Secular trends in Acinetobacter baumannii resistance in respiratory and blood stream specimens in the United States, 2003 to 2012: A survey study.

BACKGROUND

Acinetobacter baumannii (AB) has evolved a variety of resistance mechanisms and exhibits unpredictable susceptibility patterns, making it difficult to select empiric therapy.

OBJECTIVE

To examine US secular trends in the resistance of AB in respiratory infections and blood stream infections (BSI) to antimicrobial agents whose effectiveness is supported in the literature

DESIGN

Survey.

METHODS

We analyzed 3 time periods (2003-2005, 2006-2008, 2009-2012) in Eurofins' The Surveillance Network for resistance of AB to the following antimicrobials: carbapenems (imipenem, meropenem, doripenem), aminoglycosides (tobramycin, amikacin), tetracyclines (minocycline, doxycycline), polymyxins (colistin, polymyxin B), ampicillin-sulbactam, and trimethoprim-sulfamethoxazole. Resistance to ≥3 drug classes defined multidrug resistance (MDR).

RESULTS

We identified 39,320 AB specimens (81.1% respiratory, 18.9% BSI). The highest prevalence of resistance was to doripenem (90.3%) followed by trimethoprim-sulfamethoxazole (55.3%), and the lowest to colistin (5.3%). Resistance to carbapenems (21.0% in 2003-2005 and 47.9% in 2009-2012) and colistin (2.8% in 2006-2008 to 6.9% in 2009-2012) more than doubled. Prevalence of MDR AB rose from 21.4% in 2003 to 2005 to 33.7% in 2006 to 2008, and remained stable at 35.2% in 2009 to 2012. In contrast, resistance to minocycline diminished from 56.5% (2003-2005) to 30.5% (2009-2012). MDR organisms were most frequent in nursing homes (46.5%), followed by general ward (29.2%), intensive care unit (28.7%), and outpatient setting (26.2%).

CONCLUSIONS

Resistance rates among AB to such last-resort antimicrobials as carbapenems and colistin are on the rise, whereas that to minocycline has declined. Nursing homes are a reservoir of resistant AB. These trends should inform not only empiric treatment of serious infections, but also approaches to infection control.