Thursday, April 30, 2009
Reposted: Assessing Community Mitigation Efforts that Should be Implemented - Second Guessing the CDC
Original 4/26 post
I admit that there are enormous information asymetries between the CDC and me -- as well as an enormous difference in expertise. I have been worried that CDC was moving too slowly -- perhaps because it has never dealt with a pandemic within institutional memory and perhaps because the White House is worried about the impact that pandemic precautions will have on the economic situation (assuming that this is a false alarm - and the flu does not spread or it remains milder than the Mexico strain). The CDC's actions seem consistent with the WHO analysis that we cannot contain the international spread of the disease -- the cat is out of the bag, the horse is out of the barn -- and all we can do is mitigate and ride out whatever this disease has in store for us.
It is gratifying to see that the US supply of Tamiflu is up to 50 million courses. That's enough to cover 15% of the population, though a tad short of the 25% goal that the federal government set. Together with the available supplies in state and local government stores, corporate stores, and health care provider supplies, it looks like there is a good chance that there is enough Tamiflu in the US to cover any probable outbreak of swine flu.
The virulence of the flu is still a question mark. No one has convincingly indicated why the Mexico experience is so much different. Certainly, there appears to be rapid human-human transmission, but most cases outside Mexico have been mild. Even so, the CDC is not placing much weight on the mild illness manifested to date in the US. In Dr. Besser's words, the CDC expects a full spectrum of disease to occur -- meaning serious illness and some deaths in the U.S.
The death toll in Mexico is reportedly about 10%, which is vastly more virulent than the 1918 flu, which killed between 20 - 50 million people (including my paternal grandmother) and reduced global domestic product between 2.4 - 16.9%. That flu killed roughly 2% of its victims, which were dominantly young, healthy adults -- the Mexico flu has killed 10% of its victims, again dominantly young, healthy adults. At that rate, we could see more than 50 million deaths with this flu if it spirals out of control. But then again, we can't simply extrapolate from the current "kill rate" because that likely reflects the most serious illnesses, not the norm.
So what should a responsible community in an unaffected state do at this point? My community, for example.
To begin an analysis of what communities should be doing, start with the pandemic severity index. Based on current data from Mexico, the case/fatality ratio appears to be Category 5. However, based on current data (admittedly still sparse from the US), the ratio has been category 1. It increased to category 4 with the first death, but has fallen back to category 3 as more confirmed cases occur in the US without additional deaths (4/29 and 4/30 update) Since CDC and WHO have still not explained the difference in ratio between genetically identical viruses, one could simply split the difference and call this a category 3 pandemic. However, since the good results in the US seem attributable to rapid treatment with effective anti-viral drugs and anti-viral supplies may not remain sufficient to treat everyone who is infected or at high risk due to close contact with infected persons, it might be prudent to treat this as a category 4 pandemic.
While there are 50 million courses in the US stock, that only covers roughly 17% of the US population with a single treatment. Preventative treatment for those in health care and public safety positions who are frequently exposed will consume up to 15 million of those courses, reducing treatment coverage down to about 12%. Assuming that both US stocks and other stocks held by state and local governments, health providers, and corporations are used only to treat the seriously ill, that should be enough for the first wave. But, the second or third waves, perhaps next fall before a vaccine is available, will be met with insufficient stores of anti-viral drugs and the virus may mutate to become resistant to the current drugs. So, it would seem wise to depend on non-pharmaceutical approaches to reduce disease incidence and conserve treatment course. In other words, to use community mitigation measures to increase social distancing so that we can contain the virus outbreaks without everyone getting exposed and a bunch of people needing treatment. (4/30 update)
It is this uncertainty that has led CDC to issue interim guidance on community mitigation because previous planning had been done based on the PSI categories
The next question is when should we act? That depends upon the WHO phase/US stage. Note that the WHO phase has been declared at a phase 5. The US stage should be considered a stage 5 (cases spread throughout the US). That means that all of the measures in the plan should be activated now. I can only speculate why the WHO and US CDC are moving more slowly -- perhaps because they believe that no one can react more rapidly. As of 4/30, it appears to me that all states, even unaffected states, are implementing their pandemic response plans. Still a day or two late and a dollar short.
But, assuming a Category 3 or 4 PSI pandemic is occurring and that we are at stage 5, what should happen? It seems to me that all of the community mitigation measures and interventions in category 4,5 should be recommended except that I would close schools for a week (and depending upon events up to 4 weeks) at this time rather than up to 12 weeks.If you click on the image below, you will be able to read the recommended measures in a separate window.
4/29 PM update
Even a day makes a difference! WHO is now considering increasing its phase to Phase 5. The US now has a death rate that exceeds 1%, so the Pandemic Severity Index in the US is a Category 4 severity, especially given the death rate in Mexico which appears to be in excess of 2% and thus a Category 5 severity. So NOW would be the time to begin all of those community mitigation efforts in every affected state....and at least most of them throughout the US.
It seems as though state and local governments are now acting aggressively to close schools whenever a probable case is identified. That appears to be an adequate response. In Oregon, state officials have suggested that closures will be for about a week -- which is enough time for exposed students to become symptomatic, seek treatment, and be diagnosed as probable cases (although not confirmed). Response seems to be catching up to the situation.