Influenza Overview: Prepare for Flu Season

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The flu is an ever-present threat to our health and wellbeing. “Despite great familiarity with this common infection, influenza never fails to surprise even the most seasoned observer,” wrote Dr. Jonathan L. Temte and Dr. Jacob P. Prunuske of the University of Wisconsin School of Medicine. The annual medical costs are estimated at $10.4 billion, and indirect costs add $76.7 billion to our financial burden.

Temte and Prunuske described the annual flu season as an epidemic curve, with approximately 86 percent of cases occurring within a nine week period in a given locality. Late January and early February are generally the peak time for influenza in the United States. The Centers for Disease Control and Prevention provides a graph of reported influenza cases on their “FluView” page at http://www.cdc.gov/flu/weekly/.

Infected individuals develop symptoms after an incubation period of one to three days. Symptoms include fever, cough, malaise, headache, nasal congestion, sore throat, and muscle pain. Most cases are not severe, but airway dysfunction and hyper-reactivity can last up to sevem weeks.

The primary drugs for treating the flu are oseltamivir (Tamiflu) and zanamivir (Relenza). Side effects of both include nausea, vomiting, and headache. Zanamivir is also associated with respiratory tract irritation.

Dr. Conall McCaughey of Royal Hospital, Belfast, UK, called influenza “the single most significant infection of humans.” He noted that the outer surface of the virus is a lipid envelope with hemagglutinin (H) and neuraminidase (N) proteins. The H protein attaches to the surface of a respiratory cell in the first step of infecting it.

Vaccines target this protein. The N protein is necessary for new virus particles to break out of the cell and spread to other cells. The primary flu drugs target this protein. Both proteins change as the virus evolves, so we can catch the flu over and over, even with healthy immune systems. Major influenza outbreaks are designated by the type of H and N proteins, such as H1N1 (2009), H1N2 (2002), H3N2 (1968), etc.

Prevention is our most important defense against influenza. McCaughey noted that the virus' lipid envelope is susceptible to drying out, so most cases are transmitted by inhalation of freshly expelled droplets: “Coughs and sneezes spread diseases.”

Good hygiene including hand washing, covering coughs and sneezes, and distance between sick and healthy people is important. Annual vaccinations also reduce the incidence and severity of influenza.

References:

1. Temte JL et al, “Seasonal influenza in primary care settings: Review for primary care physicians”, Wisconsin Medical Journal 2010; 109(4): 193. http://www.ncbi.nlm.nih.gov/pubmed/20945720

2. McCaughey C, “Influenza: A virus of our times”, Ulster Medical Journal 2010; 79(2): 46-51.
http://www.ncbi.nlm.nih.gov/pubmed/21116418

Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.

Reviewed September 13, 2011
by Michele Blacksberg R.N.
Edited by Jody Smith

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