Tag Archives: Viruses

Covid-19 Review: Airborne Transmission Of Viruses

In a very good article, the Journal ‘Science’ has collated a lot of basic science regarding aerosol transmissions in viral infection generally, and Covid-19 in particular.

Click here to read article in Science Magazine

Early in the epidemic, I thought that large droplet transmission, which fell to the floor, and was transmitted by fomites and hand autoinoculation into the respiratory membranes, was more important. The main thesis of the article is that it is not large droplets, but aerosol particles that mainly transmit.

The secondary assertion is that aerosols can be up to 100 µm microns in diameter and still be transmitted by inhalation. they also stated that particle size of equal or less than 5 µm contain more virus particles than all the larger particles put together in spite of the greater mass of the larger particles . Normal speaking creates about 1000 aerosol particles per minute, And normal breathing about 7200 aerosol particles per liter of exhaled  air. Coughing is more sporadic and tends to produce the larger droplets which don’t stay airborne as long, but I wouldn’t count on it.  

There is a tremendous difference between individuals as to the number of particles they generate. It’s estimated that 10 to 20% of individuals account for 80 to 90% of the virus.

Slide number two  deals with viral load and infectivity which is a function of the pH value, electrical charge, and other characteristics of the virus. An important point is that even though there is lots of viral RNA, that doesn’t mean that the virus is infective. Once again there’s a tremendous difference between the infective viable virus content of the aerosols from infected patient to patient. He stated that in one room with two Covid patients, they were 6 to 74 TCID/50 per liter, which means you’re almost certain to be infected if you don’t have a mask that filters out the virus, or some kind of purification in the room.

Slide Three was very interesting to me. The persistence  in hours graphed against the aerosol particles size. 100 µm particles stay in the air only about five seconds, 5 µm particles stay in the air for 30 minutes, and one micrometer particles will stay in the air for 12 hours or more.

The fourth slide talks about factors affecting the distribution of indoor aerosols. There may be certain parts of the room where the particles congregate , depending on the ventilation type, whether natural, mechanical or filtered, flow patterns within the room, and indoor filtration and killing devices such as ultraviolet light.

Mention is made of the CO2 level in the room as a measure of air circulation. There is a higher CO2 in the air with lots of people and poor ventilation. The recommendation is that 7-8 ppm is about the highest acceptable level, and the possibility of using a portable HEPA filter would not be a bad idea for people frequenting indoor restaurants. Of course, outdoor air with its breezes, dispersion, less humidity, higher ultraviolet and usually Greater dispersion of people is preferable to indoor contact.

Some other interesting points are that children produce less aerosol particles because they have a smaller number of bronchi. I thought the bacteria were less likely to be aerosol transmitted than viruses, but they state that the R0 of tuberculosis can be as high as 4.3, vs. 7-8 for covid. The typical tuberculosis bacillus is relatively large, and yet is only 2 µm in length, well within the size of an aerosol particle.

–Dr. C


The common cold is the most common human disease in the world. So, why haven’t we found a cure yet?!

Called human rhinoviruses, these respiratory viruses measure between 15 to 30 nanometers in diameter, making them some of the smallest types of viruses out there. And it’s partly thanks to the viruses’ genetic makeup that they’re so good at replicating.

Human rhinoviruses travel like most other respiratory viruses via nasal secretions, which can be released through sneezing, or through contact with fomites, which are surfaces like a keyboard or a doorknob that can help spread the virus from one person to another. From there, all it takes is for a hand to touch one of the body’s mucous membranes like the eyes, nose, or mouth and bam — the virus has gained entry.

Soon after infection, coughing, sneezing, headaches, a mild fever and body aches can soon follow. And these symptoms may easily be confused with those of the flu. But unlike the flu, where symptoms start quite suddenly, it can take a couple of days for cold symptoms to fully develop. And they usually last anywhere from 7 to 14 days.


The skin is the protective barrier between the inside of our bodies and the outside world of microorganisms, parasites and toxins. It is often the site of inflammation and infections.

In past times, before the advent of cleanliness and antibiotics, mankind was plagued by erysipelas, boils, carbuncles, and other severe infections of the skin, which are rarely seen now. The beta hemolytic streptococcus and Staphylococcus aureus were ubiquitous in the past, and mostly are contained today.

Severe Infections presently require some skin abnormality, immune deficiency, neglect, animal bite or other breach of skin integrity to be a problem. Antibiotic resistance, however, is allowing some organisms like MERSA to make a comeback.

ECZEMA. or Atopic Dermatitis, was common in my medical practice. This condition weakens the skin barrier, allowing Staphylococcal infection to gain a foothold. In my day, If there were a flare of eczema severity, antibiotics would often help. Leg edema and swelling. such as from heart failure, especially coupled with diabetes and blood vessel disease is also an invitation to infection, such as cellulitis.

Redness, swelling, warmth and pain- the classic rubor, tumor, calor and dolor- as well as swollen local lymph nodes and fever often betray infection of the skin. Please see the recently posted infographic on celulitis.

IMMUNE DEFICIENCY raises the likelihood and risk of severe skin infections. Infection from “flesh-eating bacteria”, often beta hemolytic streptococci in deep tissue planes , is a medical emergency. Immediate surgery is often needed.

Disproportionate PAIN after injury or surgery is often a clue. Certain age groups have characteristic skin infections, such as the scalded skin syndrome of infants, and the acne of adolescents. Viruses, molds, and arthropods can also infect the skin.

Viruses, such as herpes in particular can simulate bacterial infection. Ringworm from fungi is easy to distinguish, but arthropod bites, and especially bee sting can look very much like bacterial infection. Scabies and mite infestation are so itchy as to be distinct.

Topical antibiotics applied on skin breaks like cuts or breaks are useful in preventing infection. These ointments and creams are like “artificial skin”. Once again, prevention is key.

–Dr. C.


It’s one of the tiniest machines on the planet — about a hundred times smaller than the average cell. It’s so small that no scientist can spot it through a typical light microscope. Only with an electron microscope can we see its spiky surface. It’s not alive, and it’s not what most of us would think of as “dead.” This teensy machine seems to survive in a kind of purgatory state, yet it has traveled across continents and oceans from host to host, and brought hundreds of nations to a standstill. Despite its diminutive size, the novel coronavirus, dubbed SARS-CoV-2, has seemingly taken the world by surprise with its virulence.