By Victoria J.

Davey, MPH, RN

Infections
Influenza A (H1N1): A Wake-Up Call
Where this virus mightor might nottake us.

cientists hypothesize that sometime this past winter, most likely in Mexico, a new influenza virus carrying genetic material from swine, human, and avian viruses infected a person. This new virus is of the influenza A species and has unusual surface hemagglutinin and neuraminidase antigens of the subtypes H1 and N1, respectively, the key proteins that allow for human infection and are the basis for the immune systems formation of protective antibodies. One human H1N1 virusa descendant of the virus that caused the 1918 pandemicis already circulating this season, but the genomic material of the new H1N1 virus is so different that human susceptibility may be nearly universal. Whenever a novel human influenza A virus appears, the global public health community worries about a pandemic.1-3 Nurses must be well informed about the origins and effects of pandemics and able to teach other health care workers and the public about preparing for, responding to, and recovering from large-scale human infection events. INFLUENZA VIRUS BASICS Influenza viruses are usually adapted to their specific animal host species, be they humans, birds, or nonhuman mammals (hereafter referred to simply as mammals). A well-adapted influenza virus evolves to infect its host easily, replicate inside its host unscathed by the hosts immune system, and use its hosts

physiologic and behavioral characteristics to optimize transmission, which is accomplished through symptoms such

usually produce mild illness, but they can be lethal, like the H5N1 avian virus that, though rarely, continues to infect humans in

The 1918 pandemic began in the spring, largely disappeared over the summer, and returned in waves for about two years.
as coughing and sneezing that are mild enough that the host isnt too likely to restrict contact with others by taking to her or his bed, thereby limiting the opportunities for transmission.4 Occasionally, genetic material in one influenza virus combines with that of other influenza viruses and crossinfects other animal species.5 State, national, and international human and animal health surveillance systems frequently find and monitor these bird human, mammalhuman, and mammalbird infections, but they may disappear as quickly as they arise. Human infections with swine virus and vice versa, for example, occur quite commonly. These cross-infections may happen when individuals of either species are in close contact while infectious, as Shinde and colleagues indicated in their analysis of the first 11 cases of influenza A (H1) infection identified in the United States.3 The cross-infections parts of Asia, Europe, and Africa. Thus far, H5N1 influenza has an estimated case fatality rate in humans of more than 60%.6 HUMAN INFLUENZA PANDEMIC BASICS Human influenza pandemics occur when novel influenza viruses arise and become easily transmissible from person to person. The word pandemic is used when a virus has the capability to be disseminated globally because the human host population has little or no immunity to it; it does not indicate the severity of the illness the virus causes. Pandemics that began in 1918, 1957, and 1968 affected most regions of the world, but each varied substantially in its effects on the human population. Pandemic viruses have other characteristics, as well. First, novel subtypes of influenza typically cause more severe illness and death in younger people, who, because they have not developed
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the intensity of their application, will vary depending on the pandemics clinical severity.8, 9 The ideal mitigation strategy, of course, is to vaccinate everyone with a strain-specific vaccine, but as a recent editorial published in the New England Journal of Medicine noted, vaccine production is a slow process, with isolation and genetic sequencing of the causative virus through distribution of the vaccine likely to take months.1 NOVEL INFLUENZA A (H1N1) ILLNESS A person infected with the novel H1N1 virus has symptoms similar to those of the classic fluthe acute onset of fever and cough in nearly all cases, often accompanied by rhinorrhea, muscle aches, fatigue, and joint pain. Less commonly and somewhat unusually for influenza, diarrhea and vomiting have occurred in approximately 25% of patients. Symptoms generally last for three to seven days. Most people recover, but as with every influenza outbreak, some people die, whether young or old, healthy or chronically ill.10 A BREWING PANDEMIC? The novel H1N1 epidemic that is rapidly spreading around the world may already bear the classic pandemic hallmarks: nearuniversal susceptibility, more infections and hospitalizations in younger people than are usual for an influenza virus, and a relatively high reproductive rate (reflecting transmissibility), compared with seasonal influenza. (This latter measure is denoted by R0, the average number of others one person infects in a susceptible population. A typical R0 for seasonal flu is 1.3; the estimated R0 for H1N1 influenza in Mexico is about 1.5. The estimated R0 for the 1918 pandemic influenza was 1.4 to 2.0.2, 11, 12)
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Purdue University virologist Suresh Mittal, whose work on influenza A (H5N1), the cause of bird flu, is being used to help create a vaccine that will be effective against the H1N1 virus, the cause of swine flu. Purdue researchers, working with the Centers for Disease Control and Prevention, announced in May that they would test the vaccine within a month. Photo by Tom Campbell, courtesy of Purdue Agricultural Communication.

partial immunity during years of exposure to seasonal influenza viruses and vaccines, mount vigorous immune responses that may damage cells. Second, pandemic illnesses sweep through communities in repeated waves over years. For example, the 1918 pandemic began in the spring, largely disappeared over the summer, and returned in waves for about two years. Third, pandemic viruses tend to be transmitted from person to person more easily than typical seasonal influenza viruses are. Finally, the degree and severity of illness, death, and societal disruption in a pandemic may differ significantly from place to place.7 The methods for lessening a pandemics effects by deterring human-to-human spread and limiting illness include administer26
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ing a vaccine, dispensing antiviral medications, and using personal protective equipment. More recently, nondrug strategies like isolating the sick; closing schools; and practicing social distancing by, for example, staying at least three feet away from others, not shaking hands or kissing, and avoiding crowds in enclosed spaces (such as buildings) have been studied in computer simulations. These simulations suggest that the best strategy for containing or delaying an influenza pandemics spread is to apply multiple countermeasures simultaneously, such as closing schools on a broad scale, having both children and adults employ social distancing techniques, and providing antiviral drugs to the sick and the exposed. The specific measures employed, as well as

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With each passing day, the clinical, scientific, and emergency management communities learn more about the H1N1 viruss characteristics, epidemiology, clinical effects, and outcomes in people of different ages and with different risk factors for influenza complications. This will help public health officials to tailor strategies for slowing the pace of the pandemic to allow time for a vaccine to be developed, for antivirals and personal protective equipment to be manufactured and distributed, and for clinicians and the public to be educated on treatment and prevention. Slowing the pandemic may also keep health care services from being overwhelmed by a surge of patients, a scenario made more serious by the potential for high absenteeism among health care staff caused by illness. WHATS AHEAD No crystal ball can tell us exactly how this virus will behave as it moves around the world. Experts in influenza pandemics, including me and my colleagues, foresee several possibilities for this country.2 The novel influenza A (H1N1) strain disappears and never reappears or appears in the future as a different novel virus. The strain, which is now causing the earliest stages of a pandemic, continues to infect people at high rates until it peaks in midsummer, when it will diminish because most of the susceptible people will have been infected and recovered. The virus disappears over the summer because it tolerates high humidity or other climatic factors poorly or because summertimes lessfrequent indoor gatherings limit its transmissibility
ajn@wolterskluwer.com

For more information about the novel H1N1 virus and pandemic, visit
www.cdc.gov/h1n1flu/index.htm for Centers for Disease Control and Prevention
resources.

www.pandemicflu.gov for a roundup of U.S. government agency H1N1 news. www.who.int/csr/en for World Health Organization resources. http://new.paho.org for daily pandemic briefings from the Pan American Health
Organization.

http://h1n1.nejm.org for the New England Journal of Medicines H1N1 Influenza

from person to person. After schools reopen in the fall, the virus may return as the same strain or a genetic variant and result in a pandemic that could peak in early winter. Which scenario is most likely? No one knows whether it will be one of these or another, but as data on the viruss biology, epidemiology, and clinical illness are gathered, predictions will become more certain and the best strategies for limiting the pandemics effects will become apparent. Nurses efforts were crucial in responding to the 1918 pandemic, and they will be equally as critical in helping health care facilities and communities prepare for, respond to, and recover from the next pandemic.13, 14 M
Victoria J. Davey is deputy chief officer for public health and environmental hazards at the Department of Veterans Affairs in Washington, DC, and a doctoral student at Uniformed Services University of the Health Sciences in Bethesda, MD. Contact author: victoria.davey@va.gov. Emerging Infections is coordinated by Eileen A. Finerty: finertye@hss.edu.

REFERENCES
1. Belshe RB. Implications of the emergence of a novel H1 influenza virus. N Engl J Med 2009. [Epub ahead of print] 2. Fraser C, et al. Pandemic potential of a strain of influenza A (H1N1): early findings. Science 2009. [Epub ahead of print]

3. Shinde V, et al. Triple-reassortant swine influenza A (H1) in humans in the United States, 20052009. N Engl J Med 2009. [Epub ahead of print] 4. Nelson MI, Holmes EC. The evolution of epidemic influenza. Nat Rev Genet 2007;8(3):196-205. 5. Weiss RA. The Leeuwenhoek Lecture 2001. Animal origins of human infectious disease. Philos Trans R Soc Lond B Biol Sci 2001;356(1410): 957-77. 6. World Health Organization. Update: WHO-confirmed human cases of avian influenza A(H5N1) infection, 25 November 200324 November 2006. Wkly Epidemiol Rec 2007;82(6):41-7. 7. Miller MA, et al. The signature features of influenza pandemics implications for policy. N Engl J Med 2009. [Epub ahead of print] 8. Centers for Disease Control and Prevention. Interim pre-pandemic planning guidance: community strategy for pandemic influenza mitigation in the United Statesearly, targeted, layered use of nonpharmaceutical interventions. Atlanta; 2007 Feb. http://www.pandemicflu.gov/plan/ community/community_mitigation.pdf. 9. Davey VJ, et al. Effective, robust design of community mitigation for pandemic influenza: a systematic examination of proposed US guidance. PLoS ONE 2008;3(7):e2606. 10. Centers for Disease Control and Prevention. Update: novel influenza A (H1N1) virus infectionsworldwide, May 6, 2009. MMWR Morb Mortal Wkly Rep 2009;58(17):453-8. 11. Ferguson NM, et al. Strategies for mitigating an influenza pandemic. Nature 2006;442(7101):448-52. 12. Mills CE, et al. Transmissibility of 1918 pandemic influenza. Nature 2004;432(7019):904-6. 13. Groft JN. Everything depends on good nursing. Can Nurse 2006; 102(3):19-22. 14. Schoch-Spana M. Hospitals full-up: the 1918 influenza pandemic. Public Health Rep 2001;116 Suppl 2:32-3.

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