RESULTS
Culture results from 373 people with CF were included in the CFA between 2015 and 2019. There were 183 females (49%) and 190 males (51%), and the mean age was 12.32 + 6.43 years. There were 1,973 culture results representing SA, PA, Achromobacter species,Burkholderia species and Stenotrophomonas maltophiliaincluded in the CFA.
There were 1250 Staphylococcus aureus (SA) isolates; 902 were MSSA (72%) and 348 MRSA (28%). SA isolate susceptibility rates between the CFA and HWA were similar except for clindamycin [Table 1]. The CFA demonstrated significantly fewer MRSA (39% vs. 83%, p<0.0001) and MSSA (71% vs. 79%, p<0.0001) isolates susceptible to clindamycin. Additionally, among the SA isolates collected the HWA demonstrated a higher proportion of MRSA than the CFA (32% versus 28% of SA isolates).
When comparing the proportion of methicillin-resistance in SA isolates among sputum versus oropharyngeal swabs in people with CF, there were fewer MSSA isolates obtained from sputum (399, 44%) compared to oropharyngeal swabs (503, 56%) and more MRSA isolates, 225 (65%) and 123 (35%) respectively. The sputum isolates were less susceptible compared to oropharyngeal isolates for SA [Table 2]. These differences were statistically significant for MSSA isolates from sputum versus oropharyngeal isolates for susceptibility to clindamycin (p=0.0202).
There were 480 PA isolates from people with CF during the study period [Table 3]. For each antimicrobial tested, CF isolates were less susceptible compared to HWA. Analysis of CF culture susceptibility information based on source, either sputum or oropharyngeal swab, was also completed for PA isolates [Table 4]. There were more PA isolates obtained from sputum (305, 64%) than from oropharyngeal swabs (175, 36%) among people with CF. Overall, PA isolates from sputum were less susceptible than oropharyngeal isolates. These differences were statistically significant for all antimicrobial’s tested except for aztreonam.
Achromobacter species,Burkholderia species and Stenotrophomonas maltophila were also included in the CFA. CFA susceptibility information is summarized in Table 5. Not all isolates have complete susceptibility reported for each antimicrobial presented. Fifty-six Achromobacter species isolates were included in analysis; all but one of these isolates were grown from sputum. ForAchromobacter species, most isolates tested were not susceptible to amikacin (41, 17%) or cefepime (39, 41%). Susceptibility to ceftazidime (56, 77%), meropenem (53, 87%) and trimethoprim/sulfamethoxazole (55, 76%) were the highest. There were 40Burkholderia species isolates analyzed; most of the isolates were obtained from sputum (n=32, 80%). The tested isolates were most susceptible to meropenem (35, 83%) and trimethoprim/sulfamethoxazole (37, 78%). There were 149 Stenotrophomonas maltophila isolates included most were obtained from sputum (n=142, 85%). Twenty percent of the isolates tested were susceptible to ceftazidime (n=125) and 91% of the isolates tested were susceptible to trimethoprim/sulfamethoxazole (n=148). Eleven isolates were tested and susceptible to minocycline (100%) and 55% (n=6) of the isolates tested were susceptible to levofloxacin.
In addition to analysis of individual isolates, annualized data were characterized to evaluate for potential changes in susceptibility over time. Over the five-year period, there did not appear to be any clinically significant changes in susceptibility patterns for PA, MRSA, and MSSA based on the percentage of overall isolates susceptible to each antimicrobial tested. Susceptibility trends over time are presented in Figure 1. Clindamycin susceptibility trends for MRSA and MSSA are not included in the figure but did not demonstrate significant changes in the CFA over time.