Monday, May 11, 2009

Swine Flu Part 2- Do You Have Swine Flu?

As promised, everyone wants one SINGLE question answered -- do I have Swine Flu??? You can go on the CDC website, like I did, and get confused. Then you can go to the WHO website and get confused. There is a whole lot of hand waving and paraphrasing for a number of reasons. First, the "flu" seems so commonly defined, no one bothers to define it anymore! Yet, there is confusion as to what exactly is the "flu." Second, illnesses are variable. If the CDC were to say "If you have swine flu, you will have these 5 symptoms..." and some guy presented with only 2 of the 5, the CDC would be in deep shit. Hooray for the American climate of litigation. Finally, the only definitive diagnosis for swine flu would be to isolate the virus from the patient, sequence the RNA and have the fancy lab machine spit out a yes/no answer. Of note, the lab machine is in Atlanta at the CDC.

Below: Influenza A
So, the answer to the simple question is simple (yes/no) but getting there is quite complicated.

The Flu vs. A Cold:
The primary scientific distinction between these two is that they are caused by different viruses. The flu is caused specifically by the influenza virus. (see previous post) The Common Cold is caused predominantly by Rhinoviruses (fall/winter) and Coronaviruses (young children, SARS). Viruses, however, are not like bacteria. We can just grow bacteria on a dish, throw a series of fancy dyes and chemicals at the sample and come out with a bug. Viruses require cells for replication, so we can't grow them in a petri dish. Doctors walk around the hospital saying "This patient has c. diff and this guy here has MRSA." (Both bacterial infections) However, we don't walk around saying "This patient has aborovirus and the guy in bed B has an arenavirus infection." Why? Because we don't know!
Below: Rhinovirus
Alright, so for the lab guys out there, sorry, your viral identification process takes too long to be practical. Now we have to rely on symptoms to distinguish a flu from a cold.
  • A cold is generally associated with cough, runny nose, sneezing, sore throat, headache. Symptoms last about 1 week. Occasionally a low-grade fever is noted.
  • The Flu has FEVER, muscle aches, weakness, headache, sore throat, cough, runny nose, sneezing. Symptoms last about a week. The influenza virus also has the ability to cause pneumonia and your regular flu season(winter) flu can be lethal in certain populations, hence, the flu vaccine.
The difference is subtle, but there. Illnesses that seem "virus-y" (think: head cold) but that also have a fever can be classified as the flu.

Variable symptoms:
Just because the textbooks say that patients sick with the influenza virus have a fever does not make it absolute. There is a very common saying in the medical world to remind physicians of this fact: "The patient hasn't read the textbook." In other words, no one is going to present as a textbook case. Beyond this, physicians are so skeptical that if a patient presents as a perfect textbook example of a particular disease, doctors start wondering if they are faking it.

Bearing this in mind, it's a good idea to stay home if you have cold OR flu symptoms, especially coughing or sneezing because the swine flu virus (as well as all the viruses discussed in this post) is transmitted through the air.

Right now, we are NOT in flu season. Our normal, annual flu epidemic (and it IS an epidemic, I promise) is in the winter months. November - March in the northern hemisphere, June - September in the southern. Fortunately for the medical community, this makes the diagnosis of Swine Flu right now much easier. If we see a patient with the classic "flu" but it's the summer, it's Swine Flu until proven otherwise. Then we take samples and send them to the hospital lab. The hospital lab machine only has the capability to diagnose one type of influenza virus -- the annual one, H1N3 (usually). If a patient has swine flu, the lab machine will spit back "unidentified influenza virus." Then the sample will get sent to the CDC in Atlanta for full genetic sequencing and definitive yes/no answer to the question "is this swine flu?"

Phew! complicated, I know.

Lange Review of Medical Microbiology and Immunology.
New York City Health Department Press Release

Next time: Why is Swine Flu so scary?


  1. Did you just say that the Rhinovirus is caused by fall/winter and the Coronavirus is caused by children/SARS?

  2. Love the summaries. Can I send them on to confused family/friends?
    - Cara

  3. Sorry about the confusion. Rhinovirus CAUSES colds in the fall and winter. Coronavirus CAUSES colds in children and SARS.

    And yes, please send them to family and friends!!

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