The burden of nonencapsulated Haemophilus influenzae in children and potential for prevention

Haemophilus influenzae Invasive Infections in Children in Vaccine Era: Phenotypic and Genotypic Characterization Tunis, Tunisia

The changing epidemiological profile of invasive Haemophilus influenzae infections (IIHi) is noted in the post-vaccination era. The aim of this study was to characterize phenotypically and genotypically invasive Haemophilus influenzae (Hi) isolates detected in Tunisian pediatric patients. A retrospective study was conducted in the microbiology laboratory of the Children's Hospital of Tunis over ten years (2013-2023). All IIHi cases were included. Molecular identification and serotyping were conducted through qPCR. Molecular typing and analysis of resistance genes were extracted from whole genome sequencing data. Fifty-three IIHi cases were collected. Children under five years old were the most affected (81%). Non-typable isolates (NTHi) were predominant (79%) followed by serotype b (17%) and serotype a (4%). Genetic diversity was observed, essentially among NTHi isolates. Resistance of Hi isolates to ampicillin, amoxicillin-clavulanic acid and cefotaxime (CTX) were 42%, 20% and 4%, respectively. Thirteen isolates (29%) produced a beta-lactamase and 14 carried the blaTEM-1 gene (kappa = 0.95). For non-enzymatic resistance, group 3 (n = 12) showed resistance to ampicillin. Groupe 4 (n = 9, NTHi) showed discordances with resistance to CTX. The emergence of resistance to CTX is concerning. Continuous surveillance through molecular tools in conjunction with phenotypic and clinical data is necessary to ensure better management of these infections.

Comparing the Microbiome of the Adenoids in Children with Secretory Otitis Media and Children without Middle Ear Effusion

BACKGROUND

The adenoids, primary sites of microbial colonization in the upper airways, can influence the development of various conditions, including otitis media with effusion (OME). Alterations in the adenoid microbiota have been implicated in the pathogenesis of such conditions.

AIM

This study aims to utilize 16S rRNA genetic sequencing to identify and compare the bacterial communities on the adenoid surfaces of children with OME and children with healthy middle ears. Additionally, we seek to assess the differences in bacterial diversity between these two groups.

MATERIALS AND METHODS

We collected adenoid surface swabs from forty children, divided into two groups: twenty samples from children with healthy middle ears and twenty samples from children with OME. The V3-V4 hypervariable region of the bacterial 16S rRNA gene was amplified and sequenced using the Illumina MiSeq platform. Alpha and beta diversity indices were calculated, and statistical analyses were performed to identify significant differences in bacterial composition.

RESULTS

Alpha diversity analysis, using Pielou's index, revealed significantly greater evenness in the bacterial communities on the adenoid surfaces of the healthy ear group compared with the OME group. Beta diversity analysis indicated greater variability in the microbial composition of the OME group. The most common bacterial genera in both groups were Haemophilus, Fusobacterium, Streptococcus, Moraxella, and Peptostreptococcus. The healthy ear group was primarily dominated by Haemophilus and Streptococcus, whereas the OME group showed higher abundance of Fusobacterium and Peptostreptococcus. Additionally, the OME group exhibited statistically significant higher levels of Alloprevotella, Peptostreptococcus, Porphyromonas, Johnsonella, Parvimonas, and Bordetella compared with the healthy ear group.

CONCLUSION

Our study identified significant differences in the bacterial composition and diversity on the adenoid surfaces of children with healthy middle ears and those with OME. The OME group exhibited greater microbial variability and higher abundances of specific bacterial genera. These findings suggest that the adenoid surface microbiota may play a role in the pathogenesis of OME. Further research with larger sample sizes and control groups is needed to validate these results and explore potential clinical applications.

Laboratory surveillance of invasive Haemophilus influenzae disease in Argentina, 2011-2019

The incorporation of Haemophilus influenzae type b (Hib) vaccine into the Argentine National Immunization Program in 1998 resulted in a dramatic decrease in the incidence of invasive disease due to this serotype. We assessed 1405 H. influenzae (Hi) isolates causing invasive infections referred to the National Reference Laboratory between 2011 and 2019. Non-encapsulated Hi were the most common strains (44.5%), followed by types b (41.1%) and a (10.0%). Significant increase in the proportion of type b was observed, from 31.2% in 2011, to 50% in 2015, correlating with the peak incidence rate, later decreasing to 33.6% by 2019. We compared the genetic relationship between clones circulating during the period of increased Hib incidence (2011-2015) and those of the prevaccination-transition period (1997-1998). Four pulsotypes predominated in both periods, G, M, P and K, G being the most common. Multi-locus sequence typing revealed that the 4 pulsotypes belonged to ST6, or one of its simple or double locus variants. Isolates from fully vaccinated individuals did not differ from those of the rest of the population studied. After ruling out aspects associated with emergence of specific clones, we concluded that factors such as low booster coverage rates, delayed vaccination schedules and use of different vaccines may have contributed to the reemergence of Hib infections.

Invasive Haemophilus influenzae Infections after 3 Decades of Hib Protein Conjugate Vaccine Use

Haemophilus influenzae serotype b (Hib) was previously the most common cause of bacterial meningitis and an important etiologic agent of pneumonia in children aged <5 years. Its major virulence factor is the polyribosyl ribitol phosphate (PRP) polysaccharide capsule. In the 1980s, PRP-protein conjugate Hib vaccines were developed and are now included in almost all national immunization programs, achieving a sustained decline in invasive Hib infections. However, invasive Hib disease has not yet been eliminated in countries with low vaccine coverage, and sporadic outbreaks of Hib infection still occur occasionally in countries with high vaccine coverage. Over the past 2 decades, other capsulated serotypes have been recognized increasingly as causing invasive infections. H. influenzae serotype a (Hia) is now a major cause of invasive infection in Indigenous communities of North America, prompting a possible requirement for an Hia conjugate vaccine. H. influenzae serotypes e and f are now more common than serotype b in Europe. Significant year-to-year increases in nontypeable H. influenzae invasive infections have occurred in many regions of the world. Invasive H. influenzae infections are now seen predominantly in patients at the extremes of life and those with underlying comorbidities. This review provides a comprehensive and critical overview of the current global epidemiology of invasive H. influenzae infections in different geographic regions of the world. It discusses those now at risk of invasive Hib disease, describes the emergence of other severe invasive H. influenzae infections, and emphasizes the importance of long-term, comprehensive, clinical and microbiologic surveillance to monitor a vaccine's impact.

One vaccine for life: Lessons from immune ontogeny

There remains a general misconception that the immune status of the fetus and neonate is immature or insufficient. However, emerging research in immune ontogeny prompts reconsideration of this orthodoxy, reframing this period instead as one of unique opportunity. Vaccine responses (qualitative and quantitative) vary between individuals, and across demographic cohorts. Elements of baseline immune status and function predict vaccine response - some of these factors are well described, others remain a subject of ongoing research, especially with the rapidly expanding field of 'omics' research, enabled by development of highly granular immune profiling techniques and increasing computational capacity. Age is one of the strongest predictive factors associated with variability in the response to vaccination; and predictable variation in response to vaccination is a key to identify the crucial underlying mechanisms. Specifically, circulating maternal antibody in the young infant can modulate immune response to vaccination, acting as an 'undercover adjuvant' that, counter to current dogma, may offer a pathway to longer lasting, higher quality immune response to vaccination. Exciting avenues for novel research in this area have the potential to dramatically alter how we protect the world's most vulnerable population - the very young.

Long Term Impact of Conjugate Vaccines on Haemophilus influenzae Meningitis: Narrative Review

H. influenzae serotype b (Hib) used to be the commonest cause of bacterial meningitis in young children. The widespread use of Hib conjugate vaccine has profoundly altered the epidemiology of H. influenzae meningitis. This short review reports on the spectrum of H. influenzae meningitis thirty years after Hib conjugate vaccine was first introduced into a National Immunization Program (NIP). Hib meningitis is now uncommon, but meningitis caused by other capsulated serotypes of H. influenzae and non-typeable strains (NTHi) should be considered. H. influenzae serotype a (Hia) has emerged as a significant cause of meningitis in Indigenous children in North America, which may necessitate a Hia conjugate vaccine. Cases of Hie, Hif, and NTHi meningitis are predominantly seen in young children and less common in older age groups. This short review reports on the spectrum of H. influenzae meningitis thirty years after Hib conjugate vaccine was first introduced into a NIP.

Invasive Haemophilus influenzae Infections in Germany After the Introduction of Routine Childhood Immunization, 2001-2016

Background

Haemophilus influenzae (Hi) serotype b (Hib) vaccination was introduced in Germany in 1990. This study presents a comprehensive overview on the burden of invasive Hi infections for 2001–2016, including serotype distribution and ampicillin resistance.

Methods

Nationwide data from statutory disease surveillance (2001–2016) were linked with laboratory surveillance data (2009–2016). Besides descriptive epidemiology, statistical analyses included multiple imputation to estimate secular trends.

Results

In 2001–2016, 4044 invasive Hi infections were reported. The mean incidence was 3.0 per million inhabitants, higher in males (3.2 vs 2.9 in females) and in the age groups <1 year (15.2) and ≥80 years (15.5). Nontypeable Hi (NTHi) caused 81% (n = 1545) of cases in 2009–2016. Of capsulated cases, 69% were serotype f and 17% serotype b. Of Hib cases eligible for vaccination, 10% (3/29) were fully vaccinated. For 2009–2016, significant increasing trends were observed for NTHi and Hif infections in the age groups <5 years and ≥60 years and for ampicillin resistance in NTHi.

Conclusions

This is one of the most comprehensive Hi data analyses since the introduction of Hib vaccines. NTHi and Hif cause an increasing disease burden among elderly patients and infants. Ampicillin resistance in NTHi must be considered in the treatment of invasive Hi infections.

Two cases of type-a Haemophilus influenzae meningitis within the same week in the same hospital are phylogenetically unrelated but recently exchanged capsule genes

Haemophilus influenzae causes common and sometimes severe adult and pediatric disease including chronic obstructive respiratory disease, otitis media and infections of the central nervous system. Serotype b strains, with a b-type capsule, have been the historical cause of invasive disease, and the introduction of a serotype b-specific vaccine has led to their decline. However, unencapsulated or non-b-type H. influenzae infections are not prevented by the vaccine and appear to be increasing in frequency. Here we report two pediatric cases of severe central nervous system H. influenzae infection presenting to the same hospital in San Diego, California during the same week in January 2016. Due to good vaccine coverage in this part of the world, H. influenzae cases are normally rare and seeing two cases in the same week was unexpected. We thus suspected a recent transmission chain, and possible local outbreak. To test this hypothesis, we isolated and sequenced whole genomes from each patient and placed them in a phylogenetic tree spanning the known diversity of H. influenzae. Surprisingly, we found that the two isolates (SD2016_1 and SD2016_2) belonged to distantly related lineages, suggesting two independent transmission events and ruling out a local outbreak. Despite being distantly related, the two isolates belong to two different lineages that have exchanged capsule loci in the recent past. Therefore, as in other bacterial pathogens, capsule switching by horizontal gene transfer may be an important evolutionary mechanism of vaccine evasion in H. influenzae.

Nontypeable Haemophilus influenzae Has Evolved Preferential Use of N-Acetylneuraminic Acid as a Host Adaptation

Host-adapted bacterial pathogens such as NTHi cannot survive out of their host environment and have evolved host-specific mechanisms to obtain nutrients and evade the immune response. Relatively few of these host adaptations have been characterized at the molecular level. NTHi utilizes sialic acid as a nutrient and also incorporates this sugar into LOS, which is important in biofilm formation and immune evasion. In the present study, we showed that NTHi has evolved to preferentially utilize the Neu5Ac form of sialic acid. This adaptation is due to the substrate preference of the enzyme CMP-Neu5Ac synthetase, which synthesizes the activated form of Neu5Ac for macromolecule biosynthesis. This adaptation allows NTHi to evade killing by a human antibody response against the nonhuman sialic acid Neu5Gc.

Nontypeable Haemophilus influenzae (NTHi) is a Gram-negative bacterial pathogen that is adapted exclusively to human hosts. NTHi utilizes sialic acid from the host as a carbon source and as a terminal sugar on the outer membrane glycolipid lipooligosaccharide (LOS). Sialic acid expressed on LOS is critical in NTHi biofilm formation and immune evasion. There are two major forms of sialic acids in most mammals, N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), the latter of which is derived from Neu5Ac. Humans lack the enzyme to convert Neu5Ac to Neu5Gc and do not express Neu5Gc in normal tissues; instead, Neu5Gc is recognized as a foreign antigen. A recent study showed that dietary Neu5Gc can be acquired by NTHi colonizing humans and then presented on LOS, which acts as an antigen for the initial induction of anti-Neu5Gc antibodies. Here we examined Neu5Gc uptake and presentation on NTHi LOS. We show that, although Neu5Gc and Neu5Ac are utilized equally well as sole carbon sources, Neu5Gc is not incorporated efficiently into LOS. When equal amounts of Neu5Gc and Neu5Ac are provided in culture media, there is ∼4-fold more Neu5Ac incorporated into LOS, suggesting a bias in a step of the LOS biosynthetic pathway. CMP-Neu5Ac synthetase (SiaB) was shown to have ∼4,000-fold-higher catalytic efficiency for Neu5Ac than for Neu5Gc. These data suggest that NTHi has adapted preferential utilization of Neu5Ac, thus avoiding presentation of the nonhuman Neu5Gc in the bacterial cell surface. The selective pressure for this adaptation may represent the human antibody response to the Neu5Gc xenoantigen.

Analysis of Invasive Nontypeable Haemophilus influenzae Isolates Reveals Selection for the Expression State of Particular Phase-Variable Lipooligosaccharide Biosynthetic Genes

Nontypeable Haemophilus influenzae (NTHi) is a major human pathogen, responsible for several acute and chronic infections of the respiratory tract. The incidence of invasive infections caused by NTHi is increasing worldwide. NTHi is able to colonize the nasopharynx asymptomatically, and the exact change(s) responsible for transition from benign carriage to overt disease is not understood. We have previously reported that phase variation (the rapid and reversible ON-OFF switching of gene expression) of particular lipooligosaccharide (LOS) glycosyltransferases occurs during transition from colonizing the nasopharynx to invading the middle ear. Variation in the structure of the LOS is dependent on the ON/OFF expression status of each of the glycosyltransferases responsible for LOS biosynthesis. In this study, we surveyed a collection of invasive NTHi isolates for ON/OFF expression status of seven phase-variable LOS glycosyltransferases. We report that the expression state of the LOS biosynthetic genes oafA ON and lic2A OFF shows a correlation with invasive NTHi isolates. We hypothesize that these gene expression changes contribute to the invasive potential of NTHi. OafA expression, which is responsible for the addition of an O-acetyl group onto the LOS, has been shown to impart a phenotype of increased serum resistance and may serve as a marker for invasive NTHi.

Isolation and Antibiotic Susceptibility Testing of Haemophilus influenzae from Nasopharynx of Children under Five Years Attending Maternal and Child Health Clinic in Mbarara Regional Referral Hospital

Background. H. influenzae remains an organism of a major public health challenge worldwide despite the availability of the Hib vaccine, particularly among children under 5 years. Information on the current carriage status and antibiotic susceptibility is key on proper health-care provision. Therefore, we conducted a study to determine H. influenzae carriage rate and antibiotic susceptibility testing of the isolates among the children. Methods. This was a cross-sectional study conducted between January and May 2018, among clinically healthy children under five years attending Maternal and Child Health (MCH) Clinic in Mbarara Regional Referral Hospital (MRRH). We carried out standard microbiology methods to culture, isolate, and identify H. influenzae, and then, we tested for their susceptibility to commonly used antibiotics following the CLSI standards. Results. Of the 248 participants included in the study, 116 (46.77%) were females and 132 (53.23%) males and 78 (31.45%) were below the age of 3 months. Fifty one of the study participants had H. influenzae in their nasopharynx, which represents 20.56% carriage (95% CI 15.49 to 25.63). There was a general high susceptibility of the isolates to the antimicrobial agents commonly used. There was 100% susceptibility to ciprofloxacin and imipenem antibiotic agents, though 6 (11.76%) and 4 (7.84%) of the isolates showed resistance to chloramphenicol and ampicillin, respectively. Conclusion. The high burden presented by H. influenzae and the resultant impact on child health require much attention to prevention of infections associated with the organism. A well-funded molecular study focusing on typing the isolates would determine the impact of the vaccine, given the carriage rates are still high.

Neonatal Immunization: Rationale, Current State, and Future Prospects

Infections take their greatest toll in early life necessitating robust approaches to protect the very young. Here, we review the rationale, current state, and future research directions for one such approach: neonatal immunization. Challenges to neonatal immunization include natural concern about safety as well as a distinct neonatal immune system that is generally polarized against Th1 responses to many stimuli such that some vaccines that are effective in adults are not in newborns. Nevertheless, neonatal immunization could result in high-population penetration as birth is a reliable point of healthcare contact, and offers an opportunity for early protection of the young, including preterm newborns who are deficient in maternal antibodies. Despite distinct immunity and reduced responses to some vaccines, several vaccines have proven safe and effective at birth. While some vaccines such as polysaccharide vaccines have little effectiveness at birth, hepatitis B vaccine can prime at birth and requires multiple doses to achieve protection, whereas the live-attenuated Bacille Calmette-Guérin (BCG), may offer single shot protection, potentially in part via heterologous ("non-specific") beneficial effects. Additional vaccines have been studied at birth including those directed against pertussis, pneumococcus, Haemophilus influenza type B and rotavirus providing important lessons. Current areas of research in neonatal vaccinology include characterization of early life immune ontogeny, heterogeneity in and heterologous effects of BCG vaccine formulations, applying systems biology and systems serology, in vitro platforms that model age-specific human immunity and discovery and development of novel age-specific adjuvantation systems. These approaches may inform, de-risk, and accelerate development of novel vaccines for use in early life. Key stakeholders, including the general public, should be engaged in assessing the opportunities and challenges inherent to neonatal immunization.

The evidence for non-typeable Haemophilus influenzae as a causative agent of childhood pneumonia

Haemophilus influenzae type b (Hib) was a major cause of bacterial pneumonia in children prior to the introduction of Hib-conjugate vaccines. The widespread use of Hib-conjugate vaccines has resulted in a significant decline in the number of cases of invasive Hib disease, including bacteraemic pneumonia, in areas where the vaccine has been implemented. In many countries, non-typeable H. influenzae (NTHI) is now the most common cause of invasive haemophilus infection in all ages. NTHI are a recognized cause of bacteraemic and non-bacteraemic pneumonia in children and in adults. Less than 10% of cases of pediatric pneumonia are bacteraemic, and children generally do not expectorate lower respiratory tract secretions, so determining the microbial cause of a non-bacteraemic pneumonia is challenging. In this commentary the evidence that NTHI is a cause of pneumonia in children is briefly reviewed.

Clinical and Molecular Epidemiology of Childhood Invasive Nontypeable Haemophilus influenzae Disease in England and Wales

INTRODUCTION

In countries with established Haemophilus influenzae type b (Hib) immunization programs, nontypeable H. influenzae (NTHi) is now responsible for nearly all invasive H. influenzae cases across all age groups.

METHODS

Public Health England (PHE) conducts enhanced national surveillance of invasive H. influenzae disease in England and Wales. Invasive NTHi isolates submitted to Public Health England from children of ages 1 month to 10 years during 2003-2010 were characterized by multilocus sequence typing (MLST). Detailed clinical information was obtained for all laboratory-confirmed cases of invasive NTHi disease in children during 2009-2013.

RESULTS

In England and Wales, there were 7797 cases of invasive H. influenzae disease diagnosed during 2000-2013 and 1585 (20%) occurred in children aged 1 month to 10 years, where NTHi was responsible for 31-51 cases (incidence, 0.53-0.92/100,000) annually. Detailed clinical follow-up of 214 confirmed NTHi cases diagnosed in this age-group during 2009-2013 revealed that 52% (n = 111) occurred in <2-year-old and 52% (n=110) had comorbidity. Bacteremic pneumonia was the most common clinical presentation (n = 99, 46%), 16% (n = 34) required intensive care and 11% (n = 23) died. Characterization by biotyping and MLST of 316 NTHi strains from children with invasive disease during 2003-2010 revealed a genetically heterogeneous population (155 MLSTs) with diverse biotypes and no association with comorbidity status, clinical disease or outcome.

CONCLUSIONS

The high level of genetic diversity in invasive NTHi strains highlights the difficulties in developing an effective vaccine against this pathogen.

Haemophilus influenzae: a potent perinatal pathogen disproportionately isolated from Indigenous women and their neonates

BACKGROUND

Nontypeable Haemophilus influenzae (NTHi) bacteraemia in pregnant women is strongly associated with pregnancy loss and preterm delivery. However, the clinical significance of isolation of NTHi from nonsterile sites is unknown.

AIMS

To examine the hypothesis that isolation of NTHi from any specimen is associated with adverse perinatal outcomes and to investigate the impression that NTHi is disproportionately isolated from indigenous women and their neonates.

MATERIALS AND METHODS

Cases where NTHi was isolated from maternal, fetal or neonatal specimens during the period from 1 July 1997 to 1 July 2009 were identified. Demographic and clinical data were extracted from case notes. Histopathological material was re-reviewed by a perinatal pathologist. Demographic and clinical features of the affected group were compared with the hospital obstetric population.

RESULTS

NTHi was isolated from maternal, fetal or neonatal specimens in 97 pregnancies. Two women had NTHi isolated during different pregnancies. Two mothers and 10 neonates were bacteraemic. Indigenous women comprised 28% of pregnancies where NTHi was isolated, compared with 6% of the hospital obstetric population (P < 0.001). Pregnancy loss occurred in six cases (6%). Median gestation at delivery was 33 weeks. Of 96 liveborn neonates, 88 (92%) required admission to a neonatal special care unit. Four liveborn neonates died (4%). Chorioamnionitis was confirmed by histology in 31/33 (93.9%) of placentas examined.

CONCLUSIONS

Isolation of NTHi occurred more commonly in indigenous women and neonates. Isolation of NTHi from any obstetric or neonatal specimen is associated with chorioamnionitis, preterm birth, pregnancy loss, early-onset neonatal sepsis and neonatal death.

PHiD-CV induces anti-Protein D antibodies but does not augment pulmonary clearance of nontypeable Haemophilus influenzae in mice

BACKGROUND

A recently-licensed 10-valent pneumococcal conjugate vaccine (PHiD-CV; Synflorix, GSK) uses Protein D from Haemophilus influenzae as a carrier protein. PHiD-CV therefore has the potential to provide additional protection against nontypeable H. influenzae (NTHi). NTHi frequently causes respiratory tract infections and is associated with significant morbidity and mortality worldwide and there is currently no vaccine.

METHODS

We developed mouse models of NTHi infection and influenza/NTHi superinfection. Mice were immunized with PHiD-CV, heat-killed NTHi, or a 13-valent pneumococcal conjugate vaccine that did not contain Protein D (PCV13; Prevenar, Pfizer) and then infected intranasally with NTHi.

RESULTS

Infection with NTHi resulted in weight loss, inflammation and airway neutrophilia. In a superinfection model, prior infection with pandemic H1N1 influenza virus (strain A/England/195/2009) augmented NTHi infection severity, even with a lower bacterial challenge dose. Immunization with PHiD-CV produced high levels of antibodies that were specific against Protein D, but not heat-killed NTHi. Immunization with PHiD-CV led to a slight reduction in bacterial load, but no change in disease outcome.

CONCLUSIONS

PHiD-CV induced high levels of Protein D-specific antibodies, but did not augment pulmonary clearance of NTHi. We found no evidence to suggest that PHiD-CV will offer added benefit by preventing NTHi lung infection.

Nasopharyngeal and Adenoid Colonization by Haemophilus influenzae and Haemophilus parainfluenzae in Children Undergoing Adenoidectomy and the Ability of Bacterial Isolates to Biofilm Production

Haemophili are pathogenic or opportunistic bacteria often colonizing the upper respiratory tract mucosa. The prevalence of Haemophilus influenzae (with serotypes distribution), and H. parainfluenzae in the nasopharynx and/or the adenoid core in children with recurrent pharyngotonsillitis undergoing adenoidectomy was assessed. Haemophili isolates were investigated for their ability to biofilm production.Nasopharyngeal swabs and the adenoid core were collected from 164 children who underwent adenoidectomy (2-5 years old). Bacteria were identified by the standard methods. Serotyping of H. influenzae was performed using polyclonal and monoclonal antisera. Biofilm formation was detected spectrophotometrically using 96-well microplates and 0.1% crystal violet.Ninety seven percent (159/164) children who underwent adenoidectomy were colonized by Haemophilus spp. The adenoid core was colonized in 99.4% (158/159) children, whereas the nasopharynx in 47.2% (75/159) children (P < 0.0001). In 32% (51/159) children only encapsulated (typeable) isolates of H. influenzae were identified, in 22.6% (36/159) children only (nonencapsulated) H. influenzae NTHi (nonencapsulated) isolates were present, whereas 7.5% (12/159) children were colonized by both types. 14.5% (23/159) children were colonized by untypeable (rough) H. influenzae. In 22% (35/159) children H. influenzae serotype d was isolated. Totally, 192 isolates of H. influenzae, 96 isolates of H. parainfluenzae and 14 isolates of other Haemophilus spp. were selected. In 20.1% (32/159) children 2 or 3 phenotypically different isolates of the same species (H. influenzae or H. parainfluenzae) or serotypes (H. influenzae) were identified in 1 child. 67.2% (129/192) isolates of H. influenzae, 56.3% (54/96) isolates of H. parainfluenzae and 85.7% (12/14) isolates of other Haemophilus spp. were positive for biofilm production. Statistically significant differences (P = 0.0029) among H. parainfluenzae biofilm producers and nonproducers in the adenoid core and the nasopharynx were detected.H. influenzae and H. parainfluenzae carriage rate was comparatively higher in the adenoid core than that in the nasopharynx in children undergoing adenoidectomy, suggesting that their involvement in chronic adenoiditis. The growth in the biofilm seems to be an important feature of haemophili colonizing the upper respiratory tract responsible for their persistence.

Development of a serological assay to predict antibody bactericidal activity against non-typeable Haemophilus influenzae

Background

Non-typeable Haemophilus influenzae (NTHi) is a Gram negative microorganism residing in the human nasopharyngeal mucosa and occasionally causing infections of both middle ear and lower respiratory airways. A broadly protective vaccine against NTHi has been a long-unmet medical need, as the high genetic variability of this bacterium has posed great challenges.

Results

In this study, we developed a robust serum bactericidal assay (SBA) to optimize the selection of protective antigens against NTHi. SBA takes advantage of the complement-mediated lysis of bacterial cells and is a key in vitro method for measuring the functional activity of antibodies. As a proof of concept, we assessed the bactericidal activity of antibodies directed against antigens known to elicit a protective response, including protein D used as carrier protein in the Synflorix pneumococcal polysaccharide conjugate vaccine. Prior to SBA screening, the accessibility of antigens to antibodies and the capacity of the latter to induce C3 complement deposition was verified by flow cytometry. Using baby rabbit serum as a source of complement, the proposed assay not only confirmed the bactericidal activity of the antibodies against the selected vaccine candidates, but also showed a significant reproducibility.

Conclusions

Considering the rapidity and cost-effectiveness of this novel SBA protocol, we conclude that it is likely to become an important tool to prove the capability of antibodies directed against recombinant antigens to induce NTHi in vitro killing and to both select new protective vaccine candidates, and predict vaccine efficacy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0420-x) contains supplementary material, which is available to authorized users.

Neonatal invasive Haemophilus influenzae disease in England and Wales: epidemiology, clinical characteristics, and outcome

BACKGROUND

Nontypeable Haemophilus influenzae (NTHi) frequently causes noninvasive upper respiratory tract infections in children but can cause invasive disease, mainly in older adults. An increased burden of invasive NTHi disease in the perinatal period has been reported by a number of studies. Here we describe the epidemiology, clinical characteristics, and outcome of neonatal invasive H. influenzae disease in England and Wales over a 5-year period.

METHODS

Public Health England conducts enhanced national surveillance of invasive H. influenzae disease in England and Wales. Detailed clinical information was obtained for all laboratory-confirmed cases in infants aged ≤31 days during 2009-2013.

RESULTS

Overall, 118 live-born neonates had laboratory-confirmed invasive H. influenzae disease: 115 (97%) were NTHi, 2 were serotype f, and 1 was serotype b. NTHi was isolated within 48 hours of birth (early-onset) in 110 of 115 (96%) cases, and 70 of 110 (64%) presented with septicemia. Only 17 mothers (15%) had suspected bacterial infection requiring antibiotics during labor. Few (8/110 [7%]) neonates had comorbidities. The incidence of early-onset NTHi increased exponentially with prematurity, from 0.9 per 100 000 (95% confidence interval [CI], .6-1.4) in term neonates to 342 per 100 000 (95% CI, 233.9-482.7) in neonates born at <28 weeks' gestation (incidence rate ratio, 365 [95% CI, 205-659]; P < .001). Case fatality for early-onset NTHi was 19% (21/110); each additional gestational week reduced the odds of dying by 21% (odds ratio, 0.79 [95% CI, .69-.90]; P < .01). A quarter of neonates who survived experienced long-term complications.

CONCLUSIONS

Early-onset neonatal NTHi disease is strongly associated with premature birth and causes significant morbidity and mortality.

Trends in the epidemiology of invasive Haemophilus influenzae disease in Queensland, Australia from 2000 to 2013: what is the impact of an increase in invasive non-typable H. influenzae (NTHi)?

Following the introduction of vaccination against Haemophilus influenzae type b (Hib), cases of invasive encapsulated Hib disease have decreased markedly. This study aimed to examine subsequent epidemiological trends in invasive H. influenzae disease in Queensland, Australia and in particular, assess the clinical impact and public health implications of invasive non-typable H. influenzae (NTHi) strains. A multicentre retrospective study was conducted from July 2000 to June 2013. Databases of major laboratories in Queensland including Queensland Forensic and Scientific Services (jurisdictional referral laboratory for isolate typing) were examined to identify cases. Demographic, infection site, Indigenous status, serotype, and mortality data were collected. In total, 737 invasive isolates were identified, of which 586 (79·5%) were serotyped. Hib, NTHi and encapsulated non-b strains, respectively, constituted 12·1%, 69·1% and 18·8% of isolates. The predominant encapsulated non-b strains were f (45·5%) and a (27·3%) serotypes. Of isolates causing meningitis, 48·9% were NTHi, 14·9% Hib, 14·9% Hie, 10·6% Hif, 6·4% Hia and 4·3% were untyped. During the study period, there was an increase in the incidence of invasive NTHi disease (P = 0·007) with seasonal peaks in winter and spring (P 0·001) and Hib (P = 0·039) than non-Indigenous patients. In Queensland, invasive H. influenzae disease is now predominantly encountered in adults and most commonly caused by NTHi strains with demonstrated pathogenicity extending to otherwise young or immunocompetent individuals. Routine public health notification of these strains is recommended and recent available immunization options should be considered.

Haemophilus influenzae: recent advances in the understanding of molecular pathogenesis and polymicrobial infections

PURPOSE OF REVIEW

Non-typeable Haemophilus influenzae (NTHi) is a human-specific mucosal pathogen and one of the most common causes of bacterial infections in children and patients with chronic obstructive pulmonary disease. It is also frequently found in polymicrobial superinfections. Great strides have recently been made in the understanding of the molecular mechanisms underlying NTHi pathogenesis.

RECENT FINDINGS

By using new methodology, such as experimental human colonization models and whole-genome approaches, investigators have shed light upon the various strategies of NTHi that are involved in pathogenesis. These include the escape of the mucociliary elevator, evasion of host immunity, survival in environments with scarce nutrients, and finally participation in polymicrobial infections. Lipooligosaccharide branching, proteinous adhesins, metabolic adaption to nutrient availability and many scavenging systems are implicated in these processes. Interestingly, genome-based studies comparing virulent and commensal strains have identified many hypothetical proteins as virulence determinants, suggesting that much regarding the molecular pathogenesis of NTHi remains to be solved.

SUMMARY

NTHi is an opportunistic pathogen and highly specialized colonizer of the human respiratory tract that has developed intricate mechanisms to establish growth and survival in the human host. Continued research is needed to further elucidate NTHi host-pathogen and pathogen-pathogen interactions.

Increased biofilm formation by nontypeable Haemophilus influenzae isolates from patients with invasive disease or otitis media versus strains recovered from cases of respiratory infections

Biofilm formation by nontypeable (NT) Haemophilus influenzae remains a controversial topic. Nevertheless, biofilm-like structures have been observed in the middle-ear mucosa of experimental chinchilla models of otitis media (OM). To date, there have been no studies of biofilm formation in large collections of clinical isolates. This study aimed to investigate the initial adhesion to a solid surface and biofilm formation by NT H. influenzae by comparing isolates from healthy carriers, those with noninvasive respiratory disease, and those with invasive respiratory disease. We used 352 isolates from patients with nonbacteremic community-acquired pneumonia (NB-CAP), chronic obstructive pulmonary disease (COPD), OM, and invasive disease and a group of healthy colonized children. We then determined the speed of initial adhesion to a solid surface by the BioFilm ring test and quantified biofilm formation by crystal violet staining. Isolates from different clinical sources displayed high levels of biofilm formation on a static solid support after growth for 24 h. We observed clear differences in initial attachment and biofilm formation depending on the pathology associated with NT H. influenzae isolation, with significantly increased biofilm formation for NT H. influenzae isolates collected from patients with invasive disease and OM compared with NT H. influenzae isolates from patients with NB-CAP or COPD and healthy colonized subjects. In all cases, biofilm structures were detached by proteinase K treatment, suggesting an important role for proteins in the initial adhesion and static biofilm formation measured by crystal violet staining.

Non-typeable Haemophilus influenzae, an under-recognised pathogen

Non-typeable Haemophilus influenzae (NTHi) is a major cause of mucosal infections such as otitis media, sinusitis, conjunctivitis, and exacerbations of chronic obstructive pulmonary disease. In some regions, a strong causal relation links this pathogen with infections of the lower respiratory tract. In the past 20 years, a steady but constant increase has occurred in invasive NTHi worldwide, with perinatal infants, young children, and elderly people most at risk. Individuals with underlying comorbidities are most susceptible and infection is associated with high mortality. β-lactamase production is the predominant mechanism of resistance. However, the emergence and spread of β-lactamase-negative ampicillin-resistant strains in many regions of the world is of substantial concern, potentially necessitating changes to antibiotic treatment guidelines for community-acquired infections of the upper and lower respiratory tract and potentially increasing morbidity associated with invasive NTHi infections. Standardised surveillance protocols and typing methodologies to monitor this emerging pathogen should be implemented. International scientific organisations need to raise the profile of NTHi and to document the pathobiology of this microbe.

Pediatric invasive Haemophilus influenzae infections in Israel in the era of Haemophilus influenzae type b vaccine: a nationwide prospective study

BACKGROUND

The conjugated Haemophilus influenzae (Hi) type b vaccine caused a marked decrease in invasive Hi disease rates. Nonencapsulated Hi infection now constitutes most invasive Hi morbidity and mortality. This study examines invasive Hi infection incidence in Israel in the postvaccine era years, 2003-2012, and characterizes the epidemiology, clinical diagnosis and case fatality rates of invasive Hi disease in children <15 years of age.

METHODS

An ongoing, nationwide prospective surveillance program for invasive Hi infections in Israel. Epidemiologic and clinical data were collected. Diagnoses were classified as meningitis, pneumonia, bacteremia/sepsis and other clinical foci.

RESULTS

Overall, 389 cases of invasive Hi infections were identified; 242 (62%) nontypable Hi (NTHi), 103 (26%) Hi type b (Hib) and 41 (11%) encapsulated non-b Hi (enbHi). Children <1 year of age accounted for 51% of the overall disease. Invasive Hi disease incidence in children <15 years of age was stable with a mean annual incidence (per 100,000) of 2.0 ± 0.4. The highest incidence of invasive Hi infections was among infants <1 year with rates of 6.2, 4.9, 1.6 and 12.7 for NTHi, Hib, enbHi and total Hi, respectively. The clinical diagnoses of NTHi and enbHi were similar, but differed from Hib with the former presenting mostly as isolated sepsis/bacteremia and the latter primarily as meningitis. Among children with invasive Hib infection, 40% were classified as vaccine failure.

CONCLUSIONS

In the post-Hib vaccination era, invasive Hi morbidity and mortality are largely attributed to NTHi sepsis. Still, with the changing epidemiology of invasive Hi, continued surveillance of all Hi strains is justified.

Oropharyngeal colonization by nontypeable Haemophilus influenzae among healthy children attending day care centers

Haemophilus influenzae colonizes the upper respiratory tract and can spread causing otitis and sinusitis. This work aimed to study the oropharyngeal carriage rate in healthy <5-year-old children attending day care centers in Oviedo, Spain in two consecutive years (January to March 2004-2005). The carriage rate was 42% (400/960) and highly variable among centers (range, 12% to 83%). Isolates were mainly identified as nontypeable H. influenzae (NTHi, 99%). Epidemiologically, 127 different genotypes were identified by PFGE with a minimum of two genotypes per center. One hundred fourteen children (12%) were included in both studies and none of them harbored the same strain over a period of time. The isolates only showed resistance to cotrimoxazol and ampicillin, presenting a shift in the level of ampicillin reduced susceptibility, showing a predominance of PBP3 mutations in 2004 and a predominance of β-lactamase production in 2005. This study proved the great genetic variability of NTHi isolates that present similar genotypic patterns in both years with no long-term carriage of the same strain.

Genome sequencing of disease and carriage isolates of nontypeable Haemophilus influenzae identifies discrete population structure

One of the main hurdles for the development of an effective and broadly protective vaccine against nonencapsulated isolates of Haemophilus influenzae (NTHi) lies in the genetic diversity of the species, which renders extremely difficult the identification of cross-protective candidate antigens. To assess whether a population structure of NTHi could be defined, we performed genome sequencing of a collection of diverse clinical isolates representative of both carriage and disease and of the diversity of the natural population. Analysis of the distribution of polymorphic sites in the core genome and of the composition of the accessory genome defined distinct evolutionary clades and supported a predominantly clonal evolution of NTHi, with the majority of genetic information transmitted vertically within lineages. A correlation between the population structure and the presence of selected surface-associated proteins and lipooligosaccharide structure, known to contribute to virulence, was found. This high-resolution, genome-based population structure of NTHi provides the foundation to obtain a better understanding, of NTHi adaptation to the host as well as its commensal and virulence behavior, that could facilitate intervention strategies against disease caused by this important human pathogen.

A PCR-high-resolution melt assay for rapid differentiation of nontypeable Haemophilus influenzae and Haemophilus haemolyticus

We have developed a PCR-high-resolution melt (PCR-HRM) assay to discriminate nontypeable Haemophilus influenzae (NTHi) colonies from Haemophilus haemolyticus. This method is rapid and robust, with 96% sensitivity and 92% specificity compared to the hpd#3 assay. PCR-HRM is ideal for high-throughput screening for NTHi surveillance and clinical trials.

Broadly protective protein-based pneumococcal vaccine composed of pneumolysin toxoid-CbpA peptide recombinant fusion protein

BACKGROUND

 Pneumococcus, meningococcus, and Haemophilus influenzae cause a similar spectrum of infections in the ear, lung, blood, and brain. They share cross-reactive antigens that bind to the laminin receptor of the blood-brain barrier as a molecular basis for neurotropism, and this step in pathogenesis was addressed in vaccine design.

METHODS

 Biologically active peptides derived from choline-binding protein A (CbpA) of pneumococcus were identified and then genetically fused to L460D pneumolysoid. The fusion construct was tested for vaccine efficacy in mouse models of nasopharyngeal carriage, otitis media, pneumonia, sepsis, and meningitis.

RESULTS

 The CbpA peptide-L460D pneumolysoid fusion protein was more broadly immunogenic than pneumolysoid alone, and antibodies were active in vitro against Streptococcus pneumoniae, Neisseria meningitidis, and H. influenzae. Passive and active immunization protected mice from pneumococcal carriage, otitis media, pneumonia, bacteremia, meningitis, and meningococcal sepsis.

CONCLUSIONS

 The CbpA peptide-L460D pneumolysoid fusion protein was broadly protective against pneumococcal infection, with the potential for additional protection against other meningeal pathogens.

CD4+ T-cell responses among adults and young children in response to Streptococcus pneumoniae and Haemophilus influenzae vaccine candidate protein antigens

We characterized cytokine profiles of CD4(+) T-helper (h) cells in adults and young children to ascertain if responses occur to next-generation candidate vaccine antigens PspA, PcpA, PhtD, PhtE, Ply, LytB of Streptococcus pneumonia (Spn) and protein D and OMP26 of non-typeable Haemophilus influenzae (NTHi). Adults had vaccine antigen-specific Th1 and Th2 cells responsive to all antigens evaluated whereas young children had significant numbers of vaccine antigen-specific CD4(+) T cells producing IL-2, (p=0.004). Vaccine antigen-specific CD4(+) T-cell populations in adults were largely of effector (TEM) and/or central memory (TCM) phenotypes as defined by CD45RA(-)CCR7(+) or CD45RA(-)CCR7(-) respectively; however among young children antigen-specific IL-2 producing CD4(+) T cells demonstrated CD45RA(+) expression (non-memory cells). We conclude that adults have circulating memory CD4(+) T cells (CD45RA(-)) that can be stimulated by all the tested Spn and NTHi protein vaccine candidate antigens, whereas young children have a more limited response.