Among residents of the 63 included facilities, there were 1,805 gram-negative organisms identified during the study period, including 1,653 isolates from SNF residents and 152 isolates from ALF residents. The three most common gram-negative organisms were E. coli (n=874), Klebsiella species (n=323); and P. mirabilis (n=285). For all organisms, there was substantial resistance to various antibiotics tested. Notably, the prevalence of levofloxacin resistance was 51% among E. coli and 29% for Klebsiella species. The prevalence of ceftazidime resistance (often used as a marker for extended-spectrum beta-lactamase (ESBL)-mediated resistance) was 26% among Klebsiella species and 12% among E. coli. Finally, 6% of Klebsiella species and 37% of Pseudomonas aeruginosa were resistant to imipenem.
Among the 63 included facilities, there were 44 skilled nursing facilities (SNFs) and 19 assisted living facilities (ALFs). There were many significant differences in antimicrobial susceptibilities when comparing ALFs and SNFs ().
Antimicrobial Susceptibilities by Type of Facility
Among the 44 SNFs, 12 facilities had <100 beds, 12 had 101-150 beds, 13 had 151-200 beds, and seven facilities had >200 beds. Among E. coli, there were significant differences in susceptibilities to the following agents (for bed sizes <100, 100-150, 151-200, and >200, respectively): aztreonam (79%, 90%, 87%, and 87%; p=0.005); cefepime (84%, 92%, 88%, and 88%; p=0.03); ceftazidime (81%, 92%, 88%, and 87%; p=0.003); and ceftriaxone (79%, 92%, 87%, and 87%; p=0.001). Among Klebsiella, there were no significant differences in susceptibilities across facilities of different sizes. Finally, among P. mirabilis, there were significant differences in susceptibilities to the following agents (for bed sizes <100, 100-150, 151-200, and >200, respectively): ampicillin-sulbactam (74%, 89%, 87%, and 92%; p=0.02); and cefazolin (74%, 91%, 88%, and 92%; p=0.02). Of note, the distribution of SNFs within a geographic region with regard to bed size was not substantively different across geographic regions.
The 44 SNFs represented six different geographic regions. The number of SNFs in each region ranged from four to 16 (median = 6.0) and the distribution by facility type and size were similar across the six regions. There were significant differences in antimicrobial susceptibilities across geographic regions ().
Antimicrobial Susceptibilities by Region