I'm in health-care, but this is not my strong suit. One of my patients says he goes to a gym, and there is a sharp edge on one of the often-used pieces of equipment that he cut himself on, and believes others have too. He asked me what is his relative risk of contracting hepatitis C from this exposure.

I found the following: in his city, there are about 37,000 residents. The incidence in his city, according to posted epidemiological studies, is 500 persons per 100,000 have the disease. The risk from published needlestick seroconversion data is that about one in 400 who are stuck with infected needles come down with the disease. Granted, this would be higher than what would be experienced in the community setting, given that the blood would dry, and presumably the titers of the virus would be lower.

Crunching this data is giving me a headache. Anyone have a sense of what the relative risk is, given the above info?

 

So I'm neither a risk analysis or math guru (I'm in healthcare software support), but I'm getting a ratio of approximately 185 people in his town that statistically would have HepC. Obviously of the 37,000 that live there no where near that many are going to be gym members either - which is a factor that reduces his risk even further. I think that knowing the total membership of the gym is probably an important part of it, because all other numbers would be factored based on a total population of 37,000 - but the actual "population" is probably closer to 500 or less. Based solely on a total gym membership of 500, given the same ratio of 500 per 100,000 that would probably take it down to a .5% chance that someone with HepC was even a member of the gym, let alone scratched themselves on that same machine - so how many have scratched themselves? 10? I would think that 10 individuals would be high, since that becomes a liability issue. And that's not even factoring in the needlestick seroconversion data. Another factor is that HepC does have a relatively long livespan outside the body - up to 3 weeks.

I think we would need some numbers on how many total gym members and how many unique users are there of that machine within a 3 week window, and at least a guess as to how many have been scratched. Essentially I think figuring an actual chance is pretty much impossible, but given the numbers we have and the numbers based on supposition (gym members & number that have scratched themselves). Just for making this wildly unlikely, but trying to pad it for possibility, let's say 50 of the 500 members have stuck themselves, and they've all done it within the past month - that seems to become a .05% chance that one of the people scratched by the machine has HepC - that's a 1 in 2000 chance. So then let's try to factor in the needlestick ratios - a 1 in 400 ratio is .25% x .05% (.0025x.0005 = .00000125) or .000125% - essentially 1 in 1,000,000.

So I think it is wildly improbable that his chances are actually that high - that's based on 50 people sticking themselves, and it all being within a short enough time frame to transmit the disease. If I had to make a guess, I'd say his actual chances are closer to 1 in 5 million, but that's purely a guess.

 

I'm an engineer, with some maths background.


I would go to the gym with my Dremel and a selection of grinding and smoothing tool inserts. Excellent American product Dremel.


Must remember to take an extension lead too, the gym may not have one (or possibly inquire why one was needed ).

 

Agreed but if he’s the kind of guy that worries enough to ask this in the first place a that matters is the binary fact - you have it or you don’t ... wouldn’t think he’s going to worry any less by not getting a test .... just my 2c

 

I too am an engineer, and am good in maths as well (in fact, I did take "Probability and Sadistics" in College), but my approach would be different...


I would tell him the probability is 100%. And sell him on taking one of those new hip HepC prescriptions for the rest of his life. Then make sure the hot pharma sales rep knows what you did, as it will increase the chances of her going to lunch with you. That is what is known as engineering a better world (...for you)

 

Vanishingly small probability of contacting Hep C in this scenario. Not worth worrying about.

 

Thanks. That's what I ball-parked and I appreciate the response.

 

So we have both @BlackTalon and myself monetizing the answer and you say not to worry! How can we sell something in this scenario???

T'aint love makes the world go round, as all y'all know


Hey M'Bob, Evitzee's right, but I'd take the Dremel anyway.

 

Don't forget that Hep C also imparts a certain patina...

 

You might think that, but in fact, like most people, when they get information that indicates that the probability of something bad happening is either less than they thought, or low in general, they adjust their anxiety accordingly.

 

I'm probably infected just reading this thread.

Thanks, guys...

 

I would say a higher risk in the sweat on the equipment


Send him this article

http://www.independent.com.mt/artic...-the-hepatitis-virus-lurking-in-sweat-178352/

 

There is an effective vaccine for hepatitis B, which is what this article refers to. As far as I know, there is no evidence that hepatitis C is transmitted in sweat.

 

I am mathematician who has worked with epidemiological models. The hardest parameter to measure in these models is the contact rate. It is at the essence of this question as well. The probability of an infection here is vanishingly small. One has to consider how long Hep. C is viable outside of the body and how often people break skin on that piece of equipment. I am with @Evitzee, but it is a fun thought experiment. If you want to answer it you will need to gather some data. However because this involves human research, it would require Institutional review. The board would deem it unethical and suggest you take @BlackTalon's advice and fix the hazard.

 

Close to zero. Probably....

 

Hep c transmits blood to blood. Wear gloves or quit sharing needles.

 

Yes; that is the obvious unknown. Hepatitis C, under certain conditions, can live on a surface for up to six weeks, according to a recent study. Thus, after that time, the whole issue is moot, because the virus particles would be non-viable. So, it is often helpful, in a scenario like this, to use the worst case, i.e., you cut yourself right after someone else did. In that case, estimating the likelihood of encountering a carrier, and the likelihood of transmission, is instructive.

 

True, the probability of transmission likely decays exponentially with time. You could overestimate transmission probability by

P= 1/400 * exp(- t / 42)

Here t is the days since the last person cut themselves on the equipment. It assumes the mean time to the virus becoming inviable is 42 days.

 

Hence the importance of National Handwashing Awareness Week (NHWAW).

 

Odds of anything of any kind happening at any point in time are 50-50, it either happens or it doesn't.
Also whatever could have happened already did.