Catching airborne diseases: 8 culprits

As outbreaks of airbourne diseases become more frequent, what are the main causes?

Outbreaks of influenza, SARS, Norovirus and Ebola virus have recently brought airborne diseases into the limelight. Some cases can affect hundreds of people in small areas, such as the outbreak of Norovirus at The Southport School on the Gold Coast

Now, thanks to new research, we have a better understanding of how tiny particles transport infection.

Microscopic particles – such as dust, water droplets and pollen – can transport bacteria, viruses and fungal spores that cause a wide range of diseases in humans and animals. Too small to be seen by the human eye, they float through the air and are carried on currents, outside buildings, inside ventilation systems, and around sewerage and drainage. When you breathe them in, they get trapped in the mucus membranes in your mouth, nose, throat or lungs, and that’s where the trouble begins.

Here we take a look at the ways infectious particles become airborne.

1. Breathing

We usually worry about people coughing their germs over us but, in fact, the simple act of breathing is also cause for concern. While each cough produces more virus particles than a breath, we exhale more often than we cough – so breathing spreads more infectious particles than coughing. However, a breath won’t carry the culprits as far, and the degree of risk depends on:

*  The distance from the infected person.

*  The time spent in their vicinity.

*  How infectious the person is.

*  The airflow.

*  The type of bacteria or virus.

2. Coughing and sneezing

High-speed airflow through the lungs, throat, nose and mouth – like a cough or a sneeze – projects mucus and saliva particles as well as ‘gas clouds’ made up of even more minute particles. MIT researchers found that droplets in these clouds can travel 5–200 times further than previously thought, while a study by Wake Forest Medical Center discovered ‘super spreaders’ who produce 32 times more viruses than ordinary folk.

When you cover your mouth to protect people in your vicinity, remember to sneeze or cough into a tissue, handkerchief or your elbow, so you don’t unconsciously transmit those very germs you’re worried about via your hand.

3. Vomiting

Beware of particles spread by mild (non-projectile) vomiting. A study of a Norovirus outbreak found that some restaurant diners developed acute gastroenteritis after another patron had vomited. They determined the infection was airborne because none of the diners came into contact with the vomit, and the rate of infection decreased in line with the distance from the table: 91% at the same table, 71% and 56% at two adjacent tables, and lower rates further away.

4. Toilet flush

As far back as 1907, the risk of airborne disease transmission from toilets was evident. Research shows that a flushing a toilet can create a 'toilet sneeze effect' which can contaminate the air with several types of bacteria and viruses, including:

*  E. coli.

*  Salmonella.

*  Norovirus.

*  Influenza.

5. Drainage systems

Infections can also move between apartments through shared sewerage systems and be dispersed through the air to neighbouring buildings. The 2003 Hong Kong SARS outbreak was traced to airborne particles originating in the sanitary system in an apartment complex where an infected visitor with diarrhoea used a toilet. It’s believed exhaust fans drew particles through the apartments’ bathroom floor drains and some must have been expelled outside, because people in nearby buildings were also infected.

6. Dust particles

Very tiny particles of dust never settle and can effectively float in still air forever. Many activities and even general maintenance, like sweeping and cleaning, can generate dust. Among the many types of dust in the natural and human environment, some particles can cause a variety of health problems, while infestations of birds and rodents can cause a build-up of material with hazardous microorganisms, such as Salmonella and Leptospira, which can become airborne when disturbed.

7. Hospitals

Patients in hospitals – and especially those in operating theatres and intensive care units – are extremely vulnerable to infections, while those with infectious diseases or injuries have impaired immune systems which make them more susceptible to disease-carrying microorganisms than healthy people. Also, hospitals are often home to pathogens that you don’t generally find in homes, workplaces or public areas.

Diseases can be spread in a variety of ways in hospitals – for example, personnel and patients release aerosols, bed linen and clothing can become contaminated, and even dust on mobile surgery lamps can carry Staph strains. Studies show that the number of airborne particles in operating theatres is related to the number of people present, their movement, and the opening and closing of doors.

8. Fungal spores

Fungal spores are found in both indoor and outdoor environments and can be small enough to be dispersed by air currents and inhaled into the lungs. Under normal conditions, healthy people are unlikely to be affected by them, however, a concentration of some species can increase the risk of infection or an allergic reaction causing asthma.

Fungi feed on organic matter, such as soil in potted plants, or in products in wet or damp conditions in buildings, such as bathroom fixtures or walls. Ground seepage, roof leaks and poorly maintained plumbing and drainage can create the kind of damp that encourages fungi to grow.

Armed with more information, we are now in a better position to stop the spread of airborne diseases. A good start is to undertake regular maintenance and cleaning regimes, as well as looking into air sterilising and odour eliminating products that will help prevent the spread of disease.

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5th February 2018
Tania Dalton, Research & Innovation, Initial Hygiene
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