SARS was a classic emerging infectious disease that quickly spread across the world. This resulted in an awakening of the Western world as to its vulnerability to emerging infectious diseases. The corona virus (CoV) family is the agent responsible for SARS. These viruses were historically
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Protective Equipment for Health Care Workers 43
noted as agents that were responsible for the common cold, along with other viruses (e.g., rhino viruses). The CoV SARS emerged in November 2003 in the Guangdong Province of southern China, although it appears to have been known as early as July 2003.5 It is likely that this virus existed in a milder form for many years and mutated to a virulent strain.6 Such occurrences are not usual and have been best illustrated by influenza outbreaks, most notably those of 1918, 1957, and 1968. SARS made worldwide headlines 7 and demonstrated how fast an infectious agent can spread, even from isolated locations in the world. The last reported case occurred in April 2004, and it was as a result of a laboratory accident.
A high infection and mortality rate became the hallmark of SARS.
What also became apparent from SARS is the vulnerability of those in the health care industry to emerging diseases.8 It was reported that healthcare workers were between 20 and 80% of SARS cases,9 which makes them one of the groups most vulnerable to emerging diseases, especially since they will see the first case of a disease well before any outbreak is recognized. This is best illustrated by the death of Dr. Carlo Urbani, who first identified the disease in Vietnam and later died from this agent through occupational transmission. Some have suggested that the disease should even be named in his honor. Overall healthcare workers also have higher risks for other hazards, such as injuries, along with the more traditional infectious diseases,10 making this population particularly vulnerable. Risks from infectious disease become of even greater importance when they are superspreaders, those that can result in multiple secondary cases of the disease from a single source contact (e.g., transmission to large numbers of people), as occurred with SARS.11 SARS has become a class example of a superspreader.
Initially it was thought that the SARS CoV was not spread by respiratory transmission, but it has later been shown to be transmittable by this route.12 Thus, as with many respiratory viruses, SARS can be spread from person to person by droplet along with other airborne routes (e.g., nebulization).13 This demonstrates that precautions for all routes of transmission must be considered for emerging infectious diseases.
Many of the cases of SARS in healthcare workers have been attributed to the lack or poor use of respiratory and personal protective equipment (PPE).14, Studies on SARS reported an infection rate ranging from about 2 to 25% even when precautionary measures were taken (Table 3.1).
It has been known for some time, even before the SARS event, that bioaerosols can be generated through a number of mechanisms. These mechanisms include: exhalation droplets (coughing, sneezing, shouting, or talking), medical procedures (e.g., nebulization), fomite transmission, and body wastes (e.g., feces).23 The higher the exhalation velocity the smaller the particles and the larger the number being formed, and
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44 Emerging Infectious Diseases
Table 3.1 Studies on SARS CoV Infection in Healthcare Workers Using N95 Respiratory Protection as Well as Other PPEa,b
Location
Infection
Rate^ Comments
Singapore15 ~4% HCW had the highest % infection rate of any group. Recommended using powered-air purifying respirator (PAPR) along with other PPE. Besides use of an N95, other types of PPE were not identified. HCW in low-risk areas were given surgical masks.
Hong Kong16 ~4% All infected workers used a N95 respirator, but did not constantly use other PPE.a Eye shields were used. In high-risk areas, some PPE was used more than once by the HCW. Study reports that surgical masks are not protective. Personnel in low-risk areas contracted SARS.
Singapore17 (Hsu et al., 2003)
5% Contact cases resulted from an index patient.
After initiating infection controlb no further transmission occurred from index patient.
Hong Kong 18 (Li et al., 2003)
~2% Strict infection control required.a Fit testing was not mentioned. Spot checks were conducted to ensure compliance. Type of mask used was not described.
Canada19 (Scales et al.,
2003)
17% Contact casesb resulted from an index patient.
A higher rate (30%) of infection for HCW from the index patient was reported for those using a surgical mask.
Hong Kong20 (Tsui et al., 2003)
~25% Study reportsc that “precautions could not prevent all HCW from contracting SARS”. Eye shields were used instead of goggles.
percentage age represents total HCW infection rate.
Hong Kong21 (Seto et al., 2003)
~5% No HCW was infected that used all PPE.
Thirteen that omitted using one type of PPE became infected. Study reported that N95 respirators and surgical masks to be effective in prevention, but not paper masks.
Note: All studies reported initiating infection control, including hand washing.
Studies reported are for populations and case reports on a single or limited number of individuals.
a PPE included N95 respirator, goggles or eye protection, gowns, and gloves.
b PPE included N95 respirator (unless noted), gowns, and gloves.
c % healthcare workers who were reported to be infected by occupational exposure.
From Lange, 2005a, with permission from the Chinese Medical Association.22
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Protective Equipment for Health Care Workers 45
generally this will result in the particles remaining suspended in the air for a longer period of time.24 Even large particles can dry out and thereby be reduced in size, as well as resuspension of particles that have been deposited on surfaces.
The mortality rate from this virus was about 10%, with many of these deaths occurring in healthcare personnel.25 Some have suggested that if proper PPE, including respirators, were employed by healthcare workers the number of cases in this group would have been diminished.26 This is supported by the suggestion that the attack rate for SARS is higher for healthcare personnel than for inpatients.27 An increased attack rate for healthcare workers is suggested as resulting from their close proximity to patients. In many cases the cause of SARS in healthcare workers can be directly traced to the aerolization of virus through nebulizers or similar equipment with cessation of use resulting in a reduction of cases.28 Aerosolization appears to be a major hazard for many organisms that can be transmitted from person to person (Koley, 2003).29
Other forms of person to person transmission not involving neubulizers could be responsible, and appear to have also occurred.30 However, with any new disease, there is a learning curve and other practical consider- ations that must first be identified before preventative measures can be fully realized. This was certainly the case for SARS CoV, and these events provide us with a valuable lesson in handling future disease events of this nature.
Infectious dose is a big question for any emerging infectious disease.
For SARS the infectious dose has not yet been estimated or clearly evaluated. Studies have reported that some infectious disease agents have an infectious dose of one organism (e.g., smallpox, tuberculosis). 31 How- ever, others require more than one organism (e.g., Yersinia pestis) for initiating an infection (pneumonic plague, also called black or bubonic plague). Using a published one-hit type model,32 it was estimated that there is a 7.7% risk of infection for one hour of exposure to an organism such as tuberculosis. Since infection rates for SARS have been reported to be 2 to 25%, and in some cases even higher using hypothetical infection risk data, applying a one-hit model for a single infectious dose, it can be suggested that the SARS CoV falls in the category of having one infective dose (single viral particle) causing disease. 33