Assessment of Carriage ofHaemophilus influenzaeType a after a Case of Invasive Disease

Prevalence of Haemophilus influenzae in the nasopharynx of children from regions with varying incidence of invasive H. influenzae serotype a disease: Canadian Immunization Research Network (CIRN) study

Haemophilus influenzae serotype a (Hia) has recently emerged as an important cause of invasive disease in the North American Arctic and Sub-Arctic regions, mainly affecting young Indigenous children. In this study, we addressed the question of whether the prevalence of Hia and all H. influenzae in the nasopharynx differed between paediatric populations from regions with high versus low incidence of invasive Hia disease. Nasopharyngeal specimens from children with acute respiratory tract infections (ARTI) collected for routine diagnostic detection of respiratory viruses were analysed with molecular-genetic methods to identify and serotype H. influenzae. In Nunavut, a region with a high incidence of invasive Hia disease, all H. influenzae and particularly Hia were found in the nasopharynx of 60.6% and 3.0% children. In Southern Ontario (Hamilton region), where Hia invasive disease is rare, the frequencies of all H. influenzae and Hia detection were 38.5% and 0.6%, respectively. In both cohorts, non-typeable H. influenzae was prevalent (57.0% and 37.9%, respectively). Considering that Hia is an important cause of severe invasive disease in Nunavut children, 3% prevalence of Hia among children with ARTI can reflect continuing circulation of the pathogen in the Northern communities that may result in invasive disease outbreaks.

An Investigation of Pediatric Case-patients With Invasive Haemophilus influenzae in Alaska, 2005-2011

BACKGROUND

Haemophilus influenzae (Hi) can cause severe disease in children. This study aimed to identify risk factors related to invasive Hi disease in Alaska children and evaluate carriage in people around them.

METHODS

From 2005 to 2011, we investigated episodes of invasive, typeable Hi disease in Alaska children <10 years old. Three age-matched control children were enrolled for each case-patient. We evaluated oropharyngeal Hi carriage in people in close contact with Hi case-patients (contacts) as well as control children and their household members. Individual and household risk factors for illness and carriage were evaluated using questionnaires and chart reviews.

RESULTS

Thirty-eight of 44 (86%) children with invasive, typeable Hi disease were recruited: 20 Hi serotype a (53%), 13 serotype b (Hib) (34%) and 5 serotype f (13%). Children with the invasive Hi disease were more likely than controls to have underlying health problems (67% vs. 24%, P = 0.001), other carriers of any Hi in their household (61% vs. 15%, P < 0.001), and inadequate Hib vaccination (26% vs. 9%, P = 0.005). People who carried Hi were younger than noncarriers (mean 12.7 vs. 18.0 years, P = 0.008). The carriage was clustered within case-patient households, with carriage in 19% of household contacts, while only 6.3% of nonhousehold contacts and 5.5% of noncontacts carried the Hi serotype of interest ( P < 0.001).

CONCLUSIONS

Factors associated with invasive Hi disease in children included underlying health problems, household carriage and inadequate Hib vaccination. The high level of carriage in case-patient households is important to consider when evaluating treatment and prophylaxis strategies.

Haemophilus influenzae Serotype a (Hia) Carriage in a Small Alaska Community After a Cluster of Invasive Hia Disease, 2018

BACKGROUND

Between May and July 2018, 4 Haemophilus influenzae serotype a (Hia) infections occurred in a remote Alaska community. We performed a public health response to prevent further illness and understand Hia carriage.

METHODS

We collected oropharyngeal samples community-wide to evaluate baseline carriage. Risk factors were evaluated by interview. We offered prophylactic rifampin to individuals in contact with invasive Hia patients (contacts) and to all children aged <10 years. Oropharyngeal samples were collected again 8 weeks after rifampin distribution. Samples were tested using real-time polymerase chain reaction and culture.

RESULTS

At baseline, 4 of 27 (14.8%) contacts and 7 of 364 (1.9%) noncontacts (P < .01) carried Hia. Contacts aged <10 years were more likely to carry Hia at any timepoint (11/18 [61%]) compared to contacts aged ≥10 years (3/34 [8.8%]), noncontacts aged <10 years (2/139 [1.4%]), and noncontacts ≥10 years (6/276 [2.2%]) (P < .001 for all). Hia carriers were clustered in 9 households (7% of total households). At the household level, carriage was associated with households with ≥1 contact (prevalence ratio [PR], 5.6 [95% confidence interval {CI}, 1.3-21.6]), crowding (PR, 7.7 [95% CI, 1.1-199.5]), and ≥3 tobacco users (PR, 5.0 [95% CI, 1.2-19.6]). Elevated carriage prevalence persisted in contacts compared to noncontacts 8 weeks after rifampin distribution (6/25 [24%] contacts, 2/114 [1.8%] noncontacts; P < .001).

CONCLUSIONS

Hia carriage prevalence was significantly higher among contacts than noncontacts. Rifampin prophylaxis did not result in a reduction of Hia carriage prevalence in this community.

Genomic Diversity of Haemophilus influenzae Serotype a in an Outbreak Community, Alaska 2018

BACKGROUND

Haemophilus influenzae serotype a (Hia) can cause severe invasive disease, especially in young children. In 2018, four invasive Hia cases occurred in an Alaska community. We used whole-genome sequencing (WGS) to evaluate the relationship of the bacteria from this community and other Alaska patients with invasive Hia.

METHODS

All carriage (15) and invasive (4) Hia isolates from the outbreak community, together with 15 non-outbreak Alaska invasive Hia surveillance isolates from 2018, were tested for antimicrobial susceptibility and characterized using WGS.

RESULTS

Phylogenetic analysis of both invasive and carriage Hia isolates revealed two major clades that differed by an average of 300 core single nucleotide polymorphisms (SNPs). All isolates from the outbreak community were clustered in one subclade, within a larger clade containing 3 non-outbreak invasive Hia isolates. Comparative genomics did not reveal any genetic mutations that distinguished carriage from invasive isolates. Three (20%) community isolates were rifampin-resistant and had a previously unreported mutation in the rpoB gene.

CONCLUSIONS

In the outbreak community, Hia isolates from carriers were indistinguishable from the invasive Hia isolates. Overall, invasive Hia isolates from Alaska in 2018 were genetically similar. The rifampin resistance mutation is concerning as rifampin is the first-line medication for Hia prophylaxis.

The changing epidemiology of invasive Haemophilus influenzae disease: Emergence and global presence of serotype a strains that may require a new vaccine for control

BACKGROUND

More than two decades after the implementation of the Hib conjugate vaccine in North America, Haemophilus influenzae serotype a (Hia) has emerged as a significant cause of invasive disease in Indigenous communities. However, little is known about the global presence of this pathogen.

METHODS

We interrogated the H. influenzae Multi-Locus Sequence Typing (MLST) website (https://pubmlst.org/hinfluenzae/) by selecting for serotype a records. We also updated our previous literature review on this subject matter.

RESULTS

Hia has been reported from at least 35 countries on six major continents. However, most Hia diseases were associated with Indigenous communities. Clonal analysis identified two clonal populations with one typified as ST-23 responsible for most invasive disease in North America and being the predominant clone described on the H. influenzae MLST website. Incidence of invasive Hia disease in Indigenous communities in North America are similar to the rates of Hib disease reported prior to the Hib conjugate vaccine era. Hia causes severe clinical diseases, such as meningitis, septicaemia, pneumonia, and septic arthritis with case-fatality rates between 5.6% and 33% depending on the age of the patient and the genetic makeup of the Hia strain.

CONCLUSION

Although invasive Hia disease can be found globally, the current epidemiological data suggest that this infection predominantly affects Indigenous communities in North America. The clinical disease of Hia and the clonal nature of the bacteria resemble that of Hib. The high incidence of invasive Hia disease in Indigenous communities, along with potential fatality and severe sequelae causing long-term disability in survivors, may support the development of a new Hia conjugate vaccine for protection against this infection similar in design to the one introduced in the 1990s to control invasive Hib disease.

Septic Arthritis and Hemarthroses Caused by Haemophilus influenzae Serotype A in Children

Invasive disease caused by Haemophilus influenzae serotype A (Hia) is rare in children. Clinical syndromes caused by Hia include meningitis, sepsis and respiratory tract infections. Septic arthritis is rare in children with invasive Hia infection and hemarthrosis has not been described in the published literature. We report a case of septic arthritis and hemarthrosis caused by Hia infection in a 2.5 year-old-boy and review invasive Hia infection in children.

Modelling the impact of vaccination on curtailing Haemophilus influenzae serotype 'a'

Haemophilus influenzae serotype a (Hia) is a human-restricted bacterial pathogen transmitted via direct contacts with an infectious individual. Currently, there is no vaccine available for prevention of Hia, and the disease is treated with antibiotics upon diagnosis. With ongoing efforts for the development of an anti-Hia protein-polysaccharide conjugated vaccine, we sought to investigate the effect of vaccination on curtailing Hia infection. We present the first stochastic model of Hia transmission and control dynamics, and parameterize it using available estimates in the literature. Since both naturally acquired and vaccine-induced immunity wane with time, model simulations show three important results. First, vaccination of only newborns cannot eliminate the pathogen from the population, even when a booster program is implemented with a high coverage. Second, achieving and maintaining a sufficiently high level of herd immunity for pathogen elimination requires vaccination of susceptible individuals in addition to a high vaccination coverage of newborns. Third, for a low vaccination rate of susceptible individuals, a high coverage of booster dose may be needed to raise the level of herd immunity for Hia eradication. Our findings highlight the importance of vaccination and timely boosting of the individual׳s immunity within the expected duration of vaccine-induced protection against Hia. When an anti-Hia vaccine becomes available, enhanced surveillance of Hia incidence and herd immunity could help determine vaccination rates and timelines for booster doses necessary to eliminate Hia from affected populations.

A review of invasive Haemophilus influenzae disease in the Indigenous populations of North America

Historically, the highest incidence rates of invasive Haemophilus influenzae disease in the world were found in North American and Australian Indigenous children. Although immunization against H. influenzae type b (Hib) led to a marked decrease in invasive Hib disease in countries where it was implemented, this disease has not been eliminated and its rates in Indigenous communities remain higher than in the general North American population. In this literature review, we examined the epidemiology of invasive H. influenzae disease in the pre-Hib vaccine era, effect of carriage on disease epidemiology, immune response to H. influenzae infection and Hib vaccination in Indigenous and Caucasian children, and the changing epidemiology after Hib conjugate vaccine has been in use for more than two decades in North America. We also explored reasons behind the continued high rates of invasive H. influenzae disease in Indigenous populations in North America. H. influenzae type a (Hia) has emerged as a significant cause of severe disease in North American Indigenous communities. More research is needed to define the genotypic diversity of Hia and the disease burden that it causes in order to determine if a Hia vaccine is required to protect the vulnerable populations.

Haemophilus influenzae serotype a as a cause of serious invasive infections

Haemophilus influenzae, particularly H influenzae serotype b (Hib), is an important pathogen that causes serious diseases like meningitis and septicaemia. Since the introduction of Hib conjugate vaccines in the 1990s, the epidemiology of invasive H influenzae disease has changed substantially, with most infections now caused by non-Hib strains. We discuss the importance of H influenzae serotype a (Hia) as a cause of serious morbidity and mortality and its global epidemiology, clinical presentation, microbiology, immunology, prevention, and control. Much like Hib, the capsule of Hia is an important virulence factor contributing to the development of invasive disease. Molecular typing of Hia has identified distinct clonal groups, with some linked to severe disease and high case-fatality rates. Similarities between Hia and Hib capsules, their clinical presentation, and immunology of infection suggest that a bivalent Hia-Hib capsular polysaccharide-protein conjugate vaccine could offer protection against these two important serotypes of H influenzae.

Haemophilus influenzae serotype a invasive disease, Alaska, USA, 1983-2011

Before introduction of Haemophilus influenzae type b (Hib) vaccines, rates of Hib disease in Alaska’s indigenous people were among the highest in the world. Vaccination reduced rates dramatically; however, invasive H. influenzae type a (Hia) disease has emerged. Cases of invasive disease were identified through Alaska statewide surveillance during1983–2011. Of 866 isolates analyzed for serotype, 32 (4%) were Hia. No Hia disease was identified before 2002; 32 cases occurred during 2002–2011 (p<0.001). Median age of case-patients was 0.7 years; 3 infants died. Incidence of Hia infection (2002–2011) among children <5 years was 5.4/100,000; 27 cases occurred in Alaska Native children (18/100,000) versus 2 cases in non-Native children (0.5/100,000) (risk ratio = 36, p<0.001). From 12/2009 to 12/2011, 15 cases of Hia disease occurred in southwestern Alaska (in children <5 years, rate = 204/100,000). Since introduction of the Hib conjugate vaccine, Hia infection has become a major invasive bacterial disease in Alaska Native children.

Invasive disease caused by Haemophilus influenzae type a in Northern Ontario First Nations communities

Seven epidemiologically unrelated cases of invasive Haemophilus influenzae type a (Hia) disease were identified in First Nations communities of Northwestern Ontario, Canada, in 2004–2008. In all cases, Hia was isolated from blood. The clinical presentation in most of the cases was moderately severe and all patients responded to antibiotic therapy. Laboratory analysis of Hia isolates from Northwestern Ontario indicated striking similarities in their phenotypic and genotypic characteristics. The findings are discussed in the context of current epidemiology of invasive Hia disease. Our data along with some published studies by others suggest an increased susceptibility to this infection among North American indigenous populations.

Evaluation of serum bactericidal antibody assays for Haemophilus influenzae serotype a

Haemophilus influenzae type a (Hia) is an important pathogen for some American Indian, Alaskan native, and Northern Canada aboriginal populations. Assays to measure serum bactericidal activity (SBA) to Hia have not been developed or validated. Here, we describe two methods for the measurement of SBA: SBA with a viability endpoint (CFU counts) and SBA with a fluorometric endpoint using alamarBlue as the metabolic indicator. Both SBA assays measure Hia-specific functional antibody and correlate with anti-Hia IgG enzyme-linked immunosorbent assay (ELISA) concentration of naturally acquired antibodies.

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.