CDC's Disease Detectives Share Results from an Investigation of CRE Cases

CDC staff show two plates growing bacteria in the presence of discs containing various antibiotics. The isolate on the left plate is susceptible to the antibiotics on the discs and is therefore unable to grow around the discs. The one on the right has a CRE that is resistant to all of the antibiotics tested and is able to grow near the disks. Photo courtesy of the CDC.

The Centers for Disease Control and Prevention (CDC) this week kicked off its 62nd Annual Epidemic Intelligence Service (EIS) Conference in Atlanta, beginning a week-long conference dedicated to showcasing the life-saving work of its current EIS officers, or disease detectives, and welcoming the incoming class of officers to the two-year postgraduate EIS program.

One of the presentations being made at the conference is "Carbapenem-Resistant Klebsiella pneumoniae Producing New Delhi Metallo-Beta-Lactamase at an Acute-Care Hospital Denver, Colorado, 2012." The four-month outbreak of a type of Carbapenem-resistant Enterobacteriaceae (CRE) known as New Delhi Metallo-Beta-Lactamase, occurred at one hospital and highlights the risk for potential organism spread of this type of CRE.

Investigators conducted whole genome sequencing in addition to other laboratory tests that identify resistance to antibiotics. Using conventional testing methods alone, all isolates appeared to match (90 percent to 95 percent similar). By adding whole genome sequencing, investigators were able to divide these closely related strains into three distinct clusters, which when correlated with patient movements and locations, revealed that transmission primarily occurred in four specific places in the hospital.

Carbapenem-resistant Klebsiella pneumonia (CRKP) are highly transmissible and cause healthcare-associated infections with >40 percent mortality. New Delhi metallo-beta-lactamase (NDM)-producing CRKP are rare in the United States. After two patients at a Denver hospital were identified with NDM-producing CRKP during JulyAugust 2012, an investigation was conducted to characterize the outbreak and prevent transmission.

Klebsiella pneumoniae. Photo courtesy of the CDC.

The CDC tested CRKP isolates by polymerase chain reaction for NDM. A case had NDM-producing CRKP isolated from clinical or active surveillance cultures (ASC) of rectal swabs collected during January 1October 30. Cases were identified through microbiology record reviews and six rounds of ASC on units where affected patients had resided. Medical records were reviewed for epidemiologic links; relatedness of CRKP isolates was evaluated by pulsed-field gel electrophoresis (PFGE) and whole-genome sequence analysis (WGS).

A third patient, admitted in May, was identified through microbiology records review. ASC identified five additional cases. Patients were aged 2375 years and had resided on 11 different units (median stay: 18 days; range: 1283 days) before case identification; three were treated for infection; five were asymptomatically colonized, and none died. All isolates were highly related by PFGE. WGS suggested three primary clusters of CRKP. Combining WGS results with epidemiology identified three units as likely transmission sites.

The researchers say their study shows that whole genome sequencing can help pinpoint the cause of outbreaks and help public health experts stop them in the future.

Our research shows how next-generation tools like whole genome sequencing can help disease detectives rapidly and accurately find and control dangerous microbes that cause healthcare-associated infections," says EIS officer Erin E. Epson, MD. "Combining traditional epidemiology with new technologies can help prevent further spread and protect more people from these highly transmissible and often deadly infections.

Abstract: Epson EE, Wendt JM, Pisney L, MacCannell D, et al.Carbapenem-Resistant Klebsiella pneumoniae Producing New Delhi Metallo-Beta-Lactamase at an Acute-Care Hospital Denver, Colorado, 2012.