Each antibiotic is scored against a list of clinically relevant bacteria (14 groups in Table 1), with 0 indicating ineffective and 1 effective.
The antibiotic spectrum index for an antibiotic is the sum of scores for the 14 bacterial groups, so ranges from 0 to 14. A broad-spectrum antibiotic will have a higher ASI.
Organisms evaluated: MSSA, MRSA, Enterococcus sp, VRE, "anaerobes", Bacteroides fragilis, Hemophilus influenzae/Moraxella, E. coli/Klebsiella, Enterobacter/Serratia/Citrobacter, ESBL, Pseudomonas sp, penicillin-resistant Streptococcus pneumoniae, "atypical", and "multi-drug resistant organism".
If a person is receiving more than 1 antibiotic per day, then the total ASI is the sum of the individual ASI's for antibiotics received. If two antibiotics are effective against the same organism then 2 points are assigned. The maximum total ASI is the number of antibiotics times the number of organisms evaluated.
Supposedly the index can aid in antibiotic stewardship. In theory the ASI per antibiotic day should decrease with an effective intervention to reduce antibiotic use.
Possible issues:
(1) The scores are 0 or 1 with no apparent intermediate scores.
(2) There appears to be no account for bacterial strain variation, and some categories include multiple genera.
(3) Comparison between hospitals would require a standardized list of organisms.
