Haemophilus influenzae type a as a cause of paediatric septic arthritis

Report of Haemophilus Influenzae serotype a intracranial infections in older children

Introduction

Haemophilus influenzae (Hi) is subdivided into typeable (a-f) and non-typeable groups. Hi serotype b (Hib) has historically been one of the important pathogens responsible for invasive infection. However, after widespread Hib vaccination, the emergence of other Hi serotypes, specifically Hi serotype a (Hia), was noted during the last few decades, mostly in children younger than 5 years of age.

Case presentation

We present two cases of severe intracranial infections with detected Hia in patients > 5 years of age within a short time frame and within the same geographic area.

Conclusion

Epidemiological studies and surveillance on Hia-related illnesses in all age groups worldwide are needed to better understand the clinical and epidemiological characteristics of Hia. This can establish a platform to develop a candidate vaccine against Hia that might protect children of all ages.

Characterization of natural bactericidal antibody against Haemophilus influenzae type a in Canadian First Nations: A Canadian Immunization Research Network (CIRN) Clinical Trials Network (CTN) study

During the last two decades, Haemophilus influenzae serotype a (Hia) emerged as an important cause of invasive disease in Canadian First Nations and Inuit, and Alaskan Native populations, with the highest rates reported in young children. Immunocompetent adults, in contrast to children, do not typically develop invasive Hia disease. To clarify factors responsible for an increased burden of invasive Hia disease in certain population groups we studied serum bactericidal activity (SBA) against Hia and quantified IgG and IgM specific to Hia capsular polysaccharide in healthy adult members of two First Nations communities: 1) with reported cases of invasive Hia disease (Northern Ontario, NO), and 2) without reported cases (Southern Ontario, SO), in comparison to non-First Nations living in proximity to the NO First Nations community, and non-First Nations elderly non-frail Canadians from across the country (total of 110 First Nations and 76 non-First Nations). To elucidate the specificity of bactericidal antibodies, sera were absorbed with various Hia antigens. Naturally acquired SBA against Hia was detected at higher rates in First Nations (NO, 80%; SO, 96%) than non-First Nations elderly Canadians (64%); the SBA titres in First Nations were higher than in non-First Nations elderly Canadians (P<0.001) and NO non-First Nations adults (P>0.05). Among First Nations, SBA was mediated predominantly by IgM, and by both antibodies specific to Hia capsular polysaccharide and lipooligosaccharide. Conclusions: The SBA against Hia is frequently present in sera of First Nations adults regardless of the burden of Hia disease observed in their community; it may represent part of the natural antibody repertoire, which is potentially formed in this population under the influence of certain epigenetic factors. Although the nature of these antibodies deserves further studies to understand their origin, the data suggest that they may represent important protective mechanism against invasive Hia disease.

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.

Haemophilus influenzae serotype f endocarditis and septic arthritis

Haemophilus influenzae represents gram-negative coccobacilli which can cause endocarditis, meningitis, septicemia, pneumonia, septic arthritis. H.influenzae exists as encapsulated and unencapsulated (non-typeable) strains. Non-typeable H.influenzae are emerging pathogens especially in elderly population. We report a case of a 73 year old woman with bacteremia, endocarditis and septic arthritis due to H.influenzae serotype f. This case emphasizes the clinical features and the key elements of diagnosis and management of infections caused by non-typeable strains of H.influenzae.