A core algorithm update was released around early August by Google famously called as Medic update because it affected many medical related websites.
Based on a research by SEO round table site, it can be said that there is a huge number of sites from medical, health, fitness and healthy lifestyle related sites were affected because of this update.
this is the first time one particular industry sites have been affected so much more than in general. Most of the previous Google updates were usually not focused on any particular set of sites.
Few other sites in other niches were impacted, such as e-commerce, insurance, finance, business to business, entertainment, deal sites, etc. The interesting thing, many of those “e-commerce” sites sell health/medical related product, so the 42% number might be closer to 50%. Currently, the reason is unknown that why Google’s so called medic update hit only medical or health related sites.