Preparing for an Influenza Pandemic Personal Protective Equipment for Healthcare Workers (2008) / Chapter Skim
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2 Understanding the Risk of Influenza to Healthcare Workers
2 Understanding the Risk of Influenza to Healthcare Workers
Pages 47-76
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. Healthcare workers are concerned about the risk of a new pandemic, especially in light of the recent outbreaks of severe acute respiratory syndrome (SARS)
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SOURCE: DHHS, 2006. This chapter provides a brief overview of the influenza virus and past pandemics and then focuses on understanding the risks to healthcare workers.
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. The influenza virus undergoes frequent changes in antigenicity due often to minor antigenic changes that result from the accumulation of point mutations (antigenic drift)
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In 1957 and 1968, reassortment events led to new viruses that resulted in pandemic influenza. The 1957 influenza virus (an H2N2 virus)
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The Next Pandemic Threat The next pandemic may come from a human or an avian influenza strain. To date, human disease caused by transmission of avian influenza viruses has occurred with the H5, H7, and H9 subtypes (Katz, 2003; WHO, 2006)
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This paucity of definitive data on influenza transmission is a critical gap in the knowledge base needed to develop and implement 2 Comparisons were made between exposed and unexposed healthcare workers. Each individual's history of poultry exposures was considered in both studies.
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Contact Transmission Contact transmission of the influenza virus requires either direct transfer of the virus between persons or indirect transfer via contact with an influenza-contaminated object (fomite) .3 In either case, transmission can result in infection only if the virus survives in an adequate infective 3 A fomite is an object (e.g., a dish, an article of clothing)
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. Droplet and Airborne Transmission Much of the discussion regarding influenza transmission has focused on the continuum between large-droplet and airborne transmission.
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The length of time that these particles remain airborne is determined by their size, their settling velocity, and air flow dynamics. When humans cough or sneeze, the exhaled aerosols commonly contain fluid from the respiratory tract that can also include infectious agents (Buckland and Tyrrell, 1964)
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. Further research is needed to understand the role of bioaerosols in the spread of infection, including the size and dispersion of the relevant continuum of droplets generated during breathing, speech, coughing, and sneezing; the infectivity and survival of microorganisms within droplets; Upper respiratory tract Nasopharyngeal Lower respiratory tract Tracheobronchial Fomites Pulmonary Sewage and water sources FIGURE 2-3 Deposition of particles in the respiratory tract.
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The authors subsequently separated infected and noninfected animals with barriers and fans, and no animal-to-animal transmission occurred. However when influenza virus was introduced into air ducts (including a U-shaped duct)
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These experiments need to use environmental conditions that mimic healthcare settings and their ventilation systems. Equally urgent is the need to develop a reliable animal model that is thought to mimic human influenza using animals that are available and can be obtained quickly when rapid testing is necessary in an epidemic setting.
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Research is needed to determine if, when, and how long viral shedding occurs; the relationship to clinical signs and symptoms; and when, or if, this leads to influenza transmission. Airborne transmission is the primary route of transmission between humans for only a few disease agents, most notably pulmonary tuberculosis (CDC, 2003b)
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Of the 30 individuals who developed influenza, 13 were healthcare workers. Approximately 35 percent of vaccinated healthcare workers developed influenza compared to 55 to 65 percent of unvaccinated healthcare workers.
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In the event of an influenza pandemic involving millions of patients and their families and caregivers, steps to increase the effectiveness of prevention measures will likely have significant impact. UNDERSTANDING THE INFLUENZA TRANSMISSION RISKS RELEVANT TO HEALTHCARE WORKERS Although much remains to be learned about the routes of influenza transmission, influenza is known to pose hazards in healthcare facilities and to healthcare workers because of its short incubation period, patient infectivity prior to clinical symptoms, and efficient spread from person to person.
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Several patient populations are of particular concern during an influenza pandemic, and their care may pose increased risk of infection to healthcare workers. As discussed earlier in this chapter, the burden of influenza is substantial in children during seasonal outbreaks and in more wide-scale epidemics or pandemics (Hall, 2007)
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. OPPORTUNITIES FOR ACTION Critical research questions about the many unknowns regarding influenza transmission and prevention need immediate attention.
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The committee has identified several key research questions that if addressed expeditiously (in the next 6 to 12 months) could have a significant impact on improving the nation's readiness for pandemic influenza; additional longer-term opportunities and research questions abound to further clarify influenza transmission and develop effective prevention strategies.
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What innovations regarding PPE are needed to enhance effectiveness? Long-Term Key Research Needs Routes of transmission and interventions: • What percentage of patients aerosolize influenza virus during an infection?
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and polymerase chain reaction assays, as well as advances in research fields such as aerobiology and mathematical modeling, to the study of seasonal influenza and avian influenza. Knowledge of influenza transmission can be furthered through a range of human studies including epidemiological analyses (e.g., Markel et al., 2007)
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In this time of preparation for an influenza pandemic, the realization of how little is known about critical aspects of the disease should prompt immediate action to coordinate multiple resources and a diversity of research expertise to address the unknowns regarding influenza transmission and prevention. SUMMARY AND RECOMMENDATION Although it has been 70 years since the influenza A virus was discovered and despite the annual toll that results from seasonal influenza and regional outbreaks, little is known about the mechanisms by which influenza is transmitted and its viability and infectivity outside the host.
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Based on the paucity of data on influenza transmission and the importance of this knowledge in refining prevention and mitigation strategies, particularly for pandemic influenza, the committee makes the following recommendation. Recommendation 1 Initiate and Support a Global Influenza Research Network The Department of Health and Human Services in collabora tion with U.S.
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2003a. Cluster of severe acute respiratory syndrome cases among protected health-care workers -- Toronto, Canada, April 2003.
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In The influenza viruses and influenza, edited by E Kilbourne.
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2004. Transmission of severe acute respiratory syndrome during intubation and mechanical ventilation.
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2003. The impact of avian influenza viruses on public health.
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2006. The guinea pig as a transmission model for human influenza viruses.
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1962. Airborne transmission of influenza virus infection in mice.
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2005. WHO checklist for influenza pandemic preparedness planning.
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2007. Avian influenza update number 95 (May 15, 2007)
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