Infection Preventionist Boot Camp, essentials for the beginner infection preventionist

by Peggy Prinz Luebbert, MS, MT(ASCP), CIC, CHSP and Ron Stoker

 The clinical laboratory is an essential component of any investigation by your facility’s infection prevention program. Laboratory personnel have a broad range of technologies from traditional methods of detecting and identifying organisms to modern molecular typing methods. If the infection preventionist (IP) applies these technologies appropriately, he/she can prevent problems and solve infection colonizations and outbreaks efficiently. In many situations, species identification and antimicrobial susceptibility testing (phenotypic methods) or DNA methods (genotypic) can determine whether the isolates are epidemiologically related.

 Let’s take a look at some of these technologies and how they can be used effectively during an IP investigation.

 Antibiotic Resistance Patterns

During an investigation, the first step  routinely performed by the IP is to look at the phenotype of the organisms. The best phenotypical typing available to the IP from the lab is to compare the minimum inhibitory concentrations (MICs) or antibiotic resistance patterns of the like organisms in question. If they differ in patterns dramatically, you can rule out that the isolates originated from a single clone or source. If the resistance patterns of isolates from different patients are similar you may be dealing with a single clone that was transmitted from patient to patient from a common source or by a common mechanism. However, identical MICs are not always enough to validate a source since many bacteria, especially those that are sensitive to multiple antibiotics, may be from multiple sources.

Case Scenario 

During surveillance of surgical site infections, an infection preventionist notices that one surgeon had two group B strep infections of his surgical sites in the last month. Strep infections rarely occur in surgical wounds so the IP is concerned that a single source might be involved in these two surgical site infections. She then looks at the MICs of both organisms and finds them to be identical in their antibiotic sensitivity and resistance patterns. After further research, she notes that these types of infections are usually associated with a carrier who participated in both surgeries. She then reviewed the environment of the cases (dates, times, room, participating staff, etc.) and found that three staff members participated in both cases; the surgeon, circulating nurse and nurse anesthetist. After input from the infection prevention committee, administration and the local labor union, nasal screening for group B strep of all three staff members was performed to identify a possible carrier. One culture—that of the circulating nurse—grew out group B strep with an identical resistance pattern to the surgical infections. This indicates that the source of the beta strep may have been this circulating nurse. However without further testing, such as pulse field gel electrophoresis, the source cannot be confirmed without a doubt. The circulating nurse was treated with appropriate antibiotics and no further cases were identified.

Polymerase Chain Reaction (PCR)

Another technique growing in popularity is the polymerase chain reaction or PCR test. It is a technique used in the molecular microbiology lab to amplify a single or few copies of DNA  generating thousands to millions of copies in a short time. The method uses cycles of repeated heating and cooling for DNA melting and the enzymatic replication of the DNA. DNA fragments along with a DNA polymerase (after which the method is named) are key components to enable selective and repeated amplification. As the PCR test progresses, the DNA generated is exponentially amplified.

Developed in 1983 by Kary Mullis, PCR is now a common and often indispensable technique used in medical and biological research labs for a variety of applications. These include DNA cloning for sequencing, DNA-based phylogeny, or functional analysis of genes; the diagnosis of hereditary diseases; the identification of genetic fingerprints (used in forensic sciences and paternity testing); and the detection and diagnosis of infectious diseases. In 1993, Mullis was awarded the Nobel Prize in Chemistry for his work on PCR.

One of the most common ways to use PCR in the infection prevention program is in the screening and detection of patients who might be carriers or colonized with MRSA. It identifies patients who might require isolation and or other methods to prevent transmission in the healthcare setting.

The molecular-based MRSA assay detects the presence of the mecA gene in Staphylococcus aureus that is responsible for conferring methicillin resistance. If present, this gene target is amplified over a billion fold within two hours and the amplification product is detected by a fluorometric detection instrument. This assay is called real-time PCR and can be completed within several hours. Traditional techniques used to detect MRSA all require a culture step, followed by an isolation of pure colonies and the performance of specialized laboratory tests to identify the isolate as S. aureus and to confirm that the organism is methicillin resistant. This conventional culture-based method may take three to five days to confirm a patient as a carrier of MRSA compared to three to four hours for the MRSA assay. Most laboratories that have PCR technology available will be able to report back the results of a PCR within eight to 24 hours depending upon the time of the day the culture was obtained.

Case Scenario

Recent guidance publications from the Association for Professionals in Infection Control and Epidemiology (APIC), Institute for Healthcare Improvement (IHI) and other agencies suggest that routine screening for MRSA of high risk patients on a regular basis may assist in limiting the transmission of the organism. Studies showed that 8 percent to 10 percent of hospitalized patients are colonized with MRSA on admission and serve as a reservoir for spread to other hospitalized patients. The sooner a patient is found to be a carrier the sooner he/she could be placed in Contact Precautions.

A rehabilitation hospital recognized that many of their patients (quadriplegics, motor vehicle accident victims, etc.) had been in intensive care units for long periods of time and therefore may be at risk of colonization of MRSA. They also knew that many of these patients had never been cultured. So they decided to do nares cultures for MRSA on all new admits, every two weeks and again on facility discharge. Testing would be performed for three months.

This prevalence study would give them some idea on how prevalent MRSA was in their population and if they were colonizing patients while they were in their care. To limit variability associated with the technique of obtaining the specimen, the laboratory trained a limited number of staff on the proper technique of swabbing of the nares, storage and transporting of the specimen. The laboratory used the PCR technique for identification of the MRSA with results usually back to the nursing unit within 24 hours. Once a patient was identified with MRSA, he/she was placed quickly in isolation to limit colonization. Initial testing found 7 percent of admissions were carriers of MRSA with no known history of the organism. Post admission testing every two weeks and on discharge identified that another 5 percent of the patients became colonized while in the facility. After research and implementation of improved hand hygiene of staff, patients and visitors, along with cleaning of exercise equipment, the facility was able to bring their colonization rate to less than 0.5 percent. The PCR testing proved extremely valuable in identifying quickly high risk patients and the poor compliance to standard precautions by healthcare workers, patients and their families.

Pulse Field Gel Electrophoresis

Pulse Field Gel Electrophoresis (PFGE) is one of our most recent tools from the lab available to us in infection prevention and personally to me the most exciting! This technique allows us to even come closer to validating a single source during an outbreak investigation. It is usually performed today in university or research laboratories but most sites have protocols for testing of body fluids from other facilities.

PFGE is a technique used for the separation of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), or protein molecules using an electric field applied to a gel matrix. DNA Gel electrophoresis is usually often after amplification of DNA via PCR. The term “electrophoresis” refers to the electromotive force that is used to move the molecules through the gel matrix. By placing the molecules in the gel and applying an electric field, the molecules will move through the matrix at different rates, determined largely by their mass. The larger the protein, the slower it will move thru the gel so that the different protein molecules will separate. After the electrophoresis is complete, the molecules in the gel are stained or marked with fluorescence or radiation to make them visible.

If several specimens from different patients or sources are initially injected next to each other, they will run parallel in individual lanes. Depending on the number of different molecules, each lane shows separation of the components from the original mixture as one or more distinct bands, one band per component. Bands in different lanes that end up at the same distance from the top contain molecules that passed through the gel with the same speed, which usually means they are approximately the same size.

Since it is hard to separate very large molecules of DNA effectively with standard gel electrophoresis, pulse field gel electrophoresis “pulses,” alternating voltage from different directions which increases the resolution of the larger molecules. This technique was first used by Schwartz and Cantor at Columbia University in 1984 but just became available to us routinely in infection prevention in the last decade.

Case Scenario

An orthopedic surgeon who performs approximately 250 hip and knee replacements annually had never had a MRSA surgical site infection of his implantations until the last month. Three organ space infections were identified with MRSA infections by the infection preventionists. The surgeon was concerned that either himself or one of the staff members present during his procedures had become colonized with MRSA and was shedding the organism. A review of the three MRSA MIC sensitivity and resistant patterns noted similar but not identical response to antibiotics. To further “fingerprint” the organisms, samples of all three specimens were sent together for Pulse Field Gel Electrophoresis. Since the test was only performed at their university laboratory weekly, results were delayed. The result was depicted as bands similar to “bar codes.” The bands were compared to standardized clones common in their locality such as USA 100 and USA 200 often seen in healthcare-associated MRSA as well as USA 300 and USA 400 more often associated with community-acquired MRSA infections. The three infections turned out to be three entirely distinct clones; all different from each other. The specimen from the patient who was a respiratory therapist in a long term care facility closely resembled USA 100—a healthcare-associated MRSA clone. Whereas another patient, who was a father of a high school wrestler, had a clone that resembled a community-acquired MRSA. The third patient with no known risk factors had a distinctly different clone closely resembling another healthcare-associated MRSA.  The infection preventionist could report back to the surgeon that the organisms were distinct. Further investigation focused on looking at breaks in aseptic technique during the procedure.

Conclusion

In summary, the clinical microbiology department and their tests are an essential component of our effective infection prevention programs. Clinical diagnostic tests such as the antimicrobial susceptibility testing, polymerase chain reaction (PCR) and Pulse Field Gel Electrophoresis (PFGE) assist us in identifying specific strains within a given bacterial species, which in turn allows us to study the epidemiology of the pathogens and then develop effective measures to prevent their spread in our facilities.

Peggy Prinz Luebbert, MS, MT(ASCP), CIC, CHSP, is the owner and consultant for Healthcare Interventions Inc., Omaha, Neb. Luebbert, a medical technologist with a master’s degree in pathology, has worked in infection control for more than 20 years, and has published and lectured extensively on a national level. She is certified in infection control and healthcare safety. Most recently, Ms. Luebbert authored the “Third Edition of the Infection Control Compliance Guide.” She is a founder and lecturer for the Infection Preventionist Boot Camp.

            Ron Stoker, MS, is the executive director of the International Sharps Injury Prevention Society (ISIPS). He has 29 years experience in the medical device industry as a researcher, marketer, educator, consultant and healthcare worker advocate. He has written more than 200 medical journal articles, primarily on sharps injury prevention, infection control, and hand hygiene. Mr. Stoker has his BS in Pre-Medical Zoology from Brigham Young University, an MS in Bioengineering from the University of Utah and an “honorary doctorate” from the school of hard-knocks. As a result of a surgical mishap he was rendered a quadriplegic in December 2006. Informed that he would never walk again, with tenacity and a “supportive and mean wife,” Mr. Stoker taught himself how to walk again. He says that he walks like an “alcoholic” but is really just a recovering quadriplegic!

            Mr. Stoker has conducted workshops and Congresses on sharps safety at national and international meetings for the last 10 years. He is a founder and lecturer for the Infection Preventionist Boot Camp Series. For more information contact Mr. Stoker at info@isips.org.