Sampling methods for the study of pneumococcal carriage: a systematic review

Streptococcus pneumoniae is an important pathogen worldwide. Accurate sampling of S. pneumoniae carriage is central to surveillance studies before and following conjugate vaccination programmes to combat pneumococcal disease. Any bias introduced during sampling will affect downstream recovery and typing. Many variables exist for the method of collection and initial processing, which can make inter-laboratory or international comparisons of data complex. In February 2003, a World Health Organisation working group published a standard method for the detection of pneumococcal carriage for vaccine trials to reduce or eliminate variability. We sought to describe the variables associated with the sampling of S. pneumoniae from collection to storage in the context of the methods recommended by the WHO and those used in pneumococcal carriage studies since its publication. A search of published literature in the online PubMed database was performed on the 1st June 2012, to identify published studies that collected pneumococcal carriage isolates, conducted after the publication of the WHO standard method. After undertaking a systematic analysis of the literature, we show that a number of differences in pneumococcal sampling protocol continue to exist between studies since the WHO publication. The majority of studies sample from the nasopharynx, but the choice of swab and swab transport media is more variable between studies. At present there is insufficient experimental data that supports the optimal sensitivity of any standard method. This may have contributed to incomplete adoption of the primary stages of the WHO detection protocol, alongside pragmatic or logistical issues associated with study design. Consequently studies may not provide a true estimate of pneumococcal carriage. Optimal sampling of carriage could lead to improvements in downstream analysis and the evaluation of pneumococcal vaccine impact and extrapolation to pneumococcal disease control therefore further in depth comparisons would be of value.

Prevalence of Streptococcus pneumoniae serotypes causing invasive and non-invasive disease in South East Asia: a review

BACKGROUND

Streptococcus pneumoniae is a major cause of bacterial infections resulting in significant morbidity and mortality worldwide. Currently, up to 13 serotypes are included in pneumococcal conjugate vaccines (PCVs). However, the serotype formulation of these vaccines was initially designed to protect children against serotypes most commonly causing invasive disease in North America, and may not reflect the serotype distribution across the world. Data regarding pneumococcal epidemiology from the other parts of the world, in particular South East Asia, has not been reviewed.

METHODS

This systematic literature review analyses published serotype data regarding S. pneumoniae isolates from South East Asian countries (defined as countries belonging to the Association of South East Asian Nations, ASEAN): Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand and Vietnam up to 3rd of March 2012.

RESULTS

Analysis of data from six ASEAN countries, from which information on pneumococcal serotypes was available, showed that the most common disease causing serotypes (in rank order) were 19F, 23F, 14, 6B, 1, 19A and 3. Serotype distribution of pneumococcal isolates was similar across the ASEAN region. Serotype level data was more commonly reported for pneumococcal isolates causing invasive pneumococcal disease than for those from non-invasive disease. Studies from Malaysia, Thailand and Singapore contributed the largest proportion of pneumococcal isolates, and serotype data, when compared to other ASEAN countries.

CONCLUSION

This review demonstrates that the majority of IPD causing serotypes in SE Asia are included in currently licensed PCVs. However, PCV's are included in the routine childhood immunisation schedule of only one of the ten countries included in this analysis. Our findings demonstrate the scarcity of information available on serotype prevalence and distribution of pneumococci in SE Asia.

Leukocyte telomere length is associated with high-risk plaques on virtual histology intravascular ultrasound and increased proinflammatory activity

OBJECTIVE

Leukocyte telomere length (LTL), a marker of cellular senescence, is inversely associated with cardiovascular events. However, whether LTL reflects plaque extent or unstable plaques, and the mechanisms underlying any association are unknown.

METHODS AND RESULTS

One hundred seventy patients with stable angina or acute coronary syndrome referred for percutaneous coronary intervention underwent 3-vessel virtual histology intravascular ultrasound; 30 372 mm of intravascular ultrasound pullback and 1096 plaques were analyzed. LTL was not associated with plaque volume but was associated with calcified thin-capped fibroatheroma (OR, 1.24; CI, 1.01-1.53; P=0.039) and total fibroatheroma numbers (OR, 1.19; CI, 1.02-1.39; P=0.027). Monocytes from coronary artery disease patients showed increased secretion of proinflammatory cytokines. To mimic leukocyte senescence, we disrupted telomeres and binding and expression of the telomeric protein protection of telomeres protein-1, inducing DNA damage. Telomere disruption increased monocyte secretion of monocyte chemoattractant protein-1, IL-6, and IL-1β and oxidative burst, similar to that seen in coronary artery disease patients, and lymphocyte secretion of IL-2 and reduced lymphocyte IL-10.

CONCLUSIONS

Shorter LTL is associated with high-risk plaque morphology on virtual histology intravascular ultrasound but not total 3-vessel plaque burden. Monocytes with disrupted telomeres show increased proinflammatory activity, which is also seen in coronary artery disease patients, suggesting that telomere shortening promotes high-risk plaque subtypes by increasing proinflammatory activity.

Molecular analysis of Streptococcus pneumoniae clones causing invasive disease in children in Singapore

Streptococcus pneumoniae remains a leading cause of serious paediatric disease. However, there are few published epidemiological data regarding invasive pneumococcal disease (IPD) in many countries in South East Asia, including Singapore. Baseline data for IPD are essential to inform policy regarding pneumococcal conjugate vaccine (PCV) use in Singapore. To our knowledge, this is the first study to use multilocus sequence typing (MLST) to investigate clonal relationships among Singaporean IPD isolates. We characterized 86 invasive pneumococci isolated from Singaporean children between 2001 and 2006 using serotyping and MLST. The objectives were to compare Singaporean MLST data to worldwide data and to assess serotype distribution in relation to current PCV formulations. We observed 50 sequence types (STs), a high proportion of which (n = 16) were novel STs. Despite the presence of these novel STs, serotype distribution was similar to that observed elsewhere. Serotypes 14, 6B, 19A and 19F accounted for 85 % of IPD cases. PCV7, PCV10 and PCV13 covered 85 %, 86 % and 97 % of IPD isolates, respectively. We have demonstrated a pressing need for larger studies to determine the molecular epidemiology and antibiotic susceptibility of circulating pneumococcal clones from both carriage and disease in Singapore.

Identification of novel pneumolysin alleles from paediatric carriage isolates of Streptococcus pneumoniae

Pneumolysin (Ply) is a major virulence factor of Streptococcus pneumoniae and is produced by all known clinical isolates of pneumococci. Pneumolysin toxoids are being considered as vaccine candidates. We investigated the diversity of pneumolysin among 194 nasopharyngeal pneumococci characterized by serotyping and multilocus sequence typing (MLST). Eight Ply protein alleles were identified, four of which were novel. The 4 novel alleles varied at 10 different amino acid positions, from a total of 147, 3 of these substitutions have been previously reported in different combinations. The protein allele correlated closely with MLST. It is critical that the presence of pneumolysin variants is considered with regards to the potential use of Ply in future vaccine formulations, as variation in Ply amino acid sequence may influence the immunogenicity of vaccines based on the presence of an individual Ply allele.

Cardiac Remote Ischemic Preconditioning in Coronary Stenting (CRISP Stent) Study: a prospective, randomized control trial

BACKGROUND

Myocyte necrosis as a result of elective percutaneous coronary intervention (PCI) occurs in approximately one third of cases and is associated with subsequent cardiovascular events. This study assessed the ability of remote ischemic preconditioning (IPC) to attenuate cardiac troponin I (cTnI) release after elective PCI.

METHODS AND RESULTS

Two hundred forty-two consecutive patients undergoing elective PCI with undetectable preprocedural cTnI were recruited. Subjects were randomized to receive remote IPC (induced by three 5-minute inflations of a blood pressure cuff to 200 mm Hg around the upper arm, followed by 5-minute intervals of reperfusion) or control (an uninflated cuff around the arm) before arrival in the catheter laboratory. The primary outcome was cTnI at 24 hours after PCI. Secondary outcomes included renal dysfunction and major adverse cardiac and cerebral event rate at 6 months. The median cTnI at 24 hours after PCI was lower in the remote IPC compared with the control group (0.06 versus 0.16 ng/mL; P=0.040). After remote IPC, cTnI was <0.04 ng/mL in 44 patients (42%) compared with 24 in the control group (24%; P=0.01). Subjects who received remote IPC experienced less chest discomfort (P=0.0006) and ECG ST-segment deviation (P=0.005) than control subjects. At 6 months, the major adverse cardiac and cerebral event rate was lower in the remote IPC group (4 versus 13 events; P=0.018).

CONCLUSIONS

Remote IPC reduces ischemic chest discomfort during PCI, attenuates procedure-related cTnI release, and appears to reduce subsequent cardiovascular events.

Remote ischemic preconditioning stimulus does not reduce microvascular resistance or improve myocardial blood flow in patients undergoing elective percutaneous coronary intervention

INTRODUCTION

Remote ischemic preconditioning (RIPC) may limit myocardial infarction by improving microvascular function and maintaining myocardial blood flow. We hypothesized that a RIPC stimulus would reduce coronary microvascular resistance and improve coronary blood flow during elective percutaneous coronary intervention (PCI).

METHOD

We prospectively recruited 54 patients with multi-vessel disease (MVD = 32) or single vessel disease awaiting elective PCI. Patients with MVD had non-target vessel (NTV) index of micro-circulatory resistance (IMR) determined, before and after target vessel (TV) PCI (cardiac RIPC). The effect of arm RIPC on serial microvascular resistance (R(p)) was assessed in patients with single vessel disease.

RESULTS

TV balloon occlusion did not alter the NTV IMR: 16.5 (12.4) baseline vs. 17.6 (11.6) post cardiac RIPC, P = 0.65 or hyperaemic transit time. Arm RIPC did not alter R( p) in patients with single vessel disease: Rp, mmHg.cm(-1).s( -1): 3.5 (1.9) baseline vs. 4.1 (3.0) post arm RIPC, P = 0.19 and coronary flow velocity remained constant.

CONCLUSION

RIPC stimuli during elective PCI do not affect coronary microvascular resistance or coronary flow in humans.

Dynamics of pneumococcal colonization in healthy Dutch children

A recent study of pneumococcal colonization in 3198 healthy children of 1-19 years of age in The Netherlands showed pneumococcal colonization in 19 % of the children, with a peak incidence of 55 % at the age of 2 years; an age-related serotype distribution was also found. In the present study, the genetic background and resistance profiles of 578 pneumococcal isolates from the latter study were characterized by means of chromosomal genotyping and susceptibility testing. In contrast to the age-related serotype distribution observed previously, the genetic background of the strains was not age related. Few strains were found showing close homology (>95 %) with the international clones Spain(9V)-3 (ten isolates showed homology), England(14)-9 (four isolates), Tennessee(23F)-4 (two isolates), CSR(14)-10 (one isolate) and Sweden(15A)-25 (one isolate). In total, 19 % of strains showed resistance to one or more antibiotics. Resistance to cotrimoxazole, tetracycline, erythromycin and penicillin was found in 12.9, 5.6, 5.0 and 2.7 % of isolates, respectively. Multidrug resistance was found in 1.9 % of strains. In conclusion, pneumococcal colonization isolates from healthy Dutch children represent a heterogeneous, mostly antibiotic susceptible, genetic population.

Proton NMR analysis of plasma is a weak predictor of coronary artery disease

Multivariate analysis of 1H-NMR spectra of blood sera was reported previously to predict angiographically defined advanced coronary artery disease (CAD) with >90% accuracy and specificity. The analysis depended mainly on the major lipid regions of the spectra, but many variables, including gender and drug treatment, affect lipid composition and are potential confounders. We have determined the predictive power of the same methodology for angiographically defined CAD using plasma samples from groups of male patients, classified by statin treatment, who had normal coronary arteries (NCAs) or CAD. Predictions for NCA and CAD groups were only 80.3% correct for patients not treated with statins and 61.3% for treated patients, compared with random correct predictions of 50%. A confidence limit of >99% was achieved for 36.2% of predictions for untreated groups and 6.2% for treated groups. Detection of CAD by 1H-NMR with >99% confidence was therefore very weak compared with angiography.

Distribution of epidemic antibiotic-resistant pneumococcal clones in Scottish pneumococcal isolates analysed by multilocus sequence typing

Sequence types of pneumococci isolated in Scotland between 1996 and 2003 were compared with those of globally prevalent antibiotic-resistant clones. Multilocus sequence typing was performed on 252 invasive pneumococcal isolates referred to the Scottish Meningococcus and Pneumococcus Reference Laboratory. Isolates were not preselected for antimicrobial resistance, patient age or disease caused. Sequence types were compared with globally significant antimicrobial-resistant clones identified by the Pneumococcal Molecular Epidemiology Network (PMEN). Sequence types identical with three of the 26 PMEN clones were present in the Scottish collection; the clones were the Spain9V-3 clone (sequence type 156, seven isolates), the England14-9 clone (sequence type 9, eight isolates) and the Utah35B-24 clone (sequence type 377, one isolate). Many Scottish isolates related to PMEN clones had lower antimicrobial MICs than those described for the corresponding PMEN type strain. A number of single- (SLVs) and double-locus variants (DLVs) were present. Fifteen SLVs related to PMEN sequence types 37, 67, 90, 81, 156, 236 and 377 were detected. The collection contained 10 DLVs related to PMEN sequence types 37, 156, 173 and 338. The majority of SLVs and DLVs were penicillin- or erythromycin-sensitive variants of the resistant PMEN type strains. Capsule switching in isolates related to the PMEN clones was also detected. The highest levels of penicillin resistance were detected in sequence type 320 (serotype 19F), which is not a PMEN clone. These data suggest that PMEN clones are not widely distributed in disease-causing isolates in Scotland.

Automation of MLST Using Third-Generation Liquid-Handling Technology

The molecular characterization of bacterial pathogens of clinical significance is increasingly important. Methods, such as multilocus sequence typing (MLST), allow bacterial strains to be characterized during case clusters, for antibiotic-resistant strains to be monitored, and for the impact of new vaccines to be assessed. Our laboratory performs MLST on Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. We have developed high-throughput automated methods to allow MLST to be performed in a time scale useful in a clinical setting. Here we describe the automation of MLST on a third-generation liquid-handling robot.

Circulating levels of MCP-1 and eotaxin are not associated with presence of atherosclerosis or previous myocardial infarction

The chemokines are a family of signalling proteins that participate in regulation of the immune system and have been implicated in the pathogenesis of vascular diseases. Deleting the gene encoding the chemokine MCP-1 in mouse models of atherosclerosis reduces lipid lesion formation and circulating chemokines are upregulated in man immediately following myocardial infarction (MI) or coronary angioplasty. We have therefore investigated whether circulating levels of two chemokines (MCP-1 and eotaxin) differ between subjects with and without atherosclerosis. We have used three different methods of measuring the presence and extent of atherosclerosis in human subjects: duplex ultrasonography of the carotid arteries and clinical diagnosis of coronary heart disease on individuals from the general population and coronary angiography on patients with suspected heart disease. There was no difference in the levels of circulating MCP-1 or eotaxin, measured by ELISA, between subjects with and without atherosclerosis. Furthermore, any increase in circulating MCP-1 following acute MI must be short-lived, since chemokine levels were not different in subjects who had had an MI previously compared to those who had not. We conclude that although there may be a transient increase in circulating chemokine levels following coronary angioplasty, there is no difference in the levels of circulating MCP-1 or eotaxin in subjects with and without atherosclerosis.

Truncated xpt gene present in invasive Streptococcus pneumoniae may have implications for MLST schemes

A serotype 1 disease-causing pneumococcus possessing a truncated xanthine phosphoribosyltransferase (xpt) housekeeping gene is described. The deletion is within the gene region used for multi-locus sequence typing (MLST) and may have occurred through genetic transformation or capsule switch between clones. The identification of this deletion in a clinical isolate therefore warrants highlighting due to potential errors that may ensue in isolate characterization and due to the fact that deletions may occur in other genes in this or other species characterized by MLST.

Clonal analysis of invasive pneumococcal isolates in Scotland and coverage of serotypes by the licensed conjugate polysaccharide pneumococcal vaccine: possible implications for UK vaccine policy

A 7-valent pneumococcal conjugate vaccine (PCV7) has gained licensure and has proven successful in the USA for preventing pneumococcal disease and reducing the incidence of antibiotic-resistant pneumococcal strains. The ability, therefore, to accurately monitor the likely effect of the introduction of PCV7 vaccine on invasive pneumococcal disease in the UK is essential. Serotyping and multilocus sequence typing was performed on invasive isolates of Streptococcus pneumoniae (n=645) from Scotland during 2003. The information gained from this was used to evaluate serotype coverage by the vaccine and the relationship between serotypes. In the present study, invasive pneumococcal disease in Scotland was caused by 33 different serotypes, consisting of 150 sequence types. Overall, 48.4% of the isolates were of serotypes included in the PCV7. Pneumococci were most frequently associated with sequence types 9, 124, and 162. PCV7 would provide protection in 71.8% of infants under 5 years of age against the serotypes in the vaccine. There was limited evidence of the potential for capsule switch among currently circulating invasive pneumococci. The successful implementation of a suitable vaccination programme should lead to a reduction in invasive pneumococcal disease in the UK as well as a reduction in antibiotic resistance of pneumococcal strains.