THE ROLE OF THE SELECTIVE THROAT CULTURE FOR BETA HEMOLYTIC STREPTOCOCCI IN THE DIAGNOSIS OF ACUTE PHARYNGITIS

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1 THE AMERICAN JOURNAL OF CLINICAL PATHOLOGY Vol. 37, No. 1, pp January, 1962 Copyright 1962 by The Williams & Wilkins Co. Printed in U.S.A. THE ROLE OF THE SELECTIVE THROAT CULTURE FOR BETA HEMOLYTIC STREPTOCOCCI IN THE DIAGNOSIS OF ACUTE PHARYNGITIS GENE H. STOLLERMAN, M.D. Department of Medicine, Northwestern University Medical School, Chicago, Illinois The etiologic diagnosis of acute respiratory disease has become, more than ever, a frustrating experience for the clinician. The availability of antibiotics offers him a therapeutic option if he can identify the infection as bacterial in nature. The possibilities for prevention of primary attacks of rheumatic fever by means of prompt and adequate therapy with penicillin, 1 when streptococcal pharyngitis is recognized, exerts further pressure upon him to treat acute respiratory disease (ARD) vigorously. The effectiveness of vaccines for prevention of adenovirus and influenza infections increases his need to identify the nature of prevailing ARD in his community. This discussion will emphasize the role of the selective throat culture for beta hemolytic streptococci in helping the clinician to distinguish between viral and bacterial infection as a cause of primary, uncomplicated sore throat. It will also emphasize the need for the medical bacteriologist to understand the clinician's problem and to provide for him convenient, inexpensive, and selective throat cultures which will help to distinguish between viral and streptococcal nasopharyngitis. THE CLINICAL DIAGNOSIS OF VIRAL AND OF STREPTOCOCCAL NASOPHARYNGITIS Unfortunately, the clinical diagnosis of the kind of streptococcal pharyngitis that occurs as a sporadic infection in a civilian community is usually a crude guess. The classical syndrome described as most typical of group A streptococcal infection 1 is as fol- Received, May 10, 1961; accepted for publication August 28. Dr. Stollerman is an Associate Professor of Medicine. This paper was part of a symposium on microbiology (under the auspices of the Council on Microbiology) at the annual meeting of the American Society of Clinical Pathologists, on September 29, I960, Chicago, Illinois. 36 lows: symptoms sudden onset of sore throat, sometimes associated with abdominal pain and nausea, especially in children, and accompanied by constitutional symptoms of malaise, headache, and feverishness; signs redness and edema of the throat and, particularly, the presence of exudate on the tonsils or tonsillar fossae; enlargement, and particularly tenderness, of the anterior cervical lymph nodes, and fever of 101 F. or greater. Helpful laboratory data, other than throat culture, include leukocytosis greater than 12,000 white blood cells per cu. mm. Although this classical syndrome is, indeed, associated with group A streptococcal infection, the full clinical picture develops in the minority of patients with nasopharyngitis, except during military or civilian epidemics. Much more common in practice is the patient with some, but not all, of the above criteria. It is not unusual for mild streptococcal disease to be associated with nonexudative pharyngitis and, conversely, for viral infections, particularly adenovirus, to produce purulent tonsillar exudate and a syndrome indistinguishable from streptococcal tonsillitis. Of particular pertinence is the recent controlled 5-year study by Siegel and associates 11 of approximately 2500 school children who sought medical attention in the outpatient department of Childrens' Memorial Hospital in Chicago for acute respiratory disease associated with soreness or redness of the throat. By means of complete bacteriologic and immunologic studies, the actual incidence of proved streptococcal infection was determined, and the results were compared with the examining physicians' clinical diagnoses. The clinician's prediction that throat cultures would be positive for beta hemolytic streptococci was correct only 55 per cent of the time. His guess that such cultures would be negative was correct approximately 70 per cent of the time. It was possible, however, to exclude

2 Jan.1962 DIAGNOSIS OP VIRAL DISEASES 37 streptococcal disease in more than half of the patients studied by the use of throat cultures made on 2 successive clays. In other populations which have been studied, streptococcal disease could be excluded with even greater frequency. The incidence of positive throat cultures for beta hemolytic streptococci decreases progressively with age in patients with sporadic acute respiratory diseases in civilian communities. In a study in Cleveland, streptococcal disease accounted for only 3 per cent of all respiratory illness. 3 In a recent study in Chicago, 4 less than 5 per cent of adults with rheumatic heart disease who had upper respiratory infections were observed to harbor group A streptococci in their throats. The patients had not been receiving chemoprophylaxis continuously. The clinical features of acute respiratory disease have been carefully studied hy Schultz and associates 9 in a population of Naval recruits, in whom the incidence of influenza and adenovirus infection was accurately determined. In this population streptococcal disease was virtually excluded by mass penicillin prophylaxis. From this study it was apparent that influenza, adenovirus, and undifferentiated acute respiratory disease could each produce the same classical clinical features of streptococcal pharyngitis, although adenovirus most frequently produced sore throat, dysphagia, and tonsillar exudate. The latter, interestingly enough, occurred in approximately 20 per cent of patients with adenovirus nasopharyngitis. It is obvious, therefore, that without bacteriologic confirmation, the clinical diagnosis of viral versus streptococcal pharyngitis is quite unsatisfactory. SELECTIVE VERSUS "COMPLETE" THROAT CULTURES In many clinical bacteriology laboratories throughout the nation today there is unfortunately a tendency toward lack of communication between the technologist and the clinician requesting bacteriologic cultures of specimens. It is not uncommon for throat swabs to be sent to the laboratories with the request for "throat culture," with little or no additional instructions. Often, painstaking attempts are made by the laboratory to identify all species of bacteria isolated from such throat swabs and to grow these organisms in pure culture for subsequent tests of sensitivity to a wide spectrum of antibiotics. Such comprehensive study of all bacterial flora grown from a throat swab is laborious, expensive, and usually quite unnecessary. Both clinicians and bacteriology technologists should be educated to the custom of designating the kind of throat culture desired and the nature of the clinical problem in the patient whose throat was swabbed. The profession has long been accustomed to the use of Klebs-Loffler medium slants when diphtheria is suspected. It is no less reasonable to request a selective technic for the prompt identification of beta hemolytic streptococci when trying to distinguish bacterial from viral pharyngitis. DIRECT INOCULATION OF SHEEP'S BLOOD AGAR PLATES WITH THROAT SWABS This method has been used extensively in many large-scale studies of acute respiratory disease in both military and civilian populations. The Committee on Prevention of Rheumatic Fever and Subacute Bacterial Endocarditis of the American Heart Association has sponsored a brochure describing the technic of this method in considerable detail. 12 This brochure has been widely distributed to the medical profession; therefore, the details of the method will not be reviewed here, but, rather, its special applications and limitations will be discussed. The advantages of sheep's blood have been emphasized repeatedly. 5 ' 13 The growth of hemophilus organisms is inhibited, and colonies of these bacteria, which closely resemble beta hemolytic streptococci, are not present to cause confusion. Sheep's blood is far superior to human blood in distinguishing "green" or alpha hemolysis from beta hemolysis. Alpha hemolysis on human blood is sometimes confused with beta hemolysis, particularly when the layer of blood agar is somewhat thin. The temptation to use discarded human bank blood to prepare blood agar plates is great because it is readily available and economical. Such blood is usually citrated, however, and citrate ions are quite toxic to the growth of group A streptococci. Further-

3 38 STOLLERMAN Vol. 37 more, beta hemolytic colonies that appear on human blood agar plates must be further identified in order to distinguish between hemophilus organisms and hemolytic streptococci. This, in itself, is an expensive procedure in terms of work time. When throat swabs are inoculated directly on the periphery of sheep's blood agar plates, and the inoculum is subsequently diluted over the surface of the plate by conventional methods of streaking with a bacteriologic loop, discrete beta hemolytic colonies may be identified after overnight incubation, and a semiquantitative estimate, 1 to 4 plus, may be made of the prevalence of beta hemolytic colonies. The clinician may be informed, by telephone if necessary, of a positive culture within 24 hr. of the time the throat was swabbed. A 24-hr. delay in initiating antibiotic therapy is not harmful except in very rare, fulminating instances of streptococcal pharyngitis. Indeed, with rare exceptions, the clinical course of uncomplicated streptococcal pharyngitis is virtually identical in penicillin-treated and in untreated patients. 2 ' 10 Moreover, the prevention of initial attacks of rheumatic fever is not influenced by a 24-hr. delay in instituting chemotherapy. In most investigators' experience, nasal cultures, in addition to throat cultures, are unnecessary unless special epidemiologic studies on carriage of organisms in the anterior nares are contemplated. When group A streptococci are the cause of acute pharyngitis, the throat culture should be positive invariably, and nasal cultures contribute little to the diagnosis. Preliminary cultures made in broth are also unnecessary, in our experience. The use of enriched, selective mediums, such as Pike's sodium azide-blood broth, 8 increases the yield of positive cultures for group A streptococci when streptococcal carriage, rather than acute infection, is the subject of study. Such elaborate and expensive methods are unnecessary in throat cultures aimed at determining the cause of sore throat. A scant growth of beta hemolytic streptococci, such as less than 10 colonies on blood agar plates, usually does not indicate that these organisms are responsible for the clinical symptoms. In frank infection, the prevalence of streptococci is great enough to be readily detected by means of the simple and rapid method of direct inoculation of blood agar plates, and more meticulous methods for isolating relatively small numbers of organisms are unnecessary for practical purposes of diagnosis. Cotton swabs which are adequately moistened with pharyngeal secretions during the process of culturing the throat may be kept for many hours at room temperature before they are used to inoculate blood agar plates. This delay will not significantly decrease the survival of group A streptococci. Thus, the physician may swab the throats of many patients in the course of a morning or an afternoon clinic and bring his cotton swabs to the laboratory toward the end of the day. There they may be inoculated and streaked on sheep's blood agar, and by the next morning he may have his report. Those patients whose cultures manifested beta hemolytic streptococci may be recalled for definitive treatment. Beta hemolytic streptococci may be further identified serologically to determine whether or not they belong to group A. If this is not feasible, bacitracin sensitivity may be determined by Maxted's disk method. 7 Bacitracin resistance virtually excludes group A organisms. A small percentage of streptococci belonging to groups other than "A" may also be very bacitracin-sensitive, but these will only cause an error of approximately 5 per cent, which will be in the conservative direction of overdiagnosis. 0 A heavy grow r th of beta hemolytic streptococci from the throat of a patient with pharyngitis usually represents group A infection; however, when the growth is meager, the probability of such organisms representing healthy or convalescent carriage, rather than infection, is greater. Chronic pharyngeal carriage of beta hemolytic streptococci in relatively small numbers is frequently observed with strains other than group A, particularly groups F and G streptococci. Therefore, the need for serologic identification of beta hemolytic streptococci, and for sensitive culture methods, is actually greater in surveys of pharyngeal carriage than in throat cultures designed to diagnose the etiology of acute pharyngitis.

4 Jan.1962 DIAGNOSIS OF VIRAL DISEASES 39 OTHER PHARYNGEAL BACTERIA AND THEIR RELATION TO ACUTE PHARYNGITIS Some clinicians and medical bacteriologists have expressed concern that concentration on the identification of beta hemolytic streptococci might lead frequently to overlooking other bacterial causes of pharyngitis. In our experience this is quite unlikely as long as the clinician is aware of a few special situations in which other bacteria may be important. In infants and very young children, hemophilus organisms may cause upper respiratory disease, particularly pertussis. When infection with these organisms is suspected, the selective sheep blood agar culture should not be ordered. In school-age children, however, and in older persons, hemophilus organisms are not a significant cause of sore throat. In fact, except for Corynebacterium di'phtheriae, potentially pathogenic bacteria generally found in the throat have relatively little significance as a primary cause of the common variety of acute pharyngitis. Pharyngeal carriage of pathogenic organisms other than group A streptococci is usually of only potential danger, in so far as they may become secondary invaders of deeper structures beyond the pharynx. Thus, throat carriage of virulent pneumococci, staphylococci, or meningococci may be suspected in the presence of certain extrapharyngeal infections. In such ininstances a throat culture should be made with the specific intent of identifying these organisms. In general, the sheep's blood agar culture will usually suffice for the isolation of colonies of these organisms, and the bacteriologist need only be alerted to the need for specifically identifying such agents. Normal flora, such as green streptococci, Staphylococcus albus, Neisseria catarrhalis, and diphtheroids, are of no clinical significance in the diagnosis of acute respiratory disease and do not warrant detailed identification. CONCLUSION In the screening of acute respiratory disease, and particularly in the diagnosis of simple sore throat, the relatively easy and inexpensive procedure of direct inoculation of sheep's blood agar plates and their subsequent gross examination for beta hemolytic colonies after incubation for 18 to 24 hr. at 37 C, constitutes a method for excluding, with reasonable assurance, the bacterial etiology of most pharyngeal infections. The presence of beta hemolytic streptococci do not necessarily prove the streptococcal etiology of a pharyngeal infection, inasmuch as the strain isolated (1) may belong to serologic groups other than group A; (2) may be group A organisms that are of relatively low virulence; (3) may be group A organisms that are present in relatively few numbers; and (4) may be group A organisms which produce an infection too mild to provoke an immune response, and thus are of little risk in initiating rheumatic fever." Unfortunately, the clinician faced with a patient who has a sore throat and a positive culture for beta hemolytic streptococci must make his decision to treat or not to treat acute respiratory disease on the basis of this information alone. It would be well to provide him with the most economical, practical, and effective means for distinguishing between viral and streptococcal pharyngitis that is currently available, namely, the throat culture made directly on sheep blood agar plates. SUMMARIO IN INTERLINGUA In examines pro acute morbo respiratori e specialmente in le diagnose de un simple mal de gurgite, le relativemente simple e incostose technica del directe inoculation de placas de agar a sanguine ovin con lor subsequente studio macroscopic pro colonias hemolytic beta post periodos de incubation de 18 a 24 horas a 37 C. constitue un methodo pro le exclusion (con grados satisfacente de certitude) del etiologia del majoritate del infectiones pharyngee. Le presentia de streptococcos hemolytic beta non prova necessarimente le etiologia streptococcal de un infection pharyngee, proque le racia isolate pote (1) pertiner a gruppos serologic altere que gruppo A, (2) esser un organismo de gruppo A con relativemente basse grados de virulentia, (3) esser un organismo de gruppo A que es presente in relativemente basse numeros, e (4) esser un organismo de gruppo A que produce un in-

5 40 STOLLERMAN Vol. 37 lection troppo leve pro provocar un responsa immunologic, de maniera que illo es de pauc importantia con respecto al periculo del initiation de febre rheumatic. Infelicemente le clinico qui se trova confrontate con un patiente qui ha mal de gurgite e un cultura positive pro streptococcos hemolytic beta debe facer su decision de tractar o nontractar pro acute morbo respiratori a gase de exclusivemente iste information. U esserea ben provider le clinico con le plus economic, practic, e efficace medio nunc existente pro le distinction inter pharyngitis virusal e streptococcal, i.e. le cultura de gurgite facite directemente in placas de agar a sanguine ovin. REFERENCES 1. American Heart Association. Committee on Prevention of Rheumatic Fever and Bacterial Endocarditis: Prevention of rheumatic fever and bacterial endocarditis through control of streptococcal infections. Mod. Concepts Cardiovas. Dis., 25 (supplement 12): 3G5-3G9, BRINK, W. Til., RAMMELKAMP, C. H., JR., DENNY, F. W., AND WANNAMAKER, L. W.: Effect of penicillin and Aureomycin on the natural course of streptococcal tonsilitis and pharyngitis. Am. J. Med., 10: , DINGLE, J. H.: The prevention of respiratory infections within families. Ann. Int. Med., 43: , JOHNSON, E. E., STOI.LERMAN, G. H., GROSS MAN, B. J., AND MCCULLOCH, H.: Streptococcal infections in adolescents and adults after prolonged freedom from rheumatic fever. I. Results of the first three years of the study. New England J. Med., 263: , KRUMWIBDB, E., AND KUTTNER, A. G.: A growth inhibitory substance for the influenza group of organisms in the blood of various animal species. The use of the blood of various animals as a selective medium for the detection of hemolytic streptococci in throat cultures. J. Exper. Med., 67: 429H41, LEVINSON, M. L., AND FRANK, P. F.: Differentiation of group A from other beta hemolytic streptococci with bacitracin. J. Bact., 69: J, MAXTED, W. R.: The use of bacitracin for identifying group A hemolytic streptococci. J. Clin. Path., 6: , PIKE, R. M.: Enrichment broth for isolating hemolj'tic streptococci from throat swabs. Proc. Soe. Exper. Biol. & Med., 57: , SCHULTZ, I., GuNDELFINGER, B., R.OSENBAUM, M., WOOLRIDGE, R., AND DEBERRY, P.: Comparison of clinical manifestations of respiratory illness due to Asian strain influenza, adenovirus and unknown cause. J. Lab. & Clin. Med., 55: , SIEGEL, A. C, AND JOHNSON, E. B.: Controlled studies of streptococcal pharyngitis in children. HI. Implications of positive cultures for hemolytic streptococci in patients with acute pharyngitis, to be published. 11. SIEGEL, A. C, JOHNSON, E. E., ANDSTOI.LER- MAN, G. H.: Controlled studies of streptococcal pharyngitis in a pediatric population. I. Factors related to the attack rate of rheumatic fever. New England J. Med., 265: , WANNAMAKER, L. W.: A Method for Culturing Beta Hemolytic Streptococci from the Throat. New York: American Heart Association, WILSON, A. T., et al.: The Streptococci, in Diagnostic Procedures and Reagents, Ed. 4. New York: American Public Health Association, to be published.