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Korean J Clin Microbiol. 2008 Apr;11(1):1-4. English.
Published online April 30, 2008.  https://doi.org/10.5145/KJCM.2008.11.1.1
Copyright © 2008 The Korean Society of Clinical Microbiology
Microbiological Characteristics of Throat Cultures from School Children in Jinju, 2006
Eun-Ha Koh and Sunjoo Kim
Department of Laboratory Medicine, Institute of Health Sciences, Gyeongsang National University School of Medicine, Jinju, Korea.

Correspondence: Sunjoo Kim, Department of Laboratory Medicine, Gyeongsang National University School of Medicine, 90, Chilam-dong, Jinju 660-702, Korea. (Tel) 82-55-750-8239, (Fax) 82-55-762-2696, Email: sjkim8239@hanmail.net
Received February 03, 2008; Accepted March 04, 2008.

Abstract

Background

Group A streptococci (GAS) are the most common cause of pharyngitis in children. The streptococci in throat cultures from healthy elementary school children in Jinju were compared with previous results.

Methods

Throat cultures were taken from 1,402 healthy school children in 2006. β-hemolytic streptococci (BHS) were identified with a bacitracin disk (0.04 U) and latex agglutination test (Seroiden Strepto Kit, Eiken, Tokyo, Japan).

Results

Two-hundred sixteen (15.4%) and 149 (10.6%) cultures grew BHS and GAS, respectively. The isolation rate of GAS was significantly lower than in 2004 (16.0%) or 2002 (16.9%) (P<0.05). Among BHS, the prevalence of group A strains (69.0%) decreased significantly compared with 2004 (84.9%) and 2002 (83.8%) (P<0.05). None of the 1st-grade children yielded BHS or GAS.

Conclusion

The isolation rates of BHS and GAS from healthy school children were lower in 2006 than in previous years. Natural immunization against the common serotypes or improvement in individual hygiene might have played roles in the reduction of isolations of GAS.

Keywords: Group A streptococci; Streptococcus pyogenes; Throat culture

INTRODUCTION

Group A streptococci (GAS) are the most common cause of pharyngitis in children. Once GAS are isolated from patients with tonsillitis, the child should be given antibiotics, such as β-lactams, macrolides, quinolones, or clindamycin, to prevent complications such as scarlet fever, rheumatic fever, or post-streptococcal glomerulonephritis[1]. Recently, severe streptococcal infections such as sepsis, necrotizing fasciitis, or toxic shock-like syndrome also have been reported in many countries[2]. Antibiotics not only reduce the duration of symptoms and signs, but also prevent the transmission of GAS to others[1].

Group A streptococci are prevalent in elementary school-age children[1, 3, 4], and healthy carriers may transmit the organisms to classmates. As it takes time to collect GAS from patients with pharyngitis, sometimes, healthy children are studied to elucidate the epidemiological characteristics of a region to guide therapy of sick children. The authors have studied throat cultures for GAS in Jinju since 1995. We continued the microbiological surveillance in 2006 and compared the results with the previous findings.

MATERIALS AND METHODS

1. Study population

A total of 760 boys and 642 girls from three elementary schools were included. Children with high fever, headache, sore throat, or cervical lymphadenopathy were excluded because we wanted to study only carriers, not patients with established bacterial tonsillitis. Although the numbers of students in each grade were different by school, all children in a chosen classroom were screened. All school grades were included from the Munsan School, whereas children from the 4th through 6th grades in the Chunjun School and only the 6th grade in the Gumsan School were included.

2. Isolation and identification of bacteria

After the student opened his or her mouth and said "ah," a cotton swab was rubbed vigorously on both tonsils and inoculated onto a blood agar plate (BAP, Asan, Seoul) followed by streaking with a loop. The BAP was incubated at 37℃ in room air for 16~18 h. A small gray colony in the center of a wide area of β-hemolysis was identified with a bacitracin disk (0.04 U, BBL Microbiology Systems, Cockeysville, MD, USA) and a latex agglutination test (Seroiden Strepto Kit, Eiken, Tokyo, Japan). Latex agglutination was performed according to the manufacturer's instructions to identify the organism as group A, B, C, or G. Bacteria were stored at -70℃ until the next experiment. The colony numbers on the BAP were classified as 1+ (<10 colony-forming units [CFU]), 2+ (10~50 CFU), 3+ (51~100 CFU), or 4+ if there were β-hemolytic streptococci (BHS) more than 100 CFU.

3. Statistical analysis

The isolation rates of BHS and GAS and the composition of each serogroup by year of isolation were analyzed using the χ2 test with the SPSS 14.0. Statistical significance was achieved if the probability was less than 5% (P<0.05).

RESULTS

Beta-hemolytic streptococci were isolated from 216 (15.4%) of 1,402 children. Classification of BHS revealed 149 (10.6%) isolates of group A, 14 (1.0%) of group B, 30 (2.1%) of group C, and 23 (1.6%) of group G streptococci (Table 1). The colony numbers were 1+ in 21.3% of children, 2+ in 32.4%, 3+ in 31.5%, and 4+ in 14.8%. None of the 1st-grade children yielded BHS or GAS, whereas 2nd- and 3rd-grade children showed the highest isolation rate of GAS. Although the isolation rates of GAS from boys and girls in each school were slightly different, the total isolation rates from boys (10.4%) and girls (10.9%) were similar (Table 2).


Table 1
β-hemolytic streptococci isolated from elementary school children in Jinju, 2006
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Table 2
Isolation rate of group A streptococci (GAS) by school and sex
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DISCUSSION

The isolation rates of BHS and GAS in 2006 were significantly lower than those of 2004 and 2002 in the same community (Fig. 1)[3, 4]. Groups C and G BHS rarely cause pharyngitis[5], but these BHS were not uncommon in 2006 (Fig. 2). Although we do not know the reason for the decline in the carrier rate from that detected in 2004 and 2002, we may speculate that either children became immunized naturally to the common serotypes or their nutrition or hygienes might have improved. A serologic opacity factor antibody study will demonstrate the status of immunologic reactivity against the common serotypes[6]. Also, the season of the study in 2006 (June to October) was different from that in 2004 (October to December), or 2002 (May), and the isolation rate probably was lower in the summer as according to other studies[7, 8]. Moreover, the microbiological culture techniques such as streaking with a loop on BAP and picking a colony from among mixed normal throat flora may have affected the isolation rates of BHS or GAS[9, 10].


Fig. 1
Comparison of isolation rates of β-hemolytic streptococci (BHS) and group A streptococci (GAS) in Jinju (P<0.05).
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Fig. 2
Distribution of serogroups of β-hemolytic streptococci in Jinju (P<0.05).
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Although the numbers of 1st-grade children are small, such that one must be cautious about drawing conclusions, it is curious that none of these children yielded BHS or GAS. We need to follow up with regional surveillance cultures in a few years to detect any change in carrier rates as these children get older.

The likelihood of BHS in numbers of more than 3+ was about 45% in 2006, which is similar to the figures observed in 2004 and 2002[3, 4]. As we suggested before[11], we cannot differentiate true infection from carriage from the colony numbers because carriers also tend to yield numerous colonies on throat culture.

Elementary school children are significant reservoirs of GAS. Epidemiologic study of BHS or GAS reveals the distribution of microbiological characteristics. Serotyping with T antisera and emm genotyping are being conducted to identify any changes of GAS serotypes or genotypes from the past. Also, the antibiotic resistance rate and its mechanisms will be investigated for the GAS isolates. Considering the high incidence of bacterial pharyngitis and its possible severe complications, the importance of monitoring changes in GAS in the community cannot be overstressed.

In conclusion, the isolation rate of BHS or GAS has decreased significantly since 2002. The likelihood of group A streptococci in decline is comparable when the isolation of groups C and G increased significantly. None of the 1st-grade children yielded BHS or GAS. Seasonal variance, natural immunization against the common serotypes, or improvement of personal nutrition or hygiene may have played a role in these changes.

References
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