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Nasopharyngeal carriage of penicillin-resistant, macrolide-resistant and multiply-resistant Streptococcus pneumoniae in day-care centers in Sofia, Bulgaria

2001; Elsevier BV; Volume: 7; Issue: 1 Linguagem: Inglês

10.1046/j.1469-0691.2001.00199.x

1469-0691

Rumyana Markovska, Tanya Strateva, Galina Gergova, Emma Keuleyan,

Bacterial Infections and Vaccines

A significant increase of penicillin-resistant, macrolide-resistant and multiply-resistant Streptococcus pneumoniae has been observed worldwide during the last 10–15 years [1Tomasz A Antibiotic resistance in Streptococcus pneumoniae.Clin Infect Dis. 1997; 24: S85-S88Crossref PubMed Google Scholar]. Resistant strains have become a challenge in the treatment of community-acquired pneumonia, meningitis, sinusitis and acute otitis media, where S. pneumoniae is one of the leading bacterial pathogens [2Pallares R Capdevila O Grau I Treatment options for resistant pneumococcal infections.Clin Microbiol Infect. 1999; 5: 453-455Google Scholar]. Nasopharyngeal carriage of S. pneumoniae in children from day-care centers has been determined to be an important epidemiologic risk factor [3Tomasz A The challenge of multiresistant Streptococcus pneumoniae: international initiatives in day-care centers and use of molecular epidemiological techniques.Clin Microbiol Infect. 1999; 5: 4564-4568Google Scholar, 4Dagan R Fraser D Givon N Yagupsky P Carriage of resistant pneumococci by children in southern Israel and impact of conjugate vaccines on carriage.Clin Microbiol Infect. 1999; 5: 4529-4537Google Scholar, 5Kristinsson K Modification of prescribers' behavior: the Iceland approach.Clin Microbiol Infect. 1999; 5: 4543-4547Google Scholar, 6Principi N Marchisio P Schito G Mannelli S Risk factors for carriage of respiratory pathogens in the nasopharynx of healthy children. Ascanius Project Collaborative Group.Pediatr Infect Dis J. 1999; 18: 517-523Crossref PubMed Scopus (175) Google Scholar, 7Ekdahl K Cars O Role of communicable disease control measures in affecting the spread of resistant pneumococci: the Swedish model.Clin Microbiol Infect. 1999; 5: 4548-4554Google Scholar]. Another well-recognized risk factor is the irrational and excessive global usage of antibiotics, particularly the antibiotics prescribed to children, that may select the resistant strains [8Dellamonica P Pradier C Dunais S Carsenti H New perspectives offered by a French study of antibiotic resistance in day-care centers.Chemotherapy. 1998; 44: 10-14Crossref PubMed Scopus (7) Google Scholar, 9Goldstein FW Penicillin-resistant Streptococcus pneumoniae: selection by both β-lactam and non-β-lactam antibiotics.J Antimicrob Chemother. 1999; 44: 141-144Crossref PubMed Scopus (49) Google Scholar, 10Guillemot D Carbon C Antibiotic use and pneumococcal resistance to penicillin: the French experience.Clin Microbiol Infect. 1999; 5: 4538-4542Google Scholar, 11Kellner JD Ford-Jones EL Streptoccocus pneumoniae carriage in children attending 59 Canadian child-care centers. Toronto Child Care Centre Study Group.Arch Pediatr Adolesc Med. 1999; 153: 495-502Crossref PubMed Scopus (79) Google Scholar]. Today, data on different high rates of resistance are available from different countries [4Dagan R Fraser D Givon N Yagupsky P Carriage of resistant pneumococci by children in southern Israel and impact of conjugate vaccines on carriage.Clin Microbiol Infect. 1999; 5: 4529-4537Google Scholar, 12Marton A Gulyas M Munoz R Tomasz A Extremely high incidence of antibiotic resistance in clinical isolates of Streptococcus pneumoniae in Hungary.J Infect Dis. 1991; 163: 542-548Crossref PubMed Scopus (260) Google Scholar, 13Ronchetti MP Merolla R Bajaksouzian S Violo G Ronchetti R Jacobs MR Antimicrobial susceptibility of Streptoccocus pneumoniae from children attending day-care centers in a central Italian city.Clin Microbiol Infect. 1998; 4: 622-626Crossref PubMed Scopus (18) Google Scholar, 14Leibovitz E Dragomir C Sfartz S et al.Nasopharyngeal carriage of multidrug-resistant Streptococcus pneumoniae in institutionalised HIV-infected and HIV-negative children in northeastern Romania.Int J Infect Dis. 1999; 3: 211-215Abstract Full Text PDF PubMed Scopus (35) Google Scholar, 15Chiou CC Liu YC Huang TS et al.Extremely high prevalence of nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among children in Kaohsiung.Taiwan J Clin Microbiol. 1998; 36: 1933-1937PubMed Google Scholar, 16Garcia deLomas J Gimeno C Millas E et al.Antimicrobial susceptibility of Streptococcus pneumoniae isolated from pediatric carriers in Spain.Eur J Clin Microbiol Infect. 1997; 16: 11-13Crossref PubMed Scopus (20) Google Scholar, 17Syrogiannopoulos GA Grivea IN Beratis NG et al.Resistance patterns of Streptococcus pneumoniae from carriers attending day-care centers in southwestern Greece.Clin Infect Dis. 1997; 25: 188-194Crossref PubMed Scopus (64) Google Scholar]. Specialized surveillance programs have been established to minimize the incidence of resistant strains [5Kristinsson K Modification of prescribers' behavior: the Iceland approach.Clin Microbiol Infect. 1999; 5: 4543-4547Google Scholar, 7Ekdahl K Cars O Role of communicable disease control measures in affecting the spread of resistant pneumococci: the Swedish model.Clin Microbiol Infect. 1999; 5: 4548-4554Google Scholar]. Data on this problem in Bulgaria are available only from children admitted to hospital [18Setchanova L Clinical isolates and nasopharyngeal carriage of antibiotic-resistant Streptococcus pneumoniae in Hospital for Infectious Disease, Sofia, Bulgaria, 1991–1993.Microb Drug Resist. 1995; 1: 79-84Crossref PubMed Scopus (16) Google Scholar]. In this pilot study, we aimed to evaluate the rate of penicillin-, macrolide- and multiply-resistant S. pneumoniae from nasopharyngeal carriage in day-care centers and to look for any correlation with the antibiotic usage that might promote their incidence. We studied 152 children from three different day-care centers, located in different regions of Sofia. The age of the children was from 1 to 6 years (mean 3.8). Nasopharyngeal specimens were obtained during October/November 1999. The swabs were inoculated on blood agar plates and incubated at 37 °Cin 5–10% CO2 for 18–24 h. Identification of S. pneumoniae was by the routine criteria: α-hemolytic colonies with typical morphology, which were susceptible to Optochin (Becton Dickinson, BBL, Cockeysville, MD, USA). Susceptibility testing was performed on Mueller–Hinton II agar (Becton Dickinson, BBL), supplemented with 5% sheep blood, according to the NCCLS [19National Committee for Clinical Laboratory Standards Performance standards for antimicrobial susceptibility testing; ninth informational supplement M100–S9. NCCLS, Wayne, Pa1999Google Scholar]. In order to test the susceptibility to penicillin, an oxacillin disk, 1 μg, was first applied, and then the strains with inhibition zones < 20 mm were tested with the penicillin E-test (AB BIODISK, Solna, Sweden), according to the instructions of the manufacturer. Susceptibility testing to the other antimicrobial agents was done by the disk diffusion method and antimicrobial disks obtained from the National Center of Infectious and Parasitic Diseases, Sofia. Phenotypes of macrolide resistance were detected by the double disk method, with disks of erythromycin 15 μg and clindamicin 2 μg [20Latini L Ronchetti M Merolla R et al.Prevalence of mef E, erm and tet (M) genes in Streptococcus pneumoniae strains from central Italy.Int J Antimkrob Agents. 1999; 13: 29-33Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar]. Information about prior antibiotic treatment (for the last 3 months) was obtained through a questionnaire given to the parents. Data on the national consumption of antibiotics were discussed [21Popova M Popova P Guencheva G Consumption of anti-infective drugs in Bulgaria for the period from 1979 to 1994.Pharm World Sci. 1979; 19: 93-100Crossref Scopus (9) Google Scholar]. The results obtained have shown that 85 of 152 studied children (55.6%) had S. pneumoniae nasopharyngeal colonization. Only one strain (1.2%) had a high level of penicillin resistance (≥ 2 mg/L). The incidence of strains with intermediate resistance (0.1–1 mg/L) was 21.2%. This rate of penicillin-resistant S. pneumoniae (PRSP) is similar to the percentages found in Italy [13Ronchetti MP Merolla R Bajaksouzian S Violo G Ronchetti R Jacobs MR Antimicrobial susceptibility of Streptoccocus pneumoniae from children attending day-care centers in a central Italian city.Clin Microbiol Infect. 1998; 4: 622-626Crossref PubMed Scopus (18) Google Scholar], Canada [11Kellner JD Ford-Jones EL Streptoccocus pneumoniae carriage in children attending 59 Canadian child-care centers. Toronto Child Care Centre Study Group.Arch Pediatr Adolesc Med. 1999; 153: 495-502Crossref PubMed Scopus (79) Google Scholar], Spain [16Garcia deLomas J Gimeno C Millas E et al.Antimicrobial susceptibility of Streptococcus pneumoniae isolated from pediatric carriers in Spain.Eur J Clin Microbiol Infect. 1997; 16: 11-13Crossref PubMed Scopus (20) Google Scholar], Greece [17Syrogiannopoulos GA Grivea IN Beratis NG et al.Resistance patterns of Streptococcus pneumoniae from carriers attending day-care centers in southwestern Greece.Clin Infect Dis. 1997; 25: 188-194Crossref PubMed Scopus (64) Google Scholar] and Portugal [22Lencastre H Sanches I Brito-Avo A et al.Carriage and antibiotic resistance of respiratory pathogens and molecular epidemiology of antibiotic resistant Streptoccocus pneumoniae colonizing children in day-care centers in Lisbon: the Portuguese day care center initiative.Clin Microbiol Infect. 1999; 5: 4555-4563Google Scholar], but relatively lower than in France [8Dellamonica P Pradier C Dunais S Carsenti H New perspectives offered by a French study of antibiotic resistance in day-care centers.Chemotherapy. 1998; 44: 10-14Crossref PubMed Scopus (7) Google Scholar], Hungary [12Marton A Gulyas M Munoz R Tomasz A Extremely high incidence of antibiotic resistance in clinical isolates of Streptococcus pneumoniae in Hungary.J Infect Dis. 1991; 163: 542-548Crossref PubMed Scopus (260) Google Scholar], Romania [14Leibovitz E Dragomir C Sfartz S et al.Nasopharyngeal carriage of multidrug-resistant Streptococcus pneumoniae in institutionalised HIV-infected and HIV-negative children in northeastern Romania.Int J Infect Dis. 1999; 3: 211-215Abstract Full Text PDF PubMed Scopus (35) Google Scholar], and Taiwan [15Chiou CC Liu YC Huang TS et al.Extremely high prevalence of nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among children in Kaohsiung.Taiwan J Clin Microbiol. 1998; 36: 1933-1937PubMed Google Scholar], and higher than in some northern countries with restricted antibiotic policies, such as Iceland [5Kristinsson K Modification of prescribers' behavior: the Iceland approach.Clin Microbiol Infect. 1999; 5: 4543-4547Google Scholar] and Sweden [7Ekdahl K Cars O Role of communicable disease control measures in affecting the spread of resistant pneumococci: the Swedish model.Clin Microbiol Infect. 1999; 5: 4548-4554Google Scholar]. The resistance rate to the other antimicrobial agents (Table 1) varied: 37.6% to tetracycline, 10.6% to chloramphenicol, 21.2% to erythromycin, 9.4% to clindamycin, and 42.3% to sulfamethoxazole–trimethoprim. As was expected, PRSP showed higher rates of resistance to the other antibiotics. All of the strains tested were 100% susceptible to rifampicin, vancomycin, ciprofloxacin and cefotaxime. (Susceptibility testing to cefotaxime was by the disk diffusion method, as it was recommended for non-invasive isolates ofS. pneumoniae by BSAC [23BSAC BSAC standardised disc sensitivity testing method. Gardiner-Caldwell Communication Ltd, Macclesfield, Cheshire1999Google Scholar].) Only 38.8% of the isolates were susceptible to all examined antibiotics. Phenotypes of antimicrobial resistance are presented in Table 2.Table 1Comparative antimicrobial susceptibility of S. pneumoniae strains from nasopharyngeal carriage in children attending day-care centers in Sofia (percentage of resistant strains)PENERYCLIVANTETCHLRIFCIPSXTAll S. pneumoniae N = 8522.421.29.4037.610.60042.3Pen-R S. pneumoniae N=1910052.631.6047.421.10063.2Pen-S S. pneumoniae N = 66012.13034.87.60036.4N, number of strains; Pen-R, penicillin resistant; Pen-S, penicillin susceptible; PEN, penicillin; TET, tetracycline; CHL, chloramphenicol; CLI, clindamycin; ERY, erythromycin; SXT, sulfamethoxazole-trimethoprim; VAN, vancomycin; CIP, ciprofloxacin; RIF, rifampicin. Open table in a new tab Table 2Resistance patterns of 85 S. pneumoniae strains from nasopharyngeal carriage in children attending day-care centersMultiple resistance phenotypesNumberOther phenotypesNumberPEN, ERY, CLI, TET4TET, SXT11PEN, ERY, CLI, TET, SXT2SXT7PEN, ERY, CHL, SXT2TET6PEN, CHL, SXT2PEN, SXT4ERY, CLI, TET, SXT2PEN, TETERY, CHL, TET2ERY, TETPEN, TET, SXT1ERY, SXTPEN, TET, ERY1PENPEN, ERY, SXT1CHLERY, CHL, TET, SXT1ERY, CHL, SXT1Susceptible, N = 33. Total, N = 85. PEN, penicillin; TET, tetracycline; CHL, chloramphenicol; CLI, clindamycin; ERY, erythromycin; SXT, sulfamethoxazole-tri-methoprim. Open table in a new tab N, number of strains; Pen-R, penicillin resistant; Pen-S, penicillin susceptible; PEN, penicillin; TET, tetracycline; CHL, chloramphenicol; CLI, clindamycin; ERY, erythromycin; SXT, sulfamethoxazole-trimethoprim; VAN, vancomycin; CIP, ciprofloxacin; RIF, rifampicin. Susceptible, N = 33. Total, N = 85. PEN, penicillin; TET, tetracycline; CHL, chloramphenicol; CLI, clindamycin; ERY, erythromycin; SXT, sulfamethoxazole-tri-methoprim. The incidence of macrolide resistance was also high (21.2%). This percentage is similar to the rates found in Spain [16Garcia deLomas J Gimeno C Millas E et al.Antimicrobial susceptibility of Streptococcus pneumoniae isolated from pediatric carriers in Spain.Eur J Clin Microbiol Infect. 1997; 16: 11-13Crossref PubMed Scopus (20) Google Scholar] and Greece [17Syrogiannopoulos GA Grivea IN Beratis NG et al.Resistance patterns of Streptococcus pneumoniae from carriers attending day-care centers in southwestern Greece.Clin Infect Dis. 1997; 25: 188-194Crossref PubMed Scopus (64) Google Scholar], although it is lower than the rates found in Italy [13Ronchetti MP Merolla R Bajaksouzian S Violo G Ronchetti R Jacobs MR Antimicrobial susceptibility of Streptoccocus pneumoniae from children attending day-care centers in a central Italian city.Clin Microbiol Infect. 1998; 4: 622-626Crossref PubMed Scopus (18) Google Scholar]. Analysis of macrolide phenotypes has shown an MLSb phenotype in 44.4% and an M phenotype in 55.6% of the strains, suggesting a mechanism of resistance by methylation of 23S rRNA, encoded by erm genes, and an efflux pump mechanism, mediated by mefE genes. This finding differs from the percentage which was found by other European authors [20Latini L Ronchetti M Merolla R et al.Prevalence of mef E, erm and tet (M) genes in Streptococcus pneumoniae strains from central Italy.Int J Antimkrob Agents. 1999; 13: 29-33Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar, 24Perez-Trallero E Pneumococcal macrolide resistance–not a myte.J Antimicrob Chemother. 2000; 45: 401-412Crossref PubMed Scopus (5) Google Scholar, 25Lagrou K Peetermans W Verhaegen J Lierde S Verbist L Eldere J Macrolide resistance in Belgian Streptococcus pneumoniae.J Antimicrob Chemother. 2000; 45: 119-121Crossref PubMed Scopus (43) Google Scholar]. In the group of the macrolide-resistant and penicillin-susceptible strains, six isolates presented the M phenotype and two the MLSb phenotype. In the group of macrolide-resistant and penicillin-resistant strains, six isolates presented the MLSb phenotype and four the M phenotype. All of the strains with the MLSb phenotype were resistant to tetracycline. The incidence of multiply-resistant (resistant to ≥ 3 different classes of antibiotic) strains was 22.3%. All of them were penicillin and/or erythromycin resistant. The order of co-resistance markers was: co-trimoxazole > tetracycline > chloramphenicol > clindamycin. Data on previous antibiotic treatment (for the last 3 months) are summarized in Table 3. From 152 questionnaires, 116 were returned. Analysis of data on prior antimicrobial treatment revealed higher antibiotic usage in children with S. pneumoniae resistant to penicillin and/or erythromycin (76%) than in children with penicillin- and/or erythromycin-susceptible S. pneumoniae (27.7%, P < 0.001) and than in children without nasopharyngeal colonization (45.4%, P < 0.01). The overview of the administered antimicrobial agents has shown that the aminopenicillins were the most often prescribed group of antibiotics. It is widely accepted, following both clinical and in vitro experiments, that aminopenicillins can select PRSPs [26Baquero F Canton R Baquero-Artigao F Current patterns and evolution of antibiotic resistance among bacterial pathogens involved in acute otitis media.Clin Microbiol Infect. 1997; 3: 3526-3533Google Scholar, 27Carsenti-Etesse H Durant J Salvador F et al.In vitro development of resistance of Streptococcus pneumoniae to β lactam antibiotics.Microb Drug Resist. 1995; 1: 85-95Crossref PubMed Scopus (8) Google Scholar]. However, in a recent logistic analysis of publications worldwide, the author argued that increased prescribing of cephalosporins, co-trimoxazole and macrolides could be more important for promoting PRSP carriage [9Goldstein FW Penicillin-resistant Streptococcus pneumoniae: selection by both β-lactam and non-β-lactam antibiotics.J Antimicrob Chemother. 1999; 44: 141-144Crossref PubMed Scopus (49) Google Scholar]. It is also important to have information about the appropriateness of antimicrobial therapy: clinical diagnosis, bacteriologic result, dosage regimen, route of administration, and duration of treatment [7Ekdahl K Cars O Role of communicable disease control measures in affecting the spread of resistant pneumococci: the Swedish model.Clin Microbiol Infect. 1999; 5: 4548-4554Google Scholar, 10Guillemot D Carbon C Antibiotic use and pneumococcal resistance to penicillin: the French experience.Clin Microbiol Infect. 1999; 5: 4538-4542Google Scholar, 26Baquero F Canton R Baquero-Artigao F Current patterns and evolution of antibiotic resistance among bacterial pathogens involved in acute otitis media.Clin Microbiol Infect. 1997; 3: 3526-3533Google Scholar]. Prom the questionnaires filled in by the parents, we have information only about the clinical diagnosis: acute otitis media (9), bronchitis (8), tonsillitis (11), acute upper respiratory tract infection (11), and unknown (12). For future investigations, it seems better to obtain such information from the medical documentation, in order to have more comprehensive and reliable data. According to contemporary knowledge about the evolution of PRSP spread, described as an advancing wave model [26Baquero F Canton R Baquero-Artigao F Current patterns and evolution of antibiotic resistance among bacterial pathogens involved in acute otitis media.Clin Microbiol Infect. 1997; 3: 3526-3533Google Scholar], a further increase in antibiotic use should support the conversion of low-level resistant pneumococci into a high-level resistant population. It is therefore essential to limit antibiotic prescribing to the cases where it is really indispensable and to take care to avoid lower antibiotic concentrations.Table 3Data on antibiotic usage in children during the last 3 monthsChildren who have received antibioticsPENAMX/AMPAMCCEFCLRSXTMore than one antibioticUnknownChildren with nasopharyngeal carriage of S. pneumoniaePEN R ERY S N=9–3–111–12PEN R ERY R N=10–3––––232PEN S ERY R N=6–211––––2Total N = 25–81211246PEN S ERY S N = 4724–312–134Children without nasopharyngeal carriage of S. pneumoniaeN = 441154215–24PEN R/S, penicillin resistant/susceptible; ERY R/S, erythromycin resistant/susceptible; PEN, phenoxymethylpenicillin; AMX, amoxycillin; AMP, ampicillin; AMC, amoxycillin–clavulanic acid; CEF, cephalosporins (cephalexin 4, cefaclor 2, cefadroxil 1, cefuroxime 1); CLR, clarithromycin; SXT, co-trimoxazole; More than one antibiotic: AMX, CEF 6; AMX, AMC 1;AMX, AMC, CEF 1. Open table in a new tab PEN R/S, penicillin resistant/susceptible; ERY R/S, erythromycin resistant/susceptible; PEN, phenoxymethylpenicillin; AMX, amoxycillin; AMP, ampicillin; AMC, amoxycillin–clavulanic acid; CEF, cephalosporins (cephalexin 4, cefaclor 2, cefadroxil 1, cefuroxime 1); CLR, clarithromycin; SXT, co-trimoxazole; More than one antibiotic: AMX, CEF 6; AMX, AMC 1;AMX, AMC, CEF 1. Regarding resistance to erythromycin, there are well-documented studies in streptococci, evaluating its relation to the consumption of macrolides, and about the decline in macrolide resistance following a decrease in macrolide usage [28Sepalla H Klaukka T Vuopio-Varkila J et al.The effect of changes in the consumption of macrolide antibiotics on erythromycin resistance in group A streptococci in Finland.N Engl J Med. 1997; 337: 441-446Crossref PubMed Scopus (1032) Google Scholar, 29Huovinen P Antibiotic usage and the incidence of resistance.Clin Microb Infect. 1999; 5: 4512-4517Google Scholar]. In this study, however, the only macrolide prescribed was clarithromycin, in four cases. The use of macrolide antibiotics is relatively low in Bulgaria [21Popova M Popova P Guencheva G Consumption of anti-infective drugs in Bulgaria for the period from 1979 to 1994.Pharm World Sci. 1979; 19: 93-100Crossref Scopus (9) Google Scholar]. Data on national antibiotic consumption show that the macrolides used in 1994 represented 0.85 DDD/1000/day, and in 1999–nearly twofold less–0.42 DDD/1000/day. The five top groups of antimicrobial agents used in the early 1990s were: (1) tetracyclines; (2) extended-spectrum penicillins; (3) sulfonamides and trimethoprim; (4) aminoglycosides; (5) narrow-spectrum penicillins and cephalosporins. Some positive change could be seen in 1999, when DDD/1000/day of the penicillins, tetracyclines, cephalosporins, and sulfonamides and trimethoprim became, respectively, 7.64, 4.24, 1.37 and 1.08 (M. Popova, personal communication). Taking into account these data, we may suppose that the use of β-lactams, tetracyclines and co-trimoxazole has promoted the emergence and selection of erythromycin-resistant S. pneumoniae strains (see also the phenotypes of resistance in Table 2). It is also probable that the different frequencies of phenotypes of macrolide resistance found in this work are related to the particularity of antibiotic consumption. From the results of this pilot study on resistant S. pneumoniae nasopharyngeal carriage, conducted in three day-care centers in Sofia, we drew the following conclusions. Concerning the incidence of resistant S. pneumoniae strains: 1.The rate of penicillin-resistant S. pneumoniae was 22.4% (1.2%, high-level resistance; 21.2%, intermediate resistance).2.The incidence of macrolide-resistant strains was 21.2% (MLSb phenotype, 44.4%; M phenotype, 55.6%).3.Multiply-resistant S. pneumoniae represented 22.3%: all of the strains were penicillin and/or macrolide resistant; the order of the co-resistant markers was: co-trimoxazole > tetracycline > chloramphenicol > clindamycin. Concerning the antibiotic usage that may promote the resistance, more children colonized by penicillin- and/or ery-thromycin-resistant pneumococci have been treated with antibiotics during the previous 3 months than the children carrying susceptible strains (P < 0.001). The incidence of resistance to penicillin was obviously related to the higher prescription of aminopenicillins, while the resistance to erythromycin could be due to the improper usage of antibiotics of different groups (β-lactams, co-trimoxazole, as well as tetracyclines in older patients). More systematic studies, comprising serotyping and molecular characterization of the strains, have to be undertaken in different centers of the country to better understand the epidemiology and resistance mechanisms in S. pneumoniae. To assess the impact of antibiotics which promote the resistance, pharmacotherapeutic data would also be necessary to evaluate the therapy. Until these data become available, a practical approach would be to minimize the misuse and overuse of antibiotics, prescribed especially for upper respiratory tract infections in pediatric patients. This work was conducted with a grant from the Alliance for the Prudent Use of Antibiotics(APUA), Boston, USA (APUA Small Grants Program for Chapter Affiliates). The authors thank also Dr Maria Popova, Bulgarian Drug Agency, for providing data on national antibiotic consumption in 1999.