Friday, November 04, 2005

Planflu, II: The Edward R. Murrow version

To understand a plan, knowing what is being planned for, helps. Planning for a pandemic isn't easy since there are few data points and the data are uncertain and lack common features. Estimated deaths in the 1918 pandemic, the severest of the last century was 500,000. The mildest pandemic was in 1968, an estimated 34,000 deaths, about the same as a "normal" seasonal influenza today.

Differences have little to do with medical care, much to do with the virulence of the virus. The current H5N1 so far has been more like a 1918 bug in nastiness, not a 1968 virus. Differences aside, in all pandemics a significant proportion of the US population (30%) has become ill and half of those will seek medical care (usually outpatient). It is this burden on medical services and the effects of absenteeism on all aspects of civil society that will be the practical and expensive consequence of a pandemic, not the fatalities.

Here are the parameters CDC planners used in framing the current plan:
  • Everyone will be susceptible to infection, as no immunity to H5N1 (or other subtype not circulating in human populations) exists.

  • CDC used an incubation period of 2 days. There is some evidence H5N1 might have a slightly longer incubation period (4 days), so CDC is using a conservative estimate. A longer incubation period would slow spread. Viral shedding would start half to one day before illness onset with highest risk of transmission greatest in the first two days, perhaps longer for children. Some people (e.g., the immunocompromised) and children will continue to shed virus for some time, although CDC did not take this into account.

  • CDC estimated a basic reproductive number R0 of 2 (an average of two new infectious cases per infectious case), perhaps slightly low. A recent estimate of R0 for the 1918 virus was between two and three.

  • Overall illness attack rate will be about 30% but vary by age--40% for school-aged children, 20% for working adults. Half of the ill will seek outpatient medical care (15% of the population, 10% of working adults). That amounts to 90 million people in the US, 45 million seeking medical care.

  • There will likely be at least two pandemic waves, each lasting 6 to 8 weeks. The virus will then continue to circulate in the population as a seasonal virus. Seasonal timing is unpredictable.

  • None of this takes into account the virulence of the virus. For moderately virulent viruses like those in the 1957/1968 pandemics, CDC estimates about 865,000 hospitalizations; for a virulent 1918-like virus, 9.9 million hospitalizations. The range for those needing ICU care is about 130,000 to 1.5 million. Need for mechanical ventilators, 65,000 to 740,000. Deaths: 200,000 to 1.9 million. The lower end of these estimates will overtop our current capacity. The upper end would be a catastrophe.
The Plan sums up the situation this way:
An annual influenza season in the U.S., on average, results in approximately 36,000 deaths, 226,000 hospitalizations, and between $1 billion and $3 billion in direct costs for medical care. This impact occurs because influenza infections result in secondary complications such as pneumonia, dehydration, and worsening of chronic lung and heart problems. Despite the severity of influenza epidemics, it is sobering to understand that the effects of seasonal influenza are moderated because most individuals have some underlying degree of immunity to recently circulating influenza viruses either from previous infections or from vaccination.

It is clear that pandemic influenza has the potential to pose disease control challenges unmatched by any other natural or intentional infectious disease event. Pandemic influenza viruses have demonstrated their ability to spread worldwide within months, or weeks, and to cause infections in all age groups. While the ultimate number of infections, illnesses, and deaths is unpredictable, and could vary tremendously depending on multiple factors, it is nonetheless certain that without adequate planning and preparations, an influenza pandemic in the 21st century has the potential to cause enough illnesses to overwhelm current public health and medical care capacities at all levels, despite the vast improvements made in medical technology during the 20th century.
The Plan goes on to say that the high degree of interconnectedness and the swiftness of travel today almost assure that a pandemic would make its way around the globe quickly.
As was amply demonstrated by the SARS outbreak, modern travel patterns may significantly reduce the time needed for pandemic influenza viruses to spread globally to a few months or even weeks. The major implication of such rapid spread of an infectious disease is that many, if not most, countries will have minimal time to implement preparations and responses once pandemic viruses have begun to spread. While SARS infections spread quickly to multiple countries, the epidemiology and transmission modes of the SARS virus greatly helped to contain the spread of this infection in 2003, along with quarantine, isolation, and other control measures. Fortunately, no widespread community transmission took place. By contrast, because influenza spreads more rapidly between people and can be transmitted by those who are infected but do not yet have symptoms, the spread of pandemic influenza to multiple countries is expected to lead to the near simultaneous occurrence of multiple community outbreaks in an escalating fashion. No other infectious disease threat, whether natural or engineered, poses the same current threat for causing increases in infections, illnesses, and deaths so quickly in the U.S. and worldwide.
So that's what the planners were planning for. Straightforward. Correct. None of it news. It says, in essence, what many have known for years. If a pandemic strikes, we're screwed.

A 1918-like influenza pandemic would tax the resources of the best prepared nation. It is an overwhelming natural catastrophe. But like other natural catastrophes (e.g., hurricane Katrina), adequately preparation makes a world of difference in mitigating the consequences. And we are not a best-prepared nation. Our government hasn't gotten us ready, and in fact, has pursued policies that severely weakened us. The Iraq mistake was an ideologically based experiment that failed in spectacular and tragic fashion, its failure affecting almost everything else. As we generate anti-American feeling abroad, we spend more at home to cope with the anticipated effects. This diverts existing resources to topics like "biodefense" which have severely distorted and weakened our public health system. The gigantic $200 billion war cost has run up an even larger deficit (caused by give-to-the-rich tax cuts) which in turn prompts budget cuts which further weaken public health.

We hear daily about "the war on terror," a war we are losing and whose vague outlines are often contrived or worse. Until now we heard almost nothing from our "leaders" about the pandemic threat public health scientists knew was ever-present. Even our preparation for terrorism was a botched job, so with the expenditure of countless billions, we are left worse off than before.

Hence the stark reality of the Pandemic Flu Plan, which has no real plans in it except to say to the states and localities, "Watch Out. Here it comes. Good night and good luck."