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Recognition of seasonal, H1N1 influenza discussed

by Michael Kilby, M.D.
Infectious Diseases
Recent recognition of a novel influenza A strain (a subtype of H1N1) has led to concerns about the possibility of an evolving pandemic. Therefore, it is timely to review some concepts about prevention and recognition of influenza in general, and to begin making plans about how faculty, staff, and their families will respond if there are increasing numbers of cases reported in our area.

Seasonal influenza
Each year, seasonal epidemics of influenza are reported in the United States, particularly between December and February in our area. Because the viral strains that predominate change from year to year, a different seasonal influenza vaccine is developed each year in attempts to predict subtypes. The most common symptoms are fever, muscle aches and dry cough. Sore throat, headache, upset stomach and diarrhea also are seen.
Influenza infections are very common and generally result in self-limited and non-life threatening illness that will improve with bed rest and supportive care (like acetaminophen, cough drops, plenty of fluids) alone. Antiviral treatments are available, but are not always very practical in that they may shorten the illness only if administered immediately when symptoms begin, they are relatively costly, and not all strains are responsive.
While influenza in a healthy person rarely leads to prolonged or severe illness, large outbreaks of influenza are associated with increases in hospitalizations and deaths, especially among the elderly, infants, and individuals with underlying medical illnesses.

H1N1 (“swine-flu like” influenza A pandemic)
In April, the first cases of a newly recognized strain of influenza A were recognized near the U.S./Mexico border. The alarming aspect of this new development has not been the severity of the illness. In fact, clinically it is not distinguishable from seasonal flu.
What has gotten the attention of infection specialists is the recognition of trends sometimes seen before large outbreaks (peak transmission outside the usual flu season, disproportionate numbers of cases in school age children and the rapid, almost simultaneous occurrence of infections all over the world). Even though the total number of cases globally is not much different than usual flu seasons, this rapid emergence of a new strain in this odd time of year constitutes a pandemic.
Initial reports suggest that the new H1N1 may be more predictably responsive to antiviral drugs than seasonal flu strains have been in recent years. However, it is likely that obtaining influenza therapy will not be practical or necessary for most cases in otherwise healthy individuals with mild symptoms. Furthermore, there may be shortages or limited access to anti-flu medications that make it necessary to restrict antiviral drugs to severely ill patients or those at special risk.
Intensive efforts are under way to make and distribute a version of the inactivated influenza vaccine containing antigens from the new outbreaks in the next month or two. Because this is such a novel strain, and few young people have ever been exposed to viruses of this kind, the H1N1 vaccination will require a second booster shot. The result is the recommendation that most people are likely to need a total of three influenza shots this fall; the usual seasonal vaccine and a two-shot series of the same type of vaccine carrying antigens derived from H1N1.

Friday, Sept. 18, 2009

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