This is something I’ve wondered about. Before body piercings, blood draws or injections, they’ll always wipe the skin with alcohol first. But how long does it take until the skin isn’t sterile anymore? A few seconds? A minute or two? An hour? Obviously at some point the bacteria on the skin will return to the baseline value, but is there a point where there’s enough to cause an infection before that?
On the other hand, my niece with diabetes would be careful to use sterile technique if she was putting in her insulin pump needle (which would stay in her body for three days), but when it came to pricking her finger to check her blood, she didn’t bother, and would even suck on her finger afterwords to get rid of any remaining blood. Sometimes she didn’t even bother to put a sterile needle in. So is it possible being careful for things other than actual surgery or IVs mainly a CYA- make the patient feel good type thing?
I had my “diabetes training” in 2015 when I was newly diagnosed, and the counselor advised against alcohol swabs before testing. I think she was suggesting that it could mess up a reading. For a finger prick, you’re not looking for sterile you’re looking for a clean reading of the blood. The hole for a finger prick seems to close up immediately. You suck your finger after literally just to get rid of the little dot of blood.
My friend with Type I just shoots her insulin through her jeans most of the time (which is different than your niece’s pump needle, obviously).
I have a diabetic friend who also shoots his insulin through his clothes. It freaked me out a bit the first time I saw him do it, but I guess the needle doesn’t get very contaminated passing through cloth?
I’ve also heard about people doing injections right though their clothes. I’m guessing it’s not an issue, but when I first heard it, my concern was that it seemed like an easy way to get cotton fever.
Interesting question. I may (or may not) have an approximate answer :
So, this goes back a long time to the 90’s when I took my undergrad vacuum technology elective. So - for semiconductor manufacture (chips, transistors, etc) - you have to print the circuit on a freshly cut surface of a semiconductor (silicon for example). Now as soon as a fresh cut is made on the semiconductor, the air molecules start attaching to the new surface. So a statistically representative time called the Monolayer time, is the time it takes for a single layer of air molecules to have deposited on the fresh surface. These are some typical values :
So for air at around room temperature, it takes 4 milliseconds at 100 Pa (0.015 psi) to form this layer and around 1 hour at 10^-7 Pa (1.5 x 10^-11 psi). It takes about 3 nano seconds for a monolayer of air at atmospheric conditions. cite
This NIH publication, gives a average concentration of 10^5 microorganism particles per m3 of air. And a m3 of air contains about 3 X 10^22 molecules of air particles. So that implies a concentration of about 3 x 10^-17 or a partial pressure of 3x10^-12 Pa.
Plugging that into the formula for monolayer formation time here, gives an answer of 1x10^8 seconds or 30,000 hours.
So that answer seems ridiculous - so it implies that the rate governing step in the spread of bacteria on your skin is the** multiplication rate** of the bacteria (or other microorganism) and **not the deposition rate **of organism from air into the skin.
Sounds like your niece and I have the same pump. And I pretty much do the same thing. Pump site change? Sterilize that. Finger prick? Unless I have goop on my hand, GO FOR IT.
Probably not the best / safest route, but when you have to prick your fingers several times a day (or hour…) sterilizing every time gets old, and it also dries you skin out.
The alcohol is not sterilizing you skin, as kayaker pointed out. It is however cleaning your skin, reducing the bacterial load, and thus greatly reducing the chance of infection.
It is definitely not just a CYA thing. Infection from needle sticks is real.
I would advise against injecting through clothes, I would think little bits of fabric are being inserted under your skin increasing your chance for an adverse reaction.
According to the WHO best practices, alcohol swabbing is mandatory for intravenous and intramuscular injections (except immunizations) but not for intradermal or subcutaneous injections. Proper hand washing protocol is required for all injections.
Getting a dangerous infection from an injection through unwashed skin is a crap shoot just like eating questionable food or just about any other means of being infected with pathogens. A dangerous pathogen has to be on your skin in the first place, it has to be on your skin at exactly the spot a very small needle tip punctures the skin, the needle has to effectively deliver the pathogen into your body, and your body has to fail to fight off the invaders. It’s a small risk in terms of numbers but a huge risk in terms of severity. If you manage to get sepsis you’d really wish you had done a quick alcohol swab despite it being unnecessary most of the time.
To answer the OP the alcohol swab (70% isopropyl alcohol or ethanol for 30 seconds) removes about 85% of flora from the treated skin area. It begins replenishing the second the alcohol dries. Within a minute or two it would be safe to consider it completely recontaminated.
The doc who taught my IV training class said, “If I were to be totally honest, I’d have to say that you could swab with spit and it would be about as effective. But we have to do it anyway.”
I don’t think anyone disagrees with that. That said, when you give yourself 4-10 shots a day, every day, you tend to get a little sloppy around this kind of stuff. Not to mention it gets really old when every time you want to eat in public you have to haul yourself off to the bathroom the minute your food shows up because OMG! nobody wants to see you pull your shirt up and give yourself a shot in the stomach because SO GROSSSS!!! :rolleyes:. Especially when you can whip your syringe out under the table, shoot up through your t-shirt, and nobody even notices you did it.
How does this compare to the iodine treatment they give the inside of your elbow before you give blood? I always understand that also to be to reduce chance of infection, but it seems longer lasting. Is the idea that you need that, since the needle is going to be in your arm for ~10 minutes?
I think so but IANAD. According to the same WHO protocol which I forgot to link in my earlier post a 2% chlorhexidine gluconate in 70% isopropyl alcohol solution is the preferred one-step way to disinfect skin before drawing blood. If that isn’t available it recommends first a 70% alcohol swab followed by iodine. Presumably that is because alcohol evaporates almost immediately but iodine (or chlorhexidine) stick to the skin and continue disinfecting it longer.
Am I correct in assuming there’s really two issues:
Pushing bacteria deep into the skin when the needle is first inserted
If the needle or is left inserted over a period of days, bacteria can migrate in the open wound.
My niece will sometimes put her insulin pump needle on the back of her arm, where it’s visible if she’s wearing a tank top or sundress. The actual spot where the needle goes into her is covered with plastic, and then a clear surgical dressing goes over the whole thing, I don’t know if this is just to keep is in place or to form a barrier to keep bacteria out, or both. I know body piercings you can’t cover the actual piercing with plastic, so you dump antiseptic on it a few times a day. Although it doesn’t really make sense if the bacteria count returns to normal after a minute anyway?