The estimates of the actual national burden and incidence for each year are based on the actual rate of use of the nucleic acid amplification test (NAAT) in that year, with adjustment for the age, sex, and race of the U.S. population. The estimates of the adjusted national burden and incidence for each year are based on an adjustment of NAAT use to the 2011 rate of 55%, with additional adjustment for the age, sex, and race of the U.S. population. The estimates of the national burden of community-associated CDI and health care–associated CDI do not always add up to the estimated total burden of CDI because of rounding.