Stories tagged epidemiology

Jun
17
2009

John Snow: Eats only vegetables, drinks only boiled water... dies of a stroke at age 41. Nuts.
John Snow: Eats only vegetables, drinks only boiled water... dies of a stroke at age 41. Nuts.Courtesy Wikimedia Commons
Here we are again, languishing in the long hours of June 17, enjoying a leisurely Snow day. A John Snow day.

Wait, you say, fractionally raising your heads from your overstuffed couches and baths full of tepid water. Didn’t John Snow actually die in June? And, like, didn’t he die on June 16, not on the 17th?

Well, yes, June 16, 1858, was in fact the day John Snow died. But I only just made up Snow day, and I wasn’t paying attention yesterday. Plus, do y’all even know who John Snow was?

Oh, John Snow was the most marvelous man! He drugged queen Victoria! He deprived thirsty communities of pump handles! He saved London from tiny invisible monsters! Oh, what a man!

John Snow was the sort of guy that posthumously gets the Cleverboots Award for Correct Thinking. Sort of like how I will surely be recognized with a Cleverboots Award years after I die, for how strikingly accurate my public ranting on the subjects of invisible lasers, lizard people, and “stay away from me, wizards!” will prove to be.

Snow was one of the first people to study the used of ether and chloroform as anesthetics. Which is to say, people had used those compounds as anesthesia before, but Snow calculated doses that would leave you somewhere between horrible pain and drugged to death. That was important. Everybody’s favorite queen of England (Victoria, duh) had Snow personally administer her anesthesia during the births of her eighth and ninth children. Once people saw Victoria doing it, everybody wanted in on anesthesia.

Snow’s greatest achievement, perhaps, came in an episode I like to call “Johnny Snow vs. Cholera.”

See, in the middle of 19th century in London, people were sort of split into three groups. There was the “Cholera is caused by poisonous gases” group. Most everybody thought that theory was the best, and it was called the “miasma theory.” There was also the “Cholera is caused by something tiny or invisible in water” group. This was pretty much what we call “germ theory,” and most everybody was all, “Germs? That’s stupid. Check your head!” And, finally, there was the “Hey, we’re actually dying of cholera over here” group, and most everybody thought they were gross.

But not John Snow! Instead of arguing and making up theories based on what seemed reasonable, he actually went out and looked at stuff. Gasp!

Without knowing for certain exactly how cholera was being transmitted (germs or miasma, or whatever), Snow began to record who in London was getting the disease, and he plotted cases on city street maps. He saw clusters of the disease in certain areas of the map, and so he looked for common elements. In the case of one outbreak, Snow realized that the majority of infected people were getting their water from one of two water companies, both of which were pulling water from a dirty (read: full of sewage) section of the Thames river. In another outbreak, Snow found that most of the victims of the disease were getting their water from a particular public pump. When John Snow had the handle of the pump removed, so that nobody could get water from anymore, the outbreak ended.

Snow’s discoveries from studying the cholera outbreaks added to the evidence for germ theory, and, perhaps more importantly, constituted a huge stride forward in the science of epidemiology. Snow wasn’t just figuring out how to cure diseases, he was tracking down where they start, and learning about how they move through populations. These are the same basic principles behind the actions health organizations still take today when dealing with outbreaks in the much larger population pools (or pool) of the 21st century.

It’s pretty interesting stuff. Check out this Snow-stravaganza: UCLA’s comprehensive page on John Snow and the cholera outbreaks.

Now enjoy what’s left of your Snow day.

May
01
2009

A research group led by Dirk Brockmann at Northwestern University has created a computer model that predicts the spread of the 2009 H1N1 influenza virus in the US. (It uses a complex set of mathematical equations to describe the movement of people and virus.)

How can you track and predict the movement of something so small?: Follow the money, of course! (This is a colorized negative stained transmission electron micrograph (TEM) showing some of the ultrastructural morphology of the A/CA/4/09 swine flu virus. Got that? Good.
How can you track and predict the movement of something so small?: Follow the money, of course! (This is a colorized negative stained transmission electron micrograph (TEM) showing some of the ultrastructural morphology of the A/CA/4/09 swine flu virus. Got that? Good.Courtesy CDC/C.S. Goldsmith and A. Balish

(Brockmann was a guest on Minnesota Public Radio's Midmorning show today, and you can listen to it online.)

The good news is that, based on what we know now, and assuming that no one takes any preventive measures, we could expect to see some 1,700 cases of swine flu in the next four weeks. Because of the preventive measures being taken wherever a suspected case of H1N1 flu has popped up, we should actually see fewer cases. (You can see Brockmann's models here.) That's lousy if you're one of the folks who picks up the virus, but not a devastating number of cases. Of course, this is a rapidly developing, fluid situation, and things may change. Still, tools like Brockmann's model help to ensure that emergency supplies and other resources get to the places likely to need them most before they're needed.

Professor's Computer Simulations Show Worst-Case Swine Flu Scenario from Northwestern News on Vimeo.

Don't have faith in computer models? Well, a second research group at Indiana University is using another model, with different equations, and getting very similar results. That's a pretty good indication that the predictions are reliable.

You might remember Brockmann from a 2006 study that used data from WheresGeorge.com, a site that allows users to enter the serial numbers from their dollar bills in order to see where they go, to predict the probability of a given bill remaining within a 10km radius over time. That gave him a very good picture of human mobility, reflecting daily commuting traffic, intermediate traffic, and long-distance air travel, all of which help to model how a disease could spread.

Apr
26
2009

Pandemic prevention in Mexico City
Pandemic prevention in Mexico CityCourtesy Chupacabras

No mass at Cathedral of Mexico City Sunday

In addition to churches, Mexico closed schools, museums, libraries and theaters, hoping to contain the outbreak of a swine flu variety that is killing people. Officials say as many as 81 people have died and more than 1,300 others are sickened from a new type of flu.

The virus contains genetic pieces from four different flu viruses; North American swine influenza, North American avian influenza, human influenza A N1H1, and swine influenza viruses found in Asia and Europe.

Swine flu symptoms

Symptoms of the flu-like illness include a fever of more than 100 degrees Fahrenheit (37.8 degrees Celsius), body aches, coughing, a sore throat, respiratory congestion and, in some cases, vomiting and diarrhea. Click this link for more key facts about swine influenza (swine flu).

Global swine flu alert

China, Russia and Taiwan plan to put anyone with symptoms of the deadly virus under quarantine. Ten students from New Zealand who took a school trip to Mexico "likely" caught this swine flu. Four possible cases of swine flu are currently under investigation in France. More than 100 students at the St. Francis Preparatory School, in Queens, New York recently began suffering a fever, sore throat and aches and pains. Some of them had recently been in Mexico.

"The United States government is working with the World Health Organization and other international partners to assure early detection and warning and to respond as rapidly as possible to this threat," Dr. Richard Besser, acting director of the CDC, said during a Friday afternoon press briefing.

How to track illnesses globally

There are several useful online resources that track health information and disease outbreaks.

  1. The World Health Organization (WHO) has an Epidemic and Pandemic Alert and Response (EPR) webpage.

    As of 26 April 2009, the United States Government has reported 20 laboratory confirmed human cases of swine influenza A/H1N1 (8 in New York, 7 in California, 2 in Texas, 2 in Kansas and 1 in Ohio).

  2. HealthMap is a website that aggregates news feeds from the WHO, Google News, ProMED, and elsewhere to map out all of the disease outbreaks. (Click the box in front of influenza under "Diseases, last 30 days" to see just flu cases.)

What is a pandemic?

The WHO's pandemic alert level is currently up to phase 3. The organization said the level could be raised to phase 4 if the virus shows sustained ability to pass from human to human. Phase 5 would be reached if the virus is found in at least two countries in the same region.

"The declaration of phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short," WHO said. Associated Press

Phase 6 would indicate a full-scale global pandemic.

Sources:

Researchers at the International AIDS Conference sifted through published papers on the risk of heterosexual HIV transmission. They say that while a popular estimate pegs the rate of HIV transmission through heterosexual sex at 1 per 1000 contacts, true rates of infectivity are all over the map and dependent on many variables. The infectivity rate for certain sorts of activities is much, much higher-- as high as 1 in 3 contacts. The take away message? "Claims in both the popular media and the peer-reviewed literature that HIV is very difficult to transmit heterosexually are dangerous in any context where the possibility of HIV exposure exists."