In many ways, COVID-19 has defied conventional medical understanding. Chief among its distinctions is a poor comprehension of how exactly it spreads. Sure, it spread in the air—but is it spread via respiratory droplets or aerosolization? The jury is still out, and experts have hypothesized that both modes of respiratory transmission may play a role. Without knowing how COVID-19 spreads, it’s impossible to ascertain just how far a distance the virus can travel. Dangerous as it is, however, COVID-19 isn’t the only infectious respiratory illness that we need to be wary of.
We’d like to take a closer look at some other dangerous diseases you can contract by simply breathing.
Respiratory droplets vs aerosolization
Before looking at the spread of other pathogens by respiration, a quick review of respiratory droplet spread vs aerosolization may be warranted.
Respiratory infections are spread via droplets of different sizes, with those > 5-10 μm in diameter referred to as respiratory droplets. Those < 5μm in diameter are called droplet nuclei. Droplet transmission transpires when an infected person respires within 1 m of somebody who is not sick. Transmission can occur through mucus membranes or fomite exposure. A person who touches a fomite and then touches the eyes or other mucus membrane can facilitate spread.
On the other hand, airborne transmission occurs by means of droplet nuclei, which linger in air for longer periods of time. For instance, the WHO hypothesizes that—based on current research—COVID-19 is mostly spread via respiratory droplets and contact routes, but it leaves the door open to aerosolization with respect to aerosolization-producing procedures, such as bronchoscopy, endotracheal intubation, open suctioning, and nebulization.
Although many of the same precautions are used in cases of respiratory droplet and airborne transmission, certain distinctions exist, according to the CDC. For instance, with airborne precautions, N95 or higher level respirators for healthcare personnel should be used. Furthermore, unlike with respiratory precautions—where a patient should isolate to a single room—with airborne precautions, the room should be a specially built airborne infection isolation room (AIIR). Moreover, healthcare worker exposure to aerosolized disease should occur only if absolutely necessary, with all exposed staff immunized. In all cases of respiratory transmission, patient transport should be limited.
To put it mildly, measles is a doozy. Its spread is airborne, and the virus can live in the air for up to 2 hours where someone with the infection has coughed or sneezed. Measles is so infectious that if a person is not immunized, the odds of being infected on exposure is 90%. To make matters worse, infected individuals can be contagious to others from 4 days before through 4 days after the characteristic rash appears. (And, if you’re wondering, measles infects only humans, not animals.)
To put the infectivity of measles in perspective, its R0 value, which can be defined as the number of secondary cases that one case would beget in a susceptible population, ranges between 3.7–203.3. In other words, in certain contexts, one person could potentially infect scores of unvaccinated or undervaccinated others. This exact nightmare scenario happened in late 2014 through early 2015 at the Disney theme parks in California, where 125 people were infected with measles.
Shingles isn’t spread from person to person, but on exposure to someone with shingles, the varicella virus is transmissible, thus leading to chickenpox. With localized shingles—confined to primary or adjacent dermatomes—transmission occurs on direct contact. Only after the lesions have crusted over is the disease no longer transmittable. However, with disseminated shingles, airborne precautions must be taken.
Only healthcare workers who have evidence of immunity (ie, vaccination) should be exposed to those with shingles.
Haemophilus influenzae can cause various types of disease including pneumonia, epiglottitis, meningitis, bacteremia, septic arthritis, otitis media, cellulitis, and purulent pericarditis, as well as endocarditis and osteomyelitis. Transmission of this infection occurs by means of respiratory droplets expired by a nasopharyngeal carrier. In neonates, exposure can occur by means of exposure to amniotic fluids or with genital tract secretions.
Avian influenza virus hits wild populations of aquatic birds hard, and outbreaks can occasionally occur in domestic poultry, which can spread to humans who work with poultry. From a public-health perspective, such outbreaks are concerning because of their pandemic potential.
The CDC recommends that people with potential exposure monitor their health for signs/symptoms 10 days post-exposure, and to notify the health department if illness develops. In addition to standard and contact precautions, airborne precautions should also be taken with respect to avian influenza. It’s best to isolate patients with avian influenza in AIIRs, but if not available, a private room should be used. Antiviral treatment should also be initiated in those with symptoms, which typically resemble uncomplicated upper respiratory infection or influenza.
Severe acute respiratory syndrome (SARS), also known as SARS-associated coronavirus (SARS-CoV), typically starts with a high fever followed by headache, discomfort, body aches, and mild respiratory symptoms. Between 10% and 20% of those infected with the virus develop diarrhea, and between 2 and 7 days, some develop a dry cough. Most patients develop pneumonia.
Compared with its epidemiologic cousin COVID-19, SARS has done a lot less damage globally. During the 2003 outbreak, 8,098 people fell ill globally, with 774 dying. Only eight Americans were infected during this outbreak, all of whom had a history of overseas travel.
According to the CDC, SARS typically spreads by close person-to-person contact. Droplet spread is most likely, although aerosolization may be possible. It can also be spread via fomites. Although deadlier than COVID-19, SARS is less transmissible. The CDC focuses on close contact being of concern with respect to the transmission of SARS.
“In the context of SARS, close contact means having cared for or lived with someone with SARS or having direct contact with respiratory secretions or body fluids of a patient with SARS. Examples of close contact include kissing or hugging, sharing eating or drinking utensils, talking to someone within 3 feet, and touching someone directly. Close contact does not include activities like walking by a person or briefly sitting across a waiting room or office,” notes the CDC.