Changing patterns of invasive Haemophilus influenzae disease in England and Wales after introduction of the Hib vaccination programme

Epidemiology and burden of Haemophilus influenzae disease in Thai children before implementation of the routine immunisation programme: A National Health Data Analysis

OBJECTIVES

To conduct the first pre-Haemophilus influenzae (Hi) type b (Hib) immunisation programme-based epidemiological study using national health data.

METHODS

We analysed National Health Security Office data, which cover 72% of the Thai population. The study population included children aged <18 years admitted for Hi disease from 2015 to 2019. Hi disease diagnosis and death were based on the International Statistical Classification of Diseases and Related Health Problems (10th revision) hospital discharge summary codes. We estimated the hospital cost per admission using diagnosis-related grouping with a global budget.

RESULTS

A total of 1125 children aged <18 years were admitted for Hi disease. During the 5-year-study, the annual incidence of Hi disease varied from 1.5 to 1.9 per 100,000 children, with an overall case fatality rate (CFR) of 2%. Pneumonia was the most common clinical form, followed by meningitis and sepsis. The incidence, clinical forms and severity of Hi disease were age specific. Infant CFR was higher than that of other age groups. The incidence of Hi disease in children aged <5 years was 4.9 per 100,000 (CFR = 2.0%). Sepsis was the primary cause of infant death, whereas pneumonia was the cause of death in children aged >5 years. The hospital cost ranged from 25,000 to 30,000 THB per admission.

CONCLUSIONS

This analysis provided epidemiological data of Hi in Thai children before the Hib routine immunisation programme. The incidence of Hi disease was lower than that previously speculated. Our results could facilitate an assessment of the impact of Hib immunisation programme in Thailand.

Molecular epidemiology of imipenem resistance in invasive Haemophilus influenzae infections in Germany in 2016

BACKGROUND

The carbapenems imipenem and meropenem play an important role in the empirical anti-infective treatment of critically ill patients. Carbapenem resistance in Haemophilus influenzae (Hi) has rarely been reported.

OBJECTIVES

We provide prevalence data for resistance to carbapenems from laboratory surveillance of invasive Hi infections in Germany in 2016.

METHODS

Phenotypic susceptibility testing against ampicillin, amoxicillin/clavulanate, cefotaxime and imipenem was carried out on 474 isolates from blood and CSF. The isolates were collected as part of the national laboratory surveillance programme. Imipenem-resistant strains were further tested for meropenem susceptibility. Molecular analysis was done by ftsI sequencing to detect mutations in PBP3, by acrR sequencing to detect alterations in the regulatory protein of the AcrAB-TolC efflux pump and by MLST.

RESULTS

No resistance to meropenem was detected. Cefotaxime resistance was rare (n = 3; 0.6%). Imipenem resistance was found in 64 strains (13.5%) using gradient agar diffusion and was confirmed in 26 isolates by broth microdilution (5.5%). Imipenem resistance occurred predominantly in Hi that were β-lactamase negative but ampicillin resistant and in those that were β-lactamase positive but nevertheless amoxicillin/clavulanate resistant. This finding suggested a β-lactamase-independent mechanism. Accordingly, sequence analysis of PBP3 identified previously described mutations. MLST of the imipenem-resistant strains, which were all non-typeable Hi, revealed a high diversity.

CONCLUSIONS

We conclude that imipenem, but not meropenem, resistance is frequent in Hi. It is likely to be supported by PBP3 mutations.

Cracking the Challenge of Antimicrobial Drug Resistance with CRISPR/Cas9, Nanotechnology and Other Strategies in ESKAPE Pathogens

Antimicrobial resistance is mushrooming as a silent pandemic. It is considered among the most common priority areas identified by both national and international agencies. The global development of multidrug-resistant strains now threatens public health care improvement by introducing antibiotics against infectious agents. These strains are the product of both continuous evolution and unchecked antimicrobial usage (AMU). The ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are the leading cause of nosocomial infections throughout the world. Most of them are now multidrug-resistant, which pose significant challenges in clinical practice. Understanding these bacteria’s resistance mechanisms is crucial for developing novel antimicrobial agents or other alternative tools to fight against these pathogens. A mechanistic understanding of resistance in these pathogens would also help predict underlying or even unknown mechanisms of resistance of other emerging multidrug-resistant pathogens. Research and development to find better antibacterial drugs and research on tools like CRISPER-Cas9, vaccines, and nanoparticles for treatment of infections that can be further explored in the clinical practice health sector have recognized these alternatives as essential and highly effective tools to mitigate antimicrobial resistance. This review summarizes the known antimicrobial resistance mechanisms of ESKAPE pathogens and strategies for overcoming this resistance with an extensive overview of efforts made in this research area.

The impact of human vaccines on bacterial antimicrobial resistance. A review

At present, the dramatic rise in antimicrobial resistance (AMR) among important human bacterial pathogens is reaching a state of global crisis threatening a return to the pre-antibiotic era. AMR, already a significant burden on public health and economies, is anticipated to grow even more severe in the coming decades. Several licensed vaccines, targeting both bacterial (Haemophilus influenzae type b, Streptococcus pneumoniae, Salmonella enterica serovar Typhi) and viral (influenza virus, rotavirus) human pathogens, have already proven their anti-AMR benefits by reducing unwarranted antibiotic consumption and antibiotic-resistant bacterial strains and by promoting herd immunity. A number of new investigational vaccines, with a potential to reduce the spread of multidrug-resistant bacterial pathogens, are also in various stages of clinical development. Nevertheless, vaccines as a tool to combat AMR remain underappreciated and unfortunately underutilized. Global mobilization of public health and industry resources is key to maximizing the use of licensed vaccines, and the development of new prophylactic vaccines could have a profound impact on reducing AMR.

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.

Predicting the Impact of Typhoid Conjugate Vaccines on Antimicrobial Resistance

Background

Empiric prescribing of antimicrobials in typhoid-endemic settings has increased selective pressure on the development of antimicrobial-resistant Salmonella enterica serovar Typhi. The introduction of typhoid conjugate vaccines (TCVs) in these settings may relieve this selective pressure, thereby reducing resistant infections and improving health outcomes.

Methods

A deterministic transmission dynamic model was developed to simulate the impact of TCVs on the number and proportion of antimicrobial-resistant typhoid infections and chronic carriers. One-way sensitivity analyses were performed to ascertain particularly impactful model parameters influencing the proportion of antimicrobial-resistant infections and the proportion of cases averted over 10 years.

Results

The model simulations suggested that increasing vaccination coverage would decrease the total number of antimicrobial-resistant typhoid infections but not affect the proportion of cases that were antimicrobial resistant. In the base-case scenario with 80% vaccination coverage, 35% of all typhoid infections were antimicrobial resistant, and 44% of the total cases were averted over 10 years by vaccination. Vaccination also decreased both the total number and proportion of chronic carriers of antimicrobial-resistant infections. The prevalence of chronic carriers, recovery rates from infection, and relative fitness of resistant strains were identified as crucially important parameters.

Conclusions

Model predictions for the proportion of antimicrobial resistant infections and number of cases averted depended strongly on the relative fitness of the resistant strain(s), prevalence of chronic carriers, and rates of recovery without treatment. Further elucidation of these parameter values in real-world typhoid-endemic settings will improve model predictions and assist in targeting future vaccination campaigns and treatment strategies.

The adhesins of non-typeable Haemophilus influenzae

INTRODUCTION

Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen of the respiratory tract and the greatest contributor to invasive Haemophilus disease. Additionally, in children, NTHi is responsible for the majority of otitis media (OM) which can lead to chronic infection and hearing loss. In adults, NTHi infection in the lungs is responsible for the onset of acute exacerbations in chronic obstructive pulmonary disease (COPD). Unfortunately, there is currently no vaccine available to protect against NTHi infections. Areas covered: NTHi uses an arsenal of adhesins to colonise the respiratory epithelium. The adhesins also have secondary roles that aid in the virulence of NTHi, including mechanisms that avoid immune clearance, adjust pore size to avoid antimicrobial destruction, form micro-colonies and invoke phase variation for protein mediation. Bacterial adhesins can also be ideal antigens for subunit vaccine design due to surface exposure and immunogenic capabilities. Expert commentary: The host-pathogen interactions of the NTHi adhesins are not fully investigated. The relationship between adhesins and the extracellular matrix (ECM) play a part in the success of NTHi colonisation and virulence by immune evasion, migration and biofilm development. Further research into these immunogenic proteins would further our understanding and enable a basis for better combatting NTHi disease.

Laryngitis, Epiglottitis and Pharyngitis

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Croup is the most common cause of stridor in children, caused by acute viral infection in most cases (parainfluenza) and mainly affects young children between 6 months and 3 years old.

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Treatment with oral corticosteroids and nebulized adrenaline reduced the rate of hospitalization and complications.

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The diagnoses of bacterial epiglottitis and viral laryngotracheobronchitis (croup) in infants and children may be confused.

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Epiglottitis is an acute inflammation of the epiglottis or supraglottis that may lead to the rapid onset of life-threatening airway obstruction caused by Haemophilus influenzae type b (Hib) and is an otolaryngologic emergency. Since the widespread implementation of a conjugate vaccine for Hib, the incidence of epiglottitis significantly declined in children and there was a consequent shift in disease from young children to adults.

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The management of epiglottitis includes securing the airways and appropriate antibiotics (ceftriaxone).

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Group A streptococcus is a frequent cause of pharyngitis that can be diagnosed by rapid antigen-detection test. Antibiotic treatment reduces the risk of complications, including rheumatic fever and acute glomerulonephritis.

Naturally acquired and conjugate vaccine-induced antibody to Haemophilus influenzae type b (Hib) polysaccharide in Malian children: serological assessment of the Hib immunization program in Mali

Haemophilus influenzae type b (Hib) conjugate vaccine for infants (6, 10, and 14 weeks of age) was introduced into the Malian Expanded Program on Immunization in July 2005, to diminish invasive Hib disease in young children. Antibodies to Hib capsular polysaccharide (PRP) were measured in infants and toddlers from an area already served by the Hib immunization program (Bamako) and in unimmunized children of the same age in a district (Kangaba) where Hib immunization had not yet begun. Among vaccinated Bamako children 6-23 months of age, 77-93% exhibited PRP titers ≥ 1.0 μg/mL, indicating long-term protection, versus only 10-23% of Kangaba children of that age. High PRP antibody titers in immunized children persisted through 2 years of age. Moreover, ∼50% of Bamako children exhibited anti-PRP titers ≥ 5.0 μg/mL; a level that impedes Hib upper respiratory carriage, and may thereby diminish the Hib transmission to the unimmunized susceptible population (i.e., providing indirect protection).

New insights into rotavirus vaccines

Rotavirus vaccines have shown to be effective and well tolerated in clinical trials. However it's crucial to point out that immunization occurs in "real-word" conditions different from ideal clinical trial settings. Thus, the impact of rotavirus vaccines in terms of effectiveness and safety needs to be evaluated in real-world conditions. Post-licensure data regarding vaccine impact, effectiveness and safety under routine use are now available and provide a "real-world view". We reviewed published data about the impact of rotavirus vaccines in the post-licensure era.

Two decades of experience with the Haemophilus influenzae serotype b conjugate vaccine in the United Kingdom

BACKGROUND

The Haemophilus influenzae serotype b (Hib) conjugate vaccine was introduced into the UK national childhood immunization program in 1992 after clinical trials reported the vaccine to be highly immunogenic in infants as young as two months of age.

OBJECTIVE

The goal of this study was to describe and comment on the impact of routine Hib immunization on the epidemiology of invasive Hib disease in the United Kingdom. In addition, the development of Hib polysaccharide and conjugate vaccines was reviewed.

METHODS

A literature search was conducted of PubMed for invasive Hib disease epidemiology in the United Kingdom. The UK Health Protection Agency Web site was also searched for relevant publications.

RESULTS

The incidence of invasive Hib incidence in children aged <5 years fell from 21/100,000 to 44/100,000 in the prevaccine era to 0.63/100,000 in 1998, with an estimated vaccine failure rate of 2.2/100,000 vaccinees. After 1999, however, invasive Hib disease increased, particularly in toddlers, and peaked in 2003. Potential reasons for the resurgence included a greater-than-expected decline in Hib antibodies after primary immunization, waning of herd immunity offered by the initial catch-up campaign, and use of a less immunogenic Hib combination vaccine containing acellular pertussis in 2000-2001. In response to the resurgence, a Hib combination vaccine containing whole-cell pertussis was reintroduced in 2002, followed by a childhood Hib booster campaign in 2003. In 2004, the recommended infant vaccine was changed to a different Hib/acellular pertussis combination vaccine containing inactivated polio, which had a satisfactory Hib response, was less reactogenic, and eliminated the risk of vaccine-associated paralytic poliomyelitis. This action was followed by introduction of a routine 12-month Hib booster in 2006. Together, these measures led to a decline in invasive Hib disease across all age groups. In 2010, there were only 30 invasive Hib cases, with 6 reported in children aged <5 years and no deaths in this age group since 2007.

CONCLUSIONS

Control of Hib disease is currently the best that has been achieved since the introduction of the routine Hib vaccination almost 20 years ago.

Acute supraglottitis in adults

OBJECTIVES

Adult supraglottitis is a potentially life-threatening airway infection. We reviewed the management and outcome of supraglottitis in 169 adults admitted to Liverpool Hospital between 1999 and 2009.

METHODS

A retrospective review was conducted of all admissions with supraglottitis in patients at least 18 years of age. The diagnosis was confirmed by fiberoptic nasolaryngoscopy or direct laryngoscopy under general anesthesia. The main outcome measure was the need for intubation or tracheotomy. Univariate analysis was performed to determine factors that led to a worse outcome.

RESULTS

There were 80 men and 89 women in the cohort, with a median age of 51 years. Of these, 140 patients were admitted to the intensive care unit for a mean duration of 2 days. The common symptoms and signs at presentation were odynophagia and dysphagia (94%), dysphonia (65%), and stridor (33%). Endotracheal intubation was performed in 16 patients, and an awake tracheotomy was required in 4 patients. Dexamethasone acetate was used in 103 patients. Thirty-five patients had diabetes mellitus as a comorbidity. The presence of diabetes was predictive of the need for intubation or tracheotomy (p < 0.05), and the use of steroids was predictive of an intensive care unit stay of 24 hours or less (p < 0.05).

CONCLUSIONS

Fiberoptic laryngoscopy is the gold standard for diagnosis of supraglottitis, and close airway monitoring is crucial. Conservative management of the airway is a viable option, but the presence of diabetes makes airway intervention more likely. The use of steroids aids in symptom alleviation and hastens resolution of airway swelling, with no negative sequelae.

Maternal and neonatal sepsis caused by Haemophilus influenzae type d

A 29-year-old pregnant woman was admitted to hospital with signs of sepsis and threatened pre-term labour. The premature neonate also showed signs of sepsis. Haemophilus influenzae biotype III was cultured from a midstream urine sample taken from the mother, maternal placental swabs and neonatal blood cultures. The placental and neonatal isolates were both found to be serotype d by PCR, and were indistinguishable by PFGE.

Haemophilus influenzae serotype b conjugate vaccine failure in twelve countries with established national childhood immunization programmes

The present study describes the clinical and immunological features of children with Hib vaccine failure, who were identified through national surveillance between 1996 and 2001 in Europe, Israel and Australia. True vaccine failure was defined as invasive Hib disease occurring ≥2 weeks after one dose, given after the first birthday, or ≥1 week after ≥2 doses, given at <1 year of age. Of the 423 cases (representing 0.2 cases per 100,000 child-years at risk) reported, 330 (78%) had received three doses in the first year of life and developed disease at a median age of 28 months. Of the remaining 93, 48 had received two doses in infancy, 34 had received four doses including a booster, and 11 had received a single dose after 12 months of age. These children developed disease at a median age of 12, 33 and 71 months, respectively. In total, 47 out of 258 children (18%) with available information had an underlying medical problem (including prematurity) and 53 out of 161 (33%) had immunoglobulin deficiency. Convalescent Hib antibody concentrations were above the putative protective concentration of 1.0 mg/L in 147/194 (76%) children; low concentrations were associated with both the presence of an underlying medical problem and young age at the time of Hib disease. Almost all children who received an additional vaccine dose developed antibodies at protective concentrations. Thus, Hib vaccine failure is rare, but can occur with any immunization schedule. Children with Hib vaccine failure should have immunoglobulin and convalescent Hib antibody concentrations measured after infection and receive additional vaccination, if required.

Community effect of Haemophilus influenzae type b vaccination in India

We assessed the effect of distribution of Haemophilus influenzae type b (Hib) vaccine in the private health care sector on Hib meningitis admissions at a referral hospital in India. The annual mean number of Hib cases was 10.7 before Hib vaccine introduction, falling to 3.8 cases following introduction (P < 0.0001). By contrast, the mean of annual numbers of pneumococcal cases were 3.0 and 4.6, (P = 0.55). Even at relatively low coverage through private sector distribution, Hib vaccine has significant community impact on Hib disease.

Invasive Haemophilus influenzae infections in Germany: impact of non-type b serotypes in the post-vaccine era

Background

Haemophilus influenzae type b (Hib) vaccination led to a significant decrease in invasive bacterial infections in children. The aim of this study was to assess a potential shift to more non-type b invasive infections in a population with high Hib vaccination coverage and to compare the burden of suffering between children with Hib, capsulated non-b and non-capsulated Hi infections.

Methods

Cases with confirmed invasive Hi infections were ascertained through two independent nationwide active surveillance systems in 1998–2005. Information on possible predisposing conditions and clinical information was available from 2001 onwards.

Results

The total number of reported non-type b Hi cases varied between 10 cases in 1998, 27 in 2000 and 14 in 2005. In each year, non-capsulated serotypes outnumbered capsulated non-type b ones. 192 cases were detected in 2001–2005, more than one half was non-type b and 88% of the non-type b cases were non-capsulated. For cases with Hib/capsulated non-type b infections the most common clinical presentation was meningitis (67% each); 89%/78% had no potential predisposing condition, 75%/72% completely recovered from disease and 6% (each) died. In contrast, meningitis was diagnosed in 34% of the non-capsulated Hi infections, septicaemia in 28% and pneumonia 21%; 62% had no potential predisposing condition, 83% completely recovered and 3% died.

Conclusion

There was no increase in non-type b Hi invasive infections during 8 years of active surveillance in Germany. Invasive disease due to non-type b Hi is not confined to children with risk factors. In patients with capsulated non-type b Hi infections the proportion of meningitis cases is similar to Hib, but double as high as in non-capsulated Hi.

Effectiveness of hexavalent vaccines against invasive Haemophilus influenzae type b disease: Germany's experience after 5 years of licensure

Vaccine effectiveness (VE) was determined with a case-cohort approach using Cox regression. Cases with confirmed systemic Hib infections in children born from 1 August 2000 to 31 December 2004 were ascertained through two independent nationwide active surveillance systems. A representative cohort of 1303 children born in the same time frame was randomly sampled in a nationwide immunisation survey. Thirty cases were eligible for VE calculation; 19 were unvaccinated and 11 vaccinated with hexavalent vaccines. VE was 68.4% (95% CI: 19.0-87.6) for incomplete primary series and 90.4% (95% CI: 70.6-96.8) for the full primary series. For full immunisation VE was 100.0% (95% CI: 52.7-100.0). Hexavalent vaccines show a high effectiveness against invasive Hib disease in Germany.

Introduction of Hib vaccine into national immunization programmes: A descriptive analysis of global trends

Despite the demonstration of effectiveness and public health impact of Hib conjugate vaccines, the majority of infants from poorest countries do not yet have access to this safe and effective preventive intervention. This paper provides a descriptive analysis of the main characteristics of countries that have included Hib vaccine in their national immunization programmes before 2006. It highlights the importance of regularly analyzing the process of decision-making involved in implementation of public health interventions, in order to learn from cumulative experience and expedite the introduction of future interventions.

The effects of mass immunization on Haemophilus influenzae type B-related orthopaedic disease

Haemophilus influenzae type B has been responsible for a significant proportion of cases of septic arthritis in children in the past. This study looks at the effects of vaccination on childhood orthopaedic infection. Data were collected from 1988 by the Public Health Laboratory Services. Data were analysed with a two-sample t-test. A total of 16 of 17 cases were attributed to H. influenzae type B. Fourteen cases occurred in 5 years before mass immunization. Only two cases occurred in the 8 years following immunization. The incidence of H. influenzae septic arthritis in children has fallen significantly since the introduction of immunization (P=0.009). Vaccination has resulted in a significant fall in the incidence of H. influenzae type B septic arthritis in children.

Changes in ascertainment of Hib and its influence on the estimation of disease incidence in the United Kingdom

Enhanced surveillance for Hib infection, initially covering Wales and five English regions, began in 1990 and in 1995 was extended to the whole of England and Wales. To determine whether changes in the ascertainment of Haemophilus influenzae may have affected estimates of Hib disease incidence, data from January 1990 to December 2003 were analysed. A total of 8887 and 4020 (45%) cases of H. influenzae and Hib respectively were reported. The proportion of isolates that were serotyped increased over time, and therefore reported incidence may have underestimated the true incidence in the early years of the study. Adjusting for this under-ascertainment, the incidence in children aged <5 years declined from a peak of 28.3/100,000 in 1991 to 0.97/100,000 in 1998 and increased to 3.8/100,000 in 2003. Following the implementation of universal vaccination a dramatic decline in the true incidence of invasive Hib disease occurred. The observation of the subsequent resurgence was real but the highest incidence reached was 85% below the corrected incidence in the pre-vaccine era. Continued high-quality surveillance is needed in order to accurately monitor and detect changes in disease incidence.

Acute bacterial meningitis in children presenting to the Royal Liverpool Children's Hospital, Liverpool, UK and the Queen Elizabeth Central Hospital in Blantyre, Malawi: a world of difference

BACKGROUND

Bacterial meningitis is a serious childhood illness worldwide. Children can now be immunised against meningitis with conjugate vaccines. The outcome of bacterial meningitis in British and Malawian children before the introduction of these vaccines was compared.

METHODS

All children with culture-positive bacterial meningitis treated in the Royal Liverpool Children's Hospital (RLCH), UK during 1984-1991 (n=197) and in the Children's Unit, Queen Elizabeth Central Hospital (QECH), Blantyre, Malawi during 1996-1997 (n=175) were studied.

RESULTS

Children at QECH presented later and were more often comatose and malnourished. Mortality was 7% in RLCH compared with 41% in QECH. Three organisms caused most cases of meningitis: N. meningitidis 56% vs 4%, H. influenzae b 27% vs 25%, and S. pneumoniae 11% vs 35% in RLCH and QECH, respectively. Mortality was lower in RLCH for each organism: N. meningitidis 10% vs 28%, H. influenzae b 6% vs 43%, S. pneumoniae 0% vs 46%.

CONCLUSIONS

Mortality from bacterial meningitis in Malawian children is much higher than in British children, even when infected with the same organisms. This might be owing to delay in presentation, malnutrition and HIV infection. Immunisation of Malawian children with conjugate vaccines should continue to develop since their risk of dying from meningitis is five times greater than that of British children.

Molecular epidemiology of Haemophilus influenzae type b causing vaccine failures in the United Kingdom

Haemophilus influenzae type b (Hib) was a major cause of pediatric disease in the United Kingdom prior to the introduction of routine Hib immunization in 1992. An unexpected resurgence of cases of vaccine failure was observed with fully vaccinated children from 1999 onward. We investigated whether Hib isolates causing vaccine failures in the United Kingdom could have undergone a change in their population structure to elude the protective effect of Hib vaccine. Molecular epidemiology studies were carried out with 376 isolates from invasive infections (164 vaccine failures and 212 controls). Genetic variability was higher in controls than in vaccine failures. Of the four major clusters obtained, cluster I comprised 92.2% of the total isolates: 156 vaccine failures (95%) and 193 (91%) controls. Cluster IV was specific for vaccine failures but included only four isolates. The increased number of cases of invasive Hib in fully vaccinated children in the United Kingdom was caused by isolates belonging not to a particular or new genotype but to genotypes already circulating in the prevaccination era, before conjugate Hib vaccines were available.

Influence of genetic and environmental factors on the immunogenicity of Hib vaccine in Gambian twins

The differences in incidence rates of Haemophilus influenzae type b disease and the variation in Hib conjugate vaccine efficacy achieved among different ethnic groups suggest genetic influences on the immune response to Hib vaccine. The serum anti-PRP antibody concentration of 43 monozygotic (MZ) and 147 dizygotic (DZ) twin pairs in the Gambia was measured using a standardised Hib ELISA. Intrapair correlations for MZ and DZ twin pairs were compared and heritability in antibody responses to Hib conjugate vaccine was estimated to be 51% (95% CI: 32-66%), indicating a significant genetic contribution in the response. We conclude that genetic factors may be involved in the variation in immune response to Hib vaccine observed in different populations and may contribute to cases of vaccine failure.

Epiglottitis in Sydney before and after the introduction of vaccination againstHaemophilus influenzaetype b disease

BACKGROUND

Acute epiglottitis due to infection with Haemophilus influenzae type b (Hib) is much less common in children following the introduction of Hib vaccination; however, adult epiglottitis cases have not decreased. In addition, epiglottitis hospitalizations are consistently more numerous than notifications and the reason for this is not clear.

AIMS

To more accurately describe the clinical, aetiological and epidemiological features of epiglottitis and to ascertain the accuracy of hospitalization data in an era of widespread Hib vaccination.

METHODS

Medical records in 11 public hospitals in three area health services in New South Wales with a principal or stay diagnosis (International Classification of Diseases (ICD)-9-CM or ICD-10-AM code) of acute epiglottitis between July 1990 and June 1992 (prior to Hib vaccination = pre-vaccine era) and July 1998 and June 2000 (widespread Hib vaccination = vaccine era) were reviewed. Case definitions of epiglottitis were applied.

RESULTS

One hundred and forty-two records were identified (114 pre-vaccine era and 28 vaccine era). Incorrect coding was more common in vaccine era records (32 vs 7%). Of correctly coded records, adults over 20 years old comprised the majority in the vaccine era (84 vs 17%). Hib bacteraemia was identified in 62% of cases in the pre-vaccine era compared to no cases in the vaccine era, despite equivalent blood cultures being taken between the two eras (84 vs 74%). Streptococcus pneumoniae was the only other organism isolated. Three deaths were recorded (1 child, 2 adults), all in the pre-vaccine era.

CONCLUSIONS

Acute epiglottitis hospitalizations in the current Hib vaccine era are predominantly in adults, and rarely are Hib or other causative organisms identified, although microbiological data are often incomplete. The discrepancy between hospitalization and notification data appears to be due to misclassification of hospitalization records.

Occurrence of Haemophilus influenzae strains in three Brazilian states since the introduction of a conjugate Haemophilus influenzae type b vaccine

Few vaccines in history have induced such a dramatic decline in incidence over such a short period of time as the Haemophilus influenzae type b (Hib) conjugate. This vaccine was introduced in 1988 in the United States, but only in 1999 was Hib immunization introduced by the Brazilian Ministry of Health as part of the routine infant National Immunization Program. The authors analyzed 229 H. influenzae (Hi) isolates from Public Health Laboratories in three Brazilian states: Pernambuco (Northeast, N = 54), Santa Catarina (South, N = 19), and Rio de Janeiro (Southeast, N = 156). The isolates were collected from Brazilian children 0-10 years of age with meningitis and other infections from 1990 to 2003 and were part of the research collection of the National Institute of Quality Control in Health, FIOCRUZ. Bacterial strains were characterized by serotyping and biotyping. During the pre-vaccination period the prevalence infection due to Hib was of 165 isolates and only 2 non-b Hi among all the notified meningitis infections caused by Hi. Our results showed a significant decrease in the prevalence of Hib meningitis from 165 to 33 isolates after 1999. However, during the post-vaccination period of 2001-2003 we observed an increase in the number of non-b Hi isolates: only 2 non-b strains isolated from 1990 to 1999 and 29 from 1999 to 2003. Based on the present data, the authors emphasize the need for more sensitive epidemiological and bacteriological studies aiming the improvement of the available Hib vaccine, in order to protect the susceptible population to infections due to other serological types of Hi and the reevaluation of immunization schedules used by the National Immunization Program.

Four and one-half-year follow-up of the effectiveness of diphtheria-tetanus toxoids-acellular pertussis/Haemophilus influenzae type b and diphtheria-tetanus toxoids-acellular pertussis-inactivated poliovirus/H. influenzae type b combination vaccines in Germany

BACKGROUND

Recently an increase in the number of invasive Haemophilus influenzae type b (Hib) cases was observed in the United Kingdom, which coincided with a temporary change from diphtheria-tetanus toxoids-wild-type pertussis to diphtheria-tetanus toxoids-acellular pertussis (DTaP) Hib vaccines. A study in Germany based on approximately 2 years of follow-up, estimated vaccine effectiveness (VE) of DTaP/Hib and DTaP-inactivated poliovirus/Hib combination vaccines against invasive Hib disease to be high.

OBJECTIVES

To assess VE of DTaP-containing Hib vaccines against Hib in Germany with the use of extended follow-up of case surveillance and vaccine uptake.

SUBJECTS AND METHODS

Cases with confirmed systemic Hib infections in children born between June 1, 1996 and December 31, 1998 were ascertained by a nationwide active surveillance system from January 1998 through June 2002. A representative subcohort of 667 children born in the same time frame was randomly sampled in a nationwide vaccine coverage survey. VE was determined with a case-cohort approach of Cox regression with time-dependent covariates.

RESULTS

Thirty-six cases of Hib disease were reported. Of these, 10 were vaccinated with DTaP-containing Hib vaccines only and 20 were not vaccinated. Of the 10 vaccinated cases, 4 had received an incomplete primary series (1-2 doses), and 6 had received the full primary series (3 doses), 3 of whom also received the booster dose. VE of combination vaccines against invasive Hib infection was 89.6% [95% confidence interval (CI), 67.0-96.7] for an incomplete primary series, 96.7% (95% CI 87.7-99.1) for a full primary series and 98.5% (95% CI 94.5-99.6) for a booster dose (irrespective of priming).

CONCLUSION

Hib combination vaccines containing acellular pertussis antigens continue to be highly effective in Germany.

Twenty year surveillance of invasive pneumococcal disease in Nottingham: serogroups responsible and implications for immunisation

AIMS

To evaluate the incidence, spectrum of clinical manifestations, and outcome of invasive pneumococcal disease (IPD) in children. To determine the major serogroups of Streptococcus pneumoniae responsible for invasive disease and the potential coverage by the new pneumococcal conjugate vaccines.

METHODS

Analysis of prospectively recorded information of all children admitted to two teaching hospitals in Nottingham with IPD between January 1980 and December 1999.

RESULTS

A total of 266 episodes of IPD in children were identified; 103 (39%) were aged <1 year and 160 (60%) <2 years. Major clinical presentations were meningitis in 86 (32%), pneumonia in 82 (31%), and bacteraemia without an obvious focus in 80 (30%). The age specific mean annual incidence rates of IPD overall among children aged <1, <2, and <5 years were 47.1, 37.8, and 20 per 100 000 population, respectively. Mortality rates for children with meningitis and non-meningitic infection were 20% and 7%, respectively. Neurological sequelae following meningitis were documented in 16 (26%) of the 61 survivors assessed. The potential coverage rates in children between the ages of 6 months and 5 years are 84% by the 7-valent, 91% by the 9-valent, and 95% by the 11-valent conjugate vaccines.

CONCLUSION

This study indicates that inclusion of a pneumococcal conjugate vaccine in the primary immunisation programme in the UK would have a considerable effect on the mortality and morbidity associated with IPD.

Safety, reactogenicity and immunogenicity of a combined hexavalent tetanus, diphtheria, acellular pertussis, hepatitis B, inactivated poliovirus vaccine and Haemophilus influenzae type b conjugate vaccine, for primary immunization of infants

Safety, reactogenicity and immunogenicity of GSK Biologicals' hexavalent DTPa-HBV-IPV/Hib vaccine (Infanrix)hexa) was assessed when used for primary vaccination at 3, 4 and 5 months of age (N = 2163), compared to the separate administration of DTPa-IPV/Hib and HBV vaccines (N = 720). A similar safety and reactogenicity profile was demonstrated for both vaccine regimens, as well as a good immune response for all antigen components. By offering protection against six diseases in a series of single injections, the hexavalent DTPa-HBV-IPV/Hib vaccine was shown to be a safe, well tolerated and immunogenic alternative to primary immunization with licensed separately administered vaccines.

Comparison of usefulness of randomly amplified polymorphic DNA and amplified-fragment length polymorphism techniques in epidemiological studies on nasopharyngeal carriage of non-typable Haemophilus influenzae

Randomly amplified polymorphic DNA (RAPD) and automated amplified-fragment length polymorphism (AFLP) techniques with fluorescently labelled primers were used to type non-serotypable Haemophilus influenzae (NTHI) isolates. Eighty-seven isolates from healthy children attending day-care centres or living at orphanages in southern Poland were investigated. Through comparison of the AFLP data with RAPD analysis, it has been concluded that the discriminatory power of AFLP for NTHI typing is higher than RAPD. Generally, the NTHI isolates analysed were highly heterogeneous, as detected with a HindIII/TaqI AFLP genotyping scheme on intra/inter similarity levels of 94 and 96 % using Pearson's correlation coefficient. The range of similarity values found for isolates from children permanently residing at a particular day-care centre was much wider than that for isolates from orphanages. AFLP can efficiently access NTHI strain diversity and can monitor their turn-over for comparative typing in local and inter-local epidemiological investigations.

Vaccines against bacterial meningitis

Meningitis remains an important cause of morbidity and mortality among children >5 years of age and is especially prevalent in developing countries. Effective routine immunization against Hib, pneumococcus and serogroupC meningococcus has had a significant impact on both invasive disease and carriage caused by these encapsulated bacteria. The major challenge in prevention of meningitis remains the delivery of vaccines worldwide, especially to resource-poor regions with the greatest disease burden.

The effect of HIV infection on paediatric bacterial meningitis in Blantyre, Malawi

AIM

To compare presentation, progress, and outcome of acute bacterial meningitis in HIV seropositive and seronegative children.

METHODS

A double blind randomised placebo controlled study of the use of dexamethasone as adjuvant therapy in acute bacterial meningitis, in children aged 2 months to 13 years, was carried out from July 1997 to March 2001. A total of 598 children were enrolled, of whom 459 were tested for HIV serostatus.

RESULTS

Of the 459 children, 34% were HIV seropositive. Their presentation was similar to HIV seronegative children but more were shocked on arrival at hospital (33/157 v 12/302), and more had a focus of infection (85/157 v 57/302). HIV positive children had a higher incidence of Streptococcus pneumoniae infections (52% v 32%). Sixty four cases relapsed; 67% were in HIV positive patients. The mortality in HIV positive children was 65% compared with 36% in HIV negative children. The number of survivors in each group was similar. Hearing loss was more common in HIV negative than HIV positive children (66.3% v 47.2%). Steroid therapy had no influence on meningitis in HIV positive children, but the mortality in HIV negative children was 61% in children given steroids, and 39% in those who did not receive steroids.

CONCLUSION

HIV seropositive children who develop bacterial meningitis have a high mortality and are prone to recurrent disease. There is an urgent need to prevent both primary and recurrent infections.

Global reduction of Hib disease: what are the next steps? Proceedings of the meeting Scottsdale, Arizona, September 22-25, 2002

On September 22 to 25, 2002, a group of infectious disease specialists, public health officials, and vaccine experts from 33 countries gathered in Scottsdale, Arizona, to discuss the epidemiology and control of disease caused by Haemophilus influenzae type b (Hib) in the era of Hib conjugate vaccines. This supplement is a synthesis of the major themes and key lessons identified at the meeting. The objectives of the conference were to review the 10-year experience with Hib conjugate vaccines, discuss strategies to reduce Hib disease rates to lowest possible levels in industrialized countries, review impediments to the introduction of Hib vaccine in developing countries, and discuss strategies for disseminating lessons learned from countries using to those not using Hib conjugate vaccines. Over 10 years of international experience with Hib conjugate vaccines has demonstrated that they are safe and effective. Routine use of Hib conjugate vaccine has consistently led to decreases in the incidence of invasive Hib disease of 90% or more across a wide range of epidemiologic situations in industrialized countries. In some countries, the vaccine has caused a near-disappearance of invasive Hib disease through a combination of direct protection and herd immunity. Developing countries that have implemented routine vaccination (eg, The Gambia, Chile) have also had substantial disease reduction. In countries where Hib conjugate vaccine is being used, reducing Hib disease incidence to the lowest possible level will depend on maintaining high vaccine coverage levels, conducting surveillance for Hib disease, and investigating Hib disease cases. The optimal Hib vaccination strategy will depend on many factors, including local epidemiology and programmatic considerations. In countries that are not using Hib conjugate vaccine, information on the local burden of Hib disease will be essential for leaders considering vaccine introduction. Where disease burden is high, a multifaceted approach is urgently needed to evaluate and overcome barriers to vaccine introduction. In areas where Hib disease burden is not well characterized, additional work will be needed to understand the epidemiology of Hib disease and to communicate the value of Hib conjugate vaccine.

Long-term persistence of immunity after immunisation with Haemophilus influenzae type b conjugate vaccine

Although Haemophilus influenzae type b (Hib) conjugate vaccines, after licensure in 1987, are now recommended for world-wide use, the duration of protective immunity afforded by them is not known. We therefore assessed the immunogenity at 9-10 years of age in 37 children who had received the first Hib conjugate, PRP-D, in infancy (the Hib-conjugate group) and were now given a dose of Hib polysaccharide (PS) as a test vaccine. The anti-Hib PS antibodies (Hib-ab) were measured before and after this test vaccination, and the values compared to those in 37 control children who had not previously received any Hib vaccine and in 13 children who had received Hib PS vaccine in infancy (the Hib-PS group). Prior to the test vaccination, the Hib-ab concentrations in the Hib-conjugate group were 3.6-fold higher than in the control group. After the test vaccination, the Hib-conjugate group had higher total Hib-ab concentrations, higher proportion of IgG and higher avidity of Hib-ab than the control or the Hib-PS group, suggesting persisting immunological memory in a Hib-c group. A mathematical model, including memory, predicted accurately the Hib-ab concentrations, which are maintained through anamnestic responses to intervening stimuli (Hib or cross-reacting bacteria).

Pgi genotyping is a surrogate for serotyping of encapsulated Haemophilus influenzae

Study of the epidemiology of invasive infections caused by encapsulated Haemophilus influenzae has been complicated by the poor sensitivity and specificity of the serologic assays used to identify specific capsular polysaccharides. The population structure of these bacteria is highly clonal, however, and serotype is highly correlated with other genetic characteristics. We sought to determine if alleles of the highly conserved phosphoglucose isomerase (pgi) gene correspond to the serotypes of encapsulated H. influenzae strains. pgi alleles of 52 well-characterized encapsulated H. influenzae isolates were amplified by PCR, sequenced, and compared to one another and to additional previously reported H. influenzae pgi alleles. Overall, 83% of the strains possessed pgi alleles associated with the major serotype a, b, e, and f clonotypes that cause the most invasive disease in the United States. Six strains (four type a and two type f) had unusual pgi alleles, which suggested that these strains belonged to less common clonotypes of encapsulated bacteria or were actually nontypeable strains. pgi genotyping may provide a simple and stable surrogate for capsular serotyping. Further studies correlating pgi typing with the expression of capsule are likely to increase our understanding of the epidemiology and pathogenesis of these infections.

Paediatric acute epiglottitis: not a disappearing entity

OBJECTIVE

Paediatric epiglottitis is a serious, potentially life-threatening condition. Since the widespread introduction of the Haemophilus influenzae type b (Hib) conjugate vaccine in the UK in October 1992, there has been a dramatic reduction in its incidence. Vaccine failure is rare. The purpose of this study is to examine the failure rate of H. influenzae type b vaccine as measured by the number of cases of Haemophilus epiglottitis in fully vaccinated children presenting to a tertiary paediatric centre. A secondary aim is to provide a retrospective review of all cases of epiglottitis over a 13-year period.

METHODS

A retrospective case-note review identifying all cases of epiglottitis presenting to Alder Hey Hospital was undertaken covering the time period December 1987-January 2001. Details of patient age, sex, source of referral, clinical presentation, management and complications along with microbiological and serological findings were obtained. There were 21 males and 19 females. The mean age was 36 months (range 6-125 months). A provisional diagnosis was made on the basis of the clinical features, confirmed by direct laryngoscopy in all but two cases and further supported in 28 cases by a positive blood culture. Of the 40 children presenting with epiglottitis, eight (20%) presented after the introduction of the Hib conjugate vaccine. H. influenzae antibody titres were measured both in the acute and convalescent phases of illness by the central Haemophilus Reference Unit in Oxford.

RESULTS

We present the clinical features, management and complications of 40 cases of acute epiglottitis. H. influenzae was isolated from blood cultures in 28 cases (70%). In 12 of these cases, H. influenzae type b was identified, seven prior to 1993 and five thereafter. Four of these five cases presenting after introduction of the Hib vaccine were known to have been fully vaccinated. One child had a history of prematurity and serum immunoglobulin estimation was abnormally low in another child. Acute Hib antibody titre was less than 1 microg/ml in two of the three cases in which this was available.

CONCLUSION

Whilst the incidence of Haemophilus type b epiglottitis has significantly diminished, vaccine failure does occur. We discuss the current understanding of clinical and immunological risk factors for vaccine failure and the significance of the Hib antibody titre. Further evaluation of vaccine failure would be of benefit. The series that we present highlights the importance of considering acute epiglottitis in the differential diagnosis of the child presenting with acute upper airway obstruction. This is particularly relevant when in future there will be fewer doctors familiar with the symptoms and signs of the disease.

The future of meningitis vaccines

Without effective vaccines meningitis remains a substantial worldwide threat with major health-care implications. A number of advances have been made in vaccine design and implementation over the last decade, with new vaccine initiatives providing substantial promise for the future reduction of global disease burden.

Effect of a fourth Haemophilus influenzae type b immunisation in preterm infants who received dexamethasone for chronic lung disease

AIM

To assess whether a fourth Hib polysaccharide-tetanus protein conjugate vaccine (PRP-T) would improve antibody response in preterm infants previously treated with dexamethasone for chronic lung disease.

METHODS

In a pilot study 12 infants born at less than 30 weeks gestation who had received corticosteroids were given a supplementary Hib dose six weeks after completion of the primary immunisation course. Serum samples obtained before and at eight weeks following the fourth Hib dose were analysed for total level and avidity of anti-PRP antibody.

RESULTS

There was no significant increase in the geometric mean titre (GMT) of anti-PRP antibody resulting from the fourth Hib immunisation (GMT: pre 2.35 micro g/ml, post 2.24 micro g/ml, p = 0.79). A subgroup of six infants had subprotective antibody levels (<1.0 micro g/ml) after the primary immunisation course, which remained subprotective following the extra Hib immunisation. Despite the poor response in total antibody level, the study group showed a significant rise in PRP specific IgG avidity following the fourth immunisation (GMAI: pre 0.076, post 0.138, p = 0.043).

CONCLUSION

An additional Hib immunisation given to recently steroid treated preterm infants six weeks after completion of the primary schedule did not augment primary immunogenicity. However, increasing avidity may imply successful priming and long term immunity to Hib.

Clinical and microbiological features of Haemophilus influenzae vulvovaginitis in young girls

AIMS

To define the clinical and microbiological features of vulvovaginitis in prepubertal girls whose genital swabs yielded Haemophilus influenzae.

METHODS

Laboratory based study and retrospective collection of clinical data from the requesting doctors.

RESULTS

Thirty eight isolates of non-capsulate Haemophilus influenzae and one of H parainfluenzae were isolated from 32 girls aged 18 months to 11 years. No other pathogens, such as beta haemolytic streptococci or yeasts, were present with H influenzae. The most common biotype was biotype II, comprising 57% of the 26 isolates biotyped. Six children had more than one episode of vulvovaginitis caused by H influenzae and a total of 14 children had recurrent vaginal symptoms.

CONCLUSION

Children who have H influenzae vulvovaginitis are at risk of recurrent symptoms. Biotype II is the one most commonly associated with this condition.

The UK Hib vaccine experience

Haemophilus influenzae type b (Hib) is an important pathogen in children <5 years of age. The Hib conjugate vaccines were the first polysaccharide-protein conjugate vaccines to be used in routine childhood schedules. Their introduction in the UK in 1992 has resulted in the near elimination of Hib disease. The UK Hib vaccine programme has a number of unique features including an accelerated schedule, absence of a booster dose, and the inclusion of a catch up component at the beginning of the programme. Collaboration between UK paediatricians, microbiologists, and public health physicians has allowed active national surveillance of Haemophilus influenzae disease and enabled important conclusions to be drawn. These include high vaccine effectiveness, the presence of herd immunity, and the frequency of risk factors in cases of vaccine failure and in cases of invasive disease due to non-b H influenzae. Parallel studies have shown the immunogenicity, induction of immunological memory, and persistence of immunity following vaccination at the UK schedule, as well as measuring the impact of vaccination on pharyngeal Hib carriage. Cases continue to occur and complacency is ill advised, particularly as other vaccines and combinations are introduced. Surveillance of H influenzae disease in the UK remains important.

Limited genetic diversity of recent invasive isolates of non-serotype b encapsulated Haemophilus influenzae

Invasive infections caused by non-type b encapsulated Haemophilus influenzae have increased in frequency in the last decade. This change prompted us to characterize the genetic relationships of 48 recently isolated invasive H. influenzae type a (Hia), e (Hie), and f (Hif) strains by comparison of restriction digest patterns (RDPs). Recent Hia isolates exhibited moderate genetic diversity, with the majority segregating into two major clonotypes. Recent Hie and, especially, Hif strains displayed considerably restricted genetic diversity. In particular, all but one Hif strain segregated into a single clonotype, and half of these isolates had identical RDPs. These results are consistent with the hypothesis that the increased incidence of disease due to non-type b encapsulated H. influenzae reflects the emergence of hypervirulent clones, especially in the case of Hif. Alternatively, it is possible that non-type b encapsulated H. influenzae strains have limited overall genetic diversity.