Rapid diagnosis of group a strep pharyngitis in the emergency department

ORIGINAL CONTRIBUTION pharyngitis, strep, rapid diagnosis

Rapid Diagnosis of Group A Strep Pharyngitis in the Emergency Department

David DuBois, MD V Gall Ray, MD, FACEP

Brian Nelson, MD, FACEP Jack B Peacock, MD

El Paso, Texas

From the Division of Trauma and Emergency Medicine, Texas Tech

University School of Medicine. El Paso. Texas.

Received for publication May 28, 1984. Revision received August 30, 1985.

Accepted for publication September 6, 1985.

Presented at the University Association for Emergency Medicine Annual Meeting in

Kansas City, Missouri, May 1985.

Address for reprints: Brian Nelson, MD, FACEE Division of Trauma and

Emergency Medicine, Texas Tech University School of Medicine, 4800

Alberta Avenue, El Paso, Texas 79905.

Two ten-minute rapid tests for diagnosing Group A streptococcal pharyngitis in 147 emergency department patients with a complaint of sore throat were evaluated using positive throat cultures as the marker for disease. Treatment was initiated solely on the basis of clinical judgment. Sen- sitivity and specificity were 78% and 93%, respectively, for the rapid test and 69% and 56%, respectively, for clinical judgment. The rapid test was significantly better than clinical judgment alone in determining the presence of disease (P < .05). The predictive values of the positive and negative alid were 78% aild 93%, respectively; for the rapid test and 38% and 85%, respectively, for clinical judgment. In the ED setting in which adequate followup is difficult, the rapid test can identify more accurately than can clinical judgment alone those patients who need therapy. [DuBois D, Ray VG, Nelson B, Peacock JB: Rapid diagnosis of Group A strep pharyngitis in the emergency department. Ann Emerg Med February 1986;15:157-159.]

I N T R O D U C T I O N Sore throat is a common complaint among patients presenting to the

emergency department.1 Although the incidence of streptococcal pharyngitis has been reported to be as low as 5% in this group of patients, and despite recent reports of decreased risk of poststreptococcal complications, the American Heart Association still advocates throat culture to identify all patients with Group A p-hemolytic streptococcal infection and appropriate antimicrobial therapy for infected patients.2-s In addition, early antibiotic treatment of streptococcal pharyngitis may result in more rapid resolution of symptoms and may prevent the development of peritonsillar abscess.t, 6

Traditionally the diagnosis of streptococcal pharyngitis is made on clinical grounds alone, by throat culture, or both. Accuracy of diagnosis on clinical grounds alone ranges from 50% to 75% in reported series, a rate unaccept- able to most physicians.7,s Because throat culture requires 24 to 48 hours for completion, followup of patients cultured but not treated at the initial visit is essential. Unfortunately, ED patient followup after throat culture has been found to be inadequate in our practice setting. Furthermore, the cost of culture and followup may exceed that of definitive antibiotic therapy, although the small but definite risk of complications of antibiotic therapy must be weighed in the balance.

Several alternative methods for diagnosis of strep throat are now available. Gram staIn of pharyngeal exudates has been advocated by some, but the sensitivity is comparable to that of clinical diagnosis alone. 9 Fluorescent antibody testing of pharyngeal secretions is more reliable, but is time con- suming and requires an experienced microscopist and fluorescent micro- scope, lo Latex agglutination of extractable soluble streptococcal antigens in pharyngeal secretions is simple, but may require up to an hour to com- plete. 11,12

More recently, diagnostic kits for rapid identification of streptococcal infection have become available. These kits require an average of ten minutes for test performance, require no special expertise, are inexpensive, and are reported "to be 95% sensitive, t3 Use of such kits in the ED might, therefore, enable the physician to make a rapid and accurate diagnosis of streptococcal pharyngitis and eliminate the need for reliance on followup or empirical

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TABLE. All patients with positive cultures - - physician versus rapid test (N = 36)

Positive Diagnosis Negative Diagnosis Positive

Rapid Test 22 6

Negative Rapid Test 3 5

The rapid test was significantly better than clinical diagnosis by Fisher's exact test (P < .05).

antimicrobial therapy. Our study examined the utility in

the ED of two commercially available ten-minute group A strep kits. Specif- ic areas addressed by the study were the reproducibility and sensitivity of the rapid test, the cost effectiveness of the rapid test when compared to cur- rent practices, the need for continued use of cultures, and the accuracy of physician diagnosis of streptococcal pharyngitis as compared to that for throat culture and the rapid test.

MATERIALS AND METHODS During a two-month period, all con-

secutive patients over the age of 2 presenting to the ED with complaint of sore throat who had received no prior antibiotic therapy were entered into the study, After evaluation of the patient, the examining physician re- corded the clinical findings, presumptive diagnosis, and proposed therapy on the study worksheet. Therapy was initiated based on clinical diagnosis.

A single swab of the tonsillar pillars and posterior pharynx was obtained from the patient, and blood agar plates (BAP) were inoculated in standard fashion for culture. Cul ture plates were incubated in a 5% CO 2 atmo- sphere at 35 C and examined at 24 and 48 hours. 14 "

After inoculation of the BAP, the

culture swab was used for the rapid test . The test k i ts used were the Culturette Brand 10-Minutes Group A Strep ID ® kit (Marion Scientific, Kan- sas City, Missouri) and the PathoDx Group A Strep ID ki t (Diagnostic Products Company, Los Angeles, Cal- ifornia). Instructions furnished with the respective test kits were followed. In brief, soluble strep antigens were extracted with nitrous acid from the swab, and the fluid obta ined was mixed with antibody-coated latex par- ticles. Agglutination of the latex parti- cles indicated the presence of Group A s t reptococcal ant igens and was a positive test. Positive and negative controls were run simultaneously.

A positive culture was used to deter- mine the presence of streptococcal pharyngitis, and results of the rapid test were compared to the culture and to the physician's clinical diagnosis. The sensitivity, specificity, and predictive values of a positive test (PVP} and a negative test (PVN) were determined for the rapid test and physician diagnosis. Is When there was a discrepancy between the culture result and the rapid test result, presumptive identification of B-hemolytic streptococcus was confirmed by coagglutination for groups A, B, C, or G. 14 The ability of the rapid test to differentiate diseased patients, when compared to clinical

judgment, was evaluated by Fisher's exact test. 16

RESULTS One hundred forty-seven patients

were evaluated by physician examina- tion, throat culture, and rapid method during a two-month winter period. Thirty-six patients (24% 1 had posRivc throat culture for streptococcal pharyngitis.

Ninety- three of the 147 pat ients (63%) were evaluated with the CuP turette ~ kit. Twenty-one (23%) had positive throat cultures, 16 of which also were positive by the rapid method (16 of 21) (sensitivity, 76%}. Seventy- two (77%) had negative cultures, 68 of which were negative by the rapid method (specificity, 94%).

Fifty-four patients (37%) were evaluated with the PathoDx ® kit. Fifteen patients (28%) were culture-positive, of which 12 also were positive by the rapid method (sensitivity, 80%). Of the 39 patients with negative cultures, 35 had negat ive resul ts by the rapid method (specificity, 90%).

Because there was no significant difference between the sensitivity or the specificity of the two test kits (P >.50), the data were combined. There were 36 patients (24%) with positive throat cultures and 111 (76%)wi th negative cultures. There were 28 true positives by the rapid test (sensitivity, 78%). There were 103 true negatives by the rapid method (specificity, 93% ). The frequency of disease in subjects with positive rapid tests, that is, the PVP, was 78%. The frequency of non- disease in subjects with negative rapid tests, that is, the PVN, was 93%.

When clinical diagnosis was compared to culture results, clinical diagnosis was correct in 25 of 36 patients (sensitivity, 69% ). Clinical diagnosis of no disease was correct in 63 of 111 cases (specificity, 57%). The PVP of

15:2 February 1986 Annals of Emergency Medicine 158/87

GROUP A STREP PHARYNGITIS DuBois et al

cl in ica l d iagnosis was 38% and the PVN was 85%.

When cl inical judgment was compared to the rapid test in patients wi th positive throat cultures, the rapid test was found to be s ign i f i can t ly more sensitive than physician diagnosis in identifying the presence of Group A s t r e p t o c o c c i in p a t i e n t s w i t h sore throat (P < .05} (Table).

Only 20 of the 147 pat ients (14%) fol lowed up the resul ts of cul tures . T h i r t e e n of these a l ready had been t rea ted at the t i m e of the i r i n i t i a l visit.

DISCUSSION The 78% sensit ivity and 93% spec-

if ici ty of the rapid tests used in our study are less than those reported in other studies, even though the labora- tory procedure was identical to that of the r e p o r t e d studies.ll-13,17"19 T h e presence of only one or two colonies of Group A [3-hemolytic streptococci was reported as a positive culture, and such low numbers of organisms may have y ie lded a fa lse-negat ive resu l t wi th the rapid tes t J 7

The cost of materials for the rapid test was approximately $1.95 per test, compared wi th $3.06 for a culture. Pa- t ient cost for throat culture in our in- s t i tut ion is $20. The cost of therapy depends on the medicat ion used and route of adminis t ra t ion; 1.2 mi l l ion units of IM benzathine penici l l in cost $20; 40 tablets of Pen-VK 250 mg cost $2.50; and 40 tablets of erythromycin 250 mg cost $7.85. Because of poor pa t i en t compl i ance and fo l lowup at our i n s t i t u t i o n , IM p e n i c i l l i n fre- quent ly is the t r ea tment me thod of choice.

T h e c u r r e n t t r e a t m e n t of s t reptococcal pharyngi t is is predicated on the p r e v e n t i o n of acu te r h e u m a t i c fever and its sequelae, more specifical- ly Class W rheumatic valvular disease requiring valve replacement surgep/. T h e i n c i d e n c e of acu te r h e u m a t i c fever, however, has fallen dramatical ly d u r i n g r e c e n t decades to approx- imate ly 0.5 cases/tU0,000/year.3, 4 Of those patients who suffer an at tack of

1.8/0 acute rheumat ic fever, ~ oJ wfl! de- velop Ctass IV rheumat ic hear t disease.2O

,_;ouH~t..a~ t h roa t cu l t u r e s in pa- t ients presenting wiuh sore throat are p e r f o r m e d a n n u a l l y in the U n i t e d States at a cost of untold thousands of dollars to identify and treat those few patients at risk of developing serious

sequelae of s t r ep tococca l infec t ion . Rapid ED diagnosis of s treptococcal pharyngitis offers the potent ial for re- ducing the cost of disease prevention as wel l as for e l imina t ing the prob- lems and costs associated wi th em- piric therapy and pat ient compliance for foUowup.

There is a carrier state of Group A 6 - h e m o l y t i c s t r e p t o c o c c i in w h i c h the p a t i e n t is c o l o n i z e d w i t h t h e organism, yet has no overt disease or risk for the development of rheumatic heart disease. These carriers have low numbers of colonies on cul ture and therefore may give a negative result w i th the rapid tes ts . 21 It wou ld be conjecture to speculate that this group of patients who do not need t reatment would be screened out by the rapid tests.

CONCLUSION Our data indicate that the two rapid

tests used in this s tudy for identifica- t ion of streptococcal antigens in pharyngeal secretions, while not as accurate as throat culture, are superior to cl inical judgment alone in establish- ing the presence of s treptococcal infection. Even though in our hands the rapid tests did not reliably identify all pa t ients requiring ant ib io t ic therapy, the rapid test may be an acceptable alternative to culture.

Rapid Strep I19 kits were supplied by Mar- ion Scientific and Diagnostics Products Company.

REFERENCES 1. Lowe R: Early treatment of streptococcal pharyngitis. Ann Emerg Med 1984; 13:440-448.

2. Paterson P: Streptococcal pharyngoton- sit!iris, in Youmans G, Patorson P, Som- mers H, et al: The BioIogic and ClinicaI Basis of Infectious Diseases, ed 2. Phila- delphia, WB Saunders, 1981, pp 199-208.

3. Land MA, Bisno AL: Acute rheumatic fever, a vanishing disease in suburbia. [AMA 1983;249:895-898.

4. Shutman ST, Redfern D: Management of Pharyngitis in at2 Era of Decl in i ,g Rheumatic Fever. Report of the Eighty- Sixth Ross Conference on Pediatric Re search. Columbus, Ohio, Ross Laborato- ~es, I984.

5. Kaplan EL, Bisno A, Derrick W, et al: Prevention of rheumatic fever. Circ~da- lion 1977;55:223-226.

6, Krober MS, Bass J, Michels G: Strep

Annals of Emergency Medicine

tococcal pharyngitis, placebo-controlled double-blind evaluation of clinical re- sponse to p e n i c i l l i n therapy. J A M A 1985;253:1271-1274.

7. Evans AS, Dick EL: Acute pharyngitis and tonsillitis in University of Wisconsin students. JAMA 1964;190:699-709.

8. Breese BB, Disney FA: The accuracy of diagnosis of beta streptococcal infections on clinical grounds. J Pediatr 1954; 44: 670-673.

9. Crawford G, Grancata F, Holmes KK: Streptococcal pharyngitis: diagnosis by Gram stain. Ann Intern Med 1979;90: 293-297.

10. Moody EC, Updyke EL: Staining bac- terial smears with fluorescent antibody. IV. Grouping streptococci with fluorescent antibody. J Bacteriol 1958;75:553- 560.

11. Edwards EA, Phillips IA, Suiter WC: Diagnosis of Group A streptococcal infections directly from throat secretions. ] Clin Microbio1 1982; 15:481-483.

12. Otero JR, Reyes S, Noriega AR: Rapid diagnosis of Group A streptococcal anti- gen extracted directly from swabs by an enzymatic procedure and used to detect pharyngitis. I Clin Microbiol 1983;18: 318-320.

13. Slifkin M, Gil GM: Evaluation of the Culterette brand ten-minute Group A Strep ID technique. ] Clin Microbiol 1984;20:12-14.

14. Finegold SM, Martin WJ: Diagnostic Microbiology, ed 6. St Louis, CV Mosby, 1982, pp 67-69.

15. Ingelfinger JA, Mosteller F, Thibodeau L, et al: Biostatistics in Clinical Medi- cine. New York, MacMillan Co, 1983.

16. Sokal RR, Rohlf JH: Biometry: The Principles and Practice of Statistics in Bi- ological Research. San Francisco, WH Freeman, 1969, pp 595-598.

17. Gerber MA: Micronitrous acid extrac- tion-coagglutination test for rapid diagnosis of streptococcal pharyngitis. J Clin Microbiol 1983; 17:170-171.

!8. Chang Mj, Mohla C: Ten-minute detection of Group A streptococci in pediatric throat swabs. J Clin Microbiol 1985; 21:258~259.

19. Miceika BG, Vitous A, Thompson K: Detection of Group A streptococcal anti- gen directly from throat swabs with a ten- minute latex agglutination test. J Clin Mi- crobiol 1985;21:467-469.

20. Tompkins RK, Burns D, Cable W: An analysis of the cost-effectiveness of phar yngitis management and acute rheumatic fever prevention. Ann I~tern Med 1977. 86:481-492.

21. Bisno AL: The rise and fall of rheu matic fever. JAMA 1985;254:538-541.

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Rapid diagnosis of group a strep pharyngitis in the emergency department

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