Antibiotic selection of multiply resistant pneumococci

Population structure, epidemiology and antibiotic resistance patterns of Streptococcus pneumoniae serotype 5: prior to PCV-13 vaccine introduction in Eastern Gambia

Background

Streptococcus pneumoniae serotype 5 is among the most common serotypes causing invasive pneumococcal disease (IPD) in The Gambia. We anticipate that introduction of the 13-valent pneumococcal conjugate vaccine (PCV-13) into routine vaccination in The Gambia will reduce serotype 5 IPD. However, the emergence of new clones that have altered their genetic repertoire through capsular switching or genetic recombination after vaccination with PCV-13 poses a threat to this public health effort. In order to monitor for potential genetic changes post-PCV-13 vaccination, we established the baseline population structure, epidemiology, and antibiotic resistance patterns of serotype 5 before the introduction of PCV-13.

Methods

Fifty-five invasive S. pneumoniae serotype 5 isolates were recovered from January 2009 to August 2011 in a population-based study in the Upper River Region of The Gambia. Serotyping was done by latex agglutination and confirmed by serotype-specific Polymerase Chain Reaction (PCR). Genotyping was undertaken using Multilocus Sequence Typing (MLST). Antimicrobial sensitivity was done using disc diffusion. Contingency table analyses were conducted using Pearson’s Chi² and Fisher’s exact test. Clustering was performed using Bionumerics version 6.5.

Results

MLST resolved S. pneumoniae serotype 5 isolates into 3 sequence types (ST), namely ST 289(6/55), ST 3339(19/55) and ST 3404(30/55). ST 289 was identified as the major clonal complex. ST 3339, the prevalent genotype in 2009 [84.6 % (11/13)], was replaced by ST 3404 [70.4 % (19/27)] in 2010 as the dominant ST. Interestingly, ST 3404 showed lower resistance to tetracycline and oxacillin (P < 0.001), an empirical surrogate to penicillin in The Gambia.

Conclusions

There has been an emergence of ST 3404 in The Gambia prior to the introduction of PCV-13. Our findings provide important background data for future assessment of the impact of PCV-13 into routine immunization in developing countries, such as The Gambia.

Risks of population antimicrobial resistance associated with chronic macrolide use for inflammatory airway diseases

Macrolide antibiotics have established efficacy in the management of cystic fibrosis and diffuse panbronchiolitis-uncommon lung diseases with substantial morbidity and the potential for rapid progression to death. Emerging evidence suggests benefits of maintenance macrolide treatment in more indolent respiratory diseases including chronic obstructive pulmonary disease and non-cystic fibrosis bronchiectasis. In view of the greater patient population affected by these disorders (and potential for macrolide use to spread to disorders such as chronic cough), widespread use of macrolides, particularly azithromycin, has the potential to substantially influence antimicrobial resistance rates of a range of respiratory microbes. In this Personal View, I explore theories around population (rather than patient) macrolide resistance, appraise evidence linking macrolide use with development of resistance, and highlight the risks posed by injudicious broadening of their use, particularly of azithromycin. These risks are weighed against the potential benefits of macrolides in less aggressive inflammatory airway disorders. A far-sighted approach to maintenance macrolide use in non-cystic fibrosis inflammatory airway diseases is needed, which minimises risks of adversely affecting community macrolide resistance: combining preferential use of erythromycin and restriction of macrolide use to those patients at greatest risk represents an appropriately cautious management approach.

Risk factors for multidrug-resistant invasive pneumococcal disease in South Africa, a setting with high HIV prevalence, in the prevaccine era from 2003 to 2008

The emergence of multidrug-resistant (MDR) Streptococcus pneumoniae complicates disease management. We aimed to determine risk factors associated with MDR invasive pneumococcal disease (IPD) in South Africa and evaluate the potential for vaccination to reduce disease burden. IPD data collected by laboratory-based surveillance from 2003 through 2008 were analyzed. Multidrug resistance was defined as nonsusceptibility to any three or more different antibiotic classes. Risk factors for multidrug resistance were evaluated using multivariable logistic regression. Of 20,100 cases of IPD identified, 3,708 (18%) had MDR isolates, with the proportion increasing from 16% (461/2,891) to 20% (648/3,326) (P < 0.001) over the study period. Serotypes included in the 13-valent pneumococcal conjugate vaccine (PCV13) accounted for 94% of MDR strains. Significant risk factors for MDR IPD included PCV13 (1,486/6,407; odds ratio [OR] of 6.3; 95% confidence interval [CI] of 5.0 to 7.9) and pediatric (3,382/9,980; OR of 12.8; 95% CI of 10.6 to 15.4) serotypes, age of <5 (802/3,110; OR of 2.0; 95% CI of 1.8 to 2.3) or ≥65 (39/239; OR of 1.5; 95% CI of 1.0 to 2.2) years versus age of 15 to 64 years, HIV infection (975/4,636; OR of 1.5; 95% CI of 1.2 to 1.8), previous antibiotic use (242/803; OR of 1.7; 95% CI of 1.4 to 2.1), previous hospital admissions (579/2,450; OR of 1.2; 95% CI of 1.03 to 1.4), urban location (883/4,375; OR of 2.0; 95% CI of 1.1 to 3.5), and tuberculosis treatment (246/1,021; OR of 1.2; 95% CI of 1.03 to 1.5). MDR IPD prevalence increased over the study period. The effect of many of the MDR risk factors could be reduced by more judicious use of antibiotics. Because PCV13 serotypes account for most MDR infections, pneumococcal vaccination may reduce the prevalence of multidrug resistance.

Intrinsic epidemicity of Streptococcus pneumoniae depends on strain serotype and antibiotic susceptibility pattern

Streptococcus pneumoniae is a major cause of invasive diseases worldwide. It spreads through an interindividual transmission, followed by usually harmless colonization of the host. Possible transmission differences reflecting intrinsic strain features (e.g., serotype and antibiotic susceptibility) have been little studied so far. In this study, we used epidemiological data from an interventional trial of S. pneumoniae carriage among kindergartners and developed a mathematical model to estimate the transmission parameters of the different strains isolated during that study. We found small but significant transmissibility differences between the observed serotypes: serotypes 3, 6A, and 19A were found to be the most epidemic, while serotypes 23F, 9V, and 14 were the least epidemic. Further analysis indicated that, within a serotype, susceptible and resistant strains had different abilities to be transmitted. Susceptible-to-resistant transmission rate ratios were computed for five serotypes; susceptible strains were significantly more epidemic than resistant strains for serotypes 6A (mean, 1.02) and 19F (1.05). Serotype 19A resistant strains were not outcompeted by susceptible strains (0.97). Nonsignificant trends were observed for serotypes 6B (1.01) and 15A (0.98). Our results support the existence of heterogeneous abilities of the different serotypes for host-to-host transmission. They also suggest that antibiotic susceptibility within a serotype affects this transmissibility. We conclude that pneumococcal strains should not be considered equally at-risk in terms of transmission. Further quantification of strain-specific epidemic potential is needed, especially in a context of extensive use of conjugate vaccines with the aim of preventing pneumococcal infections.

Ten years of surveillance for invasive Streptococcus pneumoniae during the era of antiretroviral scale-up and cotrimoxazole prophylaxis in Malawi

Objective

To document trends in invasive pneumococcal disease (IPD) in a central hospital in Malawi during the period of national scale-up of antiretroviral therapy (ART) and cotrimoxazole prophylaxis.

Methods

Between 1 January 2000 and 31 December 2009 almost 100,000 blood cultures and 40,000 cerebrospinal fluid (CSF) cultures were obtained from adults and children admitted to the Queen Elizabeth Central Hospital, Blantyre, Malawi with suspected severe bacterial infection.

Results

4,445 pneumococcal isolates were obtained over the 10 year period. 1,837 were from children: 885 (19.9%) from blood and 952 (21.4%) from CSF. 2,608 were from adults: 1,813 (40.8%) from blood and 795 (17.9%) from CSF. At the start of the surveillance period cotrimoxazole resistance was 73.8% and at the end was 92.6%. Multidrug resistance (MDR) was present in almost one third of isolates and was constant over time. Free ART was introduced in Malawi in 2004. From 2005 onwards there was a decline in invasive pneumococcal infections with a negative correlation between ART scale-up and the decline in IPD (Pearson's correlation r = −0.91; p<0.001).

Conclusion

During 2004–2009, national ART scale-up in Malawi was associated with a downward trend in IPD at QECH. The introduction of cotrimoxazole prophylaxis in HIV-infected groups has not coincided with a further increase in pneumococcal cotrimoxazole or multidrug resistance. These data highlight the importance of surveillance for high disease burden infections such as IPD in the region, which will be vital for monitoring pneumococcal conjugate vaccine introduction into national immunisation programmes.

Measuring acceptable treatment failure rates for community-acquired pneumonia: potential for reducing duration of treatment and antimicrobial resistance

OBJECTIVE

This study was designed to establish the rates of treatment failure for community-acquired pneumonia that are acceptable to knowledgeable and experienced physicians, in order to facilitate the interpretation of existing studies and the design of new studies aimed at optimizing the duration of antibiotic therapy. Reducing the duration of antibiotic therapy is one strategy for reducing antibiotic exposure and thereby minimizing the potential for the emergence of antimicrobial resistance.

DESIGN

Survey soliciting the acceptable failure rate for treatment given to an adult patient with uncomplicated community-acquired pneumonia treated with standard-of-care therapy in the outpatient setting. Analysis was performed using a modification of established methods of contingent valuation analysis.

PARTICIPANTS

Six hundred eighty infectious diseases physicians in North America who were also members of the Emerging Infections Network of the Infectious Diseases Society of America.

RESULTS

Three hundred seventy-five (55.1%) of 680 physicians responded to the survey. The median acceptable failure rate for treatment was 13.5%. Five hundred ten respondents (75.0%) found a failure rate of 7.3% acceptable, and 170 respondents (25.0%) found a failure rate of 19.8% acceptable.

CONCLUSIONS

This study identified the failure rates for treatment of community-acquired pneumonia that were acceptable to infectious disease physicians. This range of acceptable treatment failure rates may facilitate the design of studies aimed at optimizing the duration of antimicrobial therapy for community-acquired pneumonia.

Risk factors for development of multiple-class resistance to Streptococcus pneumoniae Strains in Belgium over a 10-year period: antimicrobial consumption, population density, and geographic location

We investigated the impact of the usage of antibiotics in ambulatory patients in Belgium in 147 defined geographical circumscriptions and at the individual isolate level. The study included 14,448 Streptococcus pneumoniae strains collected by the Belgium national reference lab from 1994 to 2004. Additional risk factors for resistance, such as population density/structure and day care attendance, were investigated for the same time-space window. A statistical model that included resistance to two or more antimicrobial classes offered the best fit for measuring the changes in nonsusceptibility to penicillin, macrolides, and tetracycline over time and place in Belgium. Analysis at the geographic level identified antimicrobial consumption with a 1-year lag (0.5% increase per additional defined daily dose) and population density as independent predictors of multiple resistance. Independent risk factors at the isolate level were age (odds ratio [OR], 1.55 for children aged <5 years), population density (7% increase in multiple resistance per 100 inhabitants/km(2)), conjugate 7-valent vaccine serotype (OR, 14.3), location (OR, 1.55 for regions bordering high-resistance France), and isolate source (OR, 1.54 for ear isolates). The expansion of multiple-resistant strains explains most of the overall twofold increase and subsequent decrease in single antimicrobial resistance between 1994 and 2004. We conclude that factors in addition to antibiotic use, such as high population density and proximity to high-resistance regions, favor multiple resistance. Regional resistance rates are not linearly related to actual antibiotic use but are linked to past antibiotic use plus a combination of demographic and geographic factors.

Bacteraemic pneumococcal pneumonia: Impact of HIV on clinical presentation and outcome

OBJECTIVES

The objectives of this study were to investigate the clinical and laboratory features, hospital course and outcome of patients with bacteraemic pneumococcal pneumonia, comparing HIV with non-HIV patients, as well as HIV patients from different parts of the world.

METHODS

This was a multicentre prospective observational study of consecutive adult cases with bacteraemic pneumococcal pneumonia in 10 countries on 6 continents.

RESULTS

A total of 768 cases were recruited, of which 200 were HIV-infected; 166 were from South Africa. Lower age, i.v. drug use, fewer co-morbid illnesses, and a higher frequency of respiratory symptoms were significantly more likely to occur in HIV patients. The 14-day mortality for the group as a whole was 14.5%, being 16% in the HIV patients and 13.9% in the non-HIV patients (not significant). When adjustments were made for age and severity of illness, HIV patients had significantly higher 14-day mortality with significant trend for increasing 14-day mortality in those with lower CD4 counts. Despite differences in various clinical and laboratory parameters in patients from different parts of the world, on multivariate analysis, when adjusting for regional differences, the HIV-infected patients were still noted to have poorer 14-day mortality.

CONCLUSIONS

This study, in contrast to previous investigations, indicates that there are significant differences in the clinical presentation and outcome of bacteraemic pneumococcal pneumonia when comparing HIV and non-HIV patients.

Serotype and antimicrobial susceptibility patterns of isolates of Streptococcus pneumoniae causing invasive disease in The Gambia 1996-2003

OBJECTIVES

To describe the characteristics of pneumococcal isolates obtained from patients with invasive pneumococcal disease in The Gambia.

METHODS

Pneumococcal isolates were obtained from children aged < or =6 years with invasive pneumococcal disease during a Haemophilus influenzae vaccine effectiveness study (1997-2002) and from patients with invasive pneumococcal disease admitted to the MRC hospital, Fajara, for routine care (1996-2003). Isolates were identified, serotyped and tested for antibiotic susceptibility.

RESULTS

Five hundred and thirty one pneumococcal isolates were obtained from 518 patients; 55 (10.6%) patients died; 415 isolates (79%) were from blood culture, 84 (16%) from CSF, and 42 (8%) from lung aspirates. Forty serogroups and serotypes were identified; six accounted for 64% and 16 for 86% of all episodes; 33.7% were of serotypes 1 and 5. 23.5% were of a 7-valent vaccine serotype, 57.1% were of a 9-valent vaccine serotype; 56% were of a 7-valent serogroup and 78% were of a 9-valent serogroup. There was a significant increase in the proportion of isolates of non-vaccine serogroup with increasing age (P < 0.0001). Antibiotic resistance had not significantly increased over time; but intermediate non-susceptibility to penicillin had risen and resistance to chloramphenicol had fallen in isolates of vaccine serotype compared with those of non-vaccine serotype.

CONCLUSIONS

The majority of invasive pneumococcal disease in The Gambia is caused by pneumococci of relatively few serogroups. A conjugate vaccine would be expected to reduce the pneumococcal disease burden substantially and to have a beneficial effect on pneumococcal antibiotic resistance to penicillins.

Pneumococcal conjugate vaccines—a European perspective

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. In the age group of < 2 years the incidence of invasive pneumococcal disease ranges from approximately 14 cases per 100,000 in Germany and the Netherlands and more than 90 per 100,000 children in Spain. The vulnerability of children to S. pneumoniae can also be demonstrated by the high rate of sequelae (> 20% in Germany) and the high mortality (7.5%) in pneumococcal meningitis. Furthermore, antibiotic resistance of S. pneumoniae is increasing in Europe, particularly in France, Spain, and Eastern European countries, whereas Germany and Northern Europe are only marginally affected. A 7-valent pneumococcal conjugate vaccine (7vPCV) that was shown to be highly efficacious in preventing invasive pneumococcal disease in infants in the USA was licensed in Europe in 2001. It is expected that broad usage of the vaccine would reduce the incidence of invasive pneumococcal disease and the levels of pneumococcal resistance significantly. Important questions have been raised regarding the effectiveness of this vaccine in high-risk populations, serotype replacement, the efficacy of this vaccine in otitis media, and the co-administration of the new vaccine with other standard childhood vaccines used in various European countries. France and Spain currently have the most-wide ranging guidelines recommending pneumococcal vaccination for children. Overall, the development of pneumococcal conjugate vaccines is a significant step in the control of pneumococcal disease in children in Europe. Further progress in pneumococcal vaccine development can be expected from conjugate vaccines including more than seven serotypes (9-valent, 11-valent).

Antibiotic Resistance in Streptococcus pneumoniae: What Does the Future Hold?

The recent emergence of strains of drug-resistant Streptococcus pneumoniae (DRSP) is a serious clinical and public health problem. Several interventions have been proposed to limit the further emergence and spread of DRSP, including campaigns for appropriate antibiotic use and the introduction of pneumococcal conjugate vaccines. Whether the current epidemic of drug resistance in S. pneumoniae is sustainable or will succumb to current efforts to limit its spread will be decided by an interaction of factors related to the pathogen (i.e., the relative fitness of the resistant strains), to the prescription of antibiotic treatment (i.e., changes in selection pressure), and to the host (i.e., the ability to slow the transmission of DRSP). Much investigation is still needed to better ascertain how maintenance of DRSP strains in the community at large is influenced by each factor and affected by current interventions that are based on these factors.

¿Cuál es la importancia de la erradicación bacteriana en el tratamiento de la infección respiratoria?

During the last few years, increasing antibiotic resistance amongst the major respiratory pathogens in the community has compromised the choice of empirical therapy for some respiratory tract infections. Of special interest has been the progressive increase in the resistance rates of Streptococcus pneumoniae to macrolides and penicillin, and of S. pyogenes to macrolides. Several studies have confirmed the association between community use of certain antibiotics and the development of resistance in S. pneumoniae and S. pyogenes. Nevertheless, not all the antibiotics have the same ability to select resistance and not all microorganisms are affected in the same way. The aim of antimicrobial therapy in respiratory tract infections is bacterial eradication. Pharmacokinetic and pharmacodynamics can be used to predict bacteriological eradication with antimicrobial therapy.

Typing and Molecular Characterization ofStreptococcus pneumoniaewith Reduced Susceptibility to Cefotaxime Isolated in Latin America

The treatment of systemic infections, especially meningitis, caused by Streptococcus pneumoniae nonsusceptible to third-generation cephalosporins, is extremely difficult due to the paucity of therapeutic options. The main objective of this study was to characterize isolates of S. pneumoniae with reduced susceptibility to cefotaxime (MICs, > or = 1 microg/ml) by different typing methods and to evaluate whether clonal dissemination of this pathogen had occurred among Latin American medical centers. A total of 46 isolates collected from respiratory tract specimens, blood cultures, cerebrospinal fluid, eye, and other sources were analyzed. The isolates were collected from Latin American medical centers located in Argentina, Brazil, Chile, Colombia, Mexico, and Uruguay through two multicenter surveillance programs, in 1997 and 1998. Isolates were serotyped and molecular typed by pulsed-field gel electrophoresis (PFGE) and automated ribotyping. Antimicrobial susceptibilities were determined to 19 drugs by reference broth microdilution methods. Ten isolates (21.7%) had cefotaxime MICs > or = 2 microg/ml, whereas 36 (78.3%) had cefotaxime MIC results at 1 microg/ml. All isolates were susceptible to gatifloxacin, levofloxacin, and vancomycin. The isolates were distributed among five major serotypes (%): 23F (39.1%), 14 (32.6%), 19F (23.9%), 9V (2.2%), and 6B (2.2%). However, distinct molecular patterns were detected among isolates with a unique serotype. Six and four PFGE patterns were identified among isolates with serotype 23F and 19F, respectively. When PFGE and automated ribotyping analyses were combined, four clusters were identified. The largest cluster (10 isolates) was represented by isolates with ribotype 18-2, major PFGE pattern I, and serotype 14. ATCC 700671 (international clone Spain 9V-3) also showed ribotype 18-2. This clone was detected in four countries: Argentina, Brazil, Chile, and Uruguay. A second cluster (8 isolates) were characterized by isolates with ribotype 17-4, PFGE type D, and serotype 23F, similar to ATCC 700669 (international clone Spain23F-1). Isolates from this cluster were identified in three countries: Brazil, Chile, and Mexico. Our results indicated that clonal dissemination of S. pneumoniae with reduced susceptibility to cefotaxime has occurred in Latin America mainly among serogroups 14, 19F, and 23F.

Drug-resistant Streptococcus pneumoniae in Community-acquired Pneumonia

The emergence of Streptococcus pneumoniae isolates resistant to not only penicillin, but to other antipneumococcal agents as well, has major public health implications. Drug-resistant S. pneumoniae are distributed worldwide, and resistance has become increasingly prevalent in the United States within the past decade. The relevance of resistance, particularly to the beta-lactams, to treatment outcome has been subject to debate. Pneumonia due to intermediate-level-resistant penicillin-resistant isolates of S. pneumoniae appears to be adequately treated by beta-lactam agents. Interpretation of resistance reports, which may be based on achievable cerebrospinal fluid levels of drug, may depend on the clinical setting, and efforts are underway to adjust breakpoints so that reports are more easily applicable to clinical practice. Infectious Diseases Society of America and American Thoracic Society guidelines, as well as others, for community-acquired pneumonia have addressed the impact of drug-resistant S. pneumoniae on antimicrobial selection.

Outpatient antibiotic use and prevalence of antibiotic-resistant pneumococci in France and Germany: a sociocultural perspective

The prevalence of penicillin-nonsusceptible pneumococci is sharply divided between France (43%) and Germany (7%). These differences may be explained on different levels: antibiotic-prescribing practices for respiratory tract infections; patient-demand factors and health-belief differences; social determinants, including differing child-care practices; and differences in regulatory practices. Understanding these determinants is crucial for the success of possible interventions. Finally, we emphasize the overarching importance of a sociocultural approach to preventing antibiotic resistance in the community.

Antimicrobial resistance among clinical isolates of Streptococcus pneumoniae in Canada during 2000

A total of 2,245 clinical isolates of Streptococcus pneumoniae were collected from 63 microbiology laboratories from across Canada during 2000 and characterized at a central laboratory. Of these isolates, 12.4% were not susceptible to penicillin (penicillin MIC, >or=0.12 microg/ml) and 5.8% were resistant (MIC, >or=2 microg/ml). Resistance rates among non-beta-lactam agents were the following: macrolides, 11.1%; clindamycin, 5.7%; chloramphenicol, 2.2%; levofloxacin, 0.9%; gatifloxacin, 0.8%; moxifloxacin, 0.4%; and trimethoprim-sulfamethoxazole, 11.3%. The MICs at which 90% of the isolates were inhibited (MIC90s) of the fluoroquinolones were the following: gemifloxacin, 0.03 microg/ml; BMS-284756, 0.06 microg/ml; moxifloxacin, 0.12 microg/ml; gatifloxacin, 0.25 microg/ml; levofloxacin, 1 microg/ml; and ciprofloxacin, 1 microg/ml. Of 578 isolates from the lower respiratory tract, 21 (3.6%) were inhibited at ciprofloxacin MICs of >or=4 microg/ml. None of the 768 isolates from children were inhibited at ciprofloxacin MICs of >or=4 microg/ml, compared to 3 of 731 (0.6%) from those ages 15 to 64 (all of these >60 years old), and 27 of 707 (3.8%) from those over 65. The MIC90s for ABT-773 and telithromycin were 0.015 microg/ml for macrolide-susceptible isolates and 0.12 and 0.5 microg/ml, respectively, for macrolide-resistant isolates. The MIC of linezolid was <or=2 microg/ml for all isolates. Many of the new antimicrobial agents tested in this study appear to have potential for the treatment of multidrug-resistant strains of pneumococci.

The rise and fall of antimicrobial resistance

Antimicrobial resistance is a growing problem in nearly every infectious disease, but the extent and rate of increase of the problem varies widely with different pathogen-drug combinations. The rate of increase of resistance depends primarily on the availability of resistant variants and the intensity of selection imposed by antimicrobial treatment (appropriately measured). Declines in resistance following antimicrobial control measures are typically faster in hospital-acquired infections than in community-acquired ones, probably owing to the dependence in the latter case on the fitness cost of resistance. Open questions and approaches for testing the hypotheses proposed here are outlined.