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‘Phantom Menace’ Superbug Spreading in U.S.
A particularly dangerous superbug, dubbed the “phantom menace” by scientists, is on the rise in the U.S., according to a report from the Centers for Disease Control and Prevention (CDC).
The superbug’s strains belong to the family of bacteria known as carbapenem-resistant Enterobacteriaceae (CRE), which are often resistant to most classes of antibiotics and cause health care-associated infections with high mortality rates. Health officials have called CRE among the country’s most urgent public health threats.
CRE strains that carry plasmid-encoded carbapenemase enzymes that inactivate carbapenem antibiotics are of greatest public health concern because of their potential for rapid global dissemination, according to the CDC. Newly described resistance in Enterobacteriaceae, such as plasmid-mediated resistance to the last-line antimicrobial colistin, recently detected in China, and resistance to the newly approved antimicrobial ceftazidime–avibactam, identified from a U.S. Klebsiella pneumoniae carbapenemase-producing isolate, highlight the continued urgency to delay the spread of CRE.
The OXA-48 carbapenemase was first identified in Enterobacteriaceae in Turkey in 2001, and OXA-48–like variants have subsequently been reported around the world. The first U.S. reports of OXA-48–like carbapenemases were published in 2013 and included retrospectively identified isolates from 2009 and two isolates collected in 2012 from patients in Virginia who had recently been hospitalized outside the U.S.
The CDC received reports of 52 CRE isolates producing OXA-48–like carbapenemases collected from 43 patients in 19 states during June 2010 to August 2015; seven of these isolates were identified retrospectively from six patients. Eight isolates from four patients were part of two different clusters in the U.S. during 2014. The number of patients from whom CRE isolates producing OXA-48–like carbapenemases were identified ranged from one in 2010 to 11 per year in 2013, 2014, and 2015. Thirty-five patients (81%) had OXA-48-like carbapenemase identified from K. pneumoniae isolates, seven (16%) from Escherichia coli isolates, one (2%) from an Enterobacter aerogenes isolate, and one (2%) from a Klebsiella ozaenae isolate. Isolates with both New Delhi metallo-beta-lactamase and OXA-48–like carbapenemase genes were obtained from five patients (12%). The most common sources were urine (22 patients [51%]) and respiratory specimens (nine patients [21%]).
Among 29 patients for whom a travel history was available, 19 (66%) had traveled internationally during the year before specimen collection, and 16 (55%) were hospitalized outside the U.S. for at least one night; these percentages increased to 76% and 64%, respectively, when cases associated with the two domestic clusters were excluded. India was the most frequently reported destination among patients with international travel (11 of 19 patients) and international hospitalization (nine of 16).
CRE that produce OXA-48–like carbapenemases have demonstrated the ability to spread in other countries and to cause outbreaks in health care settings, according to the CDC. Factors potentially contributing to the spread of these organisms include the high transfer efficiency of the plasmid containing OXA-48–like genes and challenges in identifying these organisms. Challenges in identification occur because of the limited testing for CRE resistance mechanisms in U.S. clinical laboratories and the different susceptibility profiles of these organisms compared with other carbapenemase-producing CRE, making them difficult to differentiate from CRE that do not produce carbapenemases.
“What we’re seeing is an assault by the microbes on the last bastion of antibiotics,” CDC Director Dr. Tom Frieden said.
Sources: CDC; December 4, 2015; and Washington Post; December 4, 2015.