By Thomas P. Fuller PhD, CIH
Recent history indicates that nurses and other health care workers should be provided with the highest level of respiratory and other personal protection in the event of any unknown or highly contagious virus.
The Severe Acute Respiratory Syndrome (SARS) outbreak in 2002 resulted in 8,450 cases. It involved 33 countries on five continents. The death rate conclusively reported by the World Health Organization (WHO) was 9.6 percent. In the infirm and elderly death rates were reported as high as 40 percent.
The WHO reported that 21 percent of all SARS cases were health care workers. But other sources reported 62 percent in Hong Kong and 43 percent in Toronto. Significantly more nurses died than doctors with a relative ratio of 10:3 in Hong Kong.
The lessons learned by the SARS incident highlighted the following weaknesses in our health care systems:
- The inability to identify and contain infectious agents
- Inadequate patient and worker surveillance and contact tracing
- Misunderstanding of methods to prevent transmission (particularly in the hospital setting)
- Unavailability of rapid diagnostics and integration of information
- A shortage of isolation equipment
- Inadequate tracking, monitoring and evaluation of patient cases
The inadequate understanding of the value, failure to use or unavailability of personnel protective equipment (PPE) was likely another significant source of agent transmission to health care workers. It is probable that the differences in worker infection rates and fatalities in different countries were closely related to the effective use of PPE in countries with lower rates.
Unfortunately, when there is an outbreak like this local and federal governments are often unprepared to offer advice on protection and control of the latest agent or its mutation. The numerous factors that must be included in determinations of protective practices include:
- Communicability
- Lethality/medical outcomes
- Treatments
- Preventions
- Diagnostics
- Susceptible populations
Other factors that are important to consider are the:
- Environmental viability of the agent
- Dose needed for infection (number of particles)
- Routes of exposure
- Environmental monitoring
- Availability of protective controls
As the SARS outbreak unfolded a broad variety of conflicting and confusing information was disseminated. It became clear only much later that the information about the modes of transmission, the virulence, and the methods to protect health care workers was grossly inadequate.
It was originally thought that the agent was similar to influenza. Droplet precautions were advised. It is assumed that many workers used surgical masks as their PPE during these early phases. Later more was learned and it was realized that the virus could also follow an airborne exposure route through aerosolization of small particles and that the agent could remain viable in the air for several hours. It is not clear when this became known to the entire international health care community and when respirators began to be used universally.
After the outbreak it was also learned that many worker and patient illnesses were hospital acquired. The virus can be transmitted by patient contamination of surfaces and materials with the SARS virus that can then infect other workers and patients by contact with mucosal tissue in eyes, mouth, and open cuts. The virus was found as far from the patients’ bedsides as nursing stations and break areas. It can be assumed that at least some health care workers exposures and deaths could be attributed to inadequate use of gloves, gowns, and hand-washing in addition to inadequate respiratory protection.
Moving forward the international health care community is trying to contain the latest outbreaks of avian viruses and understand how the agents are changing and moving through the environment and species. The avian virus H5N1 has been shown to be particularly infective and lethal with a death rate of about 50 percent (WHO HHS). The virus has also been confirmed to be transmissible from birds to humans with several workers in Asia becoming infected via close proximity to infected birds or poultry products.
At this time the WHO has issued a Pandemic Alert Phase 3, defined as "Human infections with a new subtype but no human-to-human spread or at most rare instances of spread to a close contact." If this virus mutates in such a way that the disease can be transmissible from human to human like SARS did a serious pandemic could become a reality. If transmission can also become transmissible via aerosolized particles and fomites like the SARS virus did, and it still has a 50 percent death rate, the consequences could be devastating to nurses and other health care workers, their families and the public.
In May 2005 the CDC issued "Interim Guidance on Infection Control Precautions for Patients with SARS and Close Contacts in Households.” These guidelines recommended the protection factors of a NIOSH-certified N95 respirator at a minimum.
On Nov. 16, 2005, protective measures suggested by the CDC, Infection Control Guidance for the Prevention and Control of Influenza in Acute-Care Facilities now called for only “the use of gloves and surgical masks.” This guidance is based upon the continued assumption that current flu strains are only transmissible person to person via large virus-laden droplets that are generated when persons cough or sneeze in close proximity (within three feet). In an earlier contradictory paper published by Steven Lenhart at the CDC National Institute for Occupational Safety and Health he states that “risks of exposure to infectious particles are likely to be predominately to aerosols consisting of evaporating droplets and droplet nuclei that remain suspended in room air for prolonged periods and not from large particle droplets. He also states that “defining a specific distance as the boundary of a health care worker’s exposure to particles exhaled by a patient with a contagious respiratory infection may be inappropriate.”
This Nov. 16 recommendation by the CDC is a non-conservative approach to worker health and safety and assumes that when and if the virus changes and can be transmitted as an aerosol, then the information would be made known immediately and additional precautions could be upgraded appropriately. If aerosolization of the virus is possible and it is viable in the air for even just a few hours, then the surgical masks recommended by the CDC on November 16, 2006 for worker protection are grossly inadequate and N95 masks, recommended earlier in May of 2005 for SARS, should be used at a minimum when in the proximity of the influenza patient.
It is not known when the virus could mutate to a strain that could be transmitted by the air. Neither is it clear when the CDC would become aware of that change, or how long it would take to send a notice to upgrade precautions out to the public. In the case of SARS the upgraded precautions appeared to come too late for many nurses and other health care workers. It is not certain that the health care system weaknesses listed above have all been fully addressed at this time.
Other factors go into the selection of respiratory PPE. The cost of N95s versus surgical masks, availability, the requirement to perform medical clearances and qualitative fit-tests, and the tasks to be performed by the worker. On the other hand when doubts exist about the severity of an occupational hazard, prudent precautionary action must be considered immediately and taken as appropriate (International Commission on Occupational Health, (2002) International code of ethics for occupational health professionals. Retrieved Jan. 1, 2004 from www.icoh.org.sg/eng/core/code_ethics_eng.pdf.
As the industrial hygiene manager at a large hospital in an urban area it is my job to anticipate, recognize, evaluate, and control hazards in the workplace. I try to work very closely with the infection control committee and hospital epidemiologists to provide insight and recommendations regarding PPE, ventilation systems and other controls to reduce employee exposures and risks.
With the threat of an influenza outbreak that can mutate and be more transmissible and virulent it seems that a more protective approach to worker and patient protection may be warranted. Unlike hazardous chemicals or even radiation, it is difficult to measure the germ load in a work environment and relate that to a “safe” worker dose. In addition, the infectivity of infectious agents is often unknown and the “safe” exposure level of workers is difficult to predict. Therefore, more conservative approaches to worker protection are warranted and even necessary.
There are numerous sources of information on infectious diseases including the WHO and other government and professional organizations. Healthcare facilities should be encouraged to seek information from all sources and set policies and programs according to the needs and capabilities of their facilities. A more protective approach may be advisable.
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