INDIANAPOLIS — Food and Drug Administration recalls in the third quarter affected about 7 million units, or about twice as much as the previous quarter, even though the number of food recalls, 252, was down 14%, according to the ExpertRecall Index.

Stericylce ExpertRecall aggregates and tracks cumulative recall data from the U.S. Consumer Product Safety Commission, the U.S. Department of Agriculture and the F.D.A. to compose the ExpertRecall Index.

Allergens represented 40% of the F.D.A. recalls, the largest cause, in the third quarter.  Salmonella, Listeria and Botulism — all related to foodborne illness — in total accounted for more than 40% of the third-quarter recalls.

Of the recalls in the quarter, 44% were classified as Class I recalls, the most serious classification,  while 47% were classified as Class II and 9% were classified as Class III. The volume of Class I and Class II units recalled increased by more than 95%, largely in part due to two separate recalls by the same company because of Salmonella contamination.

One F.D.A. recall affected 2.5 million units. Three affected between 500,000 and 1 million units, and eight affected between 100,000 and 500,000 units. Third-quarter documented recalls were initiated by 136 companies. Forty faced more than one recall. One company faced 24 recalls in the quarter while three companies faced more than 10 recalls.