prevalence       
noun [ U ] uk/ˈprev.əl.əns/ us/ˈprev.əl.əns/
 流行,盛行;普遍,广泛
the fact that something is very common or happens often
  the prevalence of smoking among teenagers 青少年吸烟的普遍性 
 The prevalence of the disease is higher in some families.  在一些家庭中,该病的发病率较高。 
 See: prevalent
 - More examples
 - Doctors are seeing an increase in the prevalence of obesity.
 - There is concern is over the prevalence of fine dust as an air pollutant.
 - There are many misconceptions about the prevalence and treatment of depression.