Low level of worrisome resistant bacterium in U.S.

nursing homes when they are transferring patients with A baumannii or other multidrug-resistant infections, so that those facilities can take appropriate precautions.

Looking at outcomes, the investigators found that in 75 percent of the cases (449), patients were hospitalized at the time of sample collection or within 30 days. Of these cases, 168 (37.4 percent) were admitted to the intensive care unit. The overall death rate was 17.9 percent (106 of 594 cases), but was significantly higher when the pathogen was isolated from a sterile site, such as blood, than when it was isolated only from urine (41.3 percent vs. 8.3 percent).

Antimicrobial susceptibility testing showed that most of the isolates were also nonsusceptible to several classes of antibiotics—cephalosporins, fluoroquinolones, trimethoprim/sulfamethoxazole, ampicillin, and piperacillin/tazobactam. But 72.9 percent were susceptible to at least one aminoglycoside, and a subset were susceptible to tigecycline and colistin. Bulens said this underscores the dangers of the pathogen, since these drugs are either associated with high toxicity or are considered last-resort antibiotics. “But at least we had some that were still susceptible,” she said.

Keeping A baumannii in check
Bulens and Kallen said it’s unclear why the incidence of carbapenem-nonsusceptible A baumannii is lower than for other HAI pathogens, but they say it could be related to low virulence and the lack of dominant clones—strains that share a common ancestor—that are capable of spreading easily from person to person.

But Kallen noted that it could also be because cases of MRSA and C difficile are being increasingly reported in non-healthcare settings, a pattern he hopes won’t be repeated.

“We really want to address these things when they are uncommon, because if you wait until they are common, like MRSA or C difficile, they’re really challenging to get a handle on,” he said. “I think what the data have shown us, as they did with CRE, is that these bugs are still in a place where, although they’re problematic, they’re relatively uncommon, and that affords us the opportunity to be aggressive about prevention and be much more successful,” he said.

Kallen said identifying new and emerging drug-resistant pathogens and stopping them before they can spread in the healthcare setting will be the focus of a new containment strategy the CDC will soon be announcing. The three-part strategy will involve increasing laboratory capacity for quick detection of drug-resistant organisms, improving infection control infrastructure, and colonization screening to detect asymptomatic patients who can spread pathogens but would otherwise fly under the radar.

“This is like a whole new mindset change at the CDC and within the US for controlling emerging and novel resistance,” said Kallen. “And Acinetobacter is right in that spot.”

— Read more in Sandra N. Bulens et al., “Carbapenem-Nonsusceptible Acinetobacter baumannii, 8 US Metropolitan Areas, 2012–2015,” Emerging Infectious Diseases 24, no. 4 (April 2018)