Antibacterial resistance patterns in Streptococcus pneumoniae isolated from elderly patients: PROTEKT years 1–5 (1999–2004)

International Journal of Antimicrobial Agents 30 (2007) 546–550

Short communication

Antibacterial resistance patterns in Streptococcus pneumoniae isolated from elderly patients: PROTEKT years 1–5 (1999–2004) Rafael Cant´on a,∗ , Serhat Unal b , David J. Farrell c a

Hospital Universitario Ram´on y Cajal, Servicio de Microbiolog´ıa, Carretera de Colmenar Km 9.1, 28034 Madrid, Spain b Hacettepe University, Department of Medicine, 06100 Ankara, Turkey c G.R. Micro Ltd., 7-9 William Road, London NW1 3ER, UK Received 10 May 2007; accepted 30 July 2007

Abstract The antibacterial susceptibilities of 6646 Streptococcus pneumoniae isolates collected in 38 countries from patients ≥65 years of age with community-acquired respiratory tract infections (RTIs) during years 1–5 of the PROTEKT study (1999–2004) were analysed. Rates of erythromycin resistance (36.0%), penicillin non-susceptibility (31.3%; 20.2% resistant plus 11.1% intermediately susceptible) and resistance to multiple antibacterials (37.2%) were stable over the 5 years. The most common macrolide resistance mechanism was erm(B) (61.4%); erm(B) + mef(A) strains increased from 5.4% (year 1) to 7.4% (year 5) (P = 0.037). Overall, 37.2% of isolates exhibited resistance to two or more antibacterials, including 15.9% resistant to both penicillin and erythromycin. Antibacterial resistance was highest in the Far East. Telithromycin resistance was rare (0.12%). Appropriate alternative empirical first-line therapies may be required for treating community-acquired RTIs in the elderly. © 2007 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. Keywords: Streptococcus pneumoniae; Geriatrics; Drug resistance, bacterial; Drug resistance, multiple; Microbial sensitivity tests

1. Introduction Community-acquired respiratory tract infections (RTIs), including community-acquired pneumonia (CAP), acute exacerbations of chronic bronchitis (AECB) and acute sinusitis, are the most common type of infectious disease treated by primary care physicians. The bacterial pathogen most frequently responsible for these infections is Streptococcus pneumoniae [1]. Both the overall incidence of communityacquired RTIs and their associated rates of morbidity and mortality are higher among the elderly than the general adult population [2,3]. In CAP, factors that contribute to this increased incidence include changes in oral and mucociliary clearance and immune dysfunction [4]. Increasing age may also influence disease aetiology; for example, one recent study found that the incidence of pneumococcal pneumonia was highest among patients ≥75 years of age [2]. ∗

Corresponding author. Tel.: +34 91 336 8330; fax: +34 91 336 8809. E-mail address: [email protected] (R. Cant´on).

The most common first-line antibacterials for communityacquired RTIs currently recommended in treatment guidelines worldwide, including those for elderly patients, are ␤-lactams (e.g. penicillin, amoxicillin and amoxicillin/clavulanic acid) and macrolides (e.g. erythromycin, azithromycin and clarithromycin) [5,6]. However, escalating rates of resistance to these agents among the common causative pathogens may threaten their continuing clinical utility [7]. For example, macrolide treatment failures have been reported in some patients infected with S. pneumoniae strains resistant to these agents in vitro [8]. The ketolide antibacterial telithromycin exhibits good in vitro activity against the common RTI pathogens (including S. pneumoniae isolates resistant to other antibacterials) as well as atypical/intracellular organisms [9]. Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin (PROTEKT) is an ongoing, longitudinal, international surveillance study established in 1999 to monitor the susceptibility of pathogens collected from patients with community-acquired RTIs to telithromycin and

0924-8579/$ – see front matter © 2007 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. doi:10.1016/j.ijantimicag.2007.07.025

R. Cant´on et al. / International Journal of Antimicrobial Agents 30 (2007) 546–550

other antibacterials. This analysis of data from the first 5 years of the study was conducted to examine the antibacterial susceptibility of S. pneumoniae isolates from patients ≥65 years of age. Genotyping analysis was also used to identify mechanisms of macrolide resistance. The overall aim was to highlight specific resistance problems associated with the treatment of community-acquired RTIs in the elderly when S. pneumoniae is involved.

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subclass erm(TR) and mef(A) macrolide resistance genes using a multiplex TaqMan® polymerase chain reaction assay (Applied Biosystems, Foster City, CA), as described previously [13]. Isolates that lacked rRNA methylation or drug efflux mechanisms were screened for other ribosomal mutations by sequencing the L4 and L22 riboprotein genes, as described previously [14]. 2.3. Statistical analysis

2. Materials and methods 2.1. Sources of isolates Isolates of S. pneumoniae were collected from adult outpatients ≥65 years of age with community-acquired RTIs (otitis media, CAP, AECB, acute exacerbations of chronic obstructive pulmonary disease and sinusitis). Patients with nosocomial RTIs were excluded; however, isolates cultured from hospitalised patients within 48 h of admission were included in the analysis. The following culture sources were considered acceptable: blood; sputum; bronchoalveolar lavage fluid; middle ear fluid (via tympanocentesis); nasopharyngeal swab or aspirate; sinus aspirate. Duplicate strains, or strains originating from existing banked collections, were not used. Details of the methods for isolate storage, transportation and identification have been reported previously [10]. A total of 150 centres in 38 countries (Argentina, Australia, Austria, Belgium, Brazil, Canada, China, Colombia, Czech Republic, Ecuador, Eire, Finland, France, Germany, Greece, Guatemala, Hong Kong, Hungary, Israel, Italy, Japan, Mexico, The Netherlands, Poland, Portugal, Russia, Saudi Arabia, Slovak Republic, South Africa, South Korea, Spain, Sweden, Switzerland, Taiwan, Turkey, UK, USA and Venezuela) provided isolates over five consecutive respiratory seasons (1999–2000 [PROTEKT year 1], 2000–2001 [year 2], 2001–2002 [year 3], 2002–2003 [year 4] and 2003–2004 [year 5]). 2.2. Antibacterial susceptibility testing and genotyping Minimum inhibitory concentrations (MICs) were determined at a central laboratory (G.R. Micro Ltd., London, UK) using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method [11]. CLSI MIC interpretive criteria (breakpoints) were used to determine antibacterial susceptibility [12]. Multiple resistance was defined according to the US Food and Drug Administration (FDA) definition as resistance to two or more of the six classes of antibacterials represented by: penicillin (MIC ≥ 2 ␮g/mL); erythromycin (MIC ≥ 1 ␮g/mL); cefuroxime (MIC ≥ 4 ␮g/mL); tetracycline (MIC ≥ 8 ␮g/mL); trimethoprim/sulfamethoxazole (MIC ≥ 4 ␮g/mL); and levofloxacin (MIC ≥ 8 ␮g/mL). Erythromycin-resistant pneumococcal isolates (MIC ≥ 1 ␮g/mL) were analysed for the presence of erm(B), erm(A)

The change in prevalence of erm(B) + mef(A) isolates over time in different countries was analysed by Fisher’s exact test. The change in global prevalence of macrolide resistance was determined by χ2 -test.

3. Results Over the 5-year study period, a total of 6646 S. pneumoniae isolates were collected from patients ≥65 years of age (year 1, n = 857; year 2, n = 1086; year 3, n = 1493; year 4, n = 1536; year 5, n = 1674). Of these, 3590 were from patients aged 65–74 years, 2330 from patients aged 75–84 years and 726 from patients aged >84 years. Overall, 31.3% of isolates (2080/6646) exhibited penicillin non-susceptibility (20.2% resistant (MIC ≥ 2 ␮g/mL) and 11.1% intermediately susceptible (MIC 0.12–1 ␮g/mL)) and 36.0% (2393/6646) were resistant to erythromycin. Co-resistance to penicillin (isolates showing intermediate susceptibility not included) and erythromycin was exhibited by 15.9% of isolates (1055/6646), whilst 37.2% (2471/6646) displayed multiple resistance phenotypes. Resistance rates did not vary greatly between each year of the study (data not shown) but showed considerable geographical variability (Fig. 1). In vitro activity and susceptibility testing results for a panel of antibacterials, stratified by patient age, are shown in Table 1. Among erythromycin-resistant isolates collected over the 5 years, the predominant macrolide resistance mechanisms were erm(B) (1470/2393; 61.4%) and mef(A) (729/2393; 30.5%). A further 136 isolates (5.7%) were positive for both erm(B) and mef(A), whilst 52 isolates (2.2%) exhibited ribosomal mutations, 1 isolate displayed the erm(A) subclass erm(TR) genotype, 1 isolate expressed both erm(A) subclass erm(TR) and mef(A) and 4 isolates were not viable for testing. The erythromycin MIC range was similar for isolates exhibiting erm(B) or erm(B) + mef(A) (4 ␮g/mL to ≥128 ␮g/mL) and for those exhibiting mef(A) or ribosomal mutations (1 ␮g/mL to ≥128 ␮g/mL). The distribution of the most common macrolide resistance mechanisms in each year of the study was (year 1/year 2/year 3/year 4/year 5, respectively): erm(B), 58.7%/63.1%/65.8%/59.5%/59.7%; mef(A), 34.3%/30.5%/28.6%/30.8%/29.9%; erm(B) + mef(A), 5.4%/ 4.2%/3.7%/6.8%/7.4%; ribosomal mutations, 1.6%/2.1%/ 1.9%/2.6%/2.4%. The increase in the global prevalence of

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R. Cant´on et al. / International Journal of Antimicrobial Agents 30 (2007) 546–550

Fig. 1. Worldwide regional differences in the incidence of penicillin non-susceptibility, erythromycin resistance and multiple resistance phenotypes among isolates of Streptococcus pneumoniae obtained from elderly patients during PROTEKT years 1–5. (a) Proportion of isolates with intermediate penicillin resistance (%). (b) Proportion of isolates with full penicillin resistance (%).

erm(B) + mef(A) was significant (year 1 compared with year 5, χ2 -test, P = 0.0368). Isolates exhibiting the erm(B) + mef(A) genotype were found in Australia (1/15 erythromycin-resistant S. pneumoniae isolates; 6.7%), Canada (1/119; 0.8%), China (8/46; 17.4%), France (1/208; 0.5%), Hong Kong (3/156; 1.9%), Hungary (1/14; 7.1%), Italy (1/147; 0.7%), Japan (29/693; 4.2%), The Netherlands (1/11; 9.1%), Russia (2/6; 33.3%), South Africa (17/26; 65.4%), South Korea (50/148; 33.8%), Spain (1/221; 0.5%), Taiwan (7/118; 5.9%), the UK (1/24; 4.2%) and the USA (12/88; 13.6%). The change in prevalence of erm(B) + mef(A) isolates over the course of the study in individual countries was not significant except in Japan where the prevalence increased from 1.9% in years 1 and 2 to 5.6% in years 4 and 5 (Fisher’s exact test, P = 0.019). There was some geographical variation in the prevalence of ribosomal mutations. In regions that provided >50 isolates over the 5 years, the prevalence of ribosomal mutations was 0.6% (7/1161) in the Far East, 1.4% (1/70) in Latin America, 2.8% (24/853) in Western Europe, 6.8% (14/207) in North America and 8.9% (5/56) in Eastern Europe. Genotype distributions for the three age groups over the 5 years were (65–74 years/75–84 years/>84 years, respectively): erm(B), 60.5%/62.2%/63.8%; mef(A), 30.6%/30.1%/30.7%; erm(B) + mef(A), 6.4%/5.1%/3.9%. The apparent decline in the frequency of erm(B) + mef(A)

with increasing age was not significant (χ2 = 5.831, P = 0.666). Only eight isolates over the 5 years exhibited resistance to telithromycin, all of which were co-resistant to erythromycin. Seven of the eight isolates exhibited erm(B)-mediated macrolide resistance and one exhibited erm(B) + mef(A).

4. Discussion The number of publications containing surveillance data specifically addressing the issue of S. pneumoniae resistance in the elderly is currently limited. Our analysis of the elderly subpopulation within the PROTEKT study shows that resistance to ␤-lactams and macrolides in patients ≥65 years of age has persisted at high levels between 1999 and 2004. Multiple resistant phenotypes were also very common, with an overall rate of nearly 40%. Penicillin non-susceptibility was ca. 30% (ca. 20% resistant and 10% showing intermediate susceptibility) over the course of the study, whilst the macrolide resistance rate remained stable at ca. 35%. A decrease in overall antibacterial resistance, but specifically not macrolide resistance, among isolates from elderly patients has been observed following the introduction of a pneumococcal conjugate vaccine programme [15]. The absence of such a general effect in the current study may

97.8 0.5–64 1 1 97.0 0.5–64 1 1 97.7 0.5–64 1 1 98.0 0.5–32 1 1

MIC, minimum inhibitory concentration; S, susceptibility.

74.5 63.9 64.0 64.0 99.8 66.0 64.0 0.015–16 0.03 to ≥128 0.03 to ≥128 0.015 to ≥64 0.002–8 0.12 to ≥32 0.12 to ≥32 8 ≥128 ≥128 ≥64 0.12 ≥32 8 0.06 0.06 0.12 0.06 0.015 0.5 0.25 74.2 65.0 65.0 65.0 99.7 68.5 66.5 0.015–16 0.03 to ≥128 0.03 to ≥128 0.015 to ≥64 0.004–1 0.12 to ≥32 0.12 to ≥32 8 ≥128 ≥128 ≥64 0.12 ≥32 8 0.06 0.06 0.12 0.06 0.015 0.25 0.5 74.0 64.4 64.4 64.3 99.7 66.3 64.6 0.015–16 0.03 to ≥128 0.03 to ≥128 0.015 to ≥64 0.002–8 0.12 to ≥32 0.12 to ≥32 8 ≥128 ≥128 ≥64 0.12 ≥32 8 0.06 0.06 0.12 0.06 0.015 0.5 0.25 74.8 63.3 63.5 63.5 99.8 65.2 63.2 8 ≥128 ≥128 ≥64 0.12 ≥32 8 0.06 0.06 0.12 0.06 0.015 0.5 0.5

0.015–16 0.03 to ≥128 0.03 to ≥128 0.015 to ≥64 0.002–4 0.12 to ≥32 0.12 to ≥32

0.008–8 0.008–8 2 2 69.3 94.4 0.008–8 0.008–8 2 2 68.1 94.0 0.008–8 0.008–8 2 2 0.008–8 0.008–8 2 2 0.03 0.03

Penicillin Amoxicillin/ clavulanic acid Cefuroxime Erythromycin Azithromycin Clarithromycin Telithromycin Tetracycline Trimethoprim/ sulfamethoxazole Levofloxacin

MIC50

MIC90

Range

69.0 95.5

0.03 0.03

Range MIC90 MIC50

MIC (␮g/mL) S (%) MIC (␮g/mL)

0.03 0.03

Range MIC90 MIC50

MIC (␮g/mL) S (%)

>84 years (n = 726) 75–84 years (n = 2330) 65–74 years (n = 3590) Antibacterial

Table 1 In vitro activity and susceptibility rates for S. pneumoniae isolates collected from elderly patients during PROTEKT years 1–5

0.03 0.03

MIC90 MIC50

MIC (␮g/mL) S (%)

Total (n = 6646)

Range

68.7 94.8

S (%)

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reflect the absence of pneumococcal vaccination programmes in most of the countries participating in the PROTEKT global study. Genotyping analysis revealed the predominance of erm(B)- and mef(A)-mediated macrolide resistance mechanisms. Despite the different levels of erythromycin resistance conferred by these mechanisms, they both may be responsible for failures of macrolide therapy [8]. However, there is concern about changes in the prevalence of pneumococcal isolates with macrolide resistance mediated by both erm(B) and mef(A) [16]. The vast majority of erm(B) + mef(A) pneumococcal strains are clonal in nature and exhibit multiple resistance [16], and continued antibacterial resistance monitoring will be needed to monitor their spread among elderly patients. The global frequency of isolates expressing erm(B) + mef(A) varied between 3.7% in year 3 and 7.4% in year 5 and increased significantly between years 1 and 5. These isolates were not ubiquitous and were found at high frequencies in countries such as China, Russia, South Africa and South Korea. However, the prevalence of erm(B) + mef(A) isolates only increased significantly in Japan over time. This may be because the low number of erm(B) + mef(A) isolates in any one country limited the power of the observation. This may be a particular concern in the data from the USA, since relatively few US isolates were included in the PROTEKT global study. The majority of isolates from the USA were included in the PROTEKT US study. In this larger cohort, a significant increase in the prevalence of erm(B) + mef(A) isolates from elderly patients has been observed over time [17]. There was no evidence that antibacterial resistance rates differed between any of the three age subgroups examined in this study. However, rates of resistance varied considerably between different regions of the world; by far the highest rates were found among isolates collected in the Far East, where penicillin resistance, macrolide resistance and multiple resistance phenotypes were all more than double the respective global rates. The high rates of pneumococcal resistance to multiple antibacterial classes observed in this study may pose a serious challenge to the treatment of community-acquired RTIs in elderly patients and highlight the need for new agents to treat RTIs caused by S. pneumoniae. Of the agents tested in the current analysis, telithromycin exhibited the most potent in vitro activity, with an overall susceptibility rate of 99.8%. Resistance to telithromycin was found to be not only rare (8 of 6646 isolates) but also at a relatively low level (MIC ≤ 8 ␮g/mL). These findings are encouraging, especially given that telithromycin has been used clinically in Europe and other countries since 2001–2002. Likewise, levofloxacin also exhibited potent in vitro activity with an overall susceptibility rate of 97.8% during the period of the PROTEKT study, which postdates the introduction of this antibacterial. A potential issue with orally administered drugs such as telithromycin is oral availability and whether the

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pharmacodynamic profile results in clearance of bacteria responsible for community-acquired RTIs. Telithromycin has a higher oral availability than macrolides such as erythromycin and azithromycin, which is not influenced by age [9]. The telithromycin concentration achieved in the lower respiratory tract is higher than the MIC of common respiratory pathogens and it has been shown to be effective in treating community-acquired RTIs in clinical trials that included elderly patients [9]. In conclusion, the continuing high prevalence of resistance to commonly used antibacterials among S. pneumoniae strains isolated from elderly patients suggests that alternative and appropriate empirical first-line therapies may be required for treating community-acquired RTIs in the elderly. Funding: The PROTEKT global study is supported by sanofi-aventis. Editorial assistance was provided by the global publications support group of sanofi-aventis. Competing interests: Research grants from Wyeth and sanofi-aventis; consultancies from Novartis and Schering Plough (R.C.). Research grants and consultancy fees from sanofi-aventis related to telithromycin research, publications and presentations (D.J.F.). Ethical approval: Not required.

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