Indian J Pediatr DOI 10.1007/s12098-013-1067-y

ORIGINAL ARTICLE

Validity of Rapid Antigen Detection Testing in Group A Beta-Hemolytic Streptococcal Tonsillopharyngitis Öznur Küçük & Suat Biçer & Tuba Giray & Defne Çöl & Gülay Çiler Erdağ & Yeşim Gürol & Çiğdem E. Kaspar & Ayça Vitrinel

Received: 17 May 2012 / Accepted: 2 May 2013 # Dr. K C Chaudhuri Foundation 2013

Abstract Objective To evaluate the utility of rapid antigen detection testing (RADT) for the diagnosis of group A beta-hemolytic streptococcal tonsillopharyngitis in children, and to detect the sensitivity and specificity of rapid antigen detection of group A beta-hemolytic streptococci from throat specimen compared with throat culture. Methods Rapid antigen detection and throat culture results for group A beta-hemolytic streptococci from outpatients attending university hospital between 1st January 2011 and 31st of December 2011 were evaluated retrospectively. The antigen test negative-throat culture positive patients were investigated for streptococcal carriage. For this purpose, the throat culture results taken from these patients were reviewed after treatment. Results Eighthundred and ninetytwo children were included in the studywith a mean age of 5.34 y. There were 639 and 253 children in two groups with age of 0–6 and 7–17 y, RADT sensitivity and specificity were found to be 59.5 % and 97.2 %, respectively. The positive predictive value was 87.1 %, whereas negative predictive value was 88.4 %. After treatment of 74 patients with throat culture positive and Ö. Küçük (*) : S. Biçer : T. Giray : D. Çöl : G. Ç. Erdağ : A. Vitrinel Department of Child Health and Diseases, Faculty of Medicine, Yeditepe University, Devlet Yolu, Ankara Cad. No: 102-104, Ataşehir, 34752, Istanbul, Turkey e-mail: [email protected] Y. Gürol Department of Medical Microbiology, Faculty of Medicine, Yeditepe University, Istanbul, Turkey Ç. E. Kaspar Department of Biostatistics, Faculty of Medicine, Yeditepe University, Istanbul, Turkey

antigen test negative. Group A beta-hemolytic streptococci were isolated in 12 of them (16.2 %) and accepted as a carrier. Conclusions The low sensitivity of the RADT may be related to streptococcal carriage in some patients. The throat culture should be repeated after treatment to detect streptococcal carriage. Keywords Child . Rapid antigen test . Streptococcal carriage . Streptococcal infection . Throat culture

Introduction Acute respiratory tract infections are very commonly seen in children. Group A beta-hemolytic streptococcus (GABHS) is the most important etiologic agent of acute tonsillopharyngitis worldwide. School-aged (5 to 15 y of age) children are mainly affected with GABHS [1–3]. Antibiotherapy is often recommended in order to prevent complications and transmission [4–6]. For reducing use of antibiotics the laboratory tests must be used to ascertain the diagnosis of GABHS tonsillopharyngitis. Throat culture is still the gold standard for diagnosis in 24–48 h. Rapid antigen detection tests (RADTs) were developed to accelerate the diagnosis in a short time. The sensitivity of RADT is variable, ranging from 75 % to 95 %, depending upon the type of commercial kit used. This variation in sensitivity has been ascribed to differences in culture methods and laboratory proficiency. This means that the odds of a false positive are lower than the odds of a false negative and a positive result may be more reliable than a negative result. Therefore, the American Academy of Pediatrics and the Infectious Diseases Society of America continue to propose corroboration of negative RADT results by throat culture [1, 7–9].

Indian J Pediatr

The positive test results (throat culture and RADT) does not differentiate between streptocococcal pharyngotonsillitis and streptococcal carriage. Repeated throat cultures will be positive in streptococcal carriers, and may increase to the use of unnecessary antibiotics and antibiotic resistance. Streptococcal carriers are likely to have lower antigen levels than those with streptococcal pharyngotonsillitis. In this study, the aim was to evalute the utility and validity of RADT for the diagnosis of GABHS tonsillopharyngitis, and determination of streptococcal carriers in the RADT negative but throat culture positive group.

Material and Methods Children who were admitted to pediatric emergency and pediatric outpatient clinics between 1st January 2011 and 31st of December 2011with acute sore throat, fever and acutely inflamed throat/tonsils with or without exudates, were included in the study. Children with obvious viral infections and those who had received antibiotics prior to testing were excluded. Rapid antigen detection and throat culture results were evaluated. RADT and throat culture were performed in all children. Two throat samples were obtained by sterile swabs simultaneously from each patient. Samples were collected with the recommended technique sampling from each tonsil and posterior pharynx, avoiding the tongue/soft palate and were immediately transported to the microbiology laboratory in the Stuart medium and Quickvue Strep A (Quidel, San Diego, USA) casette test was applied and for culture, specimen was inoculated on 5 % blood sheep agar and identified according to bacitracin and trimethoprim-sulphametaxazole susceptibility from beta-hemolytic colonies. The patients were subdivided into two groups according to their ages. Group I: 0–6 y olds and group II: 7–17 y olds. The utility and validity of RADT was evaluated by analysing of the sensitivity, specificity, positive predictive value, and negative predictive value. The results were evaluated according to age groups. The RADT negative and throat culture positive patients were investigated for streptococcal carriage. For this purpose, the throat culture results taken from these patients were reviewed in a subsequent period of infection. Primary study parameters were RADT’s sensitivity, specificity, positive predictive value, and negative predictive value. The accuracy of the RADT was measured by the area under the Receiver Operating Characteristic (ROC) curve.

Results Eight hundred and ninety two children, 518 boys (58 %) and 374 girls (42 %) were included in the index study, with a mean

age of 5.34 y. There were 639 and 253 children in the group I and group II, respectively. RADT was positive in 147 patients (16.5 %) and negative in 745 patients (83.5 %), although throat culture was positive in 215 patients (24.1 %) and negative in 677 patients (75.9 %), RADT and throat culture both were positive in 128 patients (14.3 %) and negative in 658 patients (73.8 %). In 19 patients (2.1 %) with RADT positive, no GABHS was seen in culture. Overall, the prevalence of GABHS was 16.5 % with rapid antigen test, and was 24.1 % with throat culture (Table 1). RADT sensitivity and specificity were found to be 59.5 % and 97.2 %, respectively (Fig. 1). In patients with GABHS pharyngotonsillitis, the positive predictive value of the RADT (the chance of a positive throat culture if the RADT is positive) was 87.0 % (128/147), whereas the negative predictive value (the change of a negative culture if the RADT is negative) was 88.3 % (658/745) (Fig. 1). In 74 patients with throat culture positive and RADT negative, the throat culture was done after treatment. GABHS was isolated from 12 patients (16.2 %) in the repeated throat culture. These patients may be carriers of GABHS. The false positivity rate was 2.1 % in the index patients. Only 19 patients had positive RADT, where their culture result was negative (Table 2). Sensitivity and specificity of the RADT according to age groups is shown in Tables 3 and 4. In group I, rapid antigen detection sensitivity and specificity was found to be 58.0 % and 97.2 %, respectively. In this age group with GABHS pharyngotonsillitis, the positive predictive value of the RADT (the chance of a positive throat culture if the RADT is positive) was 83.7 % (72/86), whereas the negative predictive value (the chance of a negative culture if the RADT is negative) was 90.6 % (501/553) (Table 3). In group II, rapid antigen detection sensitivity and specificity was found to be 61.5 % and 96.9 %, respectively. In patients with GABHS pharyngotonsillitis, the positive predictive value of the RADT (the chance of a positive throat culture if the RADT is positive) was 91.8 % (56/61), whereas the negative predictive value (the chance of a negative culture if the RADT is negative) was 81.8 % (157/192) (Table 4). The prevalence of GABHS was significantly different between groups. In group II, it was found to be high (35.9 %) compared to group I (19.4 %) (p0.05).

Discussion Inappropriate use of antibiotics has been identified as an increasing problem in pediatric practice and leads to development of multidrug-resistant bacteria. Antibiotics constitute 19.8 % of all medications in developing countries, whereas ratio is 9.9 % in the whole world [10]. Generally, viral or bacterial etiological agents of pharyngotonsillitis are clinically indistinguishable in children, therefore, methods have been sought to detect GABHS prior to prescribing antibiotics [11]. RADT has been widely used to identify cause of pharyngotonsillitis/sore throat to help the physicians make decision of antibiotic treatment without delay. In the literature, RADT has high sensitivity for the diagnosis of streptococcal pharyngotonsillitis in children, varying from 73 % to 97 % [9, 12–14]. The sensitivity of RADT in the index study was detected to be 59.5 %, and is low when compared with other studies. The low sensitivity of RADT has been reported in only one study, in which RADT had a sensitivity

of only 55 % compared with throat culture [15]. The sensitivity of RADT shows a great variability due to some factors. It can be related to difference of laboratory kits, skills of personnel, prevalence of GABHS, the technique of specimen collection, and the presence of GABHS on the swab [16–18]. The technique to obtain specimens must be adequate and uniform in the diagnosis of GABHS. Collection of specimens may be difficult in children, especially in young ones. For this reason, sensitivity of RADT was evaluated in different age groups: In group II (7–17 y olds), sensitivity was found to behigh (61.5 %) compared to group I (0–6 y olds) (58.0 %). This difference was not statistically significant; it may be related for thedifficulty of specimen collection in young group. Another cause of low sensitivy of RADT may be related to test kits. Sarıkaya et al. performed an investigation to determine the sensitivity and specificity of RADT, by using the same kit, the sensitivity was found to be 68.2 % in patients older than 18 y [18]. In another study, by using the same kit, the sensitivity and specificity of RADT in the 0–9 y olds group were determined to be 70 % and 97.8 %, respectively [19]. In the index study, the specificity of RADT was 97.2 % whereas 68.7 % to 99 % in other studies [14, 16, 20–22]. The commercial test kit usage in the present study may be the cause of high specificity of RADT. The positive predictive value is important in the diagnosis of GABHS, for the decision to start antibiotic therapy. If the RADT result is positive, there is no need to wait for detection of GABHS in throat culture to start the therapy. In the index study, the positive predictive value of rapid antigen test was 87.0 %. This value ranged from 65.2 % to 90.0 % in other studies [14, 16, 18, 22]. The false positivity rate was lower in the index study (2.1 %) compared to other studies [11, 15, 16, 18, 23] in which few Table 4 Sensitivity and specificity of the rapid antigen test in the 7–17 age group

Table 2 Sensitivity and specificity of the rapid antigen test Rapid antigen test

Percentage (%)

Range

Sensitivity Specificity Positive Predictive Value Negative Predictive Value

59.5 % 97.2 % 87.0 % 88.3 %

52.6 % 95.6 % 80.5 % 85.8 %

to to to to

66.2 % 98.3 % 92.0 % 90.5 %

Group II (7–17 y old)

Culture (+) n

Culture (−) n

Total n

Rapid antigen test (+) Rapid antigen test (−) Total

56 35 91

5 157 162

61 192 253

GABHS prevalence: 35.9 %; sensitivity: 61.5 %; specificity: 96.9 %; positive predictive value: 91.8 %; negative predictive value: 81.8 %

Indian J Pediatr

patients received unnecessary antibiotic treatment. This may be related with inadequate sample detection for throat culture in children. In addition, other groups of Streptococcus species (e.g., Streptococcus milleri, Streptococcus intermedius) in the normal throat flora sharing the same carbohydrate antigen may cause false positive results [24–26]. In the study by Cabbarpur et al. the false positive rate was found to be 2.47 % [27]. The negative predictive value of RADT was calculated as 88.3 % in the index study, which varies between 88.0 % to 94.2 % in other studies [14, 16, 18, 22]. This alerts to the fact that 11.7 % of patients with negative tests had positive throat cultures. RADT may be used in diagnosis of GABHS without throat culture if false negative results are less than 2.4 % [17]. The false negativity was 11.7 % (87/745) in the index study. It means that RADT can not replace throat culture, in fact 11.7 % of the patients who were not given antibiotic therapy required therapy. This ratio is greater than many other studies, therefore, the negative RADT results must be confirmed by throat culture to prevent complications of GABHS pharyngotonsillitis in countries where GABHS prevalence is high [1, 7–9, 16, 28]. Antibiotics are used at a greater ratio (19.8 %) in developing countries, however, this ratio is 9.9 % in other countries [10]. In recent studies, screening all children with pharyngotonsillitis by performing RADT has been found to be effective to reduce the rate of antibiotic administration [29, 30]. If GABHS grows in the throat culture, complications will not appearbefore starting antibiotic therapy. Bythis approach prevention of antibiotic abuse, decreasing resistance to antibiotics and gettingeconomical benefit can be acquired. Positive test results (including throat culture) do not distinguish patients with acute GABHS infection from those who are carriers of GABHS with viral infection. Up to 21.2 % of school children may be “carriers of bacteria with no symptoms” [30]. Throat culture is more sensitive for detecting small amounts of colonieswhereas antigen levels could be lower in carriers so some of the negative test results may be associated with streptococcal carriage. This may be an explanation for the low sensitivity of RADT. In 74 patients with throat culture positive and RADT negative, the throat culture was repeated after treatment. GABHS was isolated from 12 of them (16.2 %) in the repeated throat cultures. These patients were evaluated as carriers of GABHS.

Conclusions Thus, RADT is reliable for detection of GABHS in children. The throat culture, despite being the gold standard in the diagnosis of GABHS, can yield results not earlier than in 24–48 h and thus, initiation of the antibiotic treatment may be delayed. RADT is a reliable method in preventing unnecessary use of antibiotics and in early initiation of treatment in case of GABHS infection. When RADT is positive, antibiotic

therapy should be started, for the prevention of the complications of GABHS tonsillopharyngitis. Streptococcal carriage may cause RADT negative-throat culture positive results. For that reason, the low sensitivity of the RADT may be related to streptococcal carriage in some patients. This problem may be solved by taking control cultures after treatment. Acknowledgments The authors would like to thank Deniz Karadeniz and Zehra Kipritçi (biologists at Yeditepe University Faculty of Medicine, Department of Clinical Microbiology) for their excellent technical assistance in analyzing group A beta-hemolytic streptococcus. They are also grateful to Asst. Prof. Erkan Karabacak (Writing Center Coordinator of Yeditepe University) for the revision of this paper in English. Conflict of Interest None.

Role of Funding Source

None.

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