user43480: EDIT:
Bumping because WillyA seems to have returned, though he is posting his aquagenic urticaria question on Medical Sciences and Skeptics for now.
This post is in part to let moderators and the community know to be on the alert for a particular user and post, and in part a question about what the policy should be for this kind of behavior.
tl;dr
What should we do when a (pair?) of users keeps posting the same question over and over again on multiple SE sites?
Full question
This user and another user (I believe, this user, but many of the posts have been autodeleted) have been repeatedly posting very similar questions on biology, medical sciences, chemistry, and skeptics, asking about blog articles and news reports on aquagenic urticaria.
Here is a recent example from biology.SE. This was the third time the question was posted in as many days. The answer did not appear to satisfy the user, since the question was subsequently posted once a day on medical sciences, and once a day on chemistry.
Some of the questions have been closed, downvoted, and autodeleted, and I don't have a link, but, if I recall, moderators and high rep users can view deleted questions. Per a moderator comment on a recent closed version of this question on skeptics, it seems possible that the two users are the same individual:

This is the fourth time this same question has been asked by you and another user from your home town, with very similar writing styles and similar refusals to accept that Aquagenic Urticaria is not a harmless skin condition, and that a newspaper writing about "allergies" to a lay audience might not be using strict medical definitions of the term. There is nothing left to explain here.

There are examples of good attempts to answer this poster here on biology (see this answer by @AliceD), and medical sciences, and chemistry, but getting an answer does not seem to satisfy the poster.
This behavior does not appear to be commercial spam, but, does feel a lot like the original message board spam... annoying repeated text. I can see an argument that the system is working here (prior questions are closed and autodeleted, current questions are closed, sometimes as duplicates, and downvoted), but for some reason it's getting under my skin (as things sometimes do). What's the policy here? Just keep downvoting and voting to close? Or is there a point where something else should be done?

user5144: Thanks for bringing this problem up here at meta.
We (the mods) try to find and identify such users/questions and act as necessary, but we can't be around always. 
So if you spot such a question or user flag the question (use the "in need of moderator intervention" point and give a short explanation why you think there is a problem) and we will have a closer look. We will usually also recognize this faster, since there is a notification in our status bar about flags.
Still, you should also downvote and vote to close such questions.

43480: <p>EDIT:
Bumping because <a href="https://medicalsciences.stackexchange.com/users/15090/willy-a">WillyA</a> seems to have returned, though he is posting his aquagenic urticaria question on <a href="https://medicalsciences.stackexchange.com/questions/18904/why-is-the-h2o-molecule-an-antigen-despite-its-tiny-size-and-simplicity">Medical Sciences</a> and <a href="https://skeptics.stackexchange.com/questions/43653/is-the-h2o-molecule-an-antigen-like-this-article-states">Skeptics</a> for now.</p>
<p>This post is in part to let moderators and the community know to be on the alert for a particular user and post, and in part a question about what the policy should be for this kind of behavior.</p>
<h1>tl;dr</h1>
<p>What should we do when a (pair?) of users keeps posting the same question over and over again on multiple SE sites?</p>
<h1>Full question</h1>
<p><a href="https://biology.stackexchange.com/users/45343/tiffanyannm">This user</a> and another user (I believe, <a href="https://biology.stackexchange.com/users/44952/willy150?tab=profile">this user</a>, but many of the posts have been autodeleted) have been repeatedly posting very similar questions on biology, medical sciences, chemistry, and skeptics, asking about blog articles and news reports on aquagenic urticaria.</p>
<p>Here is <a href="https://biology.stackexchange.com/questions/77612/is-it-logical-for-someone-to-be-allergic-to-the-water-molecule-but-be-perfectly">a recent example</a> from biology.SE. This was the third time the question was posted in as many days. The answer did not appear to satisfy the user, since the question was subsequently posted once a day on medical sciences, and once a day on chemistry.</p>
<p>Some of the questions have been closed, downvoted, and autodeleted, and I don't have a link, but, if I recall, moderators and high rep users can view deleted questions. Per a moderator comment on <a href="https://skeptics.stackexchange.com/questions/42368/is-it-possible-for-someone-to-be-allergic-to-the-h2o-molecule">a recent closed version of this question on skeptics</a>, it seems possible that the two users are the same individual:</p>
<blockquote>
<p>This is the fourth time this same question has been asked by you and another user from your home town, with very similar writing styles and similar refusals to accept that Aquagenic Urticaria is not a harmless skin condition, and that a newspaper writing about &quot;allergies&quot; to a lay audience might not be using strict medical definitions of the term. There is nothing left to explain here.</p>
</blockquote>
<p>There are examples of good attempts to answer this poster here on biology (see <a href="https://biology.stackexchange.com/a/77613/43480">this answer</a> by @AliceD), and <a href="https://medicalsciences.stackexchange.com/a/16930/14173">medical sciences</a>, and <a href="https://chemistry.stackexchange.com/a/99971/68342">chemistry</a>, but getting an answer does not seem to satisfy the poster.</p>
<p>This behavior does not appear to be commercial spam, but, does feel a lot like the original message board spam... annoying repeated text. I can see an argument that the system is working here (prior questions are closed and autodeleted, current questions are closed, sometimes as duplicates, and downvoted), but for some reason it's getting under my skin (as things sometimes do). What's the policy here? Just keep downvoting and voting to close? Or is there a point where something else should be done?</p>
 5144: <p>Thanks for bringing this problem up here at meta.
We (the mods) try to find and identify such users/questions and act as necessary, but we can't be around always. </p>

<p>So if you spot such a question or user flag the question (use the "in need of moderator intervention" point and give a short explanation why you think there is a problem) and we will have a closer look. We will usually also recognize this faster, since there is a notification in our status bar about flags.</p>

<p>Still, you should also downvote and vote to close such questions.</p>
