Airborne transmission

Tiny bits can float in the air.

They come from a sneeze or a cough. They can also come from talking. These bits can stay in the air for a long time. They can even travel a long way.

We breathe these bits in through our nose or mouth. This can make us or animals sick. We can help stay safe by using masks. Good air flow in a room also helps. Being careful helps keep everyone healthy.

Some germs can travel through the air. This is called airborne transmission.

These germs move in tiny bits. We call these bits aerosols. They can also move in larger droplets.

People make these bits when they breathe, talk, cough, or sneeze. Some bits are very large. They usually fall to the ground within 2 meters. Other bits are much smaller. These small aerosols can stay in the air for a long time. They can even travel a long distances. For example, a sneeze can throw droplets many meters away.

When we breathe, these bits enter our nose or throat. They can then reach our lungs. This can make people or animals sick. Many diseases spread this way, like measles or chickenpox.

We can use ways to stay safe. Wearing a mask helps block the bits. Some masks, like N95 respirators, work best for small aerosols.

Good air flow also helps. Using fans or filters can clean the air in a room. This keeps the germs from staying in one place.

Some germs move through the air to find new people or animals. This is called airborne transmission.

These germs can be viruses, bacteria, or fungi. They travel in tiny bits called aerosols or in larger droplets. People create these bits when they talk, cough, or sneeze. They also happen when people raise dust or flush toilets. These small particles can stay floating in the air for a long time. This allows them to travel much farther than larger droplets.

How these bits move depends on their size. Large droplets are bigger than 100 micrometers. These usually fall to the ground within 2 meters. Smaller particles can stay suspended in air currents. A sneeze can project these droplets for ten meters or more. Some bits are about 20 micrometers in size. These travel with air from coughs or air conditioning. They act like aerosols but eventually fall due to gravity. These particles can enter the nose, throat, or lungs. Once inside, they can spread through the whole body.

Scientists study many different diseases that use this path. Some infections only spread through aerosols, which are called obligate infections. Tuberculosis is a well-known example of this type. Other diseases are preferential, like chickenpox. This means they can use different paths but mostly use aerosols. Some diseases are opportunistic, like the influenza virus. This means they usually use other paths but can use aerosols in certain conditions. Even animals can get sick this way. Newcastle disease is an airborne disease that affects poultry worldwide.

Many factors change how well these germs spread. The weather and the room environment matter a lot. Temperature and relative humidity are very important. If humidity is below 35%, viruses can stay in the air longer. The CDC suggests keeping indoor humidity between 40% and 60%. Wind, air pollution, and even solar radiation can play a role. In cities, diseases might spread faster than in rural areas. Crowded rooms and poor ventilation also make it easier for germs to move.

We can use many layers of protection to stay safe. One way is to wear a face mask. Surgical masks help with large droplets. However, smaller aerosols need special masks like N95 or FFP3 respirators. Another way is to improve the air in a room. Good ventilation and air filters can remove germs. This is an engineering solution that helps everyone in a space. We can also use vaccines to help our bodies fight germs. Following good hygiene and staying apart from sick people also helps lower the risk.

Airborne transmission occurs when infectious diseases spread through small particles suspended in the air. These particles can be viruses, bacteria, or fungi. This method of spread is a major concern in both human and veterinary medicine.

When an infected person breathes, talks, coughs, or sneezes, they release these particles into the environment. Other activities, such as raising dust or flushing toilets, can also generate infectious aerosols. These pathogens typically enter a new host through the nose, throat, sinuses, or lungs. Once inhaled, the microbes can affect the respiratory system and spread throughout the body.

Scientists used to distinguish between respiratory droplets and aerosols, but that distinction is no longer used. Instead, particles exist on a continuum of sizes. The fate of a particle depends on its initial size and environmental conditions. Larger droplets, which are greater than 100 micrometers, usually settle on the ground within 2 meters. Smaller particles can remain suspended in air currents for much longer periods. Particles in the 20 micrometer range are particularly interesting. They initially travel with airflows from coughs or air conditioning like aerosols. However, they eventually fall due to gravity, acting as "jet riders."

Different diseases use airborne transmission in different ways. Some are classified as obligate airborne infections. These spread only through aerosols, such as tuberculosis. Others are considered preferential airborne infections. These can use different routes but mainly rely on aerosols, like the chickenpox virus. Finally, some are opportunistic airborne infections. These typically use other modes of transmission but can spread via aerosols under favorable conditions, such as the influenza virus. Some pathogens are also anisotropic. This means their different modes of transmission can cause different types of diseases or varying levels of severity. For example, Yersinia pestis and Francisella tularensis can cause severe pneumonia when inhaled.

Environmental factors heavily influence how effectively these diseases spread. Temperature and relative humidity (RH) are among the most important factors. Relative humidity affects how quickly droplets evaporate. For instance, a 30 micrometer droplet can evaporate in seconds. If the relative humidity falls below 35%, infectious viruses may stay in the air longer. The CDC recommends maintaining indoor humidity between 40% and 60% to reduce viral infectivity. Other factors include wind, air pollution, and solar radiation. Even geographic details like latitude, altitude, and proximity to large bodies of water can be relevant to how diseases move.

Human environments and behaviors also play a significant role. Poor ventilation allows aerosols to spread undisturbed in indoor spaces. Crowded rooms increase the likelihood of encountering an infected person. In cities, airborne diseases often spread more rapidly than in rural areas. Interestingly, rural areas may favor higher airborne fungal dissemination. During the COVID-19 pandemic, researchers noted a direct link between insufficient ventilation and increased transmission. While increasing air changes per hour is helpful, understanding specific airflow patterns is even more crucial for safety.

To manage these risks, experts use a layered approach. This involves multiple levels of intervention to reduce the chance of infection. Individual actions include wearing masks and practicing good hand hygiene. Institutional measures include surface disinfection, improved ventilation, and air filtration. At the medical level, vaccination is a key tool. Public health measures include testing, contact tracing, and quarantine. Using multiple layers ensures that if one method fails, others are still in place to protect people.

Engineering solutions are considered higher on the hierarchy of control than personal protective equipment (PPE). These include high-efficiency particulate filters and effective ventilation systems. Portable air filters can be a useful solution when existing ventilation is inadequate. When using masks, the type of mask must match the particle size. Fluid-resistant surgical masks can prevent the inhalation of large droplets. However, smaller aerosols require high-level filtration masks, such as N95 respirators in the US or FFP3 respirators in the EU. Using these specialized masks has been shown to reduce infection rates among healthcare staff.