Disease Transmission Theories
In the second century AD, Galen, a Greek physician to Roman emperors, observed, "When many sicken and die at once, we must look to a single common cause, the air we breathe." Miasma theory, which was prevalent from the Middle Ages to the 1800s, presumed that illness was transmitted by poisonous vapors filled with particles from decomposed matter. The belief in this theory was so strong that even after John Snow demonstrated in 1854 that cholera was waterborne, an official government investigation concluded that the epidemic was caused by vapors from the River Thames.
The concept of airborne transmission of diseases suffered a blow in 1910 when Dr. Charles V. Chapin, a pioneer in US public health practice who had studied accumulated disease transmission theories, came to the following conclusion about airborne transmission of disease: "Without denying the possibility of such infection, it may be fairly affirmed that there is no evidence that it is an appreciable factor in the maintenance of our most common contagious diseases." However, he did concede that, "It is assumed that tuberculosis, as it occurs in human beings, is usually an airborne disease... and there is more reason for such an assumption concerning this than concerning most diseases."
Modern Diseases and Disputes
How respiratory diseases are transmitted and what form of personal protective equipment (PPE) (eg, surgical mask vs respirator) offers sufficient protection against pathogens that can be aerosolized and inhaled are controversial issues. The current debate about respiratory protection has existed at least since the 1994 Centers for Disease Prevention and Control (CDC) recommendation that respiratory protection at least as effective as an N95 respirator be used by healthcare personnel (HCP) providing care for patients with infectious tuberculosis. At the time this guidance was issued, many infection control professionals did not think this level of protection was warranted, despite the fact that in the early 1990s a number of HCP became infected with multidrug-resistant tuberculosis in the workplace, prompting the recommendation. Even today, some infection control professionals do not believe this level of protection is necessary for tuberculosis.
More recently, controversy has arisen about the modes of transmission and appropriate respiratory protection against severe acute respiratory syndrome (SARS), as well as against avian, pandemic, and seasonal influenza. During the 2003 SARS outbreak in Toronto, Canada, 169 HCP became infected with SARS and 2 nurses and a physician died. Infection control professionals in Toronto insisted that SARS was primarily transmitted by large droplets that do not travel far from an infectious person. Therefore, N95 respirators were not initially recommended for HCP working with patients who had SARS and as the outbreak continued, Ontario provincial directives on the use of N95 respirators changed and were not always clear and consistent. After the outbreak, the government of Ontario conducted an investigation about the outbreak.
During interviews for the investigation, some of the Ontario hospital leaders who argued against the use of N95 respirators during the outbreak still contended that more scientific evidence was needed to support the use of respirators for SARS. The final report of the investigation concluded that if there was 1 single take-home message from the outbreak it was that the precautionary principle -- the principle that safety comes first and that reasonable efforts to reduce risk need not await scientific proof -- should be heeded.
In 2009, a new strain of H1N1influenza was detected in California. Because the virulence of the new strain was unknown and because early reports from Mexico suggested that the new strain was causing deaths in young adults, CDC and the California Department of Public Health applied the precautionary principle and recommended that HCP providing care for those with H1N1 use respiratory protection at least as effective as an N95 respirator. Although knowledge about the new strain was still evolving, many state and local health departments subsequently issued their own guidance stating that respirators were not necessary and that surgical masks were sufficient. These state and local recommendations appeared to have less to do with the presumed virulence of the strain than with the belief that influenza virus is not transmitted by inhalation, making respirators unnecessary.
Medscape Infectious Diseases © 2011
Cite this: Kathleen H. Harriman, Lisa M. Brosseau. Controversy: Respiratory Protection for Healthcare Workers - Medscape - Apr 28, 2011.