What's happening in the United States ?
has held another useful briefing on the progress of H1N1 swine flu in the United States. Since the US is the global centre of the outbreak with far more cases than anywhere else, though fewer deaths than in Mexico, we can learn from that experience about how the virus is behaving now and what may happen in the coming months.
Dr Daniel Jernigan, Deputy Director of the Influenza Division at the Centers for Disease Control and Prevention made :
"The U.S. will likely continue to see influenza activity through the summer, and at this point we're anticipating that we will see the novel H1N1 continue with activity probably all the way into our flu season in the fall and winter. The amount of activity we expect to be low, and then pick up later. In terms of the numbers of infections that have been laboratory confirmed as H1N1, there are now more than 17,800 of those in the United States, including around 1,600 that have been hospitalized and 44 that have died. As we have been saying all along, these numbers are likely an underestimate of the number of cases that are out there. There are some surveys that indicate that the amount of disease in the areas that are having activity with H1N1 is perhaps around 7% of the population reporting symptoms due to influenza-like illness. The virus continues to impact mostly younger people. So far it is not causing significant illness and death in the elderly like we would see with seasonal influenza. And the symptoms that are being reported are consistent with influenza, that being predominantly fever, cough, some shortness of breath, fatigue and chills. There is some vomiting and diarrhea that have been associated with cases of this infection. Everyone needs to be alert to the symptoms of the illness, and especially if you have underlying conditions, such as asthma, diabetes and heart disease."
For me, the 7% figure jumps out. That would mean many millions of cases in the US already, and would be good news because it would mean that the risk of serious illness or death (already small) was even lower. Earlier CDC estimates reckoned that 19 out of 20 cases were going undetected. Jon Cohen from Science Magazine put this question:
"Jon Cohen: Dr. Jernigan, you said there might be as many as 100,000 Americans infected. With the finding that 7% had influenza-like illness in affected communities, that extrapolates to 20 million Americans. Could you give an estimate that's more up to date than the 100,000?
"Dan Jernigan: "Well, the 100,000, as you know, is a rough generalization to try to give a sense of the magnitude of infections that might be there relative to the numbers of laboratory confirmed that we actually had. And so as you can see, in some areas, where there have been a lot of transmissions, like New York City, they're finding maybe around 7% of the community was infected, or had influenza-like illness. There's some other parts of the U.S. where some of our preliminary data suggests the same thing. I think it would be inaccurate to try and take an attack rate of 7% or an area that's highly affected and apply that to the U.S. population. Because as we all know, the amount of disease is different in different parts of the U.S. And so clearly there are hundreds of thousands of cases that have occurred in the U.S. We are working to get a very good estimate of that. But at this point, it would be incorrect to take that percent and apply it to the U.S."
So the CDC clearly doesn't yet have a clear idea of the true number of cases in the US beyond saying that there have clearly been hundreds of thousands. One final quote from Dr Jernigan on those who are most at risk of complications responding to a question from Emma Hitt at MedScape:
"Dan Jernigan: Your question is, what numbers of individuals that are hospitalized have underlying diseases, and about 70% have some kind of underlying disease. The most predominant of that is asthma. The second being diabetes. Immunocompromised status, either through cancer chemotherapy or other compromising conditions is about 13%. And chronic underlying heart disease. The things that we see normally as underlying diseases that are associated with increased influenza risk are the same that we're seeing with H1N1."
Cases seem to be declining in New York, one of the worst affected areas. For those interested in the impact on health and hospitalisations in the city, there is more detail available from the
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