BACKGROUND: Shigella sonnei causes an infection characterized by diarrhea (sometimes bloody), fever, and nausea typically lasting 4-7 days. The pathogen is highly transmissible from person to person and is responsible for an average of 220 reported cases and 6 outbreaks a year in Kentucky. Although data from the National Antimicrobial Resistance Monitoring System (NARMS) have revealed that antimicrobial resistance in Shigella sonnei is common, data from Kentucky’s isolates submitted to NARMS have never been reviewed by state personnel.
METHODS: Shigella sonnei isolates were sent to the NARMS laboratory for antimicrobial susceptibility testing using broth micro dilution to determine the minimum inhibitory concentrations for each of the 15 antimicrobial agents on the NARMS panel. Antimicrobial resistance data for Kentucky were downloaded from the NARMS website and analyzed using IBM SPSS Statistics. Kentucky data were compared to national data obtained from the 2013 NARMS Annual Human Isolates Report.
RESULTS: A total of 84 human Shigella sonnei isolates from Kentucky were sent to the NARMS laboratory from 2004-2014. The majority of isolates displayed resistance to Streptomycin (64.3%) and Ampicillin (84.5%). Approximately one fifth of isolates were resistant to Sulfisoxazole (16.7%) and Trimethoprim-Sulfamethoxazole (21.4%). A minority of isolates displayed resistance to Amoxicillin-clavulanic acid (1.2%), Chloramphenicol (1.2%) and Tetracycline (3.6%). These results are comparable to national data, in which 81.9% of isolates were resistant to Streptomycin, 52.9% to Ampicillin, and 1.6% to Chloramphenicol. In contrast, a much higher percentage of isolates from the national database displayed resistance to Sulfisoxazole (33.1%), Trimethoprim-Sulfamethoxazole (41.4%), and Tetracycline (24.2%). Of the Kentucky isolates, 6.0% were pan-susceptible to all antimicrobials on the NARMS panel, 36.9% were resistant to only one class of antimicrobials, and 57.2% were resistant to more than one class of antimicrobials. These data are comparable to the national database in which 4.2% were pan-susceptible, 32.7% were resistant to one class of antimicrobials, and 63.1% were resistant to more than one class of antimicrobials.
CONCLUSIONS: Although Shigella isolates from Kentucky generally displayed less antimicrobial resistance than those from the national database, the vast majority was still resistant to at least one class of antimicrobials. This is concerning because drug resistance combined with high transmissibility increases the likelihood that future Shigella outbreaks will be larger, occur more frequently, and be more difficult to treat. Continued antimicrobial resistance testing of Shigella isolates is critical to monitor changes in antimicrobial sensitivity and to ensure appropriate antimicrobial treatment.