Infections due to Haemophilus influenzae serotype E: microbiological, clinical, and epidemiological features

Clinical significance of isolation of Haemophilus no ducreyi in genital samples. Systematic review

INTRODUCTION AND OBJECTIVES

Currently, the microbiological diagnosis of genital infections is carried out with molecular methods, which allow the detection of less frequent etiological agents but with potential pathogenic importance, such as Haemophilus spp. The objective of this review is to analyse and highlight the clinical importance of the isolation of Haemophilus spp. in genital and rectal infections, excluding Haemophilus ducreyi.

MATERIAL AND METHODS

A systematic review was carried out based on an exhaustive search of the publications included in the MEDLINE database up to August 5, 2021, on the presence of Haemophilus spp. in genital and rectal infections, excluding H. ducreyi.

RESULTS

After reviewing what was described in the literature, Haemophilus spp. (excluding H. ducreyi: HSNOD) was detected in 2397 episodes of genital infection, the most frequently isolated species being H. influenzae and H. parainfluenzae. Most of the episodes (87,6%) are constituted by single isolation. There is a slight predominance in women (48,3%) where it can cause vaginitis, salpingitis, endometritis or complications during pregnancy. In men, the clinical picture usually corresponds to urethritis. Most of the samples correspond to vaginal and urethral exudates, with a minority representation at the rectal level (2.3%).

CONCLUSION

HSNOD plays a relevant pathogenic role in episodes of genital infection, so microbiological diagnostic protocols must include methods that allow their detection, as well as include them in the etiological spectrum of this type of clinical picture.

Synthesis of Pseudooligosaccharides Related to the Capsular Phosphoglycan of Haemophilus influenzae Type a

Synthesis of spacer-armed pseudodi-, pseudotetra-, and pseudohexasaccharides related to the capsular phosphoglycan of Haemophilus influenzae type a, the second most virulent serotype of H. influenzae (after type b), was performed for the first time via iterative chain elongation using H-phosphonate chemistry for the formation of inter-unit phosphodiester bridges. These compounds were prepared for the design of neoglycoconjugates, as exemplified by the transformation of the obtained pseudohexasaccharide derivative into a biotinylated glycoconjugate suitable for use in immunological studies, particularly in diagnostic screening systems as a coating antigen for streptavidin-coated plates and chip slides.

Case Report: Invasive Non Type b Haemophilus influenzae in Immunocompromised Children

Case series

Patients: Male, 2-year-old • Male, 4-year-old • Male, 2-year-old

Final Diagnosis: Immunodeficiency and Hib

Symptoms: Fever • lethargy • reduced food intake

Medication: —

Clinical Procedure: —

Specialty: Immunology

Emergence of a clone of invasive fucK-negative serotype e Haemophilus influenzae in British Columbia

BACKGROUND

Introduction of the Haemophilus influenzae serotype b (Hib) conjugate vaccine has changed the epidemiology of invasive H. influenzae disease, with most infections now caused by non-typeable (non-encapsulated) and non-Hib encapsulated strains.

METHODS

We describe nine invasive serotype e H. influenzae (Hie) from British Columbia that were determined to have complete deletion of their fucose operon genes. These nine isolates were recovered from blood cultures of three female and six male patients during 2011-2018, with eight recovered in the past 4 years.

RESULTS

All nine isolates were biotype IV, with eight showing identical pulsed field gel electrophoresis (PFGE) profiles, whereas the ninth showed 95% similarity. PFGE analysis also showed these fucose operon-negative Hie to be most (94%) similar to the multi-locus sequence type (ST)-18, the most common ST among Hie in British Columbia. These nine fucose operon-negative Hie represented 27.3% of the 33 invasive Hie isolated in British Columbia from 2010 to 2018.

CONCLUSION

Deletion of the fucose operon did not appear to impact the transmission ability of these strains or their ability to cause invasive disease.

Identification of Haemophilus influenzae serotype e strains missing the fucK gene in clinical isolates from Japan

Introduction. Certain nontypeable Haemophilus influenzae cannot be assigned a sequence type (ST) by Multilocus Sequence Typing (MLST) due to the lack of the fucK gene, one of seven MLST loci in H. influenzae, which encodes a fucose-operon enzyme.Aims. To confirm whether the loss of fucK is also found in the encapsulated strains, we analysed clinical isolates of H. influenzae serotype e (Hie).Methodology. We conducted MLST, PFGE, and antimicrobial susceptibility tests of 45 Hie strains; the majority (n=43) were derived from respiratory samples of pediatric patients at Chiba Children's Hospital between 2000 and 2016. The two remaining strains were obtained from the blood of elderly patients with invasive H. influenzae diseases (IHiDs) between 2015 and 2016 at general hospitals. For the fucK-negative strains, PCR analysis for fucose operon was also performed.Results. Four STs (ST18, 122, 621 and 1758) were assigned to 13 strains, and remaining 32 (including one associated with IHiD) were fucK-negative, completely missing the fucose operon. The allelic profiles of six other loci were identical among 31 strains and to that of ST18, 122 and 621, and these strains were genetically closely related. Forty of 45 isolates were ampicillin-sensitive.Conclusions. The loss of fucK was frequently observed in clinical isolates of Hie from children. Moreover, fucK-negative Hie may be the cause of IHiD in adult patients. The majority of Hie, including fucK-negative strains, were shown to be clonally related and were ampicillin sensitive. This represents the first report examining fucK losses in encapsulated H. influenzae.

Insights into the population structure and pan-genome of Haemophilus influenzae

The human-restricted bacterium Haemophilus influenzae is responsible for respiratory infections in both children and adults. While colonization begins in the upper airways, it can spread throughout the respiratory tract potentially leading to invasive infections. Although the spread of H. influenzae serotype b (Hib) has been prevented by vaccination, the emergence of infections by other serotypes as well as by non-typeable isolates (NTHi) have been observed, prompting the need for novel prevention strategies. Here, we aimed to study the population structure of H. influenzae and to get some insights into its pan-genome. We studied 305H. influenzae strains, enrolling 217 publicly available genomes, as well as 88 newly sequenced H. influenzae invasive strains isolated in Portugal, spanning a 24-year period. NTHi isolates presented a core-SNP-based genetic diversity about 10-fold higher than the one observed for Hib. The analysis of key factors involved in pathogenesis, such as lipooligosaccharides, hemagglutinating pili and High Molecular Weight-adhesins, suggests that NTHi shape its virulence repertoire, either by acquisition and loss of genes or by SNP-based diversification, likely towards host immune evasion and persistence. Discreet NTHi subpopulations structures are proposed based on core-genome supported with 17 candidate genetic markers identified in the accessory genome. Additionally, this study provides two bioinformatics tools for in silico rapid identification of H. influenzae serotypes and NTHi clades previously proposed, obviating laboratory-based demanding procedures. The present study constitutes an important genomic framework that could lay way for future studies on the genetic determinants underlying invasiveness and disease and population structure of H. influenzae.

Inactivation of the Thymidylate Synthase thyA in Non-typeable Haemophilus influenzae Modulates Antibiotic Resistance and Has a Strong Impact on Its Interplay with the Host Airways

Antibacterial treatment with cotrimoxazol (TxS), a combination of trimethoprim and sulfamethoxazole, generates resistance by, among others, acquisition of thymidine auxotrophy associated with mutations in the thymidylate synthase gene thyA, which can modify the biology of infection. The opportunistic pathogen non-typeable Haemophilus influenzae (NTHi) is frequently encountered in the lower airways of chronic obstructive pulmonary disease (COPD) patients, and associated with acute exacerbation of COPD symptoms. Increasing resistance of NTHi to TxS limits its suitability as initial antibacterial against COPD exacerbation, although its relationship with thymidine auxotrophy is unknown. In this study, the analysis of 2,542 NTHi isolates recovered at Bellvitge University Hospital (Spain) in the period 2010–2014 revealed 119 strains forming slow-growing colonies on the thymidine low concentration medium Mueller Hinton Fastidious, including one strain isolated from a COPD patient undergoing TxS therapy that was a reversible thymidine auxotroph. To assess the impact of thymidine auxotrophy in the NTHi-host interplay during respiratory infection, thyA mutants were generated in both the clinical isolate NTHi375 and the reference strain RdKW20. Inactivation of the thyA gene increased TxS resistance, but also promoted morphological changes consistent with elongation and impaired bacterial division, which altered H. influenzae self-aggregation, phosphorylcholine level, C3b deposition, and airway epithelial infection patterns. Availability of external thymidine contributed to overcome such auxotrophy and TxS effect, potentially facilitated by the nucleoside transporter nupC. Although, thyA inactivation resulted in bacterial attenuation in a lung infection mouse model, it also rendered a lower clearance upon a TxS challenge in vivo. Thus, our results show that thymidine auxotrophy modulates both the NTHi host airway interplay and antibiotic resistance, which should be considered at the clinical setting for the consequences of TxS administration.

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.

Epidemiology of vaccine-preventable invasive diseases in Catalonia in the era of conjugate vaccines

We investigated the incidence and distribution of cases of invasive pneumococcal disease (IPD), invasive meningococcal disease (IMD) and invasive Hemophilus influenzae disease (IHiD) notified by hospital laboratories to the Microbiological Reporting System of Catalonia between 2005 and 2009. Incidence rates were compared using the rate ratio (RR) and 95% CI were calculated. A value of p < 0.05 was considered statistically significant. Of the 6,661 cases, 6,012 were IPD, 436 IMD and 213 IHiD. The global annual incidence per 10 ( 5) inhabitants was 16.62 (95% CI 16.20-17.04) for IPD, 1.21 (95% CI 1.09-1.32) for IMD and 0.59 (95% CI 0.51-0.67) for IHiD. IPD increased in 2009 compared with 2005 (RR:1.55, 95%CI: 1.43-1.70) and IMD and IHiD remained stable. Pneumonia was the most-frequent clinical manifestation of IPD (75.6%) and IHiD (44.1%) and meningoencephalitis with or without sepsis for IMD (70.6%). The male:female ratio was 1.37 for IPD, 1.0 for IMD and 1.15 for IHiD. The age groups with the highest incidence were the ≤ 2 y and 2-4 y groups for IPD (66.40 and 50.66/100,000 persons-year) and IMD (14.88 and 7.26/100,000 persons-year) and the ≤ 2 y and ≥ 65 y groups for IHiD (1.88 and 1.89/100,000 persons-year). The most-frequent serotypes were serotype 1 (19.0%) in IPD and untypeable serotypes (60.8%) in IHiD. Serogroup B (78.3%) was the most frequent in IMD. S. pneumoniae is the most-frequent agent causing invasive disease in Catalonia. The main clinical manifestations were pneumonia in IPD and IHiD and meningitis in IMD. The main causative agent of meningitis was N. meningitidis in people aged < 20 y and S. pneumoniae in people aged ≥ 20 y. Vaccination with conjugate vaccines may reduce the risk of infectious disease in our setting.

Invasive Haemophilus influenzae serotype e and f disease, England and Wales

Incidence of serotype e was 3-fold lower than serotype f, but it caused more severe clinical disease.

Changes in serotype distribution of Haemophilus influenzae meningitis isolates identified through laboratory-based surveillance following routine childhood vaccination against H. influenzae type b in Brazil

Following routine childhood vaccination against Haemophilus influenzae type b (Hib) disease in Brazil in 1999, passive laboratory surveillance reported increasing numbers of non-b serotypes and nontypeable H. influenzae (NTHi) from meningitis cases. To characterize this increase, we analyzed data on 3910 H. influenzae isolated from cerebrospinal fluid or blood from meningitis cases that were sent to the national reference laboratory for serotyping from 1990 to 2008. Hib accounted for 98% of H. influenzae meningitis isolates received during 1990-1999 versus 59% during 2000-2008, while non-b serotypes increased from 1% to 19% and NTHi increased from 2% to 22% of H. influenzae isolates received during the two periods. Higher proportions of non-b serotypes and NTHi than Hib were isolated from blood rather than cerebrospinal fluid. Estimated incidence rates for H. influenzae meningitis for Sao Paulo state remained below 1 case per million population during 2000-2008, although annual incidence of NTHi meningitis (mean, 0.03 cases per 100,000 population) increased in several age groups. Changes in surveillance for H. influenzae following introduction of Hib conjugate vaccine likely contributed to increased numbers of non-b and nontypeable H. influenzae meningitis isolates received at the national reference laboratory.

Molecular typing methods for outbreak detection and surveillance of invasive disease caused by Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae, a review

Invasive disease caused by the encapsulated bacteria Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae remains an important cause of morbidity and mortality worldwide, despite the introduction of successful conjugate polysaccharide vaccines that target disease-associated strains. In addition, resistance, or more accurately reduced susceptibility, to therapeutic antibiotics is spreading in populations of these organisms. There is therefore a continuing requirement for the surveillance of vaccine and non-vaccine antigens and antibiotic susceptibilities among isolates from invasive disease, which is only partially met by conventional methods. This need can be met with molecular and especially nucleotide sequence-based typing methods, which are fully developed in the case of N. meningitidis and which could be more widely deployed in clinical laboratories for S. pneumoniae and H. influenzae.

Naturally fluctuating low incidence of invasive pneumococcal infections not affected by large-scale haemophilus influenzae type B vaccination

BACKGROUND

Since many pathogens colonize the child's oro/nasopharynx in a similar manner, elimination of diseases such as those caused by Haemophilus influenzae type b (Hib) has a potential of augmenting other serious infections. Streptococcus pneumoniae is an agent of special interest now that Hib conjugates have been used widely for more than 2 decades.

PATIENTS AND METHODS

All blood and cerebrospinal fluid isolations of Hib and S. pneumoniae were collected prospectively from 85,000 Finnish children at age 0-15 years by one central laboratory during 27 years.

RESULTS

Hib vaccination, launched in 1986-1988, led to a quick decline of cases until the last was detected in 1991. In the next few years, the incidence of bacteremic S. pneumoniae infections increased, but now for 15 years, the numbers of cases have been slowly declining. This finding is not explained by less active sample-taking because the number of blood cultures have almost doubled in the past years.

CONCLUSIONS

Large-scale Hib vaccination does not increase the incidence of pneumococcal diseases which continue their year-to-year fluctuation at low levels. Only a years-long follow-up permits conclusions on a vaccination's potential influence on the epidemiology of other diseases.

Invasive Haemophilus influenzae Disease, Europe, 1996-2006

An international collaboration was established in 1996 to monitor the impact of routine Haemophilus influenzae type b (Hib) vaccination on invasive H. influenzae disease; 14 countries routinely serotype all clinical isolates. Of the 10,081 invasive H. influenzae infections reported during 1996-2006, 4,466 (44%, incidence 0.28 infections/100,000 population) were due to noncapsulated H. influenzae (ncHi); 2,836 (28%, 0.15/100,000), to Hib; and 690 (7%, 0.036/100,000), to non-b encapsulated H. influenzae. Invasive ncHi infections occurred in older persons more often than Hib (median age 58 years vs. 5 years, p<0.0001) and were associated with higher case-fatality ratios (12% vs. 4%, p<0.0001), particularly in infants (17% vs. 3%, p<0.0001). Among non-b encapsulated H. influenzae, types f (72%) and e (21%) were responsible for almost all cases; the overall case-fatality rate was 9%. Thus, the incidence of invasive non-type b H. influenzae is now higher than that of Hib and is associated with higher case fatality.

Antibiotic resistance in Haemophilus influenzae decreased, except for beta-lactamase-negative amoxicillin-resistant isolates, in parallel with community antibiotic consumption in Spain from 1997 to 2007

The susceptibility to 14 antimicrobial agents and the mechanisms of aminopenicillin resistance were studied in 197 clinical isolates of Haemophilus influenzae--109 isolated in 2007 (study group) and 88 isolated in 1997 (control group). Community antibiotic consumption trends were also examined. H. influenzae strains were consecutively isolated from the same geographic area, mostly from respiratory specimens from children and adults. Overall, amoxicillin resistance decreased by 8.4% (from 38.6 to 30.2%). Beta-lactamase production decreased by 15.6% (from 33 to 17.4%, P = 0.01), but amoxicillin resistance without beta-lactamase production increased by 7.1% (from 5.7 to 12.8%). All beta-lactamase-positive isolates were TEM-1, but five different promoter regions were identified, with Pdel being the most prevalent in both years, and Prpt being associated with the highest amoxicillin resistance. A new promoter consisting of a double repeat of 54 bp was detected. Community consumption of most antibiotics decreased, as did the geometric means of their MICs, but amoxicillin-clavulanic acid and azithromycin consumption increased by ca. 60%. For amoxicillin-clavulanic acid, a 14.2% increase in the population with an MIC of 2 to 4 microg/ml (P = 0.02) was observed; for azithromycin, a 21.2% increase in the population with an MIC of 2 to 8 microg/ml (P = 0.0005) was observed. In both periods, the most common gBLNAR (i.e., H. influenzae isolates with mutations in the ftsI gene as previously defined) patterns were IIc and IIb. Community consumption of trimethoprim-sulfamethoxazole decreased by 54%, while resistance decreased from 50 to 34.9% (P = 0.04). Antibiotic resistance in H. influenzae decreased in Spain from 1997 to 2007, but surveillance should be maintained since new forms of resistances may be developing.

Capsule gene analysis of invasive Haemophilus influenzae: accuracy of serotyping and prevalence of IS1016 among nontypeable isolates

We evaluated the accuracy of serologic capsule typing by analyzing capsule genes and related markers among invasive Haemophilus influenzae isolates before and after the introduction of H. influenzae serotype b (Hib) conjugate vaccines. Three hundred and sixty invasive H. influenzae isolates were collected as part of Active Bacterial Core surveillance within the Georgia Emerging Infections Program between 1 January 1989 and 31 July 1998. All isolates were biotyped, serotyped by slide agglutination serotyping (SAST), and evaluated using PCR capsule typing. Nontypeable H. influenzae (NTHi) isolates were probed with Hib cap-gene-containing plasmid pUO38 and with IS1016; a subset was examined with phosphoglucose isomerase (pgi) genotyping and pulsed-field gel electrophoresis (PFGE). Discrepancies between SAST and PCR capsule typing were found for 64/360 (17.5%) of the isolates; 48 encapsulated by SAST were NTHi by PCR, 8 NTHi by SAST were encapsulated by PCR, 6 encapsulated by SAST were a different capsule type by PCR, and 2 encapsulated by SAST were capsule-deficient Hib variants (Hib-minus). None of the PCR-confirmed NTHi isolates demonstrated homology with residual capsule gene sequences; 19/201 (9.5%) had evidence of IS1016, an insertion element associated with division I H. influenzae capsule serotypes. The majority of IS1016-positive NTHi were biotypes I and V and showed some genetic relatedness by PFGE. In conclusion, PCR capsule typing was more accurate than SAST and Hib-minus variants were rare. IS1016 was present in 9.5% of NTHi isolates, suggesting that this subset may be more closely related to encapsulated organisms. A better understanding of NTHi may contribute to vaccine development.

Haemophilus influenzae type e meningitis and bacteremia in a healthy adult

Haemophilus influenzae type b causes more than 95% of serious H. influenzae meningitis. H. influenzae type e (Hie) has been implicated in a few cases of meningitis. Here, we present an adult Saudi patient with Hie meningitis and review the literature. The patient, a 19-year-old Saudi male with no significant past medical history, was noted by his family to have some changes in his mentation, confusion and refusal to eat; subsequently, he became unresponsive. Cerebrospinal fluid and blood culture grew Hie. The patient was treated with intravenous ceftriaxone with full recovery.

Characteristics of Haemophilus influenzae type b responsible for meningitis in Poland from 1997 to 2004

Two hundred forty-five H. influenzae isolates responsible for meningitis in Poland from 1997 to 2004 were studied. Among these, 233 (95.1%) belonged to serotype b (Hib), 2 belonged to serotype f, and 10 were noncapsulated. The relatedness of all isolates was evaluated by pulsed-field gel electrophoresis (PFGE), and selected representatives were evaluated by multilocus sequence typing. Resistance to ampicillin was identified in 34 (14.6%) of the Hib isolates and was associated with the production of beta-lactamase only. Except for four isolates nonsusceptible to chloramphenicol, all isolates were susceptible to cefotaxime, ciprofloxacin, and rifampin. The PFGE analysis divided the Hib isolates into five PFGE types; however, all of them were possibly related. The most common PFGE type, with 25 subtypes, was characteristic for 97.4% of the isolates. The most prevalent PFGE subtype found in our study was also the most common among the Hib isolates responsible for invasive disease in Italy and the Czech Republic and was found among isolates causing lower respiratory tract infections in Poland. The most prevalent sequence types (STs) in the studied group were ST6 and ST92. Four new STs were found: ST188, ST189, ST190, and ST268. Results of this study support the evidence that the genetic structure of encapsulated H. influenzae is clonal. The continuing high number of meningitis cases due to Hib in Poland underlines the need for mass vaccination against Hib in Poland.

Invasive Infections with Haemophilus influenzae Serotype a Containing an IS1016-bexA Partial Deletion: Possible Association with Virulence

BACKGROUND

Recent reports of invasive Haemophilus influenzae non-b capsular serotypes in the era since development of conjugate vaccines have prompted concern about serotype replacement. Unusual clusters of invasive infection due to H. influenzae serotype a with clinical features that resemble those of infection due to H. influenzae serotype b have been described. A unique feature often associated with more-virulent H. influenzae serotype a isolates is the IS1016-bexA partial deletion, which was previously identified in the capsule locus of H. influenzae serotype b strains. We report the clinical, epidemiologic, and molecular genetic features of 2 cases of severe disease caused by H. influenzae serotype a.

METHODS

Invasive H. influenzae isolates were serotyped with standard serological methods, and molecular typing was done with PCR. The capsular genotype of each isolate was characterized with PCR, partial sequencing, and Southern blot hybridization. Further strain typing was performed with pulsed-field gel electrophoresis.

RESULTS

We identified 2 children with severe invasive disease due to H. influenzae serotype a. Both H. influenzae serotype a isolates contained the identical pulsed-field gel electrophoresis pattern and capsular genotype. An IS1016-bexA partial deletion in the capsule gene locus similar to that found in H. influenzae serotype b was identified in both isolates by means of PCR and sequencing of the IS1016-bexA junction.

CONCLUSIONS

We describe 2 cases of severe invasive disease due to H. influenzae serotype a with the putative virulence-enhancing IS1016-bexA partial deletion and duplication of the capsule locus. Our data support the hypothesis that this mutation may be associated with virulence in non-b capsular serotypes of H. influenzae.

Prevalence and serotype distribution of encapsulated Haemophilus influenzae isolates from patients with lower respiratory tract infections in Poland

Among 1,272 H. influenzae isolates obtained from patients with lower respiratory tract infections, 5.6% were found to be encapsulated. The most common were serotypes b (40.3%) and e (38.9%) followed by serotypes f (16.7%) and d (4.1%). All encapsulated isolates within a particular serotype showed high genetic homogeneity and did not produce beta-lactamases.

Analysis of invasive Haemophilus influenzae infections after extensive vaccination against H. influenzae type b

Little clinical and microbiological information is available about invasive Haemophilus influenzae infection after widespread vaccination against H. influenzae type b (Hib). We conducted an active community surveillance study on invasive H. influenzae during a 2-year period in a community of more than 5 million people after vaccination against Hib in children was introduced. The median incidence was 16.3 cases/100000 persons per year in children less than 1-year-old and 4.41 cases/100000 persons in children less than <5 years old. The highest incidence in adults was observed in patients greater than 70 years old. Clinical diagnoses included bacteremia, pneumonia, and meningitis. Of the H. influenzae-infected patients, 74.3% had underlying predisposing conditions, including impaired immunity and respiratory diseases. A total of 73.6% of the isolates were nontypeable and 16.5, 6.6, and 3.3% were types b, f, and e, respectively. Infections due to capsulated strains b, e, and f were evenly distributed between children and adults. Ampicillin and cotrimoxazole resistance occurred at frequencies of 24.2 and 48.4%, respectively. Antibiotic resistance was more prevalent in capsulated than in noncapsulated H. influenzae. Invasive isolates were highly resistant to antibiotics that were used infrequently in the community. Nontypeable H. influenzae were genetically much more heterogeneous than capsulated strains. Capsule-deficient mutants (b(-)) were not detected. Plasmid carriage was linked to antibiotic resistance and capsulated strains. Over the study period, the incidence of invasive H. influenzae infections, either encapsulated or not, did not increase. In the post-Hib vaccination era, most invasive infections were due to noncapsulated strains and occurred in the extreme ages of life in patients with predisposing conditions.