Table 1.
Conceptual illustration of spectrum score calculation for an antimicrobial regimen
| Step 1: Populate susceptibility percentage for organism domains, convert values to ordinal scale (ordinal values shown in parentheses) A,B,C,D | ||||||
|---|---|---|---|---|---|---|
| Organism domain | Vancomycin susceptibility (%) | Vancomycin ordinal score | Cefepime susceptibility (%) | Cefepime ordinal score | Vancomycin + cefepime joint susceptibility B | Vancomycin + cefepime joint ordinal score |
| Staphylococcus aureus | 99.3 | 4 | 51.2 | 2 | 99.6 | 4 |
| Streptococcus pneumoniae | 98.2 | 4 | 92.5 | 4 | 99.9 | 4 |
| Enterococcus faecium | 18.4 | 0 | NA | 0 | 18.4 | 0 |
| Enterococcus faecalis | 94.7 | 4 | NA | 0 | 94.7 | 4 |
| Escherichia coli | NA | 0 | 92.4 | 4 | 92.4 | 4 |
| Klebsiella spp. | NA | 0 | 84.5 | 4 | 84.5 | 4 |
| Other enterobacteriaceaeC | NA | 0 | 91.3 | 4 | 91.3 | 4 |
| Pseudomonas aeruginosa | NA | 0 | 78.0 | 3 | 78.0 | 3 |
| Acinetobacter spp. | NA | 0 | 42.6 | 2 | 42.6 | 2 |
| Stenotrophomonas spp. | NA | 0 | 36.6 | 1 | 36.6 | 1 |
| Haemophilus influenzae | NA | 0 | 95.4 | 4 | 95.4 | 4 |
| Bacteroides spp. | NA | 0 | NA | 0 | NA | 0 |
| Legionella spp. | NA | 0 | NA | 0 | NA | 0 |
| Mycoplasma spp. | NA | 0 | NA | 0 | NA | 0 |
| Step 2: Weight susceptibilities for coverage against intrinsically resistant organisms, sum organism domain scores to create antibiotic regimen spectrum score E | ||||||
| Organism domain | Vancomycin weighted ordinal score | Cefepime weighted ordinal score | Vancomycin + cefepime weighted ordinal score | |||
| Staphylococcus aureus | 5 | 2.5 | 5 | |||
| Streptococcus pneumoniae | 4 | 4 | 4 | |||
| Enterococcus faecium | 0 | 0 | 0 | |||
| Enterococcus faecalis | 4 | 0 | 4 | |||
| Escherichia coli | 0 | 5 | 5 | |||
| Klebsiella spp. | 0 | 5 | 5 | |||
| Other enterobacteriaceaeC | 0 | 4 | 4 | |||
| Pseudomonas aeruginosa | 0 | 5.25 | 5.25 | |||
| Acinetobacter spp. | 0 | 2.5 | 2.5 | |||
| Stenotrophomonas spp. | 0 | 1 | 1 | |||
| Haemophilus influenzae | 0 | 4 | 4 | |||
| Bacteroides spp. | 0 | 0 | 0 | |||
| Legionella spp. | 0 | 0 | 0 | |||
| Mycoplasma spp. | 0 | 0 | 0 | |||
| Spectrum Score | 13.0 | 33.25 | 39.75 | |||
Spectrum Score Calculations for Individual and Combination Antibiotic Regimens. AValues populated with susceptibility data. Susceptibility estimates for combinations where all antimicrobials possessed activity against the species obtained by calculating one minus the joint probability of resistance to all antibiotics in the regimen, assuming that susceptibility was independent for each antibiotic. BOther enterobacteriaceae included: Citrobacter spp., Enterobacter spp., Morganella spp., Proteus spp., Providencia spp., Serratia spp. CNA = No intrinsic activity. DOrdinal values were 0 for no intrinsic bacterial activity or susceptibility < 20%, 1 for > 20 but < 40%, 2 for >40 but < 60%, 3 for >60 but < 80%, 4 > 80 %. EA weight of 1.25 was applied to ordinal domain values for Staphylococcus aureus, Escherichia coli, Klebsiella spp., Acinetobacter spp., Enterococcus faecium, and a weight of 1.75 was applied to spectrum score values for Pseudomonas aeruginosa.