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The Role of the Microbiology Laboratory in Surveillance and Control of Nosocomial Infections ROBERT A. WEINSTEIN, M.D., AND GEORGE F. MALLISON, M.P.H. Weinstein, Robert A., and Mallison, George F.: The role of the microbiology laboratory in surveillance and control of nosocomial infections. Am J Clin Pathol 69: 130-136, 1978. The microbiology laboratory's rapid and consistent identification of nosocomial pathogens is a keystone in the surveillance and control of hospital-acquired infections. In addition, the laboratory serves as a source of expert consultation for clinicians and infection control personnel and as an "early warning center" for infection problems. In making its contributions to infection control most effective, the laboratory must recognize its capabilities and limitations, must insure that the materials and methods it uses and the specimens it processes meet high standards, must provide retrievable records, and must have a good working knowledge of microbiologic technics used to evaluate both endemic and epidemic infections. Moreover, because laboratory workers come into contact daily with potentially infectious specimens and isolates, the laboratory's contributions to infection control should also include the prevention and surveillance of laboratory-acquired infections. (Key words: Clinical microbiology; Infection control; Nosocomial infections; Laboratory-acquired infections.) U.S. Department of Health, Education and Welfare, Public Health Service, Center for Disease Control, Bureau of Epidemiology, Atlanta, Georgia Major Contributions towards Surveillance and Control Laboratories generally contribute directly to the surveillance and control of nosocomial infections in five ways. First, the laboratory records are an important surveillance tool and data source. Because more than 80% of infections subsequently judged to be nosocomial may be cultured in hospitals with active infection surveillance and control programs, 56 the data gathered by infection control personnel during "laboratory rounds," together with data gathered from "clinical rounds," form an important base for calculation of infection rates for various pathogens, by site of infection and by hospital service. 15 SINCE THE EARLY 1950's, when widespread hospital-acquired staphylococcal disease first focused attention on the problem of nosocomial infections, the hospital and laboratory burden created by nosocomial pathogens has increased greatly.1-4-7'33'68 At present in the United States, nosocomial infections affect more than 1.5 million patients each year and add more than one billion dollars to the cost of healthcare delivery. 56 Although hospital laboratory capacities are often strained by the sheer number of routine specimens to be processed, each hospital also looks to its lab for support in activities related to prevention, surveillance, and control of hospital-acquired infections. 1,32 In this paper, we present the major contributions that we feel the microbiology laboratory can and should make toward infection control, we discuss specific activities that can assist the laboratory in making its contributions most effective, and we suggest how laboratory-acquired infections may be prevented and controlled. Second, the laboratory results are a potential "early-warning system" for the emergence within a hospital of highly infectious pathogens, multiplyresistant organisms, and clusters of unusual infections. In hospitals where formal surveillance has not yet been established, laboratory workers may in fact be the only personnel to see ward-by-ward culture results and thus be in a position to detect infection trends. Third, the microbiology laboratory is often called upon for expertise in microbiologic sampling of the hospital environment. Since surveillance of patient disease and upgrading of patient-care policies and practices should be the primary focuses of infection control programs, microbiology and infection control personnel should be prepared to curtail routine microbiologic sampling and testing sharply. 115,61 Fourth, during nosocomial epidemics laboratory personnel may conduct culture surveys of patients, hospital personnel, and the environment. Large numbers of cultures may have to be obtained, processed, and evaluated over a short period. Data gathered by microbiology personnel in such surveys may be crucial in identifying the reservoir and mode of spread of epidemic organisms. Finally, a clinically oriented member of the labora- Received April 12, 1976; received revised manuscript January 21, 1977; accepted for publication January 21, 1977. Dr. Weinstein's present address is Department of Medicine, University of Chicago Hospitals, Chicago, Illinois 60637. Address reprint requests to Hospital Infections Branch, Bacterial Diseases Division, Bureau of Epidemiology, Center for Disease Control, Atlanta, Georgia 30333. 0002-9173-78-0200—0130$00.85 © Ame:rican Society of Clinical Pathologists 130 ROLE OF THE LABORATORY IN INFECTION CONTROL Vol. 69 . No. 2 tory staff can contribute significantly by serving on the infection control committee. 5,15,32,4 ° Input by this member of the committee is essential in maintaining a harmonious working relationship between clinical, infection control, and microbiology personnel. Specific Activities Regular Assessment and Handling of Specimen Collection Improperly collected or transported specimens 28 may give inaccurate results even in the best clinical laboratories, and are likely to result in improper clinical decisions by physicians, unnecessary labor by laboratory personnel, excessive patient charges, and misleading epidemiologic data. Certain laboratory findings suggest specific handling errors. For example, the frequent recovery of two or more different organisms or the frequent finding of 10 3 -10 4 organisms per ml in clean-voided urine specimens strongly suggests unsatisfactory technic in collecting specimens, a delay in transporting specimens to the laboratory, or a delay in culturing the specimens after receipt. 36 The frequent failure to culture organisms from deep abscesses of patients who are not receiving antibiotics, or the failure to isolate pathogens seen on Gram-stained material from presumed anaerobic infections, suggests the use of aerobic transport vials, delay (or inappropriate refrigeration) of specimens in transit, or the use of inadequate laboratory technics for isolating anaerobes. 217 The finding of negative acid-fast cultures from a high percentage of specimens with positive acid-fast smears suggests unsatisfactory sputum collection and handling, errors in staining, or errors in culture technic. 6770 To help avoid such problems, it is important to assess specimen collection and handling regularly. An ongoing analysis of the frequency with which probable contaminants are isolated from clinical specimens provides an indirect measure of specimen collection on the ward. Once these data have been compiled, wards with the highest frequencies of polymicrobial urine specimens, for example, can be singled out for evaluation and, when necessary, intensive inservice education by laboratory or infection control personnel. Likewise, personnel who draw blood specimens that frequently contain diphtheroids, coagulasenegative staphylococci, or other probable skin contaminants may need to be reinstructed in aseptic technic. Periodic review of the relative incidence of false-positive acid-fast smears may highlight problems in sputum collection and processing. 70 Microscopic preview of certain types of specimens may help to avert culturing inadequately collected 131 material. For example, after a prospective study at the Mayo Clinic showed that sputum specimens with more than ten squamous epithelial cells per low-power (xlOO) Gram-stained field were usually contaminated with oropharyngeal secretions, all such specimens at that institution have been rejected for bacteriologic culture (and the staff submitting the specimen notified).42 Scoring systems for use in determining acceptable sputum, wound, vaginal, cervical, and other specimens have also been described. 3 - 4 Periodically, matched specimens (one taken directly to the laboratory and cultured immediately and the other transported in the usual manner) should be examined to determine whether a significant transport delay exists. 31 Some hospitals also use laboratory slips that require recording both the time the specimen was collected and the time the laboratory received it, so that transport time can be continuously monitored and the culturing of excessively old specimens avoided. With the increasing recognition of anaerobes as potential nosocomial pathogens, laboratory personnel need to be especially alert for errors in collection or transport of anaerobic specimens. 217 - 22 ' 23 ' 41 Large numbers of anaerobic organisms are present in the normal flora of the skin, oral cavity, and gastrointestinal tract; thus, swabs from superficial portions of skin or mucous membrane lesions, specimens of expectorated sputum (or bronchoscope specimens), and any materials contaminated with feces should be considered inappropriate for anaerobic culture. Frequent submission of such specimens, or of specimens such as urine that are rarely infected by anaerobes, 54 for anaerobic culture suggests the need for in-service education of hospital personnel. Accurate and Consistent Identification of Isolates Recognition and evaluation of hospital-acquired infections depends on accurate and consistent identification of microorganisms. Not infrequently, CDC personnel investigate an apparent outbreak only to find that the problem resulted from errors in or changes in laboratory procedures. For example, an "outbreak" of Staphylococcus aureus infections was caused by delayed reading of coagulase tests, resulting in the misidentification of coagulase-negative organisms as coagulase-positive. In another hospital, improvements in laboratory technic that allowed accurate identification of Herellea vaginicola organisms, for the first time in that institution, resulted in an apparent "outbreak of Herellea infections." Of even greater concern, incomplete identification or misidentification of organisms may obscure real 132 WEINSTEIN AND MALLISON problems and make retrospective epidemiologic investigation impossible. For example, a report of'' Klebsiella-aerobacter group" is not only phrased in obsolete terminology but also fails to distinguish between Klebsiella and Enterobacter, organisms that are characterized by different antimicrobial sensitivities and may have different epidemiologic patterns within the hospital. 63 Along the same lines, identifying an isolate as Pseudomonas cepacia, an organism frequently associated with illness caused by contaminated dilute aqueous benzalkonium chloride or similar antiseptics, ,2,18 provides much more epidemiologic information than identifying it as "pseudomonas species." Each hospital microbiology laboratory should maintain the capability of identifying gram-negative organisms to the genus level with at least 95% accuracy; and such isolates from adequately collected and transported specimens and especially from serious infections, as those involving blood or cerebrospinal fluid, should be speciated whenever possible. (The problems of evaluation and speciation of mixed cultures have been the subject of several recent communications.3'4,35, 'i8) Species should be determined by biochemical characterization, not by colonial morphology. Some hospitals may find it advantageous to employ commercial multi-test media " k i t s " for biochemical testing. 16 ' 25 ' 30 ' 34 ' 49,30 ' 38-60 Information about various systems may be obtained from state public health laboratories or from the Bureau of Laboratories, CDC. In addition, public health and other reference laboratories can provide assistance in identifying unusual isolates. Rapid dissemination of data from the microbiologist to the clinician 8 may be facilitated by providing both preliminary and final copies of culture results. To facilitate surveillance of nosocomial infections and of all infections requiring isolation or notification of public health authorities, a copy of positive culture results should also be sent to the infection control nurse. Reports of all positive blood, cerebrospinal fluid, and tuberculosis smears and cultures should be telephoned immediately to the appropriate clinicians and to infection control personnel. Antibiotic Susceptibility Testing The "Kirby-Bauer" single-disk diffusion method 6 12-14,66 o r a n equivalent test system is recommended for antibiotic sensitivity testing. The epidemiologic value of sensitivity patterns may be enhanced by including certain antibiotics that do not necessarily provide clinically useful information. For this reason the Bacterial Diseases Division, CDC, currently recommends that two disk sets, of 12 antibiotics each, be used; one set is for gram-negative and the A.J.C.P. • February 1978 other for gram-positive aerobic isolates.* While alternative sets, employing fewer disks, have been advocated for routine clinical use, 44 the few extra disks selected here primarily for epidemiologic purposes are inexpensive, and all 12 disks can be placed in the same dispenser and applied simultaneously to one agar plate. Moreover, while the results from a limited disk set allow treatment decisions for individual patients, the results from the additional disks have proved valuable to some institutions in identifying and evaluating episodes of cross-infection and common-source infection. Results from these disks have also been helpful in tracing low-frequency infections occurring in many different hospitals. For example, during a recent nationwide outbreak of bacteremia, susceptibility of Enterobacter agglomerans blood isolates to nitrofurantoin and naladixic acid assisted in identifying epidemic strains from contaminated commercial intravenous products. 39 Furthermore, comparison of the expected and observed susceptibility patterns for organisms can provide valuable taxonomic and quality control information.46 At least annually, in cooperation with the infection control committee, the laboratory should distribute to all clinicians a summary of sensitivity patterns for various sites and major pathogens. The infection control committee and/or a medical staff committee may wish to review antibiotic utilization at this time. 3757 ' 71 Furthermore, if a list of the cost (per unit dose) of each antibiotic is included in the summary, clinicians may be motivated and assisted in reducing costs for patient care. The infection control committee may decide not to include in clinical reports the results of sensitivities performed for epidemiologic purposes only or those performed on antibiotics the hospital wishes to control. When this is the case, clinicians should be informed of which antibiotics are being tested routinely but not reported. Retrievable Laboratory Records Laboratory records should be retained at least 2 - 3 years to facilitate retrospective epidemiologic investigations and use of laboratory data for qualitycontrol activities. Culture data for inpatients and outpatients should be maintained separately and should be recorded so that results are readily available by type of specimen, pathogen, and date. The source of each specimen, the date of collection, the pa* The gram-negative set should contain: nitrofurantoin, chloramphenicol, amikacin, trimethoprim-sulfamethoxazole, cephalothin, tetracycline, gentamicin, naladixic acid, ampicillin, colistin, carbenicillin, and kanamycin. The gram-positive set should contain: penicillin, clindamycin, cephalothin, streptomycin, erythromycin, sulfathiazole, vancomycin, chloramphenicol, tetracycline, methicillin, kanamycin, and neomycin. Vol. 69 • No. 2 ROLE OF THE LABORATORY IN INFECTION CONTROL tient's name, hospital number, hospital service, and ward, and the final isolate identification(s) should be recorded. The results of antimicrobial sensitivity tests and any special biochemical (or typing) reactions may also be entered. Bound log books for each major type of specimen (blood, wound and skin, cerebrospinal fluid, urine, stool, sputum and respiratory, and other) provide simple, inexpensive, and epidemiologically useful records. Sole reliance on a filing system of loose laboratory slips is not recommended, since specific data are difficult to retrieve and are easily lost. When available, computer storage of all results is advantageous—though non-computerized rapid retrieval and sorting systems may also be useful.53 Quality Control Participating in proficiency testing programs helps the laboratory maintain competence, particularly when proficiency test specimens are submitted to the laboratory in a blind fashion and are handled routinely. Hospital-supported, continuing education is very important for "personnel quality control"—particularly if small laboratories are to remain abreast of technological advances. 21 In addition to these and the other quality control activities that are discussed above, selected laboratory materials, media, and methods may be examined periodically."••43-48-51 The Manual for Quality Control Procedures for Microbiological Laboratories,19 available from the CDC Bureau of Laboratories, offers a comprehensive discussion of this subject. Despite quality control within the laboratory, erroneous microbiology results related to the inadvertent use of faulty or contaminated materials outside the laboratory may be overlooked by both clinician and microbiologist. For instance, an "outbreak" of false-positive Gram stains of cerebrospinal fluid was recently caused by nonviable contaminants in the specimen tubes in a lot of commercial lumbar puncture trays. 69 Similarly, contaminated skin antiseptics, Vacutainer tubes, penicillinase, and blood culture media have all been implicated in outbreaks of pseudobacteremia. 9,12,38,45 Such sources of error should be considered when culture or stain results do not appear to reflect clinical or epidemiologic findings accurately. Microbiologic Sampling and the Investigation Nosocomial Outbreaks of When microbiology personnel are asked for advice about microbiologic sampling, they should be prepared to recommend methods for culturing, and they should also be prepared to recommend who and 133 what should (and should not) be sampled. In the absence of an epidemic situation, sampling should be minimal. All steam and ethylene-oxide-gas sterilizers should be checked at least once each week with a suitable live-spore preparation; 5 ethylene-oxidegas sterilizers should also be checked with each load of items that will come into contact with blood or other tissues. Hospital-prepared infant formulas should be cultured each week. Instruments that touch mucous membranes but are disinfected rather than sterilized before use, such as inhalation and anesthesia equipment and endoscopes, may be sampled on a spot-check basis as needed to insure adequacy of disinfection. Although commercial patient-care items labeled sterile (such as intravascular catheters and fluids) have occasionally been contaminated with viable organisms that can cause patient disease, routine sampling of these items is not recommended because of the low frequency of contamination and because of the difficulty and expense of performing adequate sterility testing. When contamination of commercial products sold as sterile is suspected, the Food and Drug Administration should be telephoned immediately. Some hospitals may occasionally do limited environmental microbial sampling for educational or housekeeping quality control purposes. However, levels of environmental contamination in hospitals have not been shown to correlate with the incidence of nosocomial disease, and CDC and the American Hospital Association therefore discourage routine environmental sampling.1-61 In-use testing of disinfectants and antiseptics is not recommended, and, furthermore, routine culturing of patients or hospital personnel for microbial carriage is not generally recommended. The investigation of an outbreak, however, often necessitates that many cultures be taken from patients, personnel, and the environment, and laboratory personnel should be prepared to recommend the most appropriate culturing procedures. 1 - 5 When patients and personnel are evaluated for microbial carriage, the culture medium is determined by the epidemic pathogen, and the sites to be cultured may include nasopharynx, throat, umbilicus, groin, rectum, vagina, skin lesions, and hands. Identification of all infected and colonized individuals may be of utmost importance in outbreaks where treatment of carriers or cohorting of affected persons is felt to be a keystone in control. However, culture surveys of patients, and especially of personnel, may be extensive and should be undertaken only when indicated as necessary by epidemiologic findings, and then carefully planned.1-27 During outbreaks, samples may also need to be 134 WEINSTEIN AND MALLISON taken from objects that appear to be epidemiologic a l ^ implicated in the spread of infections, such as patient-care supplies or equipment, medicines, antiseptics, soap dispensers, lubricants, hand lotions, food, kitchen equipment, water, ice, and air. While there are no standard technics for culturing many of these objects, there are definitely good and bad approaches. The guidelines given below should be helpful in most situations; however, when questions arise it is best to consult a public health or other reference laboratory before undertaking any large survey that might produce misleading information. Many objects may be cultured by premoistened swab of, careful rinse with, or immersion in brainheart infusion broth enriched with 0.5% beef extract. Whenever the object being cultured may contain residual disinfectant, the broth should contain 0.07% lecithin and 0.5% Polysorbate-80 as neutralizers. The initial broth culture may be allowed both a 4- and a 24-hour enrichment period before being plated onto agar appropriate for the isolation of the implicated pathogen(s). When necessary, the enrichment broth can be modified for specific epidemic pathogens (for example, tetrathionate brilliant green broth would be most appropriate for salmonella enrichment), and the enrichment and isolation procedures may be adapted for quantification. 3 Samples of water or (melted) ice may be cultured by passing the suspect fluid through a .45-/xm (or .22-^u,m) Millipore filter and then culturing the filter in broth or directly on agar. Air sampling may be performed with either settling plates or sophisticated instruments. 20 However, air-borne spread of nosocomial bacterial infections is probably very uncommon and, when suspected, should be evaluated by someone with experience in this field. Sampling of suspect intravenous fluids (or blood products) requires careful aseptic technic and is described elsewhere. 5,24 During culture surveys, unusual characteristics of epidemic isolates, such as resistance to multiple antibiotics or heavy metals, may enable these organisms to grow selectively on a specially prepared medium incorporating antimicrobial agents (thus decreasing the effort and time required to work up specimens from the survey). Laboratory personnel should be prepared to make and pretest such media as needed. 3,52 Epidemiologically important isolates may need special typing and, if so, should be forwarded to state or local reference laboratories.t Although hospital laboratory personnel may not have the facilities to perform specialized typing procedures, they should know which organisms are typable 28 t The current federal regulations for packaging etiologic agents for air transport may be obtained from the Office of Biosafety, CDC. A.J.C.P. • February 1978 and which laboratories can perform the procedures. Furthermore, in cooperation with infection control personnel, the laboratory personnel should subculture and save epidemiologically important isolates, whether such isolates are from outbreaks or from single cases of unusual or potentially epidemic diseases. A system for reviewing and periodically discarding these isolates must of course also be set up. Finally, to facilitate all the microbiologic activities that are necessitated by an outbreak, the laboratory (or Infection Control Committee) should have a contingency fund to enable personnel, materials, and space to be temporarily assigned to epidemic aid support. Individual patients should not bear the cost of the contingency fund; rather, costs to the laboratory of investigating an epidemic, as well as costs of laboratory inovations that are discussed in this paper, should be evaluated by hospital administration in arriving at basic charges for all patients. Prevention of Laboratory-acquired Infection Because of the possibility for frequent contact between laboratory personnel and infectious materials, infection control within the microbiology laboratory is an important, although often overlooked, aspect of hospital infection control. The infectious materials in any laboratory will vary depending on the prevalence of various pathogens in the hospital, on the extent to which the laboratory attempts to isolate viral, fungal, or mycobacterial organisms, and on the nature of any research undertaken. However, despite institutional variations, several general comments can be made regarding prevention and control of laboratory-acquired infections. Nationwide, the three most common causes of laboratory-acquired infections, accounting for approximately a third of known cases, are hepatitis (a particular problem with glassware washers and other laboratory workers who come in contact with blood), tuberculosis, and brucellosis. 26,47,64,63 In addition, etiologic agents of shigellosis, tularemia, psittacosis, Q fever, amebiasis, and especially coccidioidomycosis, although infrequently encountered in many laboratories, are infectious enough to be considered among the next most common causes of reported laboratoryacquired disease. The extents to which other agents may cause inapparent or seemingly non-laboratoryrelated infections, which can only be measured by surveying laboratory workers periodically for seroconversion or recent infectious illness, are not known; however, experiences with hepatitis B suggest that seroconversion to some organisms may be quite extensive before it is detected. Vol. 69 . No. 2 ROLE OF THE LABORATORY IN INFECTION CONTROL Excessive exposure to infectious material occurs most frequently because of accidents involving needles and syringes, broken glassware, or spilled cultures. 2 "- 47 " 2 " 4 Accidental puncture of skin with a contaminated needle is, of course, a hazard to any hospital employee. In addition, in the laboratory, infectious aerosols may be unwittingly created when syringes are used improperly."4 Because of this hazard, clotted blood or pus should not be homogenized through a needle, and only Luer-lock syringes should be used in the laboratory. Moreover, when air bubbles are being expelled from a syringe or when a needle is being withdrawn through the stopper of a culture or vaccine bottle, an alcohol-soaked cotton ball should be used to shield the needle. Pipettes may also transmit diseases in the laboratory. 10 " 4 In addition to the obvious risk created by mouth-pipetting or improper disposal of contaminated pipettes, infectious aerosols may be created when the contents of a pipette, even the last drops, are forcibly expelled. Aerosols may also be liberated when infectious materials are macerated, ground, blended, or centrifuged, and when ampules of lyophilized bacteria or viruses are opened.47-62-64 All new laboratory personnel should be familiarized with the hazards of disease transmission within the laboratory. It is hoped that an introductory course on laboratory safety will encourage good technic and help personnel to understand the rules prohibiting mouthpipetting, drinking, smoking, and eating in the laboratory and the rules requiring handwashing, adequate waste disposal, surface decontamination, and the use of protective clothing, safety cabinets, and hoods. A reference source for decontamination methods within the laboratory and for the types of precautions necessary for different organisms and procedures is available from the CDC Office of Biosafety.11 To assess the adequacy of infection control within the laboratory, the health of laboratory personnel should be monitored routinely. Staff should be given pre-employment and at least annual skin tests for tuberculosis, followed by chest x-rays when indicated. Periodic screening of laboratory personnel for hepatitis-B antigen seroconversion may be helpful in determining high-risk areas in the laboratory. In general, a log of all laboratory accidents and their outcomes should be kept, work habits should be discussed with accident-prone employees, 29 and the possibility of laboratory-acquired disease should be considered whenever personnel develop unusual infectious illnesses. Acknowledgments. The experiences of many past and present members of the Hospital Infections Branch and Epidemiologic Investigations Lab Branch, Bureau of Epidemiology, CDC, as well as the authors' experiences with a large group of hospitals that 135 have cooperated with the CDC's program for national surveillance of nosocomial infections, have been invaluable in the preparation of this manuscript. References 1. American Hospital Association: Infection Control in the Hospital. Chicago, American Hospital Association, 1974 2. Balows A. Dehaan RM. Dowell VR, et al (editors): Anaerobic Bacteria. Springfield, 111., Charles C Thomas, 1974 3. Bartlett RC: A plea for clinical relevance in medical microbiology. Am J Clin Pathol 61:867-872, 1974 4. Bartlett RC: Control of cost and medical relevance in clinical microbiology. Am J Clin Pathol 64:518-524, 1975 5. 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