Upper respiratory colonization by Streptococcus pneumoniae in healthy pre-school children in south-east Poland

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Abstract

Objective

Carriage of Streptococcus pneumoniae in upper respiratory tract of healthy children is a major factor in the horizontal transmission of pneumococcal strains, especially between children attending day-care centers and may be also the source of infection in other individuals. During 8-month prospective study including 3 seasons (autumn, winter, spring), we determined risk factors for S. pneumoniae colonization in general and colonization at 2 or 3 time points in healthy pre-school children, including penicillin non-susceptible likewise multidrug resistant strains.

Methods

Pneumococcal cultures were obtained from 311 children aged 3–5. Finally, a total of 342 isolates were identified. Resistance of pneumococcal isolates was determined and information about potential risk factors were obtained from questionnaires.

Results

A total of 72.4% children were colonized by pneumococci at least once, including 8.4% children colonized at 3 time points, 25.4% children – twice and 38.6% children – only once. Penicillin non-susceptible pneumococcal colonization was found in 36.3% children at least once while multidrug-resistant pneumococcal colonization in 34.1% children. Of the 10.9% and 10.6% children were colonized at 2 or 3 time points by penicillin non-sussceptible and multidrug-resistant isolates, respectively. Pneumococcal colonization (in general or by non-susceptible to penicillin isolates) was independently associated with day care attendance, having no siblings, frequent respiratory tract infections and higher number of antibiotic courses. Children attending day care center, with frequent respiratory tract infections, exposed to tobacco smoke were prone to colonization by multidrug-resistant isolates. Risk of colonization at 2 or 3 time points by pneumococcal isolates, including penicillin-nonsusceptible isolates, was associated with age and day care attendance while multidrug-resistant pneumococcal colonization was found to be significantly higher in children aged 3, with frequent respiratory tract infections and higher number of antibiotic courses.

Conclusion

These results indicate high rate of upper respiratory colonization by S. pneumoniae in healthy preschool children in Poland, including colonization by penicillin non-susceptible and multidrug-resistant pneumococci.

Introduction

Streptococcus pneumoniae is carried in nasopharynx of young children usually without clinical consequences but is also an important aetiologic agent of a wide range of diseases, from minor infections to life-threatening invasive diseases. The epidemiological relationship between strains colonizing healthy children and strains causing pneumoccocal infections has been documented before [1]. Nasopharyngeal carriage in healthy children is a major factor in the horizontal transmission of pneumococcal strains, especially between children attending day-care centers (DCCs) or to other family members and may be also the source of infection in other individuals. Moreover, pneumococcal nasopharyngeal isolates reflect the strains currently circulating in the community [1], [2].

The well-known risk factors that promote S. pneumoniae carriage in children include overcrowding (e.g., DCC attendance), exposure in the family, number of siblings, passive smoking, age or female gender [3], [4]. Colonization rate of S. pneumoniae increases during the first months of life [5] and the highest prevalence is observed in children under 3, followed by some decrease among children of preschool age [6], [7]. The nasopharynx can be colonized by pneumococci for up to few months, depending on serotype of the isolate and age of the host [8], [9]. Young children are frequently colonized for prolonged periods with the same serotypes [10].

Although penicillin has traditionally been an effective treatment for pneumococcal infections, in recent years the increasing prevalence of penicillin-nonsusceptible pneumococci has resulted in decreasing effectiveness of antibiotic therapy. Moreover, these strains often cross-resistant, not only to other β-lactam drugs, such as cephalosporins, but also to non-β-lactam classes, e.g., macrolides, tetracyclines, chloramphenicol or trimetoprim/sulfamethoxazole [11], [12]. Nasopharyngeal carriage of drug-resistant strains plays a crucial role in their spread in children, especially in those coming into close contact, such as children attending DCC. Respiratory tract infections, often caused by pneumococci, are the most common reason for antibiotic prescription in children. Antibiotic use is considered to be one of important risk factors of nasopharyngeal carriage of drug-resistant pneumococci. The prospective studies demonstrated clear direct effect of antibiotic treatment on carriage of drug-resistant S. pneumoniae and links between antibiotic use and resistance have been consistently found at every ecological level: in patients [13], small human communities (for instance day care center) [14], different geographical areas of the same country [15] and in different countries [16].

The aim of our study was to identify risk factors for nasopharyngeal colonization by S. pneumoniae in healthy pre-school children and to determine the susceptibility of pneumococcal isolates to antimicrobial agents. We performed an 8-month prospective study to determine pneumococcal colonization during three seasons: autumn, winter, and spring in the same group of children. We determined risk factors for colonization in general and colonization at 2 or 3 time points, separately. We also analyzed risk factors for these phenomena in case of penicillin non-susceptible (PNSSP), likewise multidrug resistant (MDR) isolates.

Section snippets

Population and questionnaire

The study enrolled 344 healthy children, aged between 3 and 5 years, whose parents agreed to participate and fill out a questionnaire. Two hundred sixty seven children were recruited from 4 day care centers (DCCs) in Lublin (85 from DCC1, 63 from DCC2, 44 from DCC3, 75 from DCC4). Seventy seven children, not attending DCC (staying at home) were recruited from 3 primary health-care practices in Lublin, Poland. Nasopharyngeal colonization of S. pneumoniae was studied three periods: in

Results

A total of 311 children aged 3–5 were included in this study: 241 children attending to four DCCs and 70 children staying at home. Demographic data of studied children are given in Table 1. During the study period, from November to June, 933 nasopharyngeal samples were obtained in three seasons. The mean duration ± SD between the first and the second sampling was 95 ± 7.9 days (median, 96 days) and between the second and the third sampling was 93.0 ± 5.2 days (median, 90 days).

Of the 376 pneumococcal

Discussion

There is limited information about the frequency of S. pneumoniae carriage in the upper respiratory tract among asymptomatic children in Poland, whereas in many other countries such studies have been conducted for a long time [3], [4], [18], [19], [20], [21]. The nasopharyngeal carriage rates of S. pneumoniae reported worldwide range from 2.3% to 62% in various populations. The highest reported carriage rate was found in children under 3 years old [3], [7], [21], [22]. Our data revealed a high

Acknowledgements

We wish to thank Renata Los, Urszula Kosikowska, Anna Biernasiuk, Marek Juda, Agnieszka Grzegorczyk, Janina Kulik, Ewa Sienkiewicz, Barbara Rozanska for their contributions to this project. We are very grateful to the pediatric practices that participated in this study including: NZOZ “Zdrowie” Lublin, NZOZ “Medicor” Lublin, “Lustmed” Justyna Nowicka Melgiew.

We thank the headmasters and staff of the DCCs and the parents and children that collaborated in the study.

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