SAN FRANCISCOCA—Distribution patterns of species was similar in hospital-associated (HA) and community-associated (CA) intra-abdominal infections (IAI) with a lower proportion of E. coli and K. pneumoniae and a higher proportion of P. aeruginosa and A. baumannii in HA IAI, as presented by Robert Badal, BS, from International Health Management Associates, Inc., Schaumburg, IL, at IDWeek 2013.

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The Infectious Diseases Society of America (IDSA) and the Surgical Infection Society (SIS) published updated guidelines for the treatment of intra-abdominal infections in 2010. Empiric therapy of these infections has been complicated by extended-spectrum β-lactamases (ESBLs), which have been spreading among Enterobacteriaceae. “Antibiotic options in the treatment of ESBL-producing organisms are limited, with carbapenems often remaining the treatment of choice,” informed Robert Badal.

The Study for Monitoring Antimicrobial Resistance Trends (SMART) has tracked and reported on the susceptibility trends of aerobic gram-negative pathogens of intra-abdominal infections (IAI) since 2002. This report summarizes the in vitro activity of amikacin (AK), ampicillin-sulbactam (AS), cefepime (CPE), cefotaxime (CFT), cefoxitin (CFX), ceftazidime (CAZ), ceftriaxone (CAX), ciprofloxacin (CP), ertapenem (ETP), imipenem (IMP), levofloxacin (LVX), and piperacillin- tazobactam (PT) against the aerobic Gram-negative bacilli isolated in 2012 in the USA.

Each of the eighteen laboratories collected up to 100 consecutive non-selected aerobic gram-negative pathogens from IAI each year for a total of 1,547 gram-negative bacilli (GNB) in 2012. IAI was defined as HA or CA if the specimen was cultured ≥48 hours or <48 hours post admission, respectively. Susceptibility was calculated for all Enterobacteriaceae, non-Enterobacteriaceae, and aerobic Gram-negative bacilli combined. Zero percent susceptibility was assumed for species with no breakpoints for any given drug.

In hospital-associated vs. community-associated intra-abdominal infections, E. coli, K. pneumonia, and P. aeruginosa was found in 35% vs. 43%, 17% vs. 18%, and 15% vs. 10% of isolates, respectively. The two most prevalent species, E. coli and K. pneumoniae, accounted for 56% of all isolates, and had ESBL rates in HA/CA of 7%/5% and 13%/5%, respectively. 97% of 1,284 Enterobacteriaceae were ETP susceptible.

ESBL rates in IAI in the USA were relatively unchanged from earlier SMART reports on North America and remain much lower than reported in most countries and regions, leading to higher levels of susceptibility to cephalosporins and fluoroquinolones, researchers concluded.

There was a significant difference between the percent of Enterobacteriaceae HA and CA IAIs that were susceptible to AS, CFT, CFX, CAZ, CAX, ETP, PT (P<0.05), as well as a significant difference between the percent of non-Enterobacteriaceae HA and CA IAIs that were susceptible to piperacillin-tazobactam (P<0.05).

For all aerobic Gram-negative bacilli combined, all study drugs except ciprofloxacin, levofloxacin, and imipenem had significantly lower susceptibility in HA than in CA infections. Amikacin (98.4%) and ertapenem (97.2%) were the most active against Enterobacteriaceae, while amikacin (84.4%) and ceftazidime (77.2%) were the most active against non-Enterobacteriaceae.

“SMART data can be useful to help guide evolving IAI guidelines for empiric therapy to reflect resistance trends,” reported Robert Badal.