, because TB has a long latency period and was treatable, it was "put aside."
Differential Pathogen Location: "Droplets are produced mainly in the throat and mouth and upper airway... not the lungs. Aerosols are produced mainly in the deep lungs." This difference in origin affects the type of pathogen primarily carried.
More Virus in Aerosols: "There was more virus in the aerosols than the droplets." This is a crucial finding that challenges the dominance of droplet theory for viruses like flu and COVID-19.
The Managerial Bottleneck: "The people who implement infection control aren't the people who are curious. They're managers." This highlights a disconnect between scientific advancements and practical implementation.
Regression and Science Denial: The author laments that "we've also regressed to a position where people don't seem to care about any mode of transmission," leading to science denial on issues like vaccine efficacy and the risks of repeat infection.
Quotes:
"How could some people in healthcare be so obstinately obsessed with droplet transmission while ignoring aerosol transmission?"
"Before WW2, scientists knew that diseases could spread on particles that floated. Airborne particles. Aerosols. Again... what went wrong..."
"There was more virus in the aerosols than the droplets."
"The people who implement infection control aren't the people who are curious. They're managers."
"But the problem about reality is that you can ignore it... but it's bigger than you. And one day it will float by on an indoor air current, and get you."
Implications:
The thread calls for a fundamental re-evaluation of disease transmission in healthcare, advocating for a greater emphasis on aerosol transmission, improved ventilation, the use of effective masks, and a more innovative and scientifically informed approach to infection control. It highlights the dangers of clinging to outdated scientific models and the importance of staying abreast of the latest research in the field.
2. Quiz & Answer Key
Understanding Aerosol Transmission: A Study Guide
Quiz: Short Answer Questions
What was Florence Nightingale's key observation about respiratory illness and ventilation, and how did she address it?
How did Semmelweis and Lister revolutionize healthcare practices, and what was the core principle behind their approach?
Before World War II, what evidence did scientists have regarding the transmission of diseases through the air?
What limitations in scientific technology during the mid-20th century led to an overemphasis on droplet transmission of pathogens?
According to the text, where are droplets primarily produced in the body, and what type of pathogen are they more likely to contain?
According to the text, where are aerosols primarily produced in the body, and what type of pathogen are they more likely to contain?
Why did droplet theory become dominant in healthcare despite earlier evidence supporting airborne transmission?
What is the author's critique of how infection control is managed in healthcare settings today?
According to the author, how do the challenges of Long COVID highlight the issues with current approaches to infection control?
What two practical measures does the author suggest for mitigating the risk of airborne disease transmission?
Quiz: Answer Key
Nightingale observed that people in unventilated rooms were more likely to get sick with respiratory illnesses. She addressed this by opening windows to improve ventilation and reduce the risk of infection.
Semmelweis and Lister introduced the concept of hand and surface hygiene, emphasizing that doctors' bodies and the surrounding environment could be sources of infection. They advocated for washing with soap to remove or kill pathogens.
Scientists had proven that sick animals could infect healthy animals with certain diseases through airborne particles – aerosols – that could float in the air. These experiments used tubes and chambers to prevent droplet transmission.
The ability to detect bacteria in droplets but not viruses in aerosols led to an overemphasis on droplet transmission. Scientists could easily grow bacteria from droplets on petri dishes, influencing their understanding.
Droplets are primarily produced in the throat, mouth, and upper airway. They are more likely to contain bacteria from the upper airway.
Aerosols are primarily produced in the deep lungs. They are more likely to contain viruses replicating in the lower lungs.
Droplet theory became dominant due to a combination of factors: the ease of detecting bacteria in droplets, the success of hand and surface hygiene, and the development of vaccines and treatments, making transmission seem less important.
The author criticizes the managerial approach to infection control, arguing that it focuses on checklists and outdated science rather than innovation and adapting to new research on airborne transmission.
The author states that Long COVID's episodic, persistent, and disabling symptoms are often overlooked. As people ignore science that makes them feel uncomfortable, they can also ignore other science, too.
10. The author suggests wearing a mask that intercepts aerosols and opening windows wide to improve ventilation, echoing Florence Nightingale's approach.
3. Essay Questions
Discuss the historical context surrounding the shift from recognizing airborne transmission to prioritizing droplet transmission in healthcare. What factors contributed to this change, and what were the consequences?
Critique the current management of infection control in healthcare settings, as described by the author. How do managerial approaches potentially hinder the implementation of effective infection prevention strategies?
Analyze the author's argument about the relationship between scientific advancements, public perception, and the willingness to accept or ignore scientific findings. How does this dynamic impact our ability to address public health challenges?
Explore the significance of ventilation and air filtration in mitigating the spread of airborne diseases, drawing upon historical examples and contemporary scientific understanding.
Discuss the public health implications of ignoring or downplaying the risks of aerosol transmission, particularly in the context of emerging infectious diseases and the phenomenon of Long COVID.
4. Glossary of Key Terms
Glossary of Key Terms
Aerosols: Tiny particles that can float in the air for extended periods due to their small size, similar to fog or smoke. They can carry pathogens and transmit diseases through inhalation.
Droplets: Larger particles expelled from the mouth and upper respiratory tract that travel through the air but fall to the ground relatively quickly.
Pathogens: Disease-causing microorganisms, such as bacteria, viruses, or fungi.
Ventilation: The process of circulating fresh air into a space and removing stale or contaminated air.
HEPA Filters: High-Efficiency Particulate Air filters. These are mechanical air filters; they work by forcing air through a fine mesh that traps particles such as pollen, pet dander, dust mites, and tobacco smoke.
Transmission: The method by which a pathogen spreads from one person or source to another. This can occur through direct contact, droplets, aerosols, or other means.
Infection Control: Measures and practices implemented to prevent the spread of infections within healthcare settings and communities.
Mitigation: Actions taken to reduce the severity or impact of a disease or risk factor.
Upper Airway: The parts of the respiratory system that are above the lungs, including the nose, throat, and larynx.
Lower Airway: The parts of the respiratory system that include the lungs, bronchi, and alveoli.
TB (Tuberculosis): An infectious disease usually caused by Mycobacterium tuberculosis (MTB) bacteria. Tuberculosis generally affects the lungs, but can also affect other parts of the body.
Long COVID: Long COVID is a condition characterized by prolonged symptoms that may follow a SARS-CoV-2 infection.
5. Timeline of Main Events
Aerosol vs. Droplet Theory: A History of Transmission Science
1850s: Florence Nightingale observes and acts on the understanding that ventilation reduces respiratory illness in hospitals. She opens windows to improve air quality, understanding its positive effect without a modern understanding of aerosol particles.
Mid-1800s: Semmelweis and Lister revolutionize healthcare with the introduction of hand and surface hygiene, recognizing doctors' bodies as potential sources of infection.
Pre-WW2: Scientists demonstrate that diseases can spread between animals through airborne particles, proving that pathogens can travel by air. The existence of aerosols, particles that float for extended periods, is recognized.
Post-WW2 (1950s-1960s): Research focuses on droplets and particles produced by humans. Bacteria are found primarily in larger droplets, while TB is found in aerosols. Because TB can be treated with antibiotics and is slow to develop, it is not seen as an urgent threat, and droplet theory becomes dominant.
Late 20th Century (1980s onward): Hospitals are designed around the concept of droplet transmission, and healthcare professionals are trained primarily on droplet theory.
Modern Era: Advances in science allow researchers to detect viruses in aerosols, revealing that viruses like influenza and COVID-19 are spread primarily through aerosols from the lower lungs. It is found that aerosols contain more virus than droplets, but droplet theory remains entrenched in healthcare practices.
Recent Times: The COVID-19 pandemic exposes the limitations of droplet theory. There is a rise in TB cases since 2022 after a prominent infectionist states there has been no change in TB cases. Despite scientific advancements, managers in infection control are slow to adopt new understandings, and the public becomes increasingly skeptical of scientific advice.
Cast of Characters
Florence Nightingale: A pioneering figure in nursing and healthcare reform. She emphasized the importance of ventilation and hygiene in hospitals, observing the connection between air quality and the spread of disease.
Semmelweis: A Hungarian physician known for introducing handwashing practices in hospitals to reduce the spread of infection, particularly puerperal fever.
Lister: A British surgeon and a pioneer of antiseptic surgery. He promoted the use of carbolic acid to sterilize surgical instruments and clean wounds, significantly reducing post-operative infections.
Wells: No further information was provided about Wells in the text.
@ukhadds: A Twitter user who shares scientific information about aerosol transmission. He is regarded as a scientist proving incredible stuff about transmission.
@1goodtern: The author of the Twitter thread, an observer and commentator on the history and science of disease transmission, with a focus on the dominance of droplet theory and the neglect of aerosol transmission.
6. FAQ
Aerosol Transmission: A Historical Misstep in Healthcare
1. What is the central argument presented in the thread?
The central argument is that healthcare's overemphasis on droplet transmission, to the neglect of aerosol transmission, is a historical misstep rooted in outdated science and perpetuated by managerial inertia. This has resulted in inadequate preventative measures against airborne diseases like flu and COVID-19, leading to increased risk of infection.
2. How did Florence Nightingale address the spread of respiratory illnesses in the 1850s, and what's the relevance of her approach today?
Florence Nightingale, despite not fully understanding the science of aerosol transmission, recognized the link between poor ventilation and respiratory illness. She advocated for opening windows to improve air circulation. This approach remains relevant today as a simple, effective way to reduce the concentration of airborne pathogens and lower infection risks.
3. What is the key difference between droplet and aerosol transmission, and why does this distinction matter?
Droplets are larger particles that travel short distances before falling to the ground, primarily originating from the upper airway (throat and mouth). Aerosols are much smaller particles that can float in the air for extended periods and travel longer distances, mainly originating from the deep lungs. This distinction matters because viruses like flu and COVID-19 replicate in the lower lungs and are primarily spread through aerosols, meaning interventions focused solely on droplets may be insufficient.
4. How did early scientific research contribute to the focus on droplet transmission, and what limitations existed at the time?
Early post-WW2 research, focusing on bacterial transmission, found that bacteria were predominantly found in larger droplets. The technologies to readily detect viruses in aerosols were not yet developed. This led to the assumption that most respiratory illnesses were spread via droplets. This limitation skewed the focus away from the potentially significant role of aerosol transmission of viral diseases like influenza.
5. Why does the author argue that management practices in healthcare have hindered the adoption of updated scientific understanding of aerosol transmission?
The author contends that healthcare management is often focused on adhering to existing protocols and checklists, rather than embracing new scientific findings. This inertia prevents the implementation of measures that address aerosol transmission, such as improved ventilation and appropriate mask usage. The author contrasts this with the groundbreaking, innovative approaches of historical figures like Semmelweis and Nightingale.
6. How have vaccines and treatments impacted the understanding and prioritization of transmission methods?
The availability of vaccines and treatments for certain diseases led to a decreased emphasis on understanding and preventing their transmission. If effective cures or preventatives exist, the specific mode of transmission became less of a concern. However, for diseases where vaccines are not fully effective or treatments are limited (such as COVID-19), understanding and mitigating transmission becomes crucial.
7. What are some of the consequences of ignoring or downplaying the importance of aerosol transmission?
Ignoring aerosol transmission can lead to inadequate protection against airborne diseases, particularly in poorly ventilated indoor spaces. This can result in increased infection rates and the potential for long-term health complications. It also fosters a disregard for scientific evidence and a reliance on outdated practices.
8. What are some examples of how ignoring science has manifested during and after the COVID-19 pandemic?
The thread argues that people have ignored or dismissed scientific findings related to the limited efficacy of certain vaccines against coronaviruses, the risks associated with repeated COVID-19 infections, and the disabling nature of Long COVID. This selective disregard for science contributes to a broader problem of mistrust and hinders efforts to address public health challenges effectively.
7. Table of Contents with Timestamps
Contents
00:00 - Introduction: "Seriously Cool Science" Brief introduction to the episode's topic on the history of disease transmission, specifically droplet versus aerosol transmission.
00:11 - Credit and Historical Context Acknowledgment of source material and introduction to how ventilation was used before germ theory was fully understood.
00:22 - Florence Nightingale's Observations Discussion of Nightingale's pioneering work in the 1850s, noting how she observed that cramped spaces increased illness and implemented ventilation as a solution.
00:56 - The Shift to Hand Washing Exploration of how Semmelweis and Lister's focus on hand washing and antiseptics shifted attention away from airborne transmission.
01:32 - Droplets vs. Aerosols Explained Definition and distinction between droplets (larger, visible, fall quickly) and aerosols (tiny, invisible, linger in air).
01:47 - Pre-WWII Scientific Understanding Discussion of how scientists before World War II had already demonstrated that particles could remain airborne for extended periods.
02:15 - Post-WWII Research Limitations Explanation of how post-war technological limitations in detecting viruses versus bacteria led to an overemphasis on droplet transmission.
02:46 - The TB Exception Analysis of tuberculosis as a known airborne disease that was treated as an exception rather than evidence of important transmission route.
03:21 - Droplet Theory Dominance Discussion of how the droplet theory shaped infection control protocols for decades.
03:37 - Consequences of Droplet Focus Examination of practical consequences: decreased emphasis on ventilation, closed windows, neglected HEPA filters.
04:10 - Limitations of One-Size-Fits-All Approaches Reflection on how assuming all pathogens spread the same way led to ineffective control measures.
04:26 - Modern Research Revelations Discussion of late 20th/early 21st century research that finally provided evidence of viruses in aerosols.
05:00 - Pathogen Habitat Differences Explanation of how different microbes prefer different locations in the body, affecting their transmission methods.
05:24 - Resistance to Scientific Change Analysis of institutional inertia in healthcare systems despite new evidence.
05:48 - Practical Applications Discussion of how understanding aerosol transmission changes our approach to protection.
06:14 - New Rules, Not Replacement Clarification that hand hygiene remains important, but additional measures are needed for airborne pathogens.
06:29 - Everyday Applications Practical examples of how awareness of aerosol transmission changes evaluation of everyday situations like public transportation.
07:02 - The Power of Knowledge Reflection on how understanding transmission mechanisms empowers better decision-making.
07:18 - Resources for Further Learning Mention of additional sources for listeners interested in learning more.
07:31 - Conclusion Final thoughts on the importance of understanding disease transmission for personal and public health.
8. Index with Timestamps
Aerosols, 01:37, 01:47, 02:37, 04:40, 04:59, 05:11, 05:28, 06:14
Air quality, 03:51, 06:42, 07:02
Airflow, 07:02
Antibiotics, 03:02
Bacteria, 02:31, 02:37, 02:46, 03:10, 04:59, 05:08
Bus example, 06:29, 06:38, 06:42, 06:47
Cigarette smoke comparison, 01:41, 01:47
Contact transmission, 01:19, 03:43
Droplet theory, 01:32, 03:24, 03:37, 05:28
Droplets, 00:05, 01:32, 02:37, 02:46, 03:43, 04:52, 05:08, 06:04, 06:14
Florence Nightingale, 00:22, 00:29, 00:35, 00:44
Flu virus, 04:40
Germ theory, 00:17, 00:35
Hand washing, 01:07, 01:12, 01:19, 01:25, 03:43, 06:04, 06:14, 06:29, 07:54
HEPA filters, 03:56
Hospitals, 00:22
Indoor spaces, 06:58
Infection control, 01:12, 03:24, 05:34
Knowledge importance, 07:02, 07:06, 07:12, 07:44, 07:50
Lister, 01:07
Lung transmission, 05:11
Microbes, 04:14, 05:04
Nightingale, Florence, 00:22, 00:29, 00:35, 00:44
Open windows, 00:44, 00:49, 07:12, 07:54
Pathogens, 02:23, 04:14, 07:37
Pre-WWII research, 01:47, 01:55
Post-WWII research, 02:15, 02:23
Restaurants, 06:58
Semmelweis, 01:07
Smog particles, 02:01
Social distancing, 06:04
Surface cleaning, 03:43
TB (Tuberculosis), 02:46, 02:50, 02:56, 03:02, 03:16
Tech limitations, 02:31, 04:30
Twitter sources, 00:11, 07:24
Upper airway, 05:08
Ventilation, 00:11, 00:17, 00:44, 03:47, 06:42, 07:12
Viral aerosols, 02:01
Viruses, 02:31, 03:10, 04:40, 04:52, 05:11, 06:14
9. Poll
10. Image (3000 x 3000 pixels)
Mind Map
Word Search
( with hints ) The words are hidden in all directions -
horizontal, vertical, diagonal, forward, and backward.
