Multistate, Population-Based Distributions of Candidate Vaccine Targets, Clonal Complexes, and Resistance Features of Invasive Group B Streptococci Within the United States, 2015-2017.

BACKGROUND: Group B Streptococcus (GBS) is a leading cause of neonatal sepsis and meningitis and an important cause of invasive infections in pregnant and nonpregnant adults. Vaccines targeting capsule polysaccharides and common proteins are under development. METHODS: Using whole genome sequencing, a validated bioinformatics pipeline, and targeted antimicrobial susceptibility testing, we characterized 6340 invasive GBS isolates recovered during 2015-2017 through population-based Active Bacterial Core surveillance (ABCs) in 8 states. RESULTS: Six serotypes accounted for 98.4% of isolates (21.8% Ia, 17.6% V, 17.1% II, 15.6% III, 14.5% Ib, 11.8% IV). Most (94.2%) isolates were in 11 clonal complexes (CCs) comprised of multilocus sequence types identical or closely related to sequence types 1, 8, 12, 17, 19, 22, 23, 28, 88, 452, and 459. Fifty-four isolates (0.87%) had point mutations within pbp2x associated with nonsusceptibility to 1 or more ß-lactam antibiotics. Genes conferring resistance to macrolides and/or lincosamides were found in 56% of isolates; 85.2% of isolates had tetracycline resistance genes. Two isolates carrying vanG were vancomycin nonsusceptible (minimum inhibitory concentration = 2 µg/mL). Nearly all isolates possessed capsule genes, 1-2 of the 3 main pilus gene clusters, and 1 of 4 homologous alpha/Rib family determinants. Presence of the hvgA virulence gene was primarily restricted to serotype III/CC17 isolates (465 isolates), but 8 exceptions (7 IV/CC452 and 1 IV/CC17) were observed. CONCLUSIONS: This first comprehensive, population-based quantitation of strain features in the United States suggests that current vaccine candidates should have good coverage. The ß-lactams remain appropriate for first-line treatment and prophylaxis, but emergence of nonsusceptibility warrants ongoing monitoring.

Validation of ß-lactam minimum inhibitory concentration predictions for pneumococcal isolates with newly encountered penicillin binding protein (PBP) sequences.

BACKGROUND: Genomic sequence-based deduction of antibiotic minimum inhibitory concentration (MIC) has great potential to enhance the speed and sensitivity of antimicrobial susceptibility testing. We previously developed a penicillin-binding protein (PBP) typing system and two methods (Random Forest (RF) and Mode MIC (MM)) that accurately predicted ß-lactam MICs for pneumococcal isolates carrying a characterized PBP sequence type (phenotypic ß-lactam MICs known for at least one isolate of this PBP type). This study evaluates the prediction performance for previously uncharacterized (new) PBP types and the probability of encountering new PBP types, both of which impact the overall prediction accuracy. RESULTS: The MM and RF methods were used to predict MICs of 4309 previously reported pneumococcal isolates in 2 datasets and the results were compared to the known broth microdilution MICs to 6 ß-lactams. Based on a method that specifically evaluated predictions for new PBP types, the RF results were more accurate than MM results for new PBP types and showed percent essential agreement (MICs agree within ±1 dilution) >97%, percent category agreement (interpretive results agree) >93%, major discrepancy (sensitive isolate predicted as resistant) rate < 1.2%, and very major discrepancy (resistant isolate predicted as sensitive) rate < 1.4% for all 6 ß-lactams. The identification of new PBP types over time was well approximated by a diminishingly increasing curve (Pearson's r = 0.99) and minimally impacted overall MIC prediction performance. CONCLUSIONS: MIC prediction using the RF method could be an accurate alternative of phenotypic susceptibility testing even in the presence of previously uncharacterized PBP types.

Genomic Epidemiology of Penicillin-Nonsusceptible Pneumococci with Nonvaccine Serotypes Causing Invasive Disease in the United States.

Conjugate vaccination against seven pneumococcal serotypes (PCV7) reduced disease prevalence due to antibiotic-resistant strains throughout the 2000s. However, diseases caused by resistant nonvaccine type (NVT) strains increased. Some of these emerging strains were derived from vaccine types (VT) that had changed their capsule by recombination. The introduction of a vaccine targeting 13 serotypes (PCV13) in 2010 has led to concern that this scenario will repeat itself. We generated high-quality draft genomes from 265 isolates of NVT pneumococci not susceptible to penicillin (PNSP) in 2009 and compared them with the genomes of 581 isolates from 2012 to 2013 collected by the Active Bacterial Core surveillance (ABCs) of the Centers for Disease Control and Prevention (CDC). Of the seven sequence clusters (SCs) identified, three SCs fell into a single lineage associated with serogroup 23, which had an origin in 1908 as dated by coalescent analysis and included isolates with a divergent 23B capsule locus. Three other SCs represented relatively deep-branching lineages associated with serotypes 35B, 15A, and 15BC. In all cases, the resistant clones originated prior to 2010, indicating that PNSP are at present dominated by descendants of NVT clones present before vaccination. With one exception (15BC/ST3280), these SCs were related to clones identified by the Pneumococcal Molecular Epidemiology Network (PMEN). We conclude that postvaccine diversity in NVT PNSP between 2009 and 2013 was driven mainly by the persistence of preexisting strains rather than through de novo adaptation, with few cases of serotype switching. Future surveillance is essential for documenting the long-term dynamics and resistance of NVT PNSP.

Cross-resistance to lincosamides, streptogramins A and pleuromutilins in Streptococcus agalactiae isolates from the USA.

Background: Streptococcus agalactiae (Group B Streptococcus, GBS) is a leading cause of meningitis, sepsis and pneumonia in neonates in the United States. GBS also causes invasive disease in older infants, pregnant women, children and young adults with underlying medical conditions, and older adults. Resistance to lincosamides in the absence of erythromycin resistance is rare in GBS, but has been previously reported in clinical isolates, both on its own or in combination with resistance to streptogramins A and pleuromutilins (L/LSA/LSAP phenotypes). Objectives: To retrospectively screen the Active Bacterial Core surveillance (ABCs) GBS isolate collection for these phenotypes in order to identify the causal genetic determinants and determine whether their frequency is increasing. Methods: Based on MIC data, 65 (0.31%) isolates susceptible to erythromycin (MIC ≤0.25 mg/L) and non-susceptible to clindamycin (MIC ≥0.5 mg/L) were identified among 21 186 GBS isolates. Genomic DNA was extracted and WGS was performed. The presence of 10 genes previously associated with LSA resistance was investigated by read mapping. Results: Forty-nine (75%) isolates carried the lsa (C) gene and expressed the LSAP phenotype, and 12 (18%) carried both the lnu (B) and lsa (E) genes and expressed the LSAP phenotype. The four remaining isolates were negative for all determinants investigated. Conclusions: While the overall observed frequency of these phenotypes among our GBS isolates was quite low (0.31%), this frequency has increased in recent years. To the best of our knowledge, this is the first time the LSAP phenotype has been reported among GBS isolates from the USA.

A systematic and functional classification of Streptococcus pyogenes that serves as a new tool for molecular typing and vaccine development.

Streptococcus pyogenes ranks among the main causes of mortality from bacterial infections worldwide. Currently there is no vaccine to prevent diseases such as rheumatic heart disease and invasive streptococcal infection. The streptococcal M protein that is used as the substrate for epidemiological typing is both a virulence factor and a vaccine antigen. Over 220 variants of this protein have been described, making comparisons between proteins difficult, and hindering M protein-based vaccine development. A functional classification based on 48 emm-clusters containing closely related M proteins that share binding and structural properties is proposed. The need for a paradigm shift from type-specific immunity against S. pyogenes to emm-cluster based immunity for this bacterium should be further investigated. Implementation of this emm-cluster-based system as a standard typing scheme for S. pyogenes will facilitate the design of future studies of M protein function, streptococcal virulence, epidemiological surveillance, and vaccine development.

Deriving group A Streptococcus typing information from short-read whole-genome sequencing data.

Typing of group A Streptococcus (GAS) is crucial for infection control and epidemiology. While whole-genome sequencing (WGS) is revolutionizing the way that bacterial organisms are typed, it is necessary to provide backward compatibility with currently used typing schemas to facilitate comparisons and understanding of epidemiological trends. Here, we sequenced the genomes of 191 GAS isolates representing 42 different emm types and used bioinformatics tools to derive commonly used GAS typing information directly from the short-read WGS data. We show that emm typing and multilocus sequence typing can be achieved rapidly and efficiently using this approach, which also permits the determination of the presence or absence of genes associated with GAS tissue tropism. We also report on how the WGS data analysis was instrumental in identifying ambiguities present in the commonly used emm type database hosted by the U.S. Centers for Disease Control and Prevention.

Pneumococcal capsular switching: a historical perspective.

BACKGROUND: Changes in serotype prevalence among pneumococcal populations result from both serotype replacement and serotype (capsular) switching. Temporal changes in serotype distributions are well documented, but the contribution of capsular switching to such changes is unknown. Furthermore, it is unclear to what extent vaccine-induced selective pressures drive capsular switching. METHODS: Serotype and multilocus sequence typing data for 426 pneumococci dated from 1937 through 2007 were analyzed. Whole-genome sequence data for a subset of isolates were used to investigate capsular switching events. RESULTS: We identified 36 independent capsular switch events, 18 of which were explored in detail with whole-genome sequence data. Recombination fragment lengths were estimated for 11 events and ranged from approximately 19.0 kb to ≥ 58.2 kb. Two events took place no later than 1960, and the imported DNA included the capsular locus and the nearby penicillin-binding protein genes pbp2x and pbp1a. CONCLUSIONS: Capsular switching has been a regular occurrence among pneumococcal populations throughout the past 7 decades. Recombination of large DNA fragments (>30 kb), sometimes including the capsular locus and penicillin-binding protein genes, predated both vaccine introduction and widespread antibiotic use. This type of recombination has likely been an intrinsic feature throughout the history of pneumococcal evolution.

Recombinational exchange of M-fibril and T-pilus genes generates extensive cell surface diversity in the global group A Streptococcus population.

Among genes present in all group A streptococci (GAS), those encoding M-fibril and T-pilus proteins display the highest levels of sequence diversity, giving rise to the two primary serological typing schemes historically used to define strain. A new genotyping scheme for the pilin adhesin and backbone genes is developed and, when combined with emm typing, provides an account of the global GAS strain population. Cluster analysis based on nucleotide sequence similarity assigns most T-serotypes to discrete pilin backbone sequence clusters, yet the established T-types correspond to only half the clusters. The major pilin adhesin and backbone sequence clusters yield 98 unique combinations, defined as "pilin types." Numerous horizontal transfer events that involve pilin or emm genes generate extensive antigenic and functional diversity on the bacterial cell surface and lead to the emergence of new strains. Inferred pilin genotypes applied to a meta-analysis of global population-based collections of pharyngitis and impetigo isolates reveal highly significant associations between pilin genotypes and GAS infection at distinct ecological niches, consistent with a role for pilin gene products in adaptive evolution. Integration of emm and pilin typing into open-access online tools (pubmlst.org) ensures broad utility for end-users wanting to determine the architecture of M-fibril and T-pilus genes from genome assemblies.IMPORTANCEPrecision in defining the variant forms of infectious agents is critical to understanding their population biology and the epidemiology of associated diseases. Group A Streptococcus (GAS) is a global pathogen that causes a wide range of diseases and displays a highly diverse cell surface due to the antigenic heterogeneity of M-fibril and T-pilus proteins which also act as virulence factors of varied functions. emm genotyping is well-established and highly utilized, but there is no counterpart for pilin genes. A global GAS collection provides the basis for a comprehensive pilin typing scheme, and online tools for determining emm and pilin genotypes are developed. Application of these tools reveals the expansion of structural-functional diversity among GAS via horizontal gene transfer, as evidenced by unique combinations of surface protein genes. Pilin and emm genotype correlations with superficial throat vs skin infection provide new insights on the molecular determinants underlying key ecological and epidemiological trends.

Inter-species gene flow drives ongoing evolution of Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis.

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an emerging cause of human infection with invasive disease incidence and clinical manifestations comparable to the closely related species, Streptococcus pyogenes. Through systematic genomic analyses of 501 disseminated SDSE strains, we demonstrate extensive overlap between the genomes of SDSE and S. pyogenes. More than 75% of core genes are shared between the two species with one third demonstrating evidence of cross-species recombination. Twenty-five percent of mobile genetic element (MGE) clusters and 16 of 55 SDSE MGE insertion regions were shared across species. Assessing potential cross-protection from leading S. pyogenes vaccine candidates on SDSE, 12/34 preclinical vaccine antigen genes were shown to be present in >99% of isolates of both species. Relevant to possible vaccine evasion, six vaccine candidate genes demonstrated evidence of inter-species recombination. These findings demonstrate previously unappreciated levels of genomic overlap between these closely related pathogens with implications for streptococcal pathobiology, disease surveillance and prevention.

Variation in pneumococcal invasiveness metrics is driven by serotype carriage duration and initial risk of disease.

Streptococcus pneumoniae is an opportunistic pathogen that, while usually carried asymptomatically, can cause severe invasive diseases like meningitis and bacteremic pneumonia. A central goal in S. pneumoniae public health management is to identify which serotypes (immunologically distinct strains) pose the most risk of invasive disease. The most common invasiveness metrics use cross-sectional data (i.e., invasive odds ratios (IOR)), or longitudinal data (i.e., attack rates (AR)). To assess the reliability of these metrics we developed an epidemiological model of carriage and invasive disease. Our mathematical analyses illustrate qualitative failures with the IOR metric (e.g., IOR can decline with increasing invasiveness parameters). Fitting the model to both longitudinal and cross-sectional data, our analysis supports previous work indicating that invasion risk is maximal at or near time of colonization. This pattern of early invasive disease risk leads to substantial (up to 5-fold) biases when estimating underlying differences in invasiveness from IOR metrics, due to the impact of carriage duration on IOR. Together, these results raise serious concerns with the IOR metric as a basis for public health decision-making and lend support for multiple alternate metrics including AR.

Invasive pneumococcal disease and pandemic (H1N1) 2009, Denver, Colorado, USA.

Pneumococcal pneumonia was a complication during previous influenza pandemics but was not evident initially during pandemic (H1N1) 2009. During October 2009 in Denver, Colorado, USA, invasive pneumococcal disease (IPD) and pandemic (H1N1) 2009 peaked simultaneously, which suggests a link. We compared cases of IPD in October 2009 with cases in February 2009, the most recent peak month of seasonal influenza. During October 2009, we observed 58 IPD cases, which was 3× the average number of IPD cases that usually occur in October in Denver. Patients with IPD in October 2009 were younger and more likely to have chronic lung disease than patients who had IPD in February 2009; a total of 10/47 patients had influenza, and 33/53 patients had influenza-like illness. Thus, ≈17%-62% cases of IPD may have been associated with pandemic (H1N1) 2009. Pneumococcal disease prevention strategies should be emphasized during future influenza pandemics.

Effect of pneumococcal conjugate vaccine on pneumococcal meningitis.

BACKGROUND: Invasive pneumococcal disease declined among children and adults after the introduction of the pediatric heptavalent pneumococcal conjugate vaccine (PCV7) in 2000, but its effect on pneumococcal meningitis is unclear. METHODS: We examined trends in pneumococcal meningitis from 1998 through 2005 using active, population-based surveillance data from eight sites in the United States. Isolates were grouped into PCV7 serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F), PCV7-related serotypes (6A, 9A, 9L, 9N, 18A, 18B, 18F, 19B, 19C, 23A, and 23B), and non-PCV7 serotypes (all others). Changes in the incidence of pneumococcal meningitis were assessed against baseline values from 1998-1999. RESULTS: We identified 1379 cases of pneumococcal meningitis. The incidence declined from 1.13 cases to 0.79 case per 100,000 persons between 1998-1999 and 2004-2005 (a 30.1% decline, P<0.001). Among persons younger than 2 years of age and those 65 years of age or older, the incidence decreased during the study period by 64.0% and 54.0%, respectively (P<0.001 for both groups). Rates of PCV7-serotype meningitis declined from 0.66 case to 0.18 case (a 73.3% decline, P<0.001) among patients of all ages. Although rates of PCV7-related-serotype disease decreased by 32.1% (P=0.08), rates of non-PCV7-serotype disease increased from 0.32 to 0.51 (an increase of 60.5%, P<0.001). The percentages of cases from non-PCV7 serotypes 19A, 22F, and 35B each increased significantly during the study period. On average, 27.8% of isolates were nonsusceptible to penicillin, but fewer isolates were nonsusceptible to chloramphenicol (5.7%), meropenem (16.6%), and cefotaxime (11.8%). The proportion of penicillin-nonsusceptible isolates decreased between 1998 and 2003 (from 32.0% to 19.4%, P=0.01) but increased between 2003 and 2005 (from 19.4% to 30.1%, P=0.03). CONCLUSIONS: Rates of pneumococcal meningitis have decreased among children and adults since PCV7 was introduced. Although the overall effect of the vaccine remains substantial, a recent increase in meningitis caused by non-PCV7 serotypes, including strains nonsusceptible to antibiotics, is a concern.

Shifting genetic structure of invasive serotype 19A pneumococci in the United States.

BACKGROUND: Following 7-valent conjugate vaccine introduction in the United States in 2000, invasive serotype (sero19A) pneumococcal disease (IPD) emerged rapidly. Sero19A IPD incidence increased slightly during 2005-2008 (from 2.3 cases to 2.5 cases per 100,000 population), whereas sero19A penicillin resistance (defined as a minimum inhibitor concentration [MIC] ≥2 µg/mL) increased significantly (from 28.7% to 43.7%). To better understand changes, we characterized sero19A isolates recovered during 2004-2008. METHODS: We performed antimicrobial susceptibility testing on all 2767 sero19A IPD isolates identified through the Centers for Disease Control Active Bacterial Core surveillance during 2004-2008. We genotyped 1804 (96.3%) of 1874 sero19A isolates recovered during 2005-2007 and all 148 year 2008 sero19A isolates from children <5 years of age. RESULTS: Resistant clonal complex (CC) 320/271(19A) increased from 20.9% (115 of 550) to 32.9% (208 of 633; P < .001) of IPD isolates during 2005-2007, which paralleled increased sero19A penicillin resistance (from 28.7% [163 of 567 isolates] to 39.5% [261 of 661 isolates]; P < .001). Total IPD due to 320/271(19A) increased during 2005-2007 and increased from 2.1 to 3.6 cases per 100,000 population during 2005-2008 in children <5 years of age. The penicillin-susceptible/intermediate, putative vaccine-escape CC695(19A) increased from 7.5% (41 of 550) to 13.6% (85 of 633) of sero19A isolates during 2005-2007 (P = .002). CONCLUSIONS: Sero19A rates may have plateaued; however, clonal shifts are increasing resistance. Increased IPD caused by CC320/271(19A) and CC695(19A) could reflect additional selective advantages in addition to resistance.

Streptococcus pneumoniae serotype 9A isolates contain diverse mutations to wcjE that result in variable expression of serotype 9V-specific epitope.

BACKGROUND: Streptococcus pneumoniae is a significant pathogen capable of expressing protective and antigenically diverse capsules. To better understand the molecular basis of capsular antigenic diversity, we investigated the hypothetical serological role of wcjE, which encodes a capsule O-acetyltransferase, in the vaccine-targeted serotype 9V and related serotype 9A. METHODS: We inactivated wcjE by recombination in a serotype 9V strain and determined wcjE sequences of 11 serotype 9A clinical isolates. We determined the antigenic phenotypes of these pneumococcal strains with serogroup 9-specific antibodies and flow cytometry. RESULTS: Inactivation of wcjE in a serotype 9V strain resulted in expression of the 9A phenotype. Each serotype 9A clinical isolate contained a distinct mutation to wcjE. Flow cytometry showed that some 9A isolates (herein named 9Aα) expressed trace amounts of 9V-specific epitopes whereas others (named 9Aß) did not express any. Recombination with 9Aα wcjE alleles into a 9Aß strain conferred partial expression of 9V-specific epitopes. CONCLUSIONS: Each serotype 9A strain independently arose from a serotype 9V strain. Furthermore, clinical isolates identified as 9A can contain mutations to wcjE that are either partially functional or completely nonfunctional, demonstrating a previously unidentified antigenic heterogeneity of serotype 9A isolates.

Geographic variation in invasive pneumococcal disease following pneumococcal conjugate vaccine introduction in the United States.

BACKGROUND: Rates of invasive pneumococcal disease (IPD) varied among the United States before pneumococcal conjugate vaccine (PCV7) introduction. We compared trends in IPD rates among diverse US sites over 10 years since PCV7 introduction. METHODS: Patients with IPD of all ages were identified through active population and laboratory-based surveillance in 8 geographic areas under continuous surveillance during 1998-2009. Isolates were serotyped. IPD incidence rates and percent changes were calculated by site, serotype group, age, and year. RESULTS: Reductions in rates of IPD ranged, by site, from 19 to 29.9 cases per 100,000 population during 1998-1999 to 11.2-18.0 cases per 100,000 population during 2009 (rate reduction, 5.1-15.3 cases per 100,000 population). Reductions in IPD rates among children aged <5 years ranged from 35.7 to 117.2 cases per 100,000 population across the sites. Reductions in rates of IPD due to PCV7 serotypes were seen in all age groups at all sites, ranging from 12 to 21.4 cases per 100,000 population during 1998-1999 to <2 cases per 100,000 population during 2009 (92%-98% reductions). Serotype 19A rates ranged from 0.4 to 1.5 cases per 100,000 population during 1998-1999 to 1.3 to 3.4 cases per 100,000 population during 2009 (rate difference, 0.9-2.8 cases per 100,000 population); modest increases were observed for most age groups across the sites. Rates of IPD due to all other serotypes ranged from 6.3 to 10.3 cases per 100,000 population during 1998-1999 to 8.3-13.6 cases per 100,000 population during 2009 (rate difference, -0.4 to 5.7 cases per 100,000 population). Across the sites, the greatest rate increases were seen in the 50-64 and >65 year age groups. CONCLUSIONS: Reductions in IPD due to vaccine serotypes were consistent across sites. Changes in serotype 19A and all other serotypes were variable. Although relative increases in non-vaccine type serotypes were large in some sites, absolute rate increases were small.

Application of TaqMan low-density arrays for simultaneous detection of multiple respiratory pathogens.

The large and growing number of viral and bacterial pathogens responsible for respiratory infections poses a challenge for laboratories seeking to provide rapid and comprehensive pathogen identification. We evaluated a novel application of the TaqMan low-density array (TLDA) cards for real-time PCR detection of 21 respiratory-pathogen targets. The performance of the TLDA was compared to that of individual real-time PCR (IRTP) assays with the same primers and probes using (i) nucleic acids extracted from the 21 pathogen strains and 66 closely related viruses and bacteria and (ii) 292 clinical respiratory specimens. With spiked samples, TLDA cards were about 10-fold less sensitive than IRTP assays. By using 292 clinical specimens to generate 2,238 paired individual assays, the TLDA card exhibited 89% sensitivity (95% confidence interval [CI], 86 to 92%; range per target, 47 to 100%) and 98% specificity (95% CI, 97 to 99%; range per target, 85 to 100%) overall compared to IRTP assays as the gold standard with a threshold cycle (C(T)) cutoff of 43. The TLDA card approach offers promise for rapid and simultaneous identification of multiple respiratory pathogens for outbreak investigations and disease surveillance.

Clinical outcome of pneumococcal meningitis during the emergence of pencillin-resistant Streptococcus pneumoniae: an observational study.

BACKGROUND: Prior to the availability of generic third-generation cephalosporins, penicillins were widely used for treatment of pneumococcal meningitis in developing countries despite concerns about rising levels of penicillin resistance among pneumococcal isolates. We examined the impact of penicillin resistance on outcomes of pneumococcal meningitis over a ten year period in an infectious diseases hospital in Brazil. METHODS: Clinical presentation, antimicrobial therapy and outcomes were reviewed for 548 patients with culture-confirmed pneumococcal meningitis from December, 1995, to November, 2005. Pneumococcal isolates from meningitis patients were defined as penicillin-resistant if Minimum Inhibitory Concentrations for penicillin were greater than 0.06 µg/ml. Proportional hazards regression was used to identify risk factors for fatal outcomes. RESULTS: During the ten-year period, ceftriaxone replaced ampicillin as first-line therapy for suspected bacterial meningitis. In hospital case-fatality for pneumococcal meningitis was 37%. Of 548 pneumococcal isolates from meningitis cases, 92 (17%) were resistant to penicillin. After controlling for age and severity of disease at admission, penicillin resistance was associated with higher case-fatality (Hazard Ratio [HR], 1.62; 95% Confidence Interval [CI], 1.08-2.43). Penicillin-resistance remained associated with higher case-fatality when initial therapy included ceftriaxone (HR, 1.68; 95% CI 1.02-2.76). CONCLUSIONS: Findings support the use of third generation cephalosporin antibiotics for treatment of suspected pneumococcal meningitis even at low prevalence of pneumococcal resistance to penicillins.

Increased penicillin nonsusceptibility of nonvaccine-serotype invasive pneumococci other than serotypes 19A and 6A in post-7-valent conjugate vaccine era.

According to population-based invasive pneumococcal surveillance in the United States during 2007, 898 (26%) of 3,511 isolates were penicillin nonsusceptible. Non-7-valent pneumococcal conjugate vaccine (PCV7) serotypes other than 19A accounted for 40% of these penicillin-nonsusceptible isolates; of these, serotypes 15A (11%), 23A (8%), 35B (8%), and 6C (5%) were most common (cumulatively 32% of penicillin-nonsusceptible isolates). Each except 6C represented a single serotype and clonal complex combination that predated the introduction of PCV7. We evaluated the genetic characteristics and nonsusceptibility to penicillin of non- PCV7 serotypes, and we found increased proportions of specific penicillin-nonsusceptible clones in serotypes 15A, 23A, 35B, and 6C, which potentially indicates a basic change of population structure within these individual serotypes.

Sustained reductions in invasive pneumococcal disease in the era of conjugate vaccine.

BACKGROUND: Changes in invasive pneumococcal disease (IPD) incidence were evaluated after 7 years of 7-valent pneumococcal conjugate vaccine (PCV7) use in US children. METHODS: Laboratory-confirmed IPD cases were identified during 1998-2007 by 8 active population-based surveillance sites. We compared overall, age group-specific, syndrome-specific, and serotype group-specific IPD incidence in 2007 with that in 1998-1999 (before PCV7) and assessed potential serotype coverage of new conjugate vaccine formulations. RESULTS: Overall and PCV7-type IPD incidence declined by 45% (from 24.4 to 13.5 cases per 100,000 population) and 94% (from 15.5 to 1.0 cases per 100,000 population), respectively (P< .01 all age groups). The incidence of IPD caused by serotype 19A and other non-PCV7 types increased from 0.8 to 2.7 cases per 100,000 population and from 6.1 to 7.9 cases per 100,000 population, respectively (P< .01 for all age groups). The rates of meningitis and invasive pneumonia caused by non-PCV7 types increased for all age groups (P< .05), whereas the rates of primary bacteremia caused by these serotypes did not change. In 2006-2007, PCV7 types caused 2% of IPD cases, and the 6 additional serotypes included in an investigational 13-valent conjugate vaccine caused 63% of IPD cases among children <5 years-old. CONCLUSIONS: Dramatic reductions in IPD after PCV7 introduction in the United States remain evident 7 years later. IPD rates caused by serotype 19A and other non-PCV7 types have increased but remain low relative to decreases in PCV7-type IPD.

Low but Increasing Prevalence of Reduced Beta-lactam Susceptibility Among Invasive Group B Streptococcal Isolates, US Population-Based Surveillance, 1998-2018.

BACKGROUND: Invasive group B Streptococcus (iGBS) isolates with mutations in the pbp2x gene that encodes penicillin binding protein 2x can have reduced beta-lactam susceptibility (RBLS) when susceptible by Clinical and Laboratory Standards Institute (CLSI) criteria. We assessed the emergence and characteristics of RBLS strains in US iGBS isolates. METHODS: We analyzed iGBS isolates from 8 multistate population-based surveillance sites from 1998 to 2018. During 1998-2014, phenotypic antimicrobial susceptibility was determined by broth microdilution; criteria for 6 antibiotics were used to identify RBLS, followed by whole-genome sequencing (WGS). WGS for all isolates was added in 2015; we used phenotypic and genotypic results of >2000 isolates to validate phenotypic RBLS criteria and genotypic predictions. Since 2016, WGS has been used to screen for RBLS with broth microdilution confirmation of predicted RBLS isolates. RESULTS: Of 28 269 iGBS isolates, 28 (0.1%) were nonsusceptible by CLSI criteria; 137 (0.5%) met RBLS criteria. RBLS isolates were detected in all Active Bacterial Core surveillance sites. The RBLS proportion increased, especially since 2013 (odds ratio, 1.17; 95% CI, 1.03-1.32); the proportion that were nonsusceptible remained stable. CONCLUSIONS: The RBSL proportion was low but increasing among US iGBS isolates. Ongoing monitoring is needed to detect emerging threats to prevention and treatment of GBS infections.