Sunday, May 03, 2009

Optimal Mesh

The Swine Flu is spreading very efficiently. It seems like modern society has the ideal configuration for spreading it. So, just as a thought experiment, what would be the ideal organization for spreading the flu? It would not be, I think, like our goods distribution system.

Let's say the flu began with a little rubber duck made in Shanghai. After getting punched out of the mold, it would tumble along the conveyor belt infecting other rubber ducks along the way and get dumped in a box, mostly with those other rubber ducks already infected. Who knows, maybe someone, a Chinese woman, would do some inspection and touch-up. Would she be wearing gloves? Maybe she'll paint on cute little eyes and eyelashes and lick the tip of the brush. I've seen people do that. But our little duck and its friends would end up in a box pretty quickly. The box would be sealed, placed in a pallet with other boxes of rubber ducks, containerized, stacked for weeks in some ship and then in higher stacks at the port in Seattle, then finally shipped to Toys-R-Us in Peoria, IL. From the truck to the shelf is a pretty efficient process these days, but someone in Peoria would have to handle these ducks. Children might play with the ducks. The customer would pick one up and place it in a cart. The cashier would scan it and bag it. And it would find a nice home. Direct customer shipments might be neater, but somebody will still be exposed.

So basically, there would be two growing nodes of infection due to transportation of goods, the one in Peoria and at the origin in Shanghai. Our global system for the distribution of goods is designed to minimize handling and reduce unnecessary dispersion. The rubber duck would have very few opportunities to infect anyone. More importantly, the rubber duck would never move very far again.

Transportation of people is an entirely different thing. Everybody drives to work to be with others where they shake hands, kiss cheeks, pick up the wrong cup, cough on the bathroom fixtures. Then they come home -- where they lick their fingers to wipe bits of jelly and chocolate off of smiling faces. The kids get shipped to school where they have even more interesting ways of uploading their microbial history. The teachers collect assorted papers and projects that have little smudges and sticky spots. Then they take the subway home, and drive to conferences or night school in the next town over. The professors mingle with their students after class, responding to questions by laughing, scratching their heads in thought, borrowing pens perhaps to sign papers. Then they fly to San Diego for their conferences.

I've heard it said that every drop of water we drink has been excreted by a thousand dinosaurs. I think about that whenever I'm breathing the air on an airplane, and possibly sitting next to a large individual. Sometimes when I come up the ramp and pass through the waiting area, there's a new crowd waiting to get on the same plane. Sometimes they crowd around, making it difficult to exit the area. There's a lot of jostling. They seem eager to be on their way. Maybe they're going to Shanghai. Maybe they'll bring some toys home for their kids.


So how would I maximize the spread of the flu? For a specific pathogen, I think it depends on the mode of transmission. For a virus that requires contact, I think the best environment is the happy suburban shuffle, where kids are carpooled to preschool in the morning, playdates and playgrounds in the afternoon, and then maybe group Suzuki lessons, with swimming on the weekends. Maybe the perfect group size is five or ten.

But for flu, it seems like jumbo jets and stadiums can't be beat. If the guy selling hotdogs is coughing on his customers, things can spread pretty quickly. Bowl games bring people from all over and drunks don't cover their coughs either. The Olympics seems like a potential Perfect Storm of infection. Thousands of sports fans, young and friendly people for the most part, will be meeting and mixing with others from every three-letter national entity that can carry a flag around an oval track. These folks will all go home on airplanes and share their experiences, visiting perhaps, all the schools and churches and arenas in a thousand scattered Peorias.


Two related questions occur to me: If we organize our networks to optimize the speed of an epidemic, does that have any bearing on the likely severity of the cases? And second, does the pyramidal structure of my proposed league of voter unions strike you as being in itself a pretty good vehicle for disease transmission?

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At Tuesday, May 05, 2009 4:11:00 PM, Blogger jj mollo said...

Scratch the airplane idea. Although Joe Biden seems to share my paranoia, the St. Petersburg Times explains pretty convincingly that airplanes are not good transmission devices. In fact, an airplane may be the safest place to be during a flu epidemic.


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