Thursday, May 21, 2009

Swine Flu Part 3A- Why is it so SCARY?

This question is actually why I began writing this series of posts in the first place. I knew that lots of people were getting infected, yada yada... but I also knew that it was not as deadly as your average seasonal flu, so I wanted to know why everyone cared so much! I just didn't get it. The truth is, it's not so much that the Swine Flu is scary now, but it has the potential to become scary, and that's what is scaring everyone.

In previous posts, I have gone over viral genetics and practical diagnostic information on Swine Flu. Bits from there will tie into today's post.

Let's start with some history. This is not the first time that we have seen Swine Flu (aka- H1N1, aka- Swine-Origin Influenza A Virus (S-OIV)). There was a small outbreak of H1N1 in the United States in 1976. During that outbreak, 200 people were infected. Companies scrambled to make a vaccine against H1N1 and were successful, but somehow something got botched. The vaccine was administered broadly in the area of the outbreak with the following results: 1 person died of the swine flu. 25 died of the vaccine. Oops. (it is important to note here that vaccine technology has improved TREMENDOUSLY since 1976 and the safety regulations in place by the FDA will prevent anything like this from happening again.)

Now we have what science is calling a "novel H1N1"... novel being the scientific word for "new." This figure shows us what happened. The colored bars represent viral RNA. On the left is the swine flu virus from 1976. On the right is the current pandemic virus. By picking up RNA from eurasian swine viruses made H1N1 newly infectious. Just as a person of Chinese ancestry is easily distinguished from a person of swedish ancestry, viruses with ancestry in different regions of the world "look" different to our immune systems.

Let's look at this outbreak. The first US case was a 10-year-old boy in california. He got sick on March 28th, 2009 and, by luck, was enrolled in a clinical trial for a new viral laboratory test at the hospital which treated him for his illness. His virus was analyzed and typed as "unspecified Influenza A subtype" (see Swine Flu part 2) and therefore sent to the CDC for analysis. It arrived at the CDC on April 15th, was discovered to be a novel H1N1 and the CDC notified the California department of health on the same day to institute epidemic investigation protocols. Around the same time, reports from Mexico were arriving at the CDC of an unidentified, severe influenza outbreak. The global health community is commending Mexico's health community and the CDC for their rapid and appropriate response. After extensive epidemiologic investigation, it is now thought that the first cases of swine flu may have hit the US as early as January of 2009 (public health lecture, Cornell U. Med Coll, May 20, 2009).

The initial reports of H1N1 in Mexico were in a town with a population of 3000. Mexican health officials reported to the CDC that 60% of the population was infected, but only 2 people died. The majority of the people infected were young adults with an average age of 27.1 yrs. Continued surveillance of global H1N1 infections has shown that the illness is most severe in patients aged 30-44 yrs old. Globally, these are the patients with the greatest rate of hospitalization. The CDC now estimates that mortality from H1N1 is 0.2% but warns that it is still too early in the pandemic to tell.

0.2%. I'm sure a lot of people have no idea if that is good or bad. The CDC tracks annual mortality (deaths) from influenza and pneumonia. aapproximately 7-9% of people infected with one of these two conditions will die annually. Comparatively, swine flu looks safe! However, an infection rate of 60% is staggeringly high. I was unable to find an estimate of how much of the population gets the seasonal flu each year, but take my word that 60% of the population infected is mind boggling.

I know I haven't answered the question, but I'm tired. I'm getting to it. The history is fascinating.

More to come....

Brownstein JS. Influenza A (H1N1) Virus , 2009 -- Online Monitoring. NEJM 2009 May 7 [epub ahead of print].
Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team. Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans. NEJM 2009 May 7 [epub ahead of print].

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