Some statistics from today's CDC H1N1 Swine Flu Briefing

The following information comes from today's press conference with Dr. Besser, Acting Director of the CDC.

Stats for the United States:

• 279 confirmed cases in 36 states
• > 99% of probable cases so far have tested positive
• > 700 probable cases in 44 states
• Median age of confirmed cases: 16 years old 
• Age range for confirmed cases: 3 months to 81yrs
• 62% of confirmed cases are in patients < 18 years old
  
• The most recent confirmed case occurred on May 1st
• 35 known hospitalizations 
• 1 known death

Because probable cases are so likely to be confirmed when they are tested, they provide us with a more clear and timely picture of where we stand in the way of actual infections right now than the number of confirmed cases.  

No matter what the situation, the "confirmed" number will always lag behind reality, but right now it's lagging even further behind because of the significant backlog of samples to be tested.  This is inevitable when a novel pathogen emerges and a new test has to be invented to deal with it; the CDC's public health laboratory scientists have exceeded any rational expectations in the speed and the quality of their response.  

Dr. Besser said that the CDC intends to start reporting probable cases on its website the near future.

He also said that the number of probable cases is likely an underestimation of the real number, as well, because the CDC's definition of a probable case requires that a person have flu-like symptoms and test positive for Influenza A, but negative for the H1 & H3 subtypes --and we know this testing is not happening for every person with influenza-like illness (ILI).

The CDC is now rolling out H1N1 Swine Flu test kits to the states, so state public health laboratories will be able to test for the virus.  Over time, this will help to reduce the backlog for confirming cases, but states will still not be able to test all possible or even probable cases.  

That's okay, though, because the point isn't to ensure that we confirm all cases of the disease, it's to ensure that we know where, when, and in whom the virus is spreading.  --That's the data we need to make sure we're taking the right steps in the right places to protect the public. 

Too soon to say

Suddenly, stories like this one abound, implying that the outbreak of H1N1 Swine Flu may not be such a big deal after all.

Of course, we all hope it turns out not to be a big deal, but as they finally got around to mentioning in paragraph 5 of the new article, it's "...too soon to be certain what the swine flu virus will do."

We are so early in this outbreak that we really don't know much about the epidemiology of this virus at all.  

• How many people have the disease?
• How many people have died?
• How readily is it transmitted from person to person?  
• What risk factors are there for infection (does it spread well among people crammed into the same airplane for several hours, but poorly in more open settings; are smokers or the elderly or some other group more likely to catch it)?  
• How lethal is the virus to those who catch it?  
• Who is most at risk of severe disease?
• When it does kill people, is it the flu infection itself (primary viral pneumonia) that causes death or is it secondary bacterial pneumonia that moves in after the flu virus is gone?
  

And it will be awhile before we have many of the answers.  In the UK, they are waiting for the results of more than 600 tests for the virus.  Mexico has a backlog of over 35,000 samples waiting to be tested, and their total number of confirmed cases shot up by nearly 250 overnight to 397 as a result of additional testing (not necessarily correlated to any new cases).  In the US, it's taking 4 days to get test results, which -with a virus that has only a 24 to 96-hour incubation period- means that our picture of confirmed cases here at home is far behind the times, as well.

And all that only goes to the epidemiological situation now.  The situation is likely to change over time, as the virus mutates.  In the case of the 1918 Pandemic, for instance, the first wave of infections spread around the world in the spring, and it was pretty mild.  It wasn't until the fall, when the next wave of infections struck, that the virus became so frighteningly lethal.

So I'm very pleased that the CDC, the Department of Health and Human Services, and the Department of Homeland Security are all continuing to take the situation very seriously and are doing an excellent job of letting the public know what we do and don't know.  

Dr. Besser, Acting Director of the CDC, has done a particularly good job of communicating the expectation that the government's response, the guidance to the public and the guidance to healthcare professionals will all continue to change as the situation evolves --and that that's a good thing. 

Yesterday's webcast on the swine flu outbreak

Here is yesterday's webcast from the Department of Health and Human Services and the Department of Homeland Security.

 
Dr. Besser, Acting Director of the CDC, Secretary Sebelius of the Department of Health and Human Services, and Secretary Napolitano of the Department of Homeland Security did an excellent job of answering questions from the public.