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Plague in the Sewers?
I stopped paying attention for a second, so I don't know how this came up, but somehow we ended up with the director of Heritage's Center for Data Analysis explaining that the dawn of proper plumbing and the end of open sewers had cut down on disease a lot and raised life expectency. Quite true. But he then named "bubonic plague" as among the diseases that have been curbed this way. That's not right is it? Plague is spread by rats, not human waste. Plus, the sewers in big American cities are full of rats and the rats aren't plague-infested. Just an offhand remark, nothing to do with Social Security, but I have a morbid interest in catastrophic infectious disease. Speaking of which, have I mentioned the Avian Flu blog enough? Unless I'm mistaken, the flu disproportionately kills the elderly, so it's quite possible (and I'm not joking) that a global pandemic and the attendant tens of millions of deaths will resolve these demographic issues for us.
Which leads to my serious point. Does anyone know how reliable these long-term demographic projections are? Wasn't it conventional wisdom among demographers in the 1970s that population was going to keep growing rapidly -- accelerating, even -- for decades and decades?
April 19, 2005 | Permalink
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My guess is that long-term demographic projections, then and now, incorporate assumptions about economic growth and agricultural output that are, shall we say, heavily oil-dependent.
Posted by: SqueakyRat | Apr 19, 2005 10:06:46 AM
In general, flus kill the elderly disproportionately. However, the 1919 flu was an example of a flu that really didn't. The flu had a massive antigenic shift that made it very lethal to a naive population (anyone under the age of, say, 40), but less lethal to the older population who, it is postulated, were exposed to a similar strain in their youth and therefore had some immunity to it.
Imagine, if you will, a foxtrot epidemic--people are going to die unless they can learn the foxtrot in 5 minutes. Now, old people who are generally more decrepit are going to die because they can't get up and dance. But old folks are going to be at an advantage relative to young folks, because they grew up dancing the foxtrot and just have to remember it. But young folks, who grew up shuffling and slam-dancing, are at a big disadvantage because they have to learn it. Sure, their youth is on their side, but their exposure is not.
Um, so what I'm saying is that a flu pandemic would not nececssarily have the silver lining of lowering Medicare expenditures through 2035. And, um, I guess I'm also telling y'all to learn the foxtrot. Slow, slow, quick, quick...
Posted by: theorajones | Apr 19, 2005 10:17:34 AM
Demographic projections are only as good as the information you put into them. They tend to start with, "if current rates of X (fertility, mortality, etc.) continued into the future, then this is what would happen." They may then play around with what happens if current rates change in some way. They work reasonably well for fairly short-term projections, when the people you're talking about are already alive and in (or at least close to) the age ranges for which the rates you're using are most applicable. Uncertainty increases the farther out in time you go, as you apply current rates to people who aren't even born (and may never be born).
Many projections in the past have been embarrassingly (for us demographers) bad. Matt's right that in the early 70s, just when (we now know) fertility had already started to turn down, demographers were still assuming population growth forever. Similarly, there was hysteria (well, as hysterical as demographers get) about the low fertility of the depression, and a number of demographers made dire predictions about shrinking and aging populations just as the baby boom was about to take off.
Posted by: MaryGarth | Apr 19, 2005 10:17:58 AM
Well, there's probably some benefit from keeping the
rats underground and mostly out of contact with
people - IIRC it's the fleas on the rats. But it's
more about cholera, dysentery, and perhaps typhoid.
Those are the big killers where sanitation is bad
and human waste gets into drinking water.
Posted by: Richard Cownie | Apr 19, 2005 10:19:17 AM
Bubonic plague is not extinct. There's a case in Oregon every once in awhile. It's limited to country areas now where it is endemic among certain borrowing rodents.
Posted by: John Emerson | Apr 19, 2005 10:20:06 AM
bubonic chronic is still widespread, however.
Posted by: praktike | Apr 19, 2005 10:20:43 AM
So I was reading this economics textbook -- the famous one, Samuelson? The edition I was reading was from the early baby boom period. I enjoyed the quaint reference to the National City Bank of New York, but more interesting was the chapter on demographics.
The population of developed countries had been ageing for decades prior to the second world war. The slow gentrification of western societies was well-known, and had been in progress since at least the late 19th centry.
Samuelson then mused that recent years had bucked the trend, and it would be interested to see how long this reversal lasted.
Well, now we know.
Posted by: Amit Dubey | Apr 19, 2005 10:21:11 AM
I thought it was the fleas on the rats not rats
Posted by: flea | Apr 19, 2005 10:21:30 AM
matt,
there's alot of problems killing lots of people would solve. Do you think it's ethical to weigh the negatives of elderly people dying against the positives of them not being around? I'm not a big fan of "silver linings" of people dying. I plan to be old someday, and I don't want people cheering my demise.
...
maybe fertility rates behave just like volatility in the stock market. There's a long-term mean, and fertility bounces around it in a Markov process (of course "p" and "q" would not be constant, instead dependent on position relative to the mean). It would then be impossible to predict demographics for very long in the future at all.
Posted by: scott lewis | Apr 19, 2005 10:27:04 AM
According to recent numbers, population peaked in 1973 and has been on the way down ever since. What's affecting the numbers is fertility rate - the number of women who go through their child-bearing years without bearing any children. There was no real way to predict the drop in fertility rates in the 80s and 90s until it happened, since there were plenty of women and they all could have had kids if they wanted. Now that they didn't, we have a fairly clear picture of declining/aging population in the US, and population numbers falling off the cliff in Western Europe. Since there are now going to be less women of child-bearing age going forward, fertility rates will have to rise fairly dramatically just to get back to replacement levels (2.01 live births/woman), but the fertility rates are actually continuing to drop even faster than previously - not just in the US, but almost everywhere in the world (including India and China).
If you are interested in this subject, I strongly recommend The Empty Cradle by Philip Longman. It lays out the situation very clearly, including economic causes and implications, and includes a really interesting idea for addressing the entitlements problem.
Posted by: Rob Salkowitz | Apr 19, 2005 10:27:09 AM
In regards to the Plague modern hygiene is probably not only relevant in a secondary sense. The periodic historical flare-ups of this disease appear to result from obscure genetic causes in the infectious organism. Normally Yersinia pestis is a harmless gut bacterium in rodents, but every now and then it undergoes a mutation whereby it secretes an adhesive substance causing it to clump together in masses that obstruct the flea’s gut, and this causes the flea to vomit it up into the creatures the flea is feeding from. For the bacterium, which feeds on the same blood that the flea ingests, entering a mamalian bloodstream is like entering the Promised Land. And when enough of these mutations occur in more or less the same time frame, you get a major epidemic. Modern sanitation of course does generally keep rats away from people, but the danger remains (out west in the US especially) that housepets, especially cats, can pick up the disease from sick rodents they catch and transmit it to their owners.
Re: Does anyone know how reliable these long-term demographic projections are?
Long term projections of any phenomenon that allows a wide range of variability are probably not worth the paper they are printed on. Old and very true saying: “Trees do not grow up to the sky”
Re: According to recent numbers, population peaked in 1973 and has been on the way down ever since.
Perhaps you mean “fertility rates”, not population? The world’s population (and the US population and even the population of most European countries) is still growing.
Posted by: JonF | Apr 19, 2005 10:34:33 AM
Posted by: theorajones:
"Um, so what I'm saying is that a flu pandemic would not nececssarily have the silver lining of lowering Medicare expenditures through 2035. And, um, I guess I'm also telling y'all to learn the foxtrot. Slow, slow, quick, quick..."
BWAHAHAHAHAHAHA!!!!!!!!!!!!
Your Arthur Murray 'magic steps' won't save you from the Foxtrot Plague; your death will merely be slower, lingering and more painful. You must learn Bronze, or unlock your ankles and learn Silver - pass those feet, cover some distance!
'Slow, quick quick' is the only path to survival.
Posted by: Barry | Apr 19, 2005 10:58:22 AM
I suspect the writer is somehow mistaking bubonic plague and Cholera. If I recall correctly, Cholera is the disease directly related to water supplies polluted by sewage. An improved sewer system would have a very direct impact on Cholera.
Posted by: Matthew | Apr 19, 2005 10:59:32 AM
Maybe so, but there are a lot more crocs in the sewers of New York than were in the streets of Europe. Sewers bad.
Posted by: jerry | Apr 19, 2005 11:14:27 AM
This guy is in particular referring to John Snow, who was profiled in Edward Tufte's books on data visualization, and traced the source of cholera in London to one particular pump, which was then shut down and saved the city.
Posted by: Andy | Apr 19, 2005 11:19:54 AM
Ineed, the water pump incident.
Population projections: You know pretty well how many old people there are going to be iin 50 years time ’coz they’re already here, being 20 years old currently. So that part can be accurate.
What you don’t know is how many children they are going to have between now and then. The UN projections have been coming down every revision because the demographers are consistently assuming that future birth rates will be higher than what we have now.
Posted by: Tim Worstall | Apr 19, 2005 11:35:04 AM
Plague is carried from rats to people by fleas. Washing - both of people and clothing - greatly reduces the risk of plague.
Posted by: JR | Apr 19, 2005 11:35:55 AM
btw- yes it was cholera (in England), and yes it was tufte.
Posted by: praktike | Apr 19, 2005 11:38:43 AM
but somehow we ended up with the director of Heritage's Center for Data Analysis explaining that the dawn of proper plumbing and the end of open sewers had cut down on disease a lot and raised life expectency.
Hang on. Some bigwig at Heritage pointed out how great it was that governments undertook massive public works projects, combined with regulation, which achieved the goal of improving the general welfare? Is there a mandatory "irony check" at the entrance for employees?
Posted by: mds | Apr 19, 2005 11:41:19 AM
> It's limited to country areas now where it is
> endemic among certain borrowing rodents.
I don't believe there is any really good understanding of why bubonic plague breaks out in large qtys ever few hunderd years. Presumably modern sanitation helps keep it under control these days, but there are plenty of places in the world with bad sanitation, high population density, and no plague - at the moment.
Cranky
Posted by: Cranky Observer | Apr 19, 2005 11:48:39 AM
Bubonic plague was largely transmitted by fleas from black rats to humans. There are other vectors, but they were much less significant. The black rat has been pushed out of its niche by the brown rat which does not act as a good vector for bubonic plague.
Interestingly, the brown rat tends to befoul grains that it gets into, which the black rat does not do. It is possible that the brown rat has caused more deaths from malnutrition than the black rat did from bubonic plague.
Posted by: Njorl | Apr 19, 2005 12:22:51 PM
Re: Washing - both of people and clothing - greatly reduces the risk of plague.
I have to wonder about that. My cats have a lot of trouble with fleas (I live in Florida; flea season is basically all year round here). We are very diligent about flea-treating them monthly with Advantage, and doing the carpets with flea-dust, and washing our stuff and (certainly!) ourselves. Nevertheless hardly a week goes by that one of those damn bugs doesn’t decide to sample the human buffet as well.
The really grave danger from Plague is if the disease goes pneumonic. Then it is passed from person to person airborn, like the flu, and can run up mind-numbing death tolls in very short time periods. This is one of my fears that terrorists might try to kick off such an outbreak, which would not be very difficult to do. Yes, the disease can be treated, but if it spread first among low income, poorly insured people you'd still have a helluva of a death toll, and major panic, before it could be gotten under control.
Posted by: JonF | Apr 19, 2005 12:34:45 PM
Yep, cholera it was. But why should the director of Heritage's Center for Data Analysis (!!) get hung up on a little piece of trivia that 1) is a single Google search away, and 2) is part of the mental furniture of anyone who's vaguely acquainted with the history of western medicine and public health.
Ignorami.
Posted by: sglover | Apr 19, 2005 1:02:00 PM
Ah, clearly none of you live in New Mexico, where we have a human case of the plague every year or two. Our rabbits carry it. All of the emergency rooms in the state are familiar with the symptoms and so people rarely, if ever, die, and it's never a very huge deal.
We did have some tourists from New York a few years back get infected, go back to NY, then develop symptoms. The hospital in NY was so freaked out, they called in the CDC, which was freaked out that the plague had gotten to New York, but calmed down once they learned that the couple had been to New Mexico. Plague in NM? Nothing to worry about...
Posted by: Maya | Apr 19, 2005 1:13:14 PM
I suspect what peaked in 1973 was world population growth. After 1973 the growth rate slowed -- that is the second difference turned negative. But that does not mean that population peaked.
Posted by: spencer | Apr 19, 2005 2:58:14 PM
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