David P. J. Turner

Clinical Impact of Antimicrobial Resistance in European Hospitals: Excess Mortality and Length of Hospital Stay Related to Methicillin-Resistant Staphylococcus aureus Bloodstream Infections

ABSTRACT Antimicrobial resistance is threatening the successful management of nosocomial infections worldwide. Despite the therapeutic limitations imposed by methicillin-resistant Staphylococcus aureus (MRSA), its clinical impact is still debated. The objective of this study was to estimate the excess mortality and length of hospital stay (LOS) associated with MRSA bloodstream infections (BSI) in European hospitals. Between July 2007 and June 2008, a multicenter, prospective, parallel matched-cohort study was carried out in 13 tertiary care hospitals in as many European countries. Cohort I consisted of patients with MRSA BSI and cohort II of patients with methicillin-susceptible S. aureus (MSSA) BSI. The patients in both cohorts were matched for LOS prior to the onset of BSI with patients free of the respective BSI. Cohort I consisted of 248 MRSA patients and 453 controls and cohort II of 618 MSSA patients and 1,170 controls. Compared to the controls, MRSA patients had higher 30-day mortality (adjusted odds ratio [aOR] = 4.4) and higher hospital mortality (adjusted hazard ratio [aHR] = 3.5). Their excess LOS was 9.2 days. MSSA patients also had higher 30-day (aOR = 2.4) and hospital (aHR = 3.1) mortality and an excess LOS of 8.6 days. When the outcomes from the two cohorts were compared, an effect attributable to methicillin resistance was found for 30-day mortality (OR = 1.8; P = 0.04), but not for hospital mortality (HR = 1.1; P = 0.63) or LOS (difference = 0.6 days; P = 0.96). Irrespective of methicillin susceptibility, S. aureus BSI has a significant impact on morbidity and mortality. In addition, MRSA BSI leads to a fatal outcome more frequently than MSSA BSI. Infection control efforts in hospitals should aim to contain infections caused by both resistant and susceptible S. aureus.

Effect of a quadrivalent meningococcal ACWY glycoconjugate or a serogroup B meningococcal vaccine on meningococcal carriage: an observer-blind, phase 3 randomised clinical trial

BACKGROUND Meningococcal conjugate vaccines protect individuals directly, but can also confer herd protection by interrupting carriage transmission. We assessed the effects of meningococcal quadrivalent glycoconjugate (MenACWY-CRM) or serogroup B (4CMenB) vaccination on meningococcal carriage rates in 18-24-year-olds. METHODS In this phase 3, observer-blind, randomised controlled trial, university students aged 18-24 years from ten sites in England were randomly assigned (1:1:1, block size of three) to receive two doses 1 month apart of Japanese Encephalitis vaccine (controls), 4CMenB, or one dose of MenACWY-CRM then placebo. Participants were randomised with a validated computer-generated random allocation list. Participants and outcome-assessors were masked to the treatment group. Meningococci were isolated from oropharyngeal swabs collected before vaccination and at five scheduled intervals over 1 year. Primary outcomes were cross-sectional carriage 1 month after each vaccine course. Secondary outcomes included comparisons of carriage at any timepoint after primary analysis until study termination. Reactogenicity and adverse events were monitored throughout the study. Analysis was done on the modified intention-to-treat population, which included all enrolled participants who received a study vaccination and provided at least one assessable swab after baseline. This trial is registered with ClinicalTrials.gov, registration number NCT01214850. FINDINGS Between Sept 21 and Dec 21, 2010, 2954 participants were randomly assigned (987 assigned to control [984 analysed], 979 assigned to 4CMenB [974 analysed], 988 assigned to MenACWY-CRM [983 analysed]); 33% of the 4CMenB group, 34% of the MenACWY-CRM group, and 31% of the control group were positive for meningococcal carriage at study entry. By 1 month, there was no significant difference in carriage between controls and 4CMenB (odds ratio 1·2, 95% CI 0·8-1·7) or MenACWY-CRM (0·9, [0·6-1·3]) groups. From 3 months after dose two, 4CMenB vaccination resulted in significantly lower carriage of any meningococcal strain (18·2% [95% CI 3·4-30·8] carriage reduction), capsular groups BCWY (26·6% [10·5-39·9] carriage reduction), capsular groups CWY (29·6% [8·1-46·0] carriage reduction), and serogroups CWY (28·5% [2·8-47·5] carriage reduction) compared with control vaccination. Significantly lower carriage rates were also noted in the MenACWY-CRM group compared with controls: 39·0% (95% CI 17·3-55·0) carriage reduction for serogroup Y and 36·2% (15·6-51·7) carriage reduction for serogroup CWY. Study vaccines were generally well tolerated, with increased rates of transient local injection pain and myalgia in the 4CMenB group. No safety concerns were identified. INTERPRETATION Although we detected no significant difference between groups at 1 month after vaccine course, MenACWY-CRM and 4CMenB vaccines reduced meningococcal carriage rates during 12 months after vaccination and therefore might affect transmission when widely implemented. FUNDING Novartis Vaccines.

The moonlighting protein fructose-1, 6-bisphosphate aldolase of Neisseria meningitidis: surface localization and role in host cell adhesion

Fructose‐1, 6‐bisphosphate aldolases (FBA) are cytoplasmic glycolytic enzymes, which despite lacking identifiable secretion signals, have also been found localized to the surface of several bacteria where they bind host molecules and exhibit non‐glycolytic functions. Neisseria meningitidis is an obligate human nasopharyngeal commensal, which has the capacity to cause life‐threatening meningitis and septicemia. Recombinant native N. meningitidis FBA was purified and used in a coupled enzymic assay confirming that it has fructose bisphosphate aldolase activity. Cell fractionation experiments showed that meningococcal FBA is localized both to the cytoplasm and the outer membrane. Flow cytometry demonstrated that outer membrane‐localized FBA was surface‐accessible to FBA‐specific antibodies. Mutational analysis and functional complementation was used to identify additional functions of FBA. An FBA‐deficient mutant was not affected in its ability to grow in vitro, but showed a significant reduction in adhesion to human brain microvascular endothelial and HEp‐2 cells compared to its isogenic parent and its complemented derivative. In summary, FBA is a highly conserved, surface exposed protein that is required for optimal adhesion of meningococci to human cells.

The role of glyceraldehyde 3-phosphate dehydrogenase (GapA-1) in Neisseria meningitidis adherence to human cells

BackgroundGlyceraldehyde 3-phosphate dehydrogenases (GAPDHs) are cytoplasmic glycolytic enzymes, which although lacking identifiable secretion signals, have also been found localized to the surface of several bacteria (and some eukaryotic organisms); where in some cases they have been shown to contribute to the colonization and invasion of host tissues. Neisseria meningitidis is an obligate human nasopharyngeal commensal which can cause life-threatening infections including septicaemia and meningitis. N. meningitidis has two genes, gapA-1 and gapA-2, encoding GAPDH enzymes. GapA-1 has previously been shown to be up-regulated on bacterial contact with host epithelial cells and is accessible to antibodies on the surface of capsule-permeabilized meningococcal cells. The aims of this study were: 1) to determine whether GapA-1 was expressed across different strains of N. meningitidis; 2) to determine whether GapA-1 surface accessibility to antibodies was dependant on the presence of capsule; 3) to determine whether GapA-1 can influence the interaction of meningococci and host cells, particularly in the key stages of adhesion and invasion.ResultsIn this study, expression of GapA-1 was shown to be well conserved across diverse isolates of Neisseria species. Flow cytometry confirmed that GapA-1 could be detected on the cell surface, but only in a siaD-knockout (capsule-deficient) background, suggesting that GapA-1 is inaccessible to antibody in in vitro-grown encapsulated meningococci. The role of GapA-1 in meningococcal pathogenesis was addressed by mutational analysis and functional complementation. Loss of GapA-1 did not affect the growth of the bacterium in vitro. However, a GapA-1 deficient mutant showed a significant reduction in adhesion to human epithelial and endothelial cells compared to the wild-type and complemented mutant. A similar reduction in adhesion levels was also apparent between a siaD-deficient meningococcal strain and an isogenic siaD gapA-1 double mutant.ConclusionsOur data demonstrates that meningococcal GapA-1 is a constitutively-expressed, highly-conserved surface-exposed protein which is antibody-accessible only in the absence of capsule. Mutation of GapA-1 does not affect the in vitro growth rate of N. meningitidis, but significantly affects the ability of the organism to adhere to human epithelial and endothelial cells in a capsule-independent process suggesting a role in the pathogenesis of meningococcal infection.

Persistence, Replacement, and Rapid Clonal Expansion of Meningococcal Carriage Isolates in a 2008 University Student Cohort

ABSTRACT A study of meningococcal carriage dynamics was performed with a cohort of 190 first-year students recruited from six residential halls at Nottingham University, United Kingdom. Pharyngeal swabs were obtained on four occasions between November 2008 and May 2009. Direct plating and culture on selective media were succeeded by identification and characterization of meningococci using PCR-based methodologies. Three serogroup Y clones and one serogroup 29E clone were highly prevalent in particular residential halls in November 2008, which is indicative of rapid clonal expansion since the start of the academic year. Persistent carriage of the same meningococcal strain for at least 5 to 6 months was observed in 45% of carriers, with infrequent evidence of antigenic variation in PorA. Sequential carriage of heterologous meningococcal strains occurred in 36% of carriers and involved strains with different capsules and antigenic variants of PorA and FetA in 83% of the cases. These clonal replacement strains also exhibited frequent differences in the presence and antigenic structures of two other surface proteins, NadA and HmbR. This study highlights the low level of antigenic variation associated with persistent carriage but, conversely, the importance of alterations in the repertoire of antigenic variants for sequential carriage of meningococcal strains. Rapid clonal expansion of potentially pathogenic strains in residential halls has implications for the implementation of public health interventions in university populations.

Influence of the combination and phase variation status of the haemoglobin receptors HmbR and HpuAB on meningococcal virulence.

Neisseria meningitidis can utilize haem, haemoglobin and haemoglobin–haptoglobin complexes as sources of iron via two TonB-dependent phase variable haemoglobin receptors, HmbR and HpuAB. HmbR is over-represented in disease isolates, suggesting a link between haemoglobin acquisition and meningococcal disease. This study compared the distribution of HpuAB and phase variation (PV) status of both receptors in disease and carriage isolates. Meningococcal disease (n = 214) and carriage (n = 305) isolates representative of multiple clonal complexes (CCs) were investigated for the distribution, polyG tract lengths and ON/OFF status of both haemoglobin receptors, and for the deletion mechanism for HpuAB. Strains with both receptors or only hmbR were present at similar frequencies among meningococcal disease isolates as compared with carriage isolates. However, >90 % of isolates from the three CCs CC5, CC8 and CC11 with the highest disease to carriage ratios contained both receptors. Strains with an hpuAB-only phenotype were under-represented among disease isolates, suggesting selection against this receptor during systemic disease, possibly due to the receptor having a high level of immunogenicity or being inefficient in acquisition of iron during systemic spread. Absence of hpuAB resulted from either complete deletion or replacement by an insertion element. In an examination of PV status, one or both receptors were found in an ON state in 91 % of disease and 71 % of carriage isolates. We suggest that expression of a haemoglobin receptor, either HmbR or HpuAB, is of major importance for systemic spread of meningococci, and that the presence of both receptors contributes to virulence in some strains.

Carriage of meningococci by university students, United Kingdom.

To the Editor: Neisseria meningitidis causes septicemia and meningitis (1). Meningococci usually persist on the nasopharyngeal mucosa of asymptomatic carriers (2). Because carriers are the only reservoir of meningococci, carriage in at-risk populations should be monitored. Meningococcal carriage rates have been assessed during 1997–8 for first-year students at the University of Nottingham (3) and in autumn during 1999–2001 for >48,000 sixth-form students (pre-university, age range 15–17 years) throughout the United Kingdom (4). Serogroup B and nongroupable strains predominated; serogroup Y strains were found in only 1%–2% of participants. From November 2008 through May 2009, to investigate persistence and spread of meningococcal strains in students living in dormitories, we conducted a longitudinal study in a cohort of 190 first-year students at the University of Nottingham. We found high rates of carriage and prevalence of serogroup Y strains (5). During September 2009 (first week of term) through March 2010, we conducted a large repeated cross-sectional study analyzing pharyngeal swabs from students in all school-year groups at Nottingham University. The objective of this study was to determine the significance of changes in overall meningococcal and serogroup Y-specific carriage rates among students. In September, first-year students were recruited on the main campus during registration and subsequently in dormitories and the main library. Undergraduates not in the first year were all recruited in the main library. This September sample of 823 first-year students represents 16.5% of the 5,000 undergraduate students registered each academic year on the main campus. Although not intentional, some overlap occurred when students were resampled during subsequent visits to the same dormitories and library, e.g., among the 557 first-year students from whom swab samples were collected in December, 74 (13%) had previously provided swab samples. Our study was approved by the Nottingham University Medical School Ethics Committee, and written informed consent was obtained from all participants. Pharyngeal swab samples were spread onto GC selective agar (Oxoid, Basingstoke, UK) and incubated at 37°C in air containing 5% CO2. After 48 hours, colonies suggestive of Neisseria spp. were examined for positive oxidase reaction; single colonies were confirmed as meningococci by amplification of meningococcal genes crgA plus ctrA and/or porA (6). PCR-based serogrouping was performed as described (6,7). Chi-square tests for significance were performed by using STATCALC (Epi Info version 6.04; Centers for Disease Control and Prevention, Atlanta, GA, USA). Among first-year students, carriage rates increased from 23.2% in late September to 55.7% by mid-December and remained at a similar level in March (Table). Among second- and third-year students, carriage rates were 34.2% and 30.5% in September, respectively, and remained at similar levels throughout the academic year. The increase in carriage among first-year students from September through December was mainly the result of a significant (23%) increase in carriage of serogroup Y strains (Table). In contrast, during the same period, carriage rates of serogroup Y strains did not change significantly among second- and third-year students (Table). Table Characteristics of meningococci carriage, University of Nottingham students, United Kingdom, 2009–10* Initial carriage rates were significantly higher for incoming (first-year) students in September 2009 than in 1997 (13.9% [3]; χ2 = 14, 1 df; p<0.0001); swabbing and culture protocols and sampling sites were identical in both studies, so the increases are real. Because 83% of students at Nottingham University come from all regions of the United Kingdom and 17% from other countries, the increased rates of carriage may reflect a nationwide change (8). Furthermore, testing within the first week of term meant that recovered strains were predominately brought into the university. Serogroup Y carriage rates for incoming students (2.9%) were significantly higher than rates detected by identical genotyping methods during 1999–2001 (1.7%–1.8% [4]; χ2 = 4.6%–6.4%, 1 df; p<0.05), suggesting that meningococcal carriage by young adults, particularly of serogroup Y strains, has increased across the United Kingdom. The major increase in serogroup Y strains among first-year students during 2009–10 probably resulted from spread of clones within dormitories, as observed in the 2008–9 study (5) and may be facilitated by characteristics of the organism, lack of immunity, or a combination of these factors. The high prevalence of serogroup Y strains in carriers may help explain the recent increased incidence of serogroup Y disease in the United Kingdom: from 20 to 62 laboratory-confirmed cases in England and Wales from 2003 through 2009 (9). In the United States during the late 1990s, a similar increase in serogroup Y carriage was linked to a concomitant increase in serogroup Y disease (10). In conclusion, in a representative UK student cohort we detected high rates of carriage and elevated prevalence of serogroup Y strains of meningococci. Any further significant increase in serogroup Y disease should lead to prompt reconsideration of the current vaccine policy in the United Kingdom.

Clinical experience with the meningococcal B vaccine, Bexsero(®): Prospects for reducing the burden of meningococcal serogroup B disease.

Although rare, invasive meningococcal disease remains an important cause of mortality and morbidity in children and young adults. Vaccines have been successfully introduced to help protect against meningococcal disease caused by serogroups A, C, W and Y, but until recently, a vaccine for serogroup B (MenB) was not available. In many industrialised countries, MenB causes the majority of meningococcal disease. Moreover, MenB outbreaks occur unpredictably, particularly in high-risk populations, such as university students. In 2013, Bexsero(®) became the first broad-coverage vaccine to be licensed for active immunisation against MenB disease. Bexsero is now licensed in more than 35 countries worldwide for varying age groups, including the EU, Australia, Brazil, Canada, Chile, Uruguay and the USA. Clinical recommendations for the use of Bexsero have been published in several countries. Recommendations include use in high-risk groups, outbreak control and routine infant immunisation. Since initial licensure, considerable clinical experience has been gained. In Canada, 43,740 individuals received Bexsero during a vaccination programme in the Saguenay-Lac-Saint-Jean region of Quebec, where local disease incidence was high. In the USA, Bexsero was administered to >15,000 individuals during two college outbreaks prior to licensure, under an Investigational New Drug protocol. In the UK, the Joint Committee on Vaccination and Immunisation has recommended the inclusion of Bexsero in the routine immunisation schedule for infants. Publically funded vaccination programmes have been initiated in Italy, and there has been widespread use of the vaccine outside of publically reimbursed programmes. Overall, >1,000,000 doses of Bexsero have been distributed in 19 countries worldwide since 2013. The emerging clinical experience with Bexsero is consistent with findings from pre-licensure clinical studies, and no new safety concerns have been identified. Additional data on length of protection, potential impact on meningococcal carriage and transmission and strain coverage have also been published and will be reviewed.

Validation of Virulence and Epidemiology DNA Microarray for Identification and Characterization of Staphylococcus aureus Isolates

ABSTRACT The human pathogen Staphylococcus aureus is isolated and characterized using traditional culture and sensitivity methodologies that are slow and offer limited information on the organism. In contrast, DNA microarray technology can provide detailed, clinically relevant information on the isolate by detecting the presence or absence of a large number of virulence-associated genes simultaneously in a single assay. We have developed and validated a novel, cost-effective multiwell microarray for the identification and characterization of Staphylococcus aureus. The array comprises 84 gene targets, including species-specific, antibiotic resistance, toxin, and other virulence-associated genes, and is capable of examining 13 different isolates simultaneously, together with a reference control strain. Analysis of S. aureus isolates whose complete genome sequences have been determined (Mu50, N315, MW2, MRSA252, MSSA476) demonstrated that the array can reliably detect the combination of genes known to be present in these isolates. Characterization of a further 43 S. aureus isolates by the microarray and pulsed-field gel electrophoresis has demonstrated the ability of the array to differentiate between isolates representative of a spectrum of S. aureus types, including methicillin-susceptible, methicillin-resistant, community-acquired, and vancomycin-resistant S. aureus, and to simultaneously detect clinically relevant virulence determinants.

Human antibody responses to the meningococcal factor H binding protein (LP2086) during invasive disease, colonization and carriage

Recombinant forms of Neisseria meningitidis factor H binding protein (fHBP) are undergoing clinical trials in candidate vaccines against serogroup B meningococcal disease. Little is known, however, about the host response to fHBP during natural carriage and disease. Here we report a longitudinal study of the antibody response to fHBP in healthy meningococcal carriers and non-carriers, and in patients with invasive meningococcal disease. Using a highly sensitive quantitative immunoassay, anti-fHBP antibodies were detected in sera from all healthy carriers and non-carriers. Carriers had significantly higher anti-fHBP antibody concentrations than non-carriers. Antibody responses similar to those seen in non-carrier subjects were detected in the sera of patients with invasive disease upon their admission to the hospital. The serum anti-fHBP antibody concentrations in these patients generally rose to reach levels similar to those seen in carriers. No correlation between levels of surface fHBP expressed in vitro by the infecting N. meningitidis strain and the magnitude of antibody responses was observed. These data suggest that fHBP is expressed in vivo during both carriage and invasive disease at levels high enough to elicit a robust antibody response.