Appropriate use of the microbiology laboratory in the diagnosis of infectious diseases

American

Journal

of Infection

Volume 1.5 Number 5

Control

October 1987

ARTlCLES

of -the in the d bus diseases use

of i

John H. Bartels, M.D. Melvin P. Weinstein, M.D. New Brunswick, New Jersey

The collection and processing of diseases is reviewed. Available appropriate use and interpretation on selection of those tests most unnecessary laboratory use. (AM

clinical specimens in the diagnosis of infectious culture methods, other laboratory tests, and their are discussed. Particular emphasis is placed likely to give a specific diagnosis while avoiding J INFECT CONTROL 1987;15:187-95)

The clinical microbiology laboratory has long provided the standard underpinnings for the etiologic diagnosis of infectious diseases. Consequently, microbiology laboratories in most hospitals now handle large numbers of specimens, often with multiple tests requested on each specimen. Although appropriate use of the laboratory always has been important, there were in the past few incentives for physicians or laboratorians. When costs were reimbursed on a per test basis, microbiology laboratories generated revenue for hospitals; however, with the advent of Diagnosis-Related Groups (DRGs), each additional test uses more of an institution’s increasingly limited resources. From the Departments of Medicine of Medicine and Dentistry of New son Medical School. Reprint requests: Wood Johnson 08903-0019.

Melvin Medical

and Pathology, University Jersey-Robert Wood John-

P. Weinstein, M.D., UMDNJ-Robert School, CN-19, New Brunswick,

NJ

Thus, appropriate use of the laboratory and elimination of unnecessary testing now have gained greater importance. We review important principles that, if adhered to, should enhance appropriate use of the microbiology laboratory. SPECIMEN

COLLECTION

Laboratory diagnosis of infectious diseases begins with the collection of clinically relevant material for culture or other testing. Specimens should be obtained, whenever possible, before the patient begins to receive antibiotics. Even a few doses of an oral antibiotic may slow or prevent the growth of organisms from blood in endocarditis or spinal fluid in bacterial meningitis, thus clouding diagnosis and possibly delaying institution of appropriate therapy. When obtaining cultures, care should be taken to bypass the normal or colonizing flora of skin and mucous membranes. This if of particular importance in specimens such as sputum 187

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and urine. Both the mouth and perineum are colonized with flora that may include potential pathogens. Unless contamination can be eliminated in specimen collection, interpretation of culture results will be difficult. The Gramstained smear can be particularly useful for assessing the quality of specimens by analysis of the cellular content, especially leukocytes and epithelial cells. In sputum specimens from patients with suspected pneumonia, the presence of polymorphonuclear leukocytes is correlated with lower respiratory tract secretions, whereas the presence of more than a few squamous epithelial cells suggests oral contamination. Leukocytes in stool specimens or drainage from wounds also may suggest bacterial infection. Gram-stains of any specimen may reveal a predominant organism and thus guide initial antibiotic therapy. All material submitted to the laboratory should be clearly and specifically labeled with the patient’s name, identifying hospital number, the exact source of the specimen, the specific test or tests desired, and the time of collection. This information allows the laboratory to begin processing the specimens without delay. In addition, providing information about the clinical diagnosis and any special pathogens that are suspected permits the laboratory to further refine its procedures to detect the organism in question. Special requests should be handled directly, either via telephone or in person, with the laboratory director or supervisor. The importance of transporting specimens promptly to the laboratory cannot be overemphasized. During long delays fastidious microorganisms may die, and hardy microorganisms may overgrow less hardy strains present initially in greater quantities. Some laboratories will reject specimens with prolonged transport delays, just as they may reject inappropriate or improperly collected specimens. BLOOD

CULTURLiS

Detection of microorganisms in the blood is one of the most useful and important means of diagnosis in infectious diseases. Bacteremia may be seen in many diseases, and blood cultures provide a specific etiologic diagnosis in many cases where other specimens are difficult

INF FCTiON

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of

CDNTRCL

either to obtain or, if positive, to interpret. Transient bacteremia may occur after manipulation of infected tissues such as abscesses, with instrumentation of mucosal surfaces that are colonized with normal flora as in dental procedures or sigmoidoscopy, or in infections such as pneumonia, meningitis, or pyelonephritis. Intermittent bacteremia frequently occurs in association with the recurrent fever spikes characteristic of undrained abscesses. Continuous bacteremia is most often seen in acute and subacute bacterial endocarditis and other intravascular infections including mycotic aneurysms. Continuous bacteremia also occurs in early stages of typhoid fever and brucellosis. In febrile patients, when the diagnosis is URclear, questions arise as to the number of blood cultures needed as well as the timing of those cultures. The yield from blood cultures is most closely related to the total volume of blood cultured.’ Studies at the Mayo Clinic showed that three 10 ml cultures were necessary to detect 99% of bacteremic episodes,‘, ’ whereas in studies at the University of Colorado, two IS ml cultures were sufficient to achieve >99% sensitivity? Obtaining more than 30 ml of blood for culture may be of value in some instances of low-grade bacteremia such as typhoid fever or brucellosis. Because different commercially available systems use from 6 to 20 ml blood per culture set, it is important to be familiar with the system being used in the laboratory. When smaller volumes per culture are obtained, more cultures will be needed to detect bacteremia. These criteria are applicable to adults and oIder children; in small children and neonates, at least 1 ml and preferably 5 ml blood should be obtained for culture. Although drawing 30 ml into one set of culture bottles may be as effective in detecting pathogens as inoculating multiple smaller sets, obtaining at least two blood cultures by independent venipuncture helps in differentiating true bacteremia from contamination. Overall, less than 3% of all positive blood cultures represent contamination4, 5; thus, the probability of a single blood culture growing a contaminant is 0.03. Because the probability of a second blood culture growing a contaminant also is 0.03, the probability that each will grow the

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same organism, and that the organism will be a contaminant, is 0.03 X 0.03 or 0.0009, less than 1 in 1000. The example of Staphylococcus epidermidis illustrates the point. This organism has been shown to be a contaminant 94% of the time it is detected in blood.4 However, if two consecutive blood cultures grow this organism, there is a much greater likelihood that it is a pathogen, and a search for a probable focus (e.g., intravenous catheter, prosthetic device), as well as appropriate therapy, is indicated. The calculation above and the example cited underscore the importance of obtaining more than a single blood culture. The timing of blood cultures may be important. Although in endocarditis and other diseases producing continuous bacteremia, blood cultures drawn at any time will detect bacteremia, this is not the case in diseases that produce only transient or intermittent bacteremia. In most cases, bacteremia associated with nonendovascular infections is cleared in a few minutes to hours. Chills and fever may not appear for about an hour after bacteremia begins.6 Knowledge of this pattern may be used in cases in which a regular pattern of fever and chills develops so that cultures may be obtained about an hour before the expected rise in temperature. Because this predictable sequence is rare, blood cultures are usually obtained only with chills and fever. Indeed, in practice the patient’s clinical status often dictates the timing of blood cultures. In patients who are unstable or acutely ill, two or three blood cultures should be obtained in rapid succession. By contrast, patients who are persistently febrile but stable often have blood cultures obtained several hours apart. The technique for obtaining blood cultures centers on careful antiseptic preparation of the skin to avoid contamination. The venipuncture site should be cleansed with isopropyl or ethyl alcohol and then with 1% to 2% tincture of iodine or 10% povidone-iodine concentrically from the center outward. The iodine solution should be allowed to dry before the venipuncture is performed. Care should be taken not to palpate and thereby contaminate the venipuncture site after cleansing. Blood may be drawn with needle and syringe or directly

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into Vacutainer-type blood culture sets (Becton Dickinson, Rutherford, N.J.) or transportation tubes. If drawn into a syringe, the needle used to obtain the blood should be replaced by a sterile needle to inoculate the culture bottles. Diaphragm tops or stoppers of culture bottles should be decontaminated with iodine or alcohol before inoculation.6 Most microbiology laboratories incubate blood cultures for 7 days. It has been found that there is little clinical value in holding routine cultures beyond this point.’ In special circumstances, however, holding cultures for a longer period may be of value. In cases where fungemia, especially caused by Cryptococcus or Histoplasma, mycobacteremia, or bacteremia with fastidious gram-negative bacilli (e.g., certain Haemophilus species, Cardiobacterium, Actinobacillus) is suspected, it is important to inform the microbiology laboratory so that cultures may be incubated for a longer period. As noted above, cultures ideally are obtained before initiating antibiotic therapy. Unfortunately, this is not always possible, and controversy has arisen over the value of blood culture systems containing antibiotic adsorbent resins. Generally, it has been found that these resins may have some value in small volume blood culture systems but they are not helpful in systems with large volumes,’ presumably because of greater dilution of antibiotics that occurs in the large volume systems. UPPER RESPIRATORY

TRACT SPECIMENS

Infectious diseases of the upper respiratory tract are among the most common encountered. Group A streptococci, Neisseria gonorrhoeae, Bordetella pertussis, and Covynebacterium diphtheriue are recognized bacterial causes of pharyngeal infection. Of these, only group A streptococci should be cultured routinely by the laboratory. If other pathogens are suspected, the clinician should contact the microbiology laboratory before obtaining specimens because special culture techniques and media are necessary. For example, if whooping cough is suspected, the laboratory will need to prepare or obtain correct culture media (e.g., Regan-Lowe or Bordet-Gengou agars) on which to culture an appropriately obtained nasopharyngeal speci-

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men. Recently, multiple nonculture methods for rapid detection of group A streptococci in pharyngeal swabs have been developed. These tests incorporate various techniques including latex agglutination, enzyme fluorescence, and enzyme immunoassay. Although these tests potentially provide rapid results, their specificity and sensitivity, particularly when performed by inexperienced individuals in a low-volume office situation, have not yet been well studied.’ Despite its known limitations, culture of group A streptococci on selective blood agar media remains the standard for diagnosis of streptococcal pharyngitis. LOWRR RIPCRITORY

TRACT

S

Specific bacteriologic diagnosis in pneumonia remains a difficult challenge in infectious diseases. Sputum cultures, although easily and inexpensively obtained without risk to the patient, remain difficult to interpret because of contamination by the normal flora of the oropharynx. Proposed means of bypassing that flora include transtracheal aspirate, transthoracic lung aspiration, fiber-optic bronchoscopy using a shielded brush, and open lung biopsy, each of which is associated with more risk and expense. Attempts to obtain sputum for culture should be made in all patients with pneumonia. All specimens should be Gram stained promptly to evaluate the quality of the sample.‘O, ‘I In general, specimens with >25 leukocytes and
Jo~~rna! of CONTROI.

ynx to be bypassed but requires some degree of technical skill as well as a cooperative patient with normal anatomy. Even if these criteria are met, there are some risks associated with this invasive procedure. Thin needle transthoracic lung aspiration is done infrequently, but in cxperienced hands it often yields a single causative organism with relatively low risk to the patient. 13fI4 Fiber-optic bronchoscopy has become an accepted procedure in the diagnosis of pulmonary neoplasms as well as for Pneumocystis carinii pneumonia in patients with acquired immunodeficiency syndrome. In diagnosis of bacterial pneumonia, however, the role of bronchoscopy is unclear, and at least one study suggests that specimens obtained via bronchoscopy do not accurately reflect the bacteria present in the lower respiratory tract because of toxic effects of anesthetics used in bronchoscopy and oropharyngeal contamination introduced when the bronchoscope is passed through the mouth.15 Therefore, we view bronchoscopic specimens for bacterial culture with suspicion. Bronchoscopy, transtracheal aspiration, open lung biopsy, and sputum provide acceptable specimens for detection of Legionella by direct fluorescent antibody technique.” Occasionally, more than one specimen may need to be obtained to detect a positive result with the direct fluorescent antibody technique. Open lung biopsy, the most invasive procedure for obtaining specimens from the lower respiratory tract, has been advocated by some as the procedure of choice in the immunocompromised host with pneumonia.‘7. Ifi Certainly, any organism isolated from such a specimen can be assumed to be a potential pathogen. CR

FL&W

Detection of microorganisms in the cerebrospinal fluid (CSF) requires that an adequate volume be obtained for culture and other studies. The Gram-stained smear of the fluid is of unquestioned importance. Although direct Gram stain of grossly purulent CSF may be positive, the yield from centrifuged fluid is substantially greater and much more likely to demonstrate an organism that then may guide initial therapy. Because the Gram stain may be negative in

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patients subsequently proved to have bacterial meningitis by culture, multiple rapid, nonculture methods have been developed. One of these, the limulus test, is a sensitive assay for endotoxin. Unfortunately, this test has been beset by a variety of problems including false positivity from glassware and other materials used in testing, as well as by a lack of standardized reagents. Moreover, even true positive results give no information as to the specific etiologic agent involved. Detection of bacterial antigens by agglutination with antisera prepared against antigens of bacteria commonly causing meningitis has been shown to be relatively sensitive. However, false positive tests do occur, and in the case of true positive tests, the Gram stain almost always is positive as well. Thus, these tests add little to patient management in the great majority of instances. At present, the role of bacterial antigen agglutination tests seems to be limited to testing CSFforHaemophiZuus infhenzae and group B streptococcal antigens in patients who are partially treated or culture-negative.” In contrast to the limited value of bacterial antigen testing, detection of cryptococcal antigen in CSF by latex agglutination is both sensitive and specific.20 The usefulness of this test is enhanced by the fact that direct visualization is frequently difficult and cultures also may be negative or slow to grow. The India ink test may be of value in the rapid detection of Cryptococcus neoformans because it is the only pathogenic encapsulated yeast. This pathogen is being seen with increasing frequency in patients with AIDS, and organisms are often so abundant that they can be easily visualized on India ink preparations even in unconcentrated CSF. However, the test is much less sensitive in patients without AIDS with cryptococcal meningitis. A test that is frequently reflexively ordered but seldom indicated is the examination of spinal fluid by stain and culture for acid-fast bacilli. In proved cases of meningeal tuberculosis, the Ziehl-Neelsen-stained smear of concentrated CSF is positive for acid-fast organisms in 22% to 87%,“, ” the latter figure being a cumulative figure after up to four specimens are obtained from successive lumbar punctures. Such tests

1911

are time-consuming for the microbiology laboratory and therefore should be limited to patients in whom there is high clinical suspicion of meningeal tuberculosis. The value of further testing of the CSF when opening pressure, protein, and cell count are normal has been studied.23-25 In patients who are not immunocompromised, routine and acid-fast cultures, VDRL, and latex agglutination tests are of no clinical value. URINARY

TRACT SPECIMENS

Urine cultures are indicated in patients with symptoms of urinary tract infection, at the time of insertion of indwelling urinary catheters, and for screening for infection during pregnancy. Applying the principle of bypassing normal flora, suprapubic aspiration of urine is the optimal means of obtaining urine for culture but is impractical in most patients. Similarly impractical in the outpatient setting but of value in hospitalized patients who cannot provide uncontaminated specimens is single catheterization. The most common and least difficult means of urine collection is the midstream “clean catch.” Care must be taken in cleansing the external genitalia and washing away any soap before collecting the specimen. Ideally, the specimen should be collected in the morning with the first voiding, or if that is not possible, then at least 2 hours after the previous voiding.26 Because the basis for deciding on the significance of a positive culture is the quantity of microorganisms present, the importance of rapidly transporting the specimen to the laboratory cannot be overemphasized. In outpatients, specimens should be collected at the laboratory, if possible. If there is to be any delay in delivering the specimen to the laboratory, it should be refrigerated or processed with an appropriate preservative kitz7 Delay in culturing urine for more than 2 hours after collection in the absence of refrigeration or processing with a preservative kit has been shown to significantly increase urinary colony counts.28 Microscopic examination of fresh, unspun urine has been shown to be a valuable screening method to select urine specimens for culture. Ninety-four percent of specimens subsequently

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found to have 2 lo5 colony-forming units (CFU) per milliliter of urine will have 2 10 leukocytes per milliliter, al bacterium per oil immersion field, or both, when examined microscopically.29, 3o Interpretation of colony counts is dependent on the patient and the manner in which the specimen was obtained. Any bacteria found in a specimen obtained by suprapubic aspirate may be significant, whereas 310’ CFU/ml in a midstream urine specimen from an asymptomatic patient is reliably associated with infection.31 In women with acute dysuria, the presence of 2100 CFU/ml of urine correlates with infection.32 In practice, we routinely identify and perform antimicrobial susceptibility tests on those organisms present in numbers 3 104/ml and will work up organisms present at 3103/ml on special request. Lower counts in midstream urine specimens from pregnant patients also may be significant.33

Although there are many recognized sexually transmitted diseases, culture is the predominant means of diagnosis only for Neisseria gonorrhoeae. Appropriate sites for culture of gonorrhea in the female include the endocervical canal, anal canal, and oropharynx when contacts in these areas have occurred. Urethral cultures are important in all males. Those with a history of orogenital contact should have oropharyngeal cultures for gonorrhea. In male homosexuals, anal cultures should be added. Cultures for gonorrhea should be inoculated promptly because delay may decrease recovery of this fastidious organism. Although the organism grows well on chocolate agar, ThayerMartin and other modified chocolate agars (e.g., Martin-Lewis agar) improve recovery by suppressing commensal genitourinary flora. The Gram stain of urethral exudate is sufficient for the diagnosis of gonococcal urethritis in males. However, culture currently is the only means by which penicillin-resistant gonococci will be detected. In most venereal diseases other than gonorrhea, nonculture methods are more important. Chlamydia trachomatis is an important pathogen in nongonococcal urethritis and pel-

INFECTION

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ot

CONTROL.

vic inflammatory disease. This organism may be cultured in cell culture systems, but this is expensive and not readily available in most microbiology laboratories. Recently, direct tests using fluorescence microscopy for this organism have been developed that use fluorescein-conjugated monoclonal antibodies for rapid and specific diagnosis.34 Collection of specimens for this test requires that urethral or endocervical specimens be obtained with a swab after removing any surface debris. Because chlamydiae are intracellular organisms, epithelial cells must be obtained and transferred onto the slide to make the diagnosis. In practice, swabs for culture for gonorrhea may be obtained first, thus clearing secretions for ease of recovery of epithelial cells for chlamydia fluorescence testing or for culture if available. Direct tests are acceptably sensitive in high prevalence populations such as in sexually transmitted disease clinics, but the predictive value of a positive test relative to cell culture in lower prevalence populations is poor.“’ Similar direct fluorescent antibody tests are also available for the diagnosis of Herpes simplex virus infections. Vesicular lesions should be used to obtain specimens. These should be unroofed and the base scraped to obtain epithelial cells for transfer to the slide. Viral cultures also are sensitive and specific but not available in most laboratories. We believe that laboratory confirmation of typical herpetic iesions seldom is needed. Routine antepartum cultures of pregnant women with a history of genital Herpes simplex are not useful because they do not correlate with viral shedding at the time of delivery.36 Wet mount preparations of vaginal specimens should be examined in patients with vaginal discharge to identify the typical organisms of Trichomonas vaginalis. The presence of leukocytes in such preparations should also be assessed because this has a good correlation with trichomoniasis.37 In cases where it is considered to be of great clinical importance, cultures for Trichomonas are possible.38 Because Treponema pallidurn, the etiologic agent of syphilis, cannot be cultured, diagnosis frequently depends on serologic confirmation. Darkheld microscopy may allows rapid diag-

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nosis; however, some technical expertise for interpretation of darkfield specimens is necessary. Specimens from either the base of the chancre in primary syphilis or from condyloma latum or mucous patches in secondary syphilis are appropriate for examination by this method. Interpretation of specimens from perianal or oral lesions may be difficult because of the presence of commensal treponemes. The presence of treponemes on darkfield microscopy may help to differentiate syphilitic chancres from those of chancroid. When chancroid is suspected, special culture media should be requested from the microbiology laboratory to isolate Haemophilus ducreyi. This organism may be cultured from swabs of the base of the ulcer in chancroid. Cultures of aspirates of buboes in this disease frequently are negative. STOOL

SPECIMENS

Diarrhea1 illness is extremely common throughout the world and is one of the most common infectious illnesses in the United States. Acute viral gastroenteritis probably accounts for most cases of diarrhea,39 but bacterial diarrheas also are frequent. Thus, attempts to detect bacterial and parasitic pathogens in feces are a significant part of the workload in any microbiology laboratory. The best specimens for culture are fresh, unformed stools. Rectal swabs are inferior for the diagnosis of clinical disease, although they may be useful in epidemiologic studies. For pinworm infections, the “Scotch tape” preparation is the preferred method for specimen collection. If there is to be delay in transport of the specimen to the laboratory, it should be placed in buffered glycerol saline solution or other transport media and refrigerated or the recovery of bacterial pathogens, particularly Shigella, will be of stools for markedly reduced.40 Screening the presence of polymorphonuclear leukocytes should be done (using the methylene blue, Gram, or other readily available stain). Most invasive bacterial diarrheas are associated with polymorphonuclear leukocytes in the stool, especially Shigella infections.4’ We advise that no more than one stool be cultured for enteric bacterial pathogens in the absence of fecal leukocytes and that formed stools not be cultured

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unless Salmonella carriage is suspected. In patients with diarrhea and polymorphonuclear leukocytes in the stool, multiple cultures should not be sent automatically in rapid succession. If the initial culture is negative, a repeat culture may then be sent. It is important to inform the laboratory if a particular pathogen is suspected because use of special selective media (e.g., thiosulfate citrate bile salts sucrose medium for vibrios) may facilitate recovery of the organism in culture. Special staining of stool can be useful as well. In outbreaks of CampyZobacter enteritis, Gram stain of the stool counterstained with carbolfuchsin rather than safranin may reveal the characteristic organisms.42 Infections with the parasites Cryptosporidium43 and Isospora belli are being found more frequently, particularly in patients with AIDS. These organisms may be seen in modified acid-fast stains of the stool but usually will be missed with conventional processing for examination of stool ova and parasites. Because the burden of organisms in patients who have AIDS often is large, diagnosis may be made in individuals with Mycobacterium avium-intracellulare and diarrhea if an acid-fast stain of feces is examined by oil immersion. Perhaps the most time-consuming and least productive of laboratory activities is examination of stool for ova and parasites. Proper processing and examination of a stool for ova and parasites takes approximately 45 minutes of technician time. Patients with diarrhea of short duration and those with polymorphonuclear leukocytes in the stool are unlikely to have a parasitic etiologic agent for the diarrhea. Because of poor patient selection and the kneejerk reaction to send “stool for O&P x 3,” the yield of examining stool for ova and parasites is very low; in our laboratory it is no greater than 5%. The best specimens for such examinations are fresh stool specimens or those obtained after a saline purge. Stools obtained after a barium enema have a lower yield and, in fact, probably should not be processed until the barium has cleared. Rectal swabs provide poor specimens for ova and parasite examination, but rectal biopsy may be useful to demonstrate the eggs of schistosomiasis.

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CULTURSS OF ww#as, AND ABSCESSES

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umu6fTI,

Wounds, like other superficial surfaces, are frequently colonized by the commensal flora of the skin. Flora of these areas usually are mixed. Swab cultures of the surface of wounds including burns, pressure sores, stasis ulcers, and surgical incisions are difficult to interpret because colonizing organisms cannot be distinguished from pathogens. The practice of obtaining such surface cultures, either as a routine or in cases of suspected infection, should be discouraged. Instead, if infection of any wound is suspected, it is best to aspirate through adjacent noninfected skin prepared with an iodophor. Quantitative cultures of wound biopsy specimens have been studied in surgical wound infections and in patients with burns and may be of value in selected circumstances such as when grafting to the wound or burn is contemplated. Biopsy of burn wounds, which almost always are colonized by a variety of bacteria, may be done after surface cleansing. Biopsy may be done with either a scalpel or dermal punch. The tissue obtained should be weighed, then homogenized and cultured in a quantitative fashion. Colony counts > 104/gram of tissue have been correlated with infection.45j 46 A similar technique has been used in surgical wounds suspected of infection. In one study, a single infecting organism was identified in 87 of 100 patients by dermal punch biopsy when more than half had multiple organisms present on surface culture.“7 Biopsy also may be appropriate in cases where unusual infections are suspected such as those caused by mycobacteria or Erysipelothrix.48 Swab cultures also should be avoided in culturing abscesses or other infected material. Swabs of pus or infected tissues such as bone contain fewer organisms and are much less likely to yield pathogenic organisms than pus aspirated into a syringe. After obtaining the specimen, any air should be expressed, and the capped syringe sent promptly to the microbiology laboratory. The above recommendations are particularly important to allow isolation of anaerobic microorganisms, which are more likely to grow from pus or tissue than from swabs (including commercially available an-

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aerobic swab kits). Any other tissues obtained at surgery and suspected of infection should be transported to the laboratory in a small amount. of sterile nonbacteriostatic saline solution. SuMfAARY We have reviewed some of the major uses of the microbiology laboratory in the clinical diagnosis of infectious diseases, and emphasized the importance of obtaining specimens that are clinically relevant and, thus, usable for both diagnosis and therapy. Clinicians should not hesitate to communicate with the laboratory when special situations arise or unusual pathogens are suspected. When there is good communication between those caring for the patient and laboratory personnel, the patient is the beneficiary. We thank Ms. the preparation

Virginia English for secretarial of the manuscript.

assistance

in

Rsferences 1. Tenney JH, Reller LB, Mirrett S, et al. Controlled evaluation of the volume of blood cultured in detection of bacteremia and fungemia. J Clin Microbial 1982;15: 558-61. 2. Washington JA. Blood cultures: principles and techniques. Mayo Clin Proc 1975;50:91-8. 3. Ilstrup DM, Washington JA. The importance of volume of blood cultured in the detection of bacteremia and fungemia. Diagn Microbial Infect Dis 1983; 1: 107-10. 4. Weinstein MP, Reller LB, Murphy JR, Lichtenstein KA. The clinical significance of positive blood cultures: a comprehensive analysis of 500 episodes of bacteremia and fungemia in adults. I. Laboratory and epidemiologic observations. Rev Infect Dis 1983;5:35-53. 5. Wilson WR, Van Scoy RE, Washington JA. Incidence of bacteremia in adults without infection. J Clin Microbiol 1975;2:94-5. 6. Reller LB, Murray PR, Mactowry JD. Blood cultures. II. In: Washington JA, ed. Cumitech IA. Washington, D.C.: American Society for Microbtology, 1982: l-11. 7. Murray PR. Determination of the optimum incubation period of blood culture broths for the detection of clinically significant septicemia. J Clin Microbial 1985; 21:481-5. 8. Washington JA, Ilstrup DM. Blood cultures: issues and controversies. Rev Infect Dis 1986;8:792-802. 9. Radetsky M, Wheeler RC, Roe MI-I, Todd JK. Comparative evaluation of kits for rapid diagnosis of group A streptococcal disease. Pediatr Infect Dts 1985;4:274-81. 10. Murray PR, Washington JA. Microscopic and bacteriologic analysis of expectorated sputum. Mayo Clin Proc 197.5;50:339-44. 11. Van Scoy RE. Bacterial sputum cultures. Mayo Clin Proc 1977;52:39-41.

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12. Barrett-Connor E. The nonvalue of sputum culture in the diagnosis of pneumococcal pneumonia. Am Rev Respir Dis 1971;103:845-8. 13. Davidson M, Tempest B, Palmer DL. Bacteriologic diagnosis of acute pneumonia. JAMA 1976;235:158-63. 14. Zavala DC, Schoell JE. Ultrathin needle aspiration of the lung in infectious and malignant disease. Am Rev Respir Dis 1981;123:125-31. 15. Bartlett JG, Alexander J, Mayhew J, et al. Should fiberoptic bronchoscopy aspirates be cultured? Am Rev Respir Dis 1976;114:73-8. 16. Edelstein PH, Beer KB, &urge JC, et al. Clinical utility of a monoclonal direct fluorescent reagent specific for Legionella pneumophila: comparative study with other reagents. J Clin Microbial 1985;22:419-21. 17. Cockerill FR, Wilson WR, Carpenter HA, et al. Open lung biopsy in immunocompromised patients. Arch Intern Med 1985;145:1398-404. 18. Wilson WR, Cockerill FR, Rosenow EC. Pulmonary disease in the immunocompromised host (2). Mayo Clin Proc 1985;60:610-31. 19. Morissey AM, Jacobs MR, Boxerbaum B. Value of bacterial antigen latex agglutination tests of body fluids in a teaching institution. In: Abstracts of the 1986 ICAAC. Washington, D.C.: American Society for Microbiology, 19&X6:109, No. 71. 20. Muchmore HG, Felton FG, Scott EN. Rapid presumptive identification of Cryptococcus neofonnans. J Clin Microbial 1978;8:166-70. 21. Hinman AR. Tuberculous meningitis at Cleveland Metropolitan General Hospital 1959 to 1963. Am Rev Respir Dis 1967;95:670-3. 22. Kennedy DH, Fallon RJ. Tuberculous meningitis. JAMA 1979;241:264-8. 23. Hayward RA, Shapiro MF, Oye RK. Laboratory testing on cerebrospinal fluid. Lancet 1987;1:1-4. 24. Crowson TW, Rich EC, Woolfrey BF, Connelly DP. Overutilization of cultures of CSF for mycobacteria. JAMA 1984;251:70-2. 25. Dans PE, Cafferty L, Otter SE, Johnson RJ. Inappropriate use of the cerebrospinal fluid venereal disease research laboratory (VDRL) test to exclude neurosyphilis. Ann Intern Med 1986;104:86-9. 26. Roberts AP, Robinson RE, Beard RW. Some factors affecting bacterial colony counts in urinary infection. Br Med J 1967;1:400-3. 27. Weinstein MP. Clinical evaluation of a urine transport kit with lyophilized preservative for culture, urinalysis, and sediment microscopy. Diagn Microbial Infect Dis 1985;3:501-8. 28. Hindman R, Tronic B, Bartlett R. Effect of delay on culture of urine. J Clin Microbial 1976;4:102-3. 29. Robins DG, White RHR, Rogers KB, Osman MS. Urine microscopy as an aid to detection of bacteriuria. Lancet 1975;1:476-8. 30. Finegold SM, Baron EJ. Microorganisms encountered in the urinary tract. In: Finegold SM, Baron EJ. Bailey and Scott’s diagnostic microbiology. 7th ed. St. Louis: CV Mosby, 1986:279-89.

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Continuing education credits for nurses, physicians, and medical technologists are available. For the CE examination and enrollment information, turn to the APIC Bulletin section in this issue.