Welcome to our Forum.  Thanks for your questions.  Before I address your specific questions, please let me emphasize some facts about HPV.  We know that over 80% of sexually active persons, even persons with a singe sexual partner, will have HPV at some time.  As a result is extraordinarily hard to determine who has given a person HPV.  In addition, carefully done studies have clearly demonstrated that nearly all HPV infections are transmitted by DIRECT sexual contact.  Studies looking for HPV DNA in the environment will often find it but that does NOT mean that the virus is likely to be transmitted through environmental or casual contact.  On the other hand, in science one can never say never and it is possible that a very, very small proportion of HPV infections are acquired through non-sexual, environmental contact.  They however are the exceptions and most experts do not suggest special precautions or concerns about acquiring the infection through non-sexual contacts or exposures.  None of the references you have found provide meaningful evidence to the contrary.  With this background, let's address your specific questions:

Thank you very much for your reply. I just have some more follow up questions (I realize this will be my last ones!)

In the case I described, what would you think the chance is in percentages that the woman after me going to the toilet catched my HPV? (very small chance is a bit difficult to interpret for me).

Somewhere else on the forum I have read that 1 percent of the HPV cases are unexplained. Does that mean that 1 percent is caused by environmental transmission?

If someone has high risk HPV and it is never checked or treated, what are the chances that somebody will have cancer in the end?

Even if the person will never be checked for HPV or cervix cancer again, would you still not advise me to warn her because of this situation?

On the reliable information website of my country it is mentioned that the chance to get HPV by a single sexual contact, if this person is infected is 70%. So that is not right? Because it is on the website that is specialized in STD’s, so I was a bit confused when you mentioned it is not common after a single sexual contact.

I realize I worry too much (especially about other people), so it would help to have some numbers.

And I want to thank you for this opportunity to ask questions! 

I'm sorry that my earlier replies have not been sufficient to allow you to move forward.  On the Forum we do our best to use available scientific data to address our clients's question.  some of your follow-up questions are beyond the realm where there are data to answer.  I'll do my best in these final answers.

Getting HPV off a toilet seat is undescribed and unproven.  the risk that your infection would be transmitted in this way if far , far less than 1%.

More often than not, the so-called unexplained occurrence of HPV is the result of exposure to a sexual partner not thought to be "risky".  Far less than 1% of HPV infections are due to environmental exposure. 

Less than 1% of undetected, untreated "high risk" (this is a poor descriptor since even "high risk HPV rarely progresses to cancer) go on to cause cancer.  Obviously routine check ups allow pre-cancerous lesions to be detected and treated.

Correct, warnings of the sort you suggest are not only unnecessary but are a potential source of unwarranted concern and even stigmatization.

I have no idea where the estimate of 70% came from. I am not aware of any high quality scientific studies which provide data on this topic.  My own guess is that less and perhaps far less than half of unprotected sexual exposures result in transmission of infection.. 

This will complete this thread.  I think you are worrying far more than is needed.  EWH