Geodog

The Bird Flu: Is a perfect storm brewing? Fools rush in where angels fear to tread

One of the side effects of running SARS Watch Org during the 2003 SARS outbreak, was seeing some wild predictions of epidemics. Every time there is news of a potential infectious disease threat, everybody who is the least bit handy with a spreadsheet starts creating a model showing that doom is upon the earth, or that there is nothing to worry about, and that public health officials are crying wolf. I came upon one of those posts tonight on BoingBoing, which annoyed me enough to take the time to write this up.

Epidemiologists have been studying infectious diseases for a little while, and they have some pretty good models. I'm not an epidemiologist, but I've studied the topic a bit. The standard model (PDF) is something like this:

r(0)= The average number of secondary infectious cases that are produced by a single index case in a susceptible population = number of contacts per unit of time * transmission probability * duration of infectiousness.

If R > 1, you have an epidemic, with how fast the disease is transmitted depending on how much greater R is than one. And public health measures seek to reduce R to < 1.

As I have written before, The bird flu is *potentially* very scary if it crosses the species barrier, as it has already done once, because:

• Transmission probability is much higher than it was with SARS. SARS usually required close personal contact to spread -- you had to be coughed on by a very sick person in a hospital, in most cases. The flu? It doesn't require large droplets to spread, and you can even get it from touching something with the virus on it.


• Duration of infectiousness and number of contacts per unit of time are both much higher as well. With SARS, you got sick very fast, and were very sick in the hospital within 24-48 hours of being contagious. So you didn't get that much of a chance to spread it to the general populace. With the flu, "adults may be able to infect others beginning 1 day before getting symptoms and up to 7 days after getting sick. That means that you can give someone the flu before you know you're sick as well as while you are sick." The onset is less sudden, and less clearly something very dangerous. (And now that the amount of vaccine in the United States has been cut in half, it would be much harder to tell who had the normal flu, which only kills 36,000 people every year, predominantly the elderly, and who had the bird flu.

Is a perfect storm brewing now? I don't know, but it is possible. We have no vaccine that works against the bird flu at the moment. If the bird flu did get established in humans, we would have to use the oldest public health tactics we have, isolation and quarantine. Given what a relatively hard to communicate illness (SARS) did to the people and economies of China, Taiwan, Hong Kong, Singapore, and Canada, it is easy to imagine the bird flu doing much, much worse. Millions of people died in 1918 from the Spanish Influenza, and nobody was travelling by airplane then.

While I don't think there is any reason to panic, nor to avoid travel to Asia, the fact remains that if the bird flu gets established in humans, there is a significant chance of a major pandemic, at least that's what Dr. Shigeru Omi, the World Health Organization's regional director for the western Pacific, has said:

"So far there are no cases of human-to-human transmission, but if the situation continues a long time, there is a high possibility that we will have [them]," Omi said at a news conference ahead of next week's western Pacific regional annual meeting in Shanghai.

"Unless intensified efforts are made to halt the spread of the virus, a pandemic is very likely to occur," Omi added.

What can be done now? Pressure our government to provide the economic incentives for private companies to look for a vaccine. According to WHO:

At the beginning of April 2004, WHO made the prototype seed strain for an H5N1 vaccine available to manufacturers. To date, only two of the world's roughly 12 major companies producing influenza vaccines have taken work on a pandemic vaccine significantly forward.

And one of those two companies was Chiron, which had such severe manufacturing problems that it just had to discard the 54 million does of normal Flu vaccine that it had prepared for this flu season.

The second thing that can be done is to pressure countries where the bird flu is endemic to take drastic measures, involving severe economic loss (i.e. killing off lots of their fowl), now. Perhaps those of us living in the wealthier countries could share the economic burden. As SARS recently reminded us, the pain of preventative measures, while bad, is a lot smaller than the pain of letting a fatal infectious disease get established. As Quinn pointed out, in a globalized world, it doesn't matter where you live.

The last thing that can be done is to strengthen our public health infrastructure, which has been deteriorating for years, and, in California at least, has been gutted in the last few years by budget cuts.

If people are looking for a good basic source of information on infectious disease epidemiology and simple models, I recommend the slides on the website of UC Berkeley's School of Public Health's Center for Infectious Disease Preparedness (where I am currently taking an excellent course, Essentials of Public Health Epidemiology), from Drs. Tomás Aragón and Wayne Enanoria. I also highly recommend Laurie Garrett's book, The Coming Plague. If you are a web junkie like me, Dr. Gerberding's communications team at the CDC does an excellent job of keeping the CDC website up to date, and Dick Thompson of the World Health Organization's Communicable Disease Surveillance & Response division has set up a section of WHO's site dedicated to Avian Influenza.

BoingBoing is a fun site, but it might not be the best place to get your information on infectious diseases.

Posted by tbishop61 at October 7, 2004 12:40 AM | TrackBack