Methods: We retrospectively reviewed all adult MSSA bacteremia from April 2010 to April 2015 at the McGill University Health Centre (Montreal, Canada). Susceptibility to penicillin, macrolides, clindamycin and trimethoprim-sulfamethoxazole (TMP-SMX) were determined in accordance with the Clinical & Laboratory Standards Institute guidelines. Only the first positive culture per patient was included.
Results: There were 324 unique episodes of MSSA bacteremia. 90 (28%) isolates were susceptible to penicillin, 229 (71%) to macrolides, 239 (74%) to clindamycin and 317 (98%) to TMP-SMX. Isolates that were penicillin resistant were more likely to also be resistant to macrolides (76/234 vs. 19/90, p=0.04) but not clindamycin (68/234 vs. 17/90, p=0.06) or trimethoprim-sulfamethoxazole (6/234 vs. 1/90, p=0.42).
The median age of patients was 67.5 years (IQR 52-78) and overall in-hospital 30-day mortality was 16.3% (53 deaths). Patients 75 and older were more likely to die (28/99, 28.3%) than those 65-74 (14/82, 17.1%) or below (11/143, 7.7%) (p<0.001). After adjustment for patient age, there was no association between penicillin resistance and either ICU admission or death.
Conclusion: More than one quarter of patients with MSSA bacteremia could be treated with parenteral penicillin. When susceptible, penicillin has prolonged time over minimal inhibitory concentration compared with other beta-lactams: providing a theoretical advantage in achieving cure while minimizing spectrum of activity. Our results may support a return to penicillin testing among invasive SA isolates in centers that have stopped.
M. P. Cheng,
T. C. Lee, None
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