Linezolid resistance in an academic center.

Background:

Linezolid (LZD) is typically prescribed for the treatment of resistant gram positive organisms. Infections by LZD-resistant organisms (LROs) entail a higher rate of Intensive Care Unit (ICU) transfers, invasive procedures, and greater length of stay.  Despite this, the epidemiology of LROs is poorly understood, with most studies being relatively small. Our study examines the characteristics and epidemiology of a large sampling of LROs within a single institution over the course of a decade.

Methods:

This retrospective study was conducted in a 1315-bed tertiary care academic medical center. A medical informatics query identified all LRO isolates from January 2004 through December 2014. Charts were reviewed for demographic and clinical data. Surveillance cultures, cultures from patients younger than 18 years old, and cultures obtained in the outpatient setting were excluded. Chi-square analysis was used to identify significant differences.

Results:

141 total LRO isolates were identified, representing 130 patients.  53 (61.6%) enterococcal isolates were vancomycin-resistant, 11 (84.6%) Staphylococcus aureus (SA) isolates and all 40 coagulase-negative staphylococcal isolates were methicillin-resistant.  The median time from patient admission until LRO isolation was 7.5 days. 9 (90%) of the patients with LZD-resistant SA had chronic lung conditions, specifically 6 with cystic fibrosis (p<0.05).  Besides SA, most LRO originated from patients treated in oncologic units (see Figure 1).  43 (33.1%) of the patients growing LRO had to be transferred to the ICU during their hospitalization, and 32 (24.6%) died during admission.  Patients with LZD-resistant Enterococcus faecium had the highest mortality at 48.4% (16 cases), however the mortality difference between patients with different isolated species was not significant (p=0.158).

  Conclusion:

This large sampling of patients with LRO demonstrates several points. Different LROs arise in different patient populations, with LZD-resistant SA presenting in the chronic pulmonary disease population, and not in oncologic patients as with other LROs.  It is also clear that LROs are associated with high morbidity and mortality, possibly as a result of the severity of underlying comorbidities.

 

Figure 1. Distribution of source patients for linezolid resistant organisms