Airborne Diseases

Airborne diseases refers to the grouping term for those human diseases that are caused by organisms that can be transmitted by the air (airborne transmission). This is an important environmental aspect for the global public health that should be considered in the new perspective of creating a more ecological green world, where such environmental threats should be significantly reduced or even eliminated. There are many diseases that can additionally be transmitted by other ways, such as blood-borne, vertical, or congenital methods. Airborne transmission occurs when droplet nuclei (evaporated droplets) less than 5 μm in size are disseminated in the air. These droplet nuclei can remain suspended in the air for some time. Droplet nuclei are the residuals of droplets, and when suspended in the air, they dry and produce particles ranging in size from 1 to 5 μm. Diseases spread by this mode include open/active pulmonary tuberculosis (TB) (due to Mycobacterium tuberculosis), measles, chicken pox (varicella-zoster virus, VZV), pulmonary plague (Yersinia pestis), and hemorrhagic fevers such as Lassa fever.

Droplet transmission occurs when there is adequate contact between the mucous membranes of the nose and mouth or conjunctivae of a susceptible person and large particle droplets (>5 μm). Droplets are usually generated by the infected person during coughing, sneezing, or talking, or when healthcare workers perform procedures such as tracheal suctioning. Diseases transmitted by this route include pneumonias (bacteria), pertussis (Bordetella pertussis), diphtheria (Corynebacterium diphteriae), severe acute respiratory syndrome (SARS) (coronavirus, SARS-CoV), influenza, mumps, and meningitis (bacteria).

In the case of tuberculosis, infection with the tubercle bacillus is usually by direct airborne transmission from person to person. For measles, which is a highly contagious infection, transmission is primarily by large respiratory droplets, increasing during the late winter and early spring in temperate climates, and after the rainy season in tropical climates. In varicella, or chicken pox, transmission is via droplets, aerosol, or direct contact, and patients are usually contagious from a few days before rash onset until the rash has crusted over. In the case of pulmonary plague, direct person-to-person transmission does occur when respiratory droplets may transfer the infection from the patient to others in close contact, but this is considered an exception. Plague is a zoonotic disease affecting rodents and is usually transmitted by fleas from rodents to other animals and to humans. Lassa fever virus is carried by rodents and transmitted by excreta, either as aerosols or by direct contact.

On the other hand, diseases such as pertussis (whooping cough), a highly contagious acute bacterial disease involving the respiratory tract and caused by Bordetella pertussis, is transmitted by direct contact with airborne discharges from the respiratory mucous membranes of infected persons. In the case of diphtheria, transmission is from person to person through droplets and close physical contact. For SARS, transmission of SARS-CoV is primarily from person to person. Its transmission to noninfected hosts apparently occurs mainly during the second week of illness, which corresponds to the peak of virus excretion in respiratory secretions and stool, and when cases with severe disease start to deteriorate clinically. Most cases of human-to-human transmission have occurred in the healthcare setting, in the absence of adequate infection-control precautions. In the case of influenza, respiratory transmission occurs mainly by droplets disseminated by unprotected coughs and sneezes. Short-distance airborne transmission of influenza viruses may occur, particularly in crowded enclosed spaces. Hand contamination and direct inoculation of virus is another possible source of transmission. For mumps, transmission occurs as in measles, as a consequence of respiratory droplets.

...