How does my doctor know if I have the flu?


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It seems like the last cases of the flu petered out just a few months ago but here we are in mid September and I just saw my first case of influenza for this new season.  “What!!!” you say, mild fear and surprise mingling to create a faint shadow in the back of your mind. Flu already? It’s too early. Are you sure?

Well, I am least as sure as you can be of anything in this wonderful, quirky world.  This post will be devoted to a brief discussion of the influenza virus. What is it? Just how dangerous is the flu? How does my doctor know whether I have the flu?  What’s the best treatment?

What is the flu? Influenza is a virus, one of the zombie-like denizens of the microbiologists’ world.  influenza’s genetic make-up grant it unique properties. With most viruses, like chicken-pox or measles, once you’ve been infected or immunized, the immune system will always recognize and crush a repeated attempt to infect you.  One infection or immunization grants permanent immunity to the disease. However, the flu virus is different. Due to antigenic drift and shift, influenza has an ever-changing set of proteins on its outer surface.  Essentially, each year the virus puts on a new costume which disguises it from your immune system. Thus, we can be infected year after year with the same virus.

What makes the flu virus so dangerous? Influenza has the ability to make sudden large changes in its genome.  These genetic shifts make the virus suddenly unrecognizable to the immune systems of large segments of the human population.  If the change is large enough, the virus can move quickly from undefended human host to the next and create the conditions for a pandemic.

How does my doctor know if I have the flu?  Believe it or not, most of the time your doctor knows the moment he sets eyes on you whether or not you have the flu.  The affected person will limp into the exam room, exhausted, pale and looking obviously ill. Most people will describe the sudden onset of a severe illness.  “Doc, I was fine this morning but all of the sudden I got a fever and I feel awful.” The victim will typically have a headache and generalized aches in the muscles and bones, followed quickly by the onset of cough, congestion and runny nose.  Essentially, your doctor sets his eyes on you and thinks, “This person appears to have been hit by a truck.” Once he has verified that you have not been hit by a truck, he will conclude that you have the flu.

Sometimes, for show, your doctor may order a confirmatory rapid influenza swab.  However, these tests have a surprising high rate of false positives and false negatives. Thus, if it returns positive in a person who appears to have been hit by a truck he will pat you on the back and say, “See what I said, you’ve got the flu!” If it returns negative, he will explain, “Well, you can’t really rely on these things anyway!  I knew you had the flu the moment I set eyes on you.”

What’s the best treatment for the flu?  Prevention is the best medicine.  Unfortunately, the antigenic shift and drift of the flu virus makes it hard to prevent.  Each year vaccine makers make their best educated guess at what the flu virus will look like in the next flu season and do their best to produce an effective vaccine.  Some years the vaccine works fairly well and some years not so much. Additionally, the relatively low rate of vaccination in the general population make it so that herd immunity never takes effect.  Fortunately, most people with a functioning immune system are going to fight off the flu after a miserable week or two. Nevertheless, influenza can be particularly mean to people with certain risk factors like chronic respiratory diseases, morbid obesity or Down syndrome.  Experts strongly recommend vaccination if you have an underlying risk factor that increases susceptibility to the flu.

There are a number of antiviral medications that interfere with the influenza viruses ability to infect or exploit cells.  These medications are most effective when given within the first 24-48 hours of illness. Unfortunately, they’ve been shown to reduce the duration of illness by ½ to 1 day.  Thus, for many people, they may not be worth the expense. However, in cases of severe illness requiring hospitalization, experts recommend the use of these types of medications.

For most people, the most effective treatments are rest, fluids and the use of over the counter medications to suppress symptoms.  Check out last week’s post on the common cold for a detailed guide to useful medications.  

P.S.  Get the generic version right next to the brand name on the shelf.  It’s half the price and works just as well.

 Frontier DPC 3 Point Summary®

  • Influenza is a viral infection that comes back every year because it can shift its genetic make-up and disguise itself from the human immune system.

  • Influenza is a severe upper respiratory illness.  Your doctor recognizes it immediately when you limp into his exam room looking as if you’ve been hit by a truck.

  • The best treatment for the flu is lots of fluids, rest and over the counter medications to suppress aches, pains, cough and congestion.