Gary Illyes, a Google Webmaster Trends Analyst for Google Switzerland, who was recruited back in 2011, responded to a few threads over the holiday break. Here are two medical related sites that are complaining they don't get traffic from Google. His response, the sites are involved in link schemes.
In one Google Webmaster Help thread the site owner said:
We are a group of six highly qualified medical professionals (two doctors, two MSc MRI radiographers and two general radiographers). We designed ‘mrimaster’ to teach radiologists and radiographers all around the world.
I would like to point out that buying links or participating in dubious link exchange campaigns is against our Webmaster Guidelines: https://support.google.com/webmasters/answer/35769
After spending a few minutes trying to find the root cause of your site's problem, I stumbled upon a few pretty low quality sites that all have an anchor back to your site with the anchor text "what is an mri". I don't know who placed them there (it might have been your SEO) but this is really bad and if I were you I'd spend some time cleaning up these kind of links.
In the next Google Webmaster Help thread the site owner said:
My site has unique content so much so that it received backlink from .ca gov, reputed public organization, facebook shares, share by email, bookmarks etc
However, for past couple of months, stats of per day visitors have nosedived. From 700 visitors a day to only 100 and sometimes 80 visitors a day.
In general the post from Amit you found can be applied on most of the situations, however you also want to read our Webmaster Guidelines, especially the section related to links: https://support.google.com/webmasters/answer/35769 More specifically: https://support.google.com/webmasters/answer/66356
After spending a few minutes trying to find issues I stumbled upon a bunch of links with the anchor text "prescription drug" and "prescription drug information" that are obviously placed for manipulating PageRank. As usual I don't know know who placed them there (it could have been your SEO), but I'd work really hard removing them.
That is called getting caught Google-handed.
Image credit to BigStockPhoto for colored hands