Ingrid Hein

May 27, 2016

ATLANTA — The use of a nasal swab alone is likely to miss about one-quarter of all multidrug-resistant organism colonizations, a study of residents in three nursing homes shows.

"Comprehensive swabbing is the only way to get really valuable data," said James McKinnell, MD, from the Los Angeles Biomedical Research Institute at the Harbor–UCLA Medical Center.

"If you're not capturing all the carriers, it's going to have some widespread implications when you look at the risks you incur with infection," he told Medscape Medical News. "Nursing homes are the perfect storm of patients carrying pathogens and at the same time at risk of getting sick if they are exposed to them."

About 2 million Americans develop antibiotic-resistant infections each year, and in 2014, roughly 23,000 of these patients died, according to recent data published in Morbidity and Mortality Weekly Report (2016;65:235-241).

In a previous literature review Dr McKinnell was involved with, the addition of oropharynx swabs to nasal swabs was shown to increase detection of methicillin-resistant Staphylococcus aureus (MRSA) colonization by 21%, the addition of rectal swabs increased detection by 20%, the addition of wound swabs increased detection by 17%, and the addition of armpit swabs increased detection by 7% (Infect Control Hosp Epidemiol. 2013;34:161-170).

Most multidrug-resistant organisms are not detected because they do not show up in a nasal swab or are not tested for. "When a facility tells me their rates are 6%, I usually add 30%" to account for all the missed and untested multidrug-resistant organisms, Dr McKinnell explained.

Zorro Technique

Dr McKinnell and his colleagues introduced the Zorro technique, so called because the motion of swabbing the left armpit, right armpit, left groin, and right groin mimics the motion the legendary character Zorro makes with his sword. By targeting more areas of the body, you get a more accurate picture of the prevalence of colonization.

The team tested 605 residents in three Southern California nursing homes. Over a 3-month period, multiple systematic random samplings were obtained from each patient. Each sampling involved a traditional nasal swab and a combined Zorro swab.

Nasal swabs were assessed for MRSA. Zorro swabs were assessed for four multidrug-resistant organisms: MRSA; vancomycin-resistant Enterococcus (VRE); extended-spectrum beta-lactamase Gram-negative-producing bacilli (ESBLs and producers); and carbapenem-resistant Enterobacteriaceae (CRE).

All multidrug-resistant organisms were identified with routine cultures.

Assessment of the 1800 swabs collected revealed that 272 (45%) residents were colonized with one multidrug-resistant organism, 70 (12%) were colonized with two, and 11 (2%) were colonized with three.

With the addition of the Zorro swab to the nasal swab, detection increased by 20%. "We found 160 patients with MRSA. If we had only done nares, we would have only found 121; we would have missed 39 carriers," Dr McKinnell reported.

Table. Prevalence of Multidrug-Resistant Organism Colonization

Organism Facility 1, % Facility 2, % Facility 3, %
Any multidrug-resistant organism 47 34 57
MRSA 38 15 34
VRE 7 19 11
ESBL 11 8 28
CRE 0 0 2


Targeted prevention becomes very difficult when nearly half of the patients in a facility are colonized with a multidrug-resistant organism, Dr McKinnell pointed out. "We need universal interventions that protect everyone, and enhanced ones for those who need more protection," he explained.

Prevention is the way to go; we need infection control so these bugs don't spread.

The culture of multiple body sites, as often occurs in Europe, "unequivocally increases the yield, and we're more likely to find colonized individuals," said Leonard Mermel, DO, from the Rhode Island Hospital in Providence.

If colonized individuals are admitted to the hospital without having been screened, "a silent transmission goes on." Then we have to isolate and try to manage the infection, Dr Mermel said.

"But the fact is, we have limited operations to respond to infection on the back end, so we really have to control them on the front end," he told Medscape Medical News.

"Darwin was right," he said. "There is something called evolution." Bacteria reproduce every 20 minutes, so they have a selection advantage. "We are limited in our antimicrobial options, and if we keep throwing broad-spectrum antibiotics at our patients, evolution will take its course."

"When 40% of people are infected with these drug-resistant organisms, we need to do something." As a society, it is important that we prioritize this, he said. "Prevention is the way to go; we need infection control so these bugs don't spread."

Dr McKinnell and Dr Mermel have disclosed no relevant financial relationships.

Society for Healthcare Epidemiology of America (SHEA) Spring 2016 Conference. Presented May 20, 2016.


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