Needles and Nitrites

Graham Shepherd muhero at
Sun Jun 7 05:46:14 EST 1998

TRKeske wrote in message
<1998060603410100.XAA01128 at>...

>I've long been bothered by the fact that health-care needle-stick
>accidents are claimed to be so low risk, yet "dirty needles" for
>drug users are so extremely effective at causing infection.
>This is a maybe a controversial point, but I question whether the
>infectivity rate for drug users should be much higher than for
>health care needlesticks, per incident.
>Drug users may inject far more often, but if the infectivity
>rate PER INCIDENT is lower than that of heterosexual
>intercourse, then you would expect to see far more heterosexuals
>with AIDS than drug users with AIDS.  In fact, it is just the
>opposite: the number of drug users with AIDS is nearly triple [3].
>I asked a microbiologist about this.  He claimed that the dangers
>for an incident of drug injection were about "1000 times" greater
>than that for a needlestick accident.
>Although this person had insisted that I be precise and quote my
>sources, he himself quoted no source for this.  I suspect that it
>was just a haphazard guess.   If the risk were really
>"1000 times greater", the proportion of drug users with AIDS
>should be even far more dramatically skewed.
>The microbiologist said that the key difference was that injecting
>directly into a vein is a far more efficient course of entry, than
>merely into muscle tissue.
>Superficially, this might seem to make sense.  However, it seems
>to me that for a virus like this, mere entry into the bloodstream,
>at all, should be quite sufficient.  There is no blood, in muscle
>tissue or anywhere else in the body, that merely sits in place.
>It has to cycle back through the whole circulatory
>system, back to the heart.  I'm sure that a percentage of blood
>cells may just get stuck somewhere and die, but I would think
>that for the most part, they keep circulating, in time, through
>the whole body.

Your whole red cell population is renewed every few months. White cells last
longer. The blood supply does not infiltrate every organ of the body
completely - most of the materials that are distributed by blood permeate
through the walls of the blood vessels into the tissues they supply, and
viruses (and some blood proteins) are too big to do this. So muscle tissue
wll not normally have this type of agent present.

>It is a recurring theme that infectivity of HIV is related to
>the dose level and concentration of the virus.  Supposedly,
>this is why AIDS doesn't spread by deep kissing, even though
>the virus is present in saliva, in low amounts.

This applies to every infectious organism. There's a minimum number of bugs
needed to achieve infection. For some bugs it may be as little as 1. But
it's usually a lot more.

>I doubt that even drug users are injecting themselves with
>needles that are dripping with visible blood.  Even the
>most hopelessly addicted souls can at least wipe a needle
>off on their sleeve.  A mouthful of saliva, that's safe, yet
>the invisible, miniscule amount of blood on a wiped-off
>needle- that manages to infect our society's undesirables,
>like crazy?

Your doubts are not well founded.

 Needle stick injury involving a needle that has been used on a randomly
selected member of a population will have a risk associated with the
incidence in that population. In the general health care population, the
incidence of infection will have a lower value than in a specialised
population with a higher incidence - eg drug users. This assumes that the
cases are otherwise identical - but if they were, how could a difference in
incidence of infection arise?

Blood borne infections are associated with multiple needle use - needle
sharing is one way, and in some places sharing of the whole syringe and drug
dose by several injectors in a "shooting gallery" is another. Injectors need
to ensure they've got a vein - so they draw blood back into the syringe
before injecting - this gives a much higher dose than the amount carried on
a used needle by itself. Once the community has one infected member, the
rate of transmission through the community will be influenced by the
behaviour of that community.

One IV drug user carried HIV from one UK city to another in the 80s and the
infection susbsequently spread throughout the drug user community in the
second city. The most dramatic effect in increasing condom use to prevent
AIDS transmission has been the reduction of rates of sexually transmitted
disease in general. Change the risk behaviour, change the risk.

One final point - blood borne diseases aren't necessarily just spread by
needle injury. I know of a case of Hep B transmission between two members of
a family who shared a razor.


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