Nasopharyngeal carriage, antimicrobial susceptibility, serotype distribution and clonal relatedness of Streptococcus pneumoniae isolates in healthy children in Malatya, Turkey

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Abstract

The aims of this study were to assess the nasopharyngeal colonisation rate, serogroup and antibiotic susceptibility patterns of Streptococcus pneumoniae strains isolated from healthy children. Of 848 children, 162 (19.1%) were found to be carriers. The carrier rate was significantly higher in the 7-year-old age group. Children from the slums of the city had higher carriage rate (23.7%) than those in the centre of the city (17.7%), but this was not statistically significant. The number of intermediate penicillin-resistant strains was 17 (10.5%). No high-level penicillin-resistant S. pneumoniae strain was found. The rates of resistance to co-trimoxazole, erythromycin, tetracycline and clindamycin were 11.7%, 4.9%, 4.3% and 3.7%, respectively. All isolates were uniformly susceptible to rifampicin, moxifloxacin, levofloxacin and vancomycin. Fourteen different serogroups were identified. The most prevalent serogroups in descending order were 9, 19, 23, 10, 6 and 18, accounting for 76.3% of the isolates. Arbitrarily primed polymerase chain reaction typing of 105 isolates revealed that 25 (23.8%) of the isolates were clonally indistinguishable. This value was 20.9% in children from the central area and 36.8% in those from the slum of the city. There was no relationship between serogroups and genotypes, i.e. strains within the same serogroup yielded the same or different genotypes, and vice versa. In conclusion, serogrouping results give a preliminary idea about the possible coverage of a future pneumococcal vaccine. Penicillin G is still a suitable agent for the empirical treatment of pneumococcal infections in our population. Living in the slum of the city may lead to both increased carriage and clustering rates of S. pneumoniae among healthy children.

Introduction

Streptococcus pneumoniae normally colonises the upper respiratory tract of healthy children. Colonised children play a major role in its spread within the family, school, daycare centre and orphanage population. This colonisation constitutes an important risk factor for development of subsequent diseases such as otitis media, sinusitis, pneumonia, blood infections and meningitis that may result in death [1], [2].

The potential risk factors for S. pneumoniae carriage are well studied and include having daycare centre and family contacts, young age, previous antibiotic consumption, underlying disease, living with smokers and recent respiratory tract infections [3], [4], [5], [6]. Although a previous study revealed that seasonal variation did not have an important effect on nasopharyngeal carriage of S. pneumoniae [7], the frequency of carriers was significantly increased in colder months in a hot tropical country (India) [8].

There is a continuous increase in antibiotic resistance among S. pneumoniae isolates over the world, reflecting circulation of resistant strains in the community [9], [10], [11]. Emergence of penicillin- and multidrug-resistant strains even in healthy carriers may complicate empirical treatment of infections due to such strains. Streptococcus pneumoniae strains are divided into more than 90 serotypes. Serotyping and drug susceptibility tests should be performed periodically to detect resistance and serotype distribution in a population, which might be helpful for appropriate empirical antibiotic therapy and design of new strategies in vaccine preparation.

Molecular typing of isolates can help to identify transmission dynamics and to direct more effective control measures. Many molecular approaches have been commonly used for demonstrating genetic relatedness among S. pneumoniae strains [12], [13], [14], [15]. Such techniques can successfully identify isolates as a cluster and as unique isolates, particularly penicillin-resistant strains, within any population.

Data regarding the frequency of carriers, antimicrobial resistance, serotypes and clonal relatedness of S. pneumoniae strains isolated from children in Malatya, a city in eastern Turkey, are lacking. The aims of the present study were to investigate the rate of nasopharyngeal colonisation, antimicrobial susceptibility, serogroups and clonal relatedness of S. pneumoniae strains isolated from healthy primary school children.

Section snippets

Study groups

The study was carried out on 848 children from three primary schools in Malatya, Malatya province, in February 2003. Malatya is a city in the east part of Turkey with 843658 inhabitants, more than half of which live in the city centre. Of the 848 children, 650 were from two schools (Group A) in the centre of the city with similar socio-economic status, and 198 were from one school (Group B) in the slum of the city. The age of children attending primary schools generally ranges from 7 to 13

Results

Of the 848 children included in this study, 470 (55.4%) were males and 378 (44.6%) were females. The age distribution is shown in Table 1. Streptococcus pneumoniae was recovered in 162 children (19.1%). Streptococcus pneumoniae was most frequently isolated from children who were 7 years old. Children from the slum of the city had a higher carriage rate than those from the central area, but this was not statistically significant (Table 2).

Of the 162 isolates tested, 23 (14.2%) yielded inhibition

Discussion

The overall rate of nasopharyngeal S. pneumoniae carriers varies among different populations. Streptococcus pneumoniae was more frequently isolated in patients than in healthy children [19]. In a study from Rome, the carriage rate was found to be 14.9%, and living with more than three persons in the same household was reported to be the only risk factor statistically associated with carriage [15]. Higher rates (19.4% and more than 75%) were also found in daycare centres in which many children

Acknowledgments

This study was supported by the Scientific and Technical Research Council of Turkey (TUBITAK). The authors thank Mrs Bennur Duman for her technical support.

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