Monday, September 28, 2009

Skewed H1N1 death rates

The Boston Globe has an interesting story on how assessing the number of deaths from H1N1 or any other type of flu is a very tricky process, and this may be leading us to be underestimating how lethal so-called "swine flu" actually is. It also discusses some quirks with reporting and how the official death toll of 593 as of the end of August jumped to just under 1600:
Marc Lipsitch, a Harvard School of Public Health epidemiologist, speculated that the official count of swine flu deaths - it stands below 1,600, as of the middle of last week - “is certainly an underestimate of the number of deaths. It may be a bad underestimate or it may be a modest underestimate, but it is certainly an underestimate.’’

For example, research from New York City, particularly hard hit by the virus in the spring, showed that almost 20 percent of the people killed by swine flu hadn’t been hospitalized, Lipsitch said, making it less likely such deaths would be linked to the disease. Multiplied across the country, that phenomenon could contribute to making the flu strain appear less lethal than it is.

Assessing swine flu’s impact was further muddied by a decision in the past month to change what counts as an H1N1 death.

Until the end of August, only cases confirmed by sophisticated labs were included in the national tally of deaths, which, by then, had climbed to 593. But state health departments, overwhelmed by the number of people infected, have mostly stopped doing the sophisticated and expensive tests to confirm swine flu.

So federal disease specialists expanded the definition to include deaths that doctors attribute to flu and pneumonia based on symptoms, and both the swine type and the seasonal strain count. Since that change was made, the count has grown by an additional 936.

Flu stands in stark contrast to other diseases that are far easier to monitor because they cause fewer cases with more distinctive symptoms. “With flu, we can have 60 million people potentially infected,’’ said Dr. Lyn Finelli, flu surveillance chief at the US Centers for Disease Control and Prevention. “We could never count all those cases, and we could never count all those deaths.’’
Note that some of this applies to "regular" flu as well. The article also suggests why H1N1 shouldn't be dismissed just because it hasn't yet killed as many as "regular" flu. In addition to the real possibility of the virus transforming into something much more (or less) pathogenic as it hops from infected person to infected person before we have a safe and widely available vaccine, there is also the fact that younger people (i.e., those born after a 1957 flu epidemic) may be more vulnerable to this new bug:
Flu viruses are capable of making subtle alterations in their genetic machinery that transform them into more - or less - fearsome pathogens. Timing is critical, too, and that’s especially true with swine flu: A vaccine isn’t expected to be widely available until mid-October, and the germ is already circulating among a population with little natural protection against it.

... A recent study found that people under 30 have little existing protection against the swine flu virus, while older adults harbor disease-fighting cells against the germ. It’s believed the older adults’ immune systems carry the memory of encounters with ancestors of the virus.
Kinda scary. Wash your hands. Stay home from work or school if you're sick with anything. Publicly chastise those who do otherwise.


  1. A similar debate took place during SARS. Some people lingered in ICU for weeks before either recovering or dying. The final mortality rate was something like 6% of all SARS patients. Besides deaths at home, another problem with calculating mortality for H1N1 is that many of the sick recover within a few days and never see a doctor. These people aren't tallied as survivors just as some of those who died at home weren't counted as fatalities.

  2. And the most recent ancestor would be the 1976 Swine Flu virus. You probably know that the vaccine killed 26 people and sickened 200 more with Guillian-Barre. One person actually died from the virus itself. I've been unable to find statistics on the total numbers of people who got the vaccine and who were diagnosed with Swine Flu in order to determine whether the virus or the vaccine was more lethal. No flu shot of any kind for me again this year, thanks.


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