Controlling blood culture contamination rates.

One of the more frustrating problems plaguing hospitals and laboratories is the rate with which bacteria external to the patient contaminate blood cultures. If specimen collectors use poor collection technique, they can introduce organisms into blood culture bottles that mislead lab technicians and physicians into thinking that patients have potentially life-threatening bacteremias when in fact they do not. The results of such misleading findings can be measured in both financial and human terms. One study shows that contaminated blood cultures can increase a patient's hospital stay by as much as 4.5 days and add more than $5,000 to the cost of treatment (adjusted for inflation since the study was published). [1,2] More importantly, incorrect data can keep patients from rejoining their families and their jobs and from reclaiming their daily lives.

Because physicians rely heavily on blood culture results to diagnose and monitor febrile patients, few results can have such a profound effect on patient care as an erroneous blood culture report.

Since the advent of cross-training for healthcare professionals, it has never been more difficult to control blood culture contamination rates. Because healthcare workers from many different disciplines within a facility are now drawing blood specimens--and the lines of authority over them are often blurred--many laboratorians are understandably frustrated and tempted to give up the fight to maintain unadulterated samples. However, recent studies have given laboratorians new ways to combat the problem. A review of these findings as well as information about sound collection practices can arm healthcare professionals with specific strategies to prevent the expensive and unfortunate consequences of poor phlebotomy technique.

The infection process

Bacteria can infect the circulatory system from intravascular and extravascular sources. Intravascularly, microorganisms can originate from infected organs, cavities, fluids (eg, cerebral spinal, synovial, or pericardial), untreated superficial wounds, abscesses, urinary tract infections, or respiratory infections. Such infections, if aggressive or left untreated, can spread rapidly throughout the body. Immunocompromised patients are especially vulnerable to isolated infections becoming systemic.

Extravascular sources of septicemia--contaminated vascular-access devices (eg, arterial lines or central venous catheters), urinary catheters, or other foreign devices--can also provide ports for bacteria to exploit the oxygen and nutrient-rich environment of the circulatory system. Regardless of the source of the infection, if an isolated infection becomes systemic, physicians must act quickly.

Reporting positive blood cultures that are not consistent with the patient's condition, diagnosis, or clinical symptoms, however, puts physicians in a quandary. Often, doctors must decide whether to ignore a result that could be life-threatening or to consume valuable hospital resources fighting an infection that might not exist. Posed with this paradox, many choose the conservative approach: administer antibiotics, extend the patient's stay, and monitor the patient with more tests. Few collection errors are as costly to the hospital, the laboratory, and the patient as blood cultures that are compromised by inattentive specimen collection practices.

According to the standards published by the American Society for Microbiology, the rate of blood culture contamination should not exceed 3% . [3] Eliminating all suspected false positives, however, is not a realistic goal. Some suspected contaminants may be associated with transient bacteremias (bacteria that exist momentarily in the bloodstream and then are engulfed by the body's cellular immune response). These bacteremias enter the bloodstream through stress or trauma to mucous membranes (eg, dental work, injuries to the nasopharyngeal cavities, or obstructed bowel) or through invasive procedures that disrupt tissue integrity (eg, urinary catheterization or colonoscopy). The average contribution of transient bacteremias to a facility's contaminated culture rate is not known. However, when a hospital finds its overall rate creeping beyond 3%, it's an indication that blood cultures are not being collected with proper attention to aseptic technique. For a listing of the rates at which different organisms con taminate blood culture samples, see Table 1.

Indicators of contamination

Fortunately, indicators exist that can alert physicians and laboratorians that the specimen might have been contaminated during collection or processing. These indicators include [4]:

* frequency of positive bottles among collections

* Gram stain results from positive bottles

* white blood cell count/differential

* number of organisms isolated

* patient symptoms

* time required for growth to become detectable.

Frequency. Blood cultures that are legitimately positive--that is, contain growth from in vivo bacteria--typically demonstrate growth in every set collected. For example, if 3 sets of cultures are collected and all 3 sets demonstrate growth, it is probable that the patient has a rampant bacterial infection. Conversely, growth in only 1 out of 3 cultures suggests contamination.

Gram stain results. Gram stains from positive cultures that demonstrate characteristics of normal skin flora should be suspect. Gram-positive cocci in clusters indicate staphylococci; small gram-positive rods appearing in palisades ("picket fence" arrangements) suggest Corynebacterium spp.; gram-positive, club-shaped rods characterize Propionibacterium spp.; and gram-positive cocci in pairs are typical of alpha and gamma streptococci. The large gram-positive rods of Bacillus spp., although not normal skin flora, are an environmental contaminant that can find their way onto the skin and ultimately into a blood culture bottle. The presence of any of these organisms hints that the puncture site might not have been cleansed with attention to antiseptic technique. Unfortunately, some of these organisms can also cause septicemia; so in the absence of other indicators, the identification of these organisms by Gram stain morphology is not reason enough to dismiss the culture as contaminated.

Elevated WBC count/abnormal differential. Legitimately positive blood cultures are often accompanied by an elevated white blood cell (WBC) count as evidence that a cellular response to an infection is taking place. Additionally, a left shift in the differential ([greater than]10% bands), with or without an elevated WBC, adds credibility to a positive blood culture. The absence of these indicators is a vote against a legitimately positive culture.

Multiple organisms isolated. True septicemias are almost exclusively caused by an infection with a singular organism. Although multiple-organism infections can occur, the presence of 2 or more organisms, especially in combination with other indicators, is usually a result of poor site preparation.

Patient symptoms. The body's natural response to bacterial invasions is to trigger a rise in temperature to bum out the pathogen. This defense might present itself in the form of "fever spikes," in which the patient experiences a rising and falling of temperature, or as constant, low-grade fevers. Legitimately septic patients, therefore, are constantly or occasionally febrile. The absence of a temperature in the presence of positive blood cultures creates a conflicting picture and raises questions about the validity of the culture result.

Time required for growth to become detectable. Patients who are legitimately septic often demonstrate immediate growth in their blood culture bottles. Assuming sufficient volumes of blood have been inoculated into the bottles, bacteria should multiply to detectable levels within 48 hours, often much sooner. Conversely, growth that is slow to emerge indicates that only a miniscule number of organisms have been inoculated into the broth, which is typical for collections contaminated from external sources.

Suspect culture results should be interpreted with consideration of all the previously mentioned factors before treating the patient for septicemia. If these indicators exist in combination, contamination is suggested. To simplify the decision-making process, many facilities adopt an algorithm based on some combination of these indicators.

Factors affecting blood culture collection

Certain factors have a critical bearing on drawing a blood culture specimen. These factors include:

* training of blood collection personnel

* location of collection site

* preparation of puncture site

* blood collection equipment

* collection volume.

Personnel. A Q-Probe study released by CAP in 1998 identified several key elements that contribute to high contamination rates. [5] One clearly determining factor was the use of a multiskilled workforce to draw blood specimens. When blood cultures were collected by personnel who were not members of a specifically designated phlebotomy team, the contamination rate was significantly higher (77%) than for members of such a team. In fact, the lowest contamination rates were associated with facilities in which 90% or more of the blood cultures were collected by a trained phlebotomy staff. A second study found a dramatic reduction in blood culture contamination (as much as 86%) when a collection staff was established (see Table 2). [3]

Several studies have projected the overall cost savings to a facility when a dedicated phlebotomy team is employed to collect blood cultures. [3,5] An editorial published in the Mayo Clinic Proceedings in 1998 calculates that "the typical savings associated with using a phlebotomy service can be predicted to be about $20 per blood culture specimen collected." [2] A study by Weinbaum et al reports that the mean hospital charges for patients with false-positive blood cultures was more than 50% higher than for similar patients with true-negative cultures. [3] The report projected that the 487-bed facility studied might save as much as $1.2 million annually if it employed a dedicated phlebotomy team to collect blood cultures.

Unfortunately, many laboratories no longer have the luxury of maintaining a dedicated team of phlebotomists. For these facilities, it is critically important to continuously monitor and educate those collecting blood for cultures to keep contamination rates as low as possible. One approach is to employ a "micro-management" strategy. A study published in the Archives of Pathology and Laboratory Medicine showed that almost a 50% reduction in contaminated blood cultures occurred when the contamination rates of each collector were monitored and individual collectors were informed of their rates. [6]

Site selection. The location of the collection site has a significant impact on the potential for a culture to be contaminated. Draws from vascular-access devices, such as arterial lines, central venous catheters, and heparin locks, have been shown to result in high contamination rates. Because these ports pass through the skin and remain there for long periods of time, they are susceptible to bacterial colonization. Colonized bacteria multiply and accumulate in and around invasive ports and can be pulled into blood specimens drawn from those sites.

To confirm that a positive blood culture is caused by colonization, a second blood culture must be drawn at the same time by skin puncture and the results compared. (Some facilities have a policy to draw peripheral cultures simultaneously whenever a culture is taken through a vascular-access device.) A negative culture by venipuncture, in conjunction with a positive culture by line draw, confirms colonization, whereas positive cultures drawn from both sites confirm septicemia. However, if the culture collected by venipuncture is contaminated because of poor technique, then it becomes necessary to compare the organisms isolated to determine if a true septicemia exists. Hence, any benefits to collecting cultures by a line draw are outweighed by the expense of confirmatory collections by venipuncture and should be avoided.

Site preparation. Proper site preparation is without question the single, most important factor in collecting uncontaminated blood cultures. Iodine-based antiseptics, sometimes used along with isopropyl alcohol, have become the industry standard for sterilizing puncture sites. Separately packaged alcohol preps and povidone swabs are available, but using them in tandem has been found to be less effective than employing commercially prepared prep kits, such as Cepti-Seal (Mediflex Hospital Products, Overland Park, KS) and Persist (Becton Dickinson, Franklin Lakes, NJ). [7]

Not all iodine compounds are equal, however. One study showed that iodine tincture is more effective in reducing contamination rates than iodine in an iodophor (eg, povidone). [8] Additionally, it appears that the effectiveness of the antiseptic is a function of who is using it. The previously mentioned CAP Q- Probe study [5] showed that preparation of puncture sites with tincture of iodine, as opposed to an iodophor, was superior in combating contamination at sites where non-phlebotomy personnel collected cultures. However, both forms of iodine were effective in facilities that employed a designated phlebotomy team. The study's authors speculate that such teams are better trained and have a greater awareness of the relationship between contact time and site asepsis.

Proper site preparation starts with a 30-60-second scrub with the antiseptic. (If isopropyl alcohol is used, it is applied first to remove most of the surface contaminants, followed by the iodine compound.) A final swabbing of the intended puncture site completes the process, starting from the center and moving outward in circles of increasing diameter until the antiseptic colors the skin 2 inches or more in all directions. Some procedures call for an initial iodine scrub followed by an alcohol cleansing, then a final application of iodine in increasingly larger concentric circles as described. Regardless, the bacteriostatic effect of iodine is directly proportional to the length of time it is allowed to remain in contact with the skin in a dried state. (Iodine com pounds are not bacteriocidal in a liquid form.) Iodine must be allowed to remain in contact with the skin in a dried state for at least 30 seconds before the puncture.

Blood culture contamination is most likely to occur during attempts to relocate difficult-to-find veins by palpation after a site has been sterilized. This practice obviously reintroduces skin contaminants to the site and, potentially, into the bottle. There are techniques, however, which make re-palpation unnecessary. Making a mental note, before cleansing, of a vein's location in relation to certain skin markers (such as pigmentation or creases) can reduce the urge to re-palpate. Collectors should resist the temptation to re-palpate a sterilized puncture site, but if unsure of a vein's location, they can re-palpate above and below the intended puncture site while avoiding the exact point of entry. Sterilizing the tip of the gloved index finger for palpation is not advised.

An additional factor identified in the CAY Q-Probe study that contributes to low contamination rates is the practice of decontaminating the top of the blood culture bottle before use. The stopper should not, however, be cleansed with an iodine solution alone because it may cause the rubber stopper to deteriorate during incubation and therefore introduce contaminants. Some facilities cleanse the tops with alcohol. Others use an iodine solution, allowing it to dry and remain in contact with the stopper for 30 seconds before removing the iodine with a fresh alcohol prep.

Equipment. Depending on the type of blood culture bottle in use, collectors will fill bottles either by using a winged infusion (butterfly) set and a vacuum-tube adapter or by drawing blood directly into a syringe through a needle or butterfly set.

Using a butterfly/adapter set. (see "Tips on collection technique," p. 37). After the puncture, the adapter should be positioned over the neck of the culture bottle and pressed downward so the interior needle punctures the bottle stopper.

(The butterfly set should never be used without the tube-holder adapter. When not concealed, the needle that punctures the stoppers poses a risk of accidental needlestick.) If both aerobic and anaerobic bottles are included in the set, the aerobic bottle should be inoculated first for 2 reasons: (1) Empty butterfly tubing has approximately 1cc of dead-space volume. If this volume of air is pulled into anaerobic bottles, it can be detrimental to some anaerobic organisms. (2) Ninety-eight percent of septicemias are caused by aerobic or anaerobic organisms that can tolerate aerobic environments (facultative anaerobes). If blood flow is interrupted and cannot be resumed before the anaerobic bottle is filled, most of the causative organisms of septicemia will still be detected.

Using a syringe. When blood is collected into a syringe--either directly or through a butterfly set--the needle should immediately and carefully be pushed through the rubber stopper and the vacuum allowed to pull in the appropriate volume.

For safety's sake, bottles should be placed on a firm surface and punctured with one hand. Using the free hand to steady the bottle puts the healthcare professional at risk for sustaining an accidental needlestick. Also, blood should not be forcefully evacuated from a syringe into culture bottles or any specimen tubes. This risks exposure to bloodborne pathogens if a specimen splatters.

The collector should allow the vacuum to pull the recommended volume of blood into the broth. However, overfilling can lead to false-positive results. To understand this consequence, one must understand how some automated systems detect growth. When bacteria multiply, they raise the concentration of [CO.sub.2] in the bottle's internal environment. Systems that measure changes in the [CO.sub.2] levels during incubation periodically monitor concentrations and compare them to the baseline levels taken when the bottle was initially loaded. When a threshold of change is exceeded, the instrument alerts the operator that a positive has been detected. However, white blood cells produce minute amounts of [Co.sub.2] If collectors become inattentive and more than the maximum recommended volume is evacuated into a bottle, the excess of WBCs can trigger alerts and force unnecessary confirmatory testing. (Inattentiveness while filling anaerobic bottles can also allow air to enter, thereby compromising the anaerobic enviro nment.)

In the past, it was common practice to change needles on syringes before evacuating specimens into culture baffles as a way of preserving sterility during the fill. However, NCCLS does not advocate this practice because of the increased risk of accidental needlesticks, and the literature suggests that this practice does not significantly reduce contamination rates. [4,9]

Collecting inadequate volumes. The optimal volume for blood culture collections from adults is considered to be 20 mL of blood per set, distributed between 2 bottles, and not to exceed 12cc per vial for reasons already discussed. Collecting volumes less than this amount reduces the potential to harvest organisms causing septicemia. If the collection yields less than the minimum volume after drawing both aerobic and anaerobic bottles, evacuating up to the maximum recommended volume into the aerobic bottle is preferred over dividing lesser amounts between 2 bottles.

If a second blood culture is ordered, it may be appropriate to collect it immediately after the first one if it can be drawn from another site. Otherwise, a 45-minute wait before collecting the second set from the same site is recommended. The rationale here is that sampling from 2 completely different bloodstreams increases the likelihood of capturing sparse and transient populations of microorganisms.

Regardless of the equipment used for the collection, if other lab work is being collected simultaneously, evacuate blood into blood culture bottles first and then fill the other lab tubes according to NCCLS's recommended order of draw. [10] To reverse the order is to contaminate the needle.

Proper equipment, correct technique, and a designated team of phle-botomists can significantly reduce a facility's blood culture contamination rate. If facilities employ these factors individually or in combination, it is reasonable to expect that fewer patients will be subjected to the human and financial costs associated with contaminated cultures. The laboratorian's challenge is to educate healthcare professionals from other disciplines to use good collection technique and prepare collection sites properly when performing phlebotomy on their patients.

Dennis J. Ernst, MT(ASCP), is the author of Phlebotomy for Nurses and Nursing Personnel and the director of the Center for Phlebotomy Education, Ramsey, IN. He also teaches phlebotomy at the University of Louisville School of Allied Health Sciences. Louisville, KY.

Suggested reading

Garza D, Becan-McBride K. Phlebotomy Handbook: Blood Collection Essentials. 5th ed. Norwalk, CT: Appleton & Lange; 1999.

National Committee for Clinical Laboratory Standards. Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture. Approved Guideline H3-A4, 4th ed. Villanova, PA: NCCLS; 1998.

References

(1.) Bates DW, Goldman L, Lee TH. Contaminant blood cultures and resource utilization: The true consequences of false-positive results. JAMA. 991;265:365-369.

(2.) Schifman R. Editorial. Mayo Clin Proc. 1998;73:703-704.

(3.) Weinbaum FI, Lavie S, Danek M, Sixsmith D, Heinrich G, Mills S. Doing it right the first time. Quality improvement and the contaminant blood culture. J Clin Micro. 1997;35(9):563-565.

(4.) Bates DW, Lee TH. Rapid classification of positive blood cultures: Prospective validation of a multivariate algorithm. JAMA. 1991;265:365-369.

(5.) Schifman R, Strand C, Meier F, Howanitz P. Blood culture contamination. Arch Pathol Lab Med. 1998;122:216-220.

(6.) Gibb P, Hill B, Chorel B, Brant R. Reduction in blood culture contamination rate by feedback to phlebotomists. Arch Pathol Lab Med. 1997;121:503-507.

(7.) Schifman R, Pindur A. The effect of skin disinfection material on reducing blood culture contamination. Am J Clin Pathol. 1993;99:536-538.

(8.) Strand C, Wajsbort R, Sturman K. Effect of iodophor vs tincture skin preparation on blood culture contamination rate. JAMA. 1993;269(8):1004-1006.

(9.) Krumholz H, Cummings S, York M. Blood culture phlebotomy: Switching needles does not prevent contamination. Ann of Intern Med 1990;113(4):290-292.

(10.) National Committee for Clinical Laboratory Standards. Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture. Approved Standard, H3-A4, 4th ed. Villanova, PA: NCCLS; 1998.

                   Percentage of organisms that exist as
                     contaminants vs true positives
Organism                           False positives   True positives
Bacillus spp.                     [greater than]90% [less than]10%
Coag-negative Staphylococcus spp. [greater than]90  [less than]10
Propionibacterium spp.            [greater than]90  [less than]10
Corynebacterium spp.                     80                20
Viridans streptococci                    50                50
Clostridium spp.                         40                60
Staphylococcus aureus spp.               25                75
Enterococcus spp.                        15                85
Source: From a presentation by Dr. Patrick Murray, University of
Maryland School of Medicine. Microbiology for the Millennium
Conference, February 17-19, 1999, Baltimore, MD.
                   Blood culture contamination rates of
                    phlebotomy vs non-phlebotomy teams
                        Contamination rates when most
                           cultures were drawn by
                                phlebotomists         non-phlebotomists
Weinbaum et al (Unit A)             1.2%                    8.4%
Weinbaum et al (Unit B)             1.0                     4.8
Schifman et al                      2.2                     3.9

Sources: Weinbaum Fl, Lavie S, Danek M, Sixsmith D, Heinrich G, Mills S. Doing it right the first time. Quality improvement and the contaminant blood culture. J Clin Micro. 1997;35(9): 563-565. Schifman R, Strand C, Meier F, Howanitz P. Blood culture contamination. Arch Pathol Lab Med. 1998;122:216-220.

Blood cultures: Protecting the collector

Blood culture collections call for the use of syringes and winged-infusion (butterfly) devices. However, both devices have been associated with increased incidences of needlestick accidents, compared with tube holders alone. One study showed that the use of butterfly sets was responsible for 35% of all accidental needlesticks to phlebotomists. [1] Increased concern over the safety of syringe draws has moved the NCCLS to urge that their use be minimized. [2]

When using syringes or butterfly sets, the following guidelines can help minimize the risk of an accidental needlestick:

* Use only needles designed with safety features.

* Never recap a needle with 2 hands.

* Never hold the bottles in 1 hand while filling from a syringe held in the other.

* Conceal or dispose of the needle device immediately after bottles are filled.

* Make sure a sharps container is within reach at the point of use.

* When puncturing stoppers with a needle or a syringe, place bottles on a firm surface and puncture with 1 hand. Using the free hand to steady. the bottle puts the healthcare professional at risk for sustaining an accidental needlestick.

* Do not try to forcefully evacuate blood from a syringe into culture bottles (or any specimen tubes). This risks exposure to bloodborne pathogens if the force results in the specimen's splattering.

References

(1.) National Committee for Clinical Laboratory Standards. Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture. Approved Standard, H3-A4. 4th ed. Villanova, PA: NCCLS; 1998.

(2.) Jagger J. Risky procedure, risky devices, risky job. Advances in Exposure Prevention. 1994;1(1).