background level of anthrax?

[asrivkin]

OK, simple question:

I know that it takes tens of thousands of spores to actually infect someone. I know that a continuous exposure to hundreds of spores (like wool sorters get, apparently) isn’t good enough. I know that anthrax is found in “the wild”, just in dirt.

I’m looking at recent events and wondering what the “background” level of anthrax is. Is it zero? If we called in a HAZMAT team to a yurt in Mongolia, or on Ford’s Theater in 1865, or someplace “clean”, would anything be detected? Would a nasal swab done on a random farmer somewhere show up with a couple of spores?

[Duck_Duck_Goose]

I don’t have an exact answer, but since it’s mainly spread by animals, I’d guess that a yurt in Mongolia would have a much higher background level of spores than a suburban shopping mall or a factory floor.

I’d expect Ford’s Theater in 1865 to have a much higher level of spores than a 21st century shopping mall, because people overall lived closer to animals back then.

The reason why they authorities didn’t push the panic button when the first guy in Florida came down with anthrax was that he was an “outdoorsman” and it was possible he’d been exposed simply by being “outdoors”, around animals like deer, which can also get anthrax. So the general background level of spores must be higher than “zero”, outdoors.

The First World has long had effective anthrax vaccination programs, so a First World farmer might not test positive for anthrax spores via a nasal swab, but I wouldn’t be surprised if he did.

http://www.tdh.state.tx.us/zoonosis/diseases/ANTHRAX/Anthrax.asp

A vaccine for livestock is frequently used in areas where anthrax is common, but the vaccine must be used before the animal is infected with the bacteria. The vaccine for livestock is not the same as the one for humans. No vaccine is available for pets.

<snip>

An effective anthrax vaccine for livestock and horses can be purchased through private veterinary practitioners, feed stores, or animal health product distributors. The injection can be administered by private veterinary practitioners or rancher personnel and is recommended for:

livestock residing in or near an area where anthrax often occurs;
and animals that will be moved into the area, such as horses transported to trail rides.

http://www.cnn.com/2001/HEALTH/conditions/10/12/anthrax.qanda/

Anthrax is global. It is more common in developing countries or countries without veterinary public health programs. Certain regions of the world (South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East) report more anthrax in animals than elsewhere.

<snip>

In countries where anthrax is common and vaccination levels of animal herds are low, humans should avoid contact with livestock and animal products and not eat meat that has not been properly prepared.

[Squink]

This search turns up this site.

Which states:

b) Thus there are areas of the world, including Nevada, in which anthrax is endemic. This results in chronic environmental contamination with resulting animal and human disease.

i) Bacillus anthracis is found most commonly in areas with neutral to mildly alkaline soil, following drought and flooding, or following excavations that disturb the soil and bring B. anthracis spores to the surface.

ii) Anthrax is transmitted while animals graze in areas that previously experience the disease and the spores contaminate the water or forage.

iii) Anthrax can be transmitted to neighboring ranches by birds, insects, or carnivorous predators.

[choosybeggar]

However, I don’t have any info for you.

I’ve been thinking along the same lines, though. Let’s say we took an office building where we knew anthrax had not been intentionally introduced and performed an environmental and exposure survey. How often would we get a positive? I think the public assumption is never or at least almost never, but my experience with biomedical assays makes me somewhat circumspect regarding this assumption.

Firstly, as asrivkin points out, there is a background level of spore contamination. An if there is a background rate of environmental contamination, there should be a corresponding rate of nasal contamination.

Secondly, all biomedical assays have a definable false positive (and false negative) rate. The false positive rate is the proportion of negative samples tested that yield a positive result. This varies with the nature of the assay, the nature of the material to be tested, and often with the skill of the individual performing the assay.

An important aspect of the error rate of these types of assays is that if applied in a situation where true positives are rare, the majority of positive results will be false positives. See this page for a basic description of relevant epidemiological concepts.

I’d like to know the nature of the field anthrax tests (anti-capsular antibody, anti-toxin antibody, anti-spore protein, rDNA hybridization???) And what are they using for confirmatory testing (they may be culturing, but maybe there is an rDNA hybridization or PCR based assay). And what I’d most like to know is has there ever been a wide scale test of the anthrax test (during a time when positives were not expected) and how did the test perform?

[lucwarm]

I agree that it’s an interesting question.

I can say, however, that every lungful of air contains many asbestos fibers.

[asrivkin]

Wow. I think this is the first time I’ve started a thread and had more than one reply.

It seems to me that this is the missing piece of information (though Duck Duck Goose and Squink point to qualitative but wholly satisfactory answers) that they should be showing on CNN and the relevant health authorities should be giving out. If we knew that 5% (or whatever) of people chosen randomly would give a positive (not a false positive-- I’m thinking of people who would have really been exposed, but exposed to a very small level through random chance spending time in a bad environment), that might relax people.

Or, it might not.