DISEASE TRANSMISSION THROUGH AN AIRBORNE ROUTE

The potential routes for the spread of infection in a dental office are direct contact with body fluids of an infected patient, contact with environmental surfaces or instruments that have been contaminated by the patient and contact with infectious particles from the patient that have become airborne.¹ There is a long history of infections that have been transmitted by an airborne route. Even before the discovery of specific infectious agents such as bacteria and viruses, the potential of infection by the airborne route was recognized. In historical reports of the bubonic plague—the “black plague”—the pneumonic form of the disease was recognized as the most deadly. Historical accounts have noted that the pneumonic form of the plague, characterized by severe coughing, has been spread from patients who had the pneumonic form of plague to those who surrounded the patient but were not necessarily in direct contact. Apparently, because the bacteria that cause plague (Yersinia pestis) were inhaled, the pneumonic form of the disease was reported to progress more rapidly than other forms of plague, and historical reports indicate that it was almost universally fatal.²

There are more recent examples of the spread of disease by an airborne route. In one published report, a number of people were exposed to tuberculosis, or TB, while on a commercial airline flight. A patient with active TB boarded an airplane in Chicago en route to Honolulu. During the flight, the patient coughed repeatedly, aerosolizing the tubercle bacillus, which then entered the airplane's ventilation system and subsequently spread to other parts of the airplane cabin. After it was confirmed that the patient had active TB, it was determined that 15 of the 55 passengers in the cabin who were tested had been exposed to TB, as confirmed by a positive tuberculin test. Passengers seated within two rows of the source patient had a higher probability of a positive skin test than did those seated elsewhere in the cabin.³

Another published example occurred in a medical office where the measles virus was spread through the ventilation system to multiple people. The source patient was a 12-year-old boy who was coughing. Of the seven people who had secondary cases of measles that were associated with him, three were never in the same room with the source patient and one entered the office an hour after he had left.⁴

More common is the apparent spread of cold and influenza viruses by airborne routes. However, the actual documentation of an airborne route for transmission of cold and influenza viruses is difficult to verify. Because cold and flu viruses can be transmitted by contact, contaminated objects and an airborne route, in a flu outbreak it often is difficult to know the exact route by which the virus is transferred.

SARS recently has been reported in China, Canada and other countries. This severe flulike illness appears to be caused by a new form of coronavirus, a family of viruses usually associated with the common cold. The exact mechanisms by which SARS is spread remains uncertain, but it is clear that the primary method is through aerosolized droplets produced by coughing or other means. In a Hong Kong apartment complex outbreak, it appeared that the disease may have been spread through ventilation systems by airborne viruses that were independent of larger droplets.⁵ The Centers for Disease Control and Prevention, or CDC, and the ADA have recommended that aerosol-producing procedures should be avoided in patients with active SARS. The ADA has pointed out that it is unlikely that any dental treatment will be performed on a patient with active SARS, owing to the fact that these patients are extremely ill and should not undergo any elective procedures.^{6, 7}

^{Continued in Part 3...} 

^{Citation: Harrel, S. K., & Molinari, J. (2004). Aerosols and splatter in dentistry: a brief review of the literature and infection control implications. Journal of the American Dental Association (1939), 135(4), 429–437. https://doi.org/10.14219/jada.archive.2004.0207}