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.