This week, the CDC released a report describing trends in carbapenem-resistant enterobacteriaceae (E. coli and relatives that are resistant to all penicillin derivatives, and are also typically resistant to most or all other drugs; CRE) and extended-spectrum beta-lactamase producing organisms (ESBL-producers, which are typically resistant to all penicillin derivatives, except for carbapenems, which are the “C” in CRE). While most media reports have treated the frequency of CREs and ESBLs as an increase, it’s not (boldface mine):
Among short-stay acute care hospitals, the percentage of Klebsiella and E. coli isolates with the ESBL phenotype remained relatively stable, ranging from 17.6% (116 of 659 isolates) in 2006 to 16.5% (694 of 4,211) in 2015, with a peak of 18.9% in 2009 (Figure 1). The percentage of CRE declined from 8.8% (35 of 397 isolates) in 2006 and 10.6% (64 of 604) in 2007 to 3.1% (115 of 3,718) in 2015 (Figure 2). During 2006–2015, the annual percentage of isolates with the ESBL phenotype declined an average of 2% (RR = 0.98, p = 0.009); during the same period, the proportion that were CRE decreased 15% per year (RR = 0.85, p<0.001). Results were unchanged when the analysis was limited to facilities that reported in all years.
That’s good news! And it’s because of things like this:
In October 2017, the Tennessee Department of Health contacted CDC regarding identification of an NDM and OXA-48–producing Klebsiella pneumoniae isolate through ARLN. Infection control assessment and screening of hospital contacts was completed and results returned within 48 hours of identification of carbapenemase presence. No transmission was identified. Because the index patient had a recent health care exposure in another country, ARLN regional laboratories expanded their services to perform CDC-recommended admission screening for patients with a history of overnight health care stays outside the United States during the preceding 6 months.
In April 2017, the Iowa Department of Public Health contacted CDC regarding IMP identified in a Proteus species isolated from a nursing home resident. The state health department assessed infection control practices and performed a point prevalence survey that identified five additional colonized residents among 30 surveyed at the nursing home. The health department conducted additional infection control assessments to ensure adherence to recommended practices and two follow-up surveys of the nursing home wing, which did not identify any additional cases.
Because infection control and epidemiology! That said, there is one disconcerting result:
During the first 9 months of 2017, among 4,442 CRE and 1,334 CRPA isolates that were tested for carbapenemases from 32 states, 1,401 (32%) CRE and 25 (1.9%) CRPA were carbapenemase producers (Table 1). Among the carbapenemase-producing isolates, 221 (15.5%) expressed carbapenemases other than KPC. Of isolates tested, 1,422 (25%) were collected in the first quarter of 2017, 2,141 (37%) in the second quarter, and 2,213 (38%) in the third quarter. During this period, the median time from specimen collection to CDC notification decreased from 37 to 13 days. The percentage of carbapenemase-producing isolates varied by organism and was highest among Klebsiella species (65%). Among carbapenemase-producing CRE, the most commonly identified carbapenemase was KPC (1,232 of 1,401 isolates, 88%); VIM was the most common carbapenemase identified in CRPA (18 of 25, 72%) (Table 1).
To identify asymptomatically colonized health care contacts of index patients, 1,489 screening tests for carbapenemases were performed during 70 surveys (defined as all screening tests performed at a single facility within a 14-day period) in 50 facilities. A median of 10.5 contacts (interquartile range = 2–25) were screened per survey. Overall, 11% of screening tests were positive for at least one of the five carbapenemases of primary public health concern (Table 2). A higher percentage of post–acute care facility contacts screened positive for carbapenemases (14% [147 of 1,074 contacts]) than did contacts from short-stay acute care hospitals (5.8% [21 of 365]) (p< 0.01).
The bad news is that, when asymptomatic patients (i.e., not people with infections) are screened, eleven percent appear to have at least one carbapenemase-carrying organism. This seems very high–even higher than what has been seen in D.C., when a similar survey was performed. That said, it’s worth remembering that the denominator is always tricky when calculating these percentages. If the median number of contacts is 10.5 over a 14-day period, then it’s obvious that most patients aren’t being surveyed. Typically, only subsets of patients are sampled (high-risk, previously in the hospital, etc.), so, in a sense, these are probably overestimates: eleven percent of healthy people showing up for sprained ankles probably aren’t CRE-positive, though if these do reflect at-risk populations, that is still troublesome. Overall, the data seem clean, in that most of the CRE isolates have KPC.
So there’s good news–the problem isn’t getting worse, and seems to be declining somewhat. Still, the frequency of CREs (and ESBLs) is clearly no longer non-negligible.