Invasive Nontypeable Haemophilus influenzae Infection Among Adults With HIV in Metropolitan Atlanta, Georgia, 2008-2018

IMPORTANCE

Invasive nontypeable Haemophilus influenzae (NTHi) infection among adults is typically associated with bacteremic pneumonia. Nontypeable H influenzae is genetically diverse and clusters of infection are uncommon.

OBJECTIVE

To evaluate an increase in invasive NTHi infection from 2017-2018 among HIV-infected men who have sex with men in metropolitan Atlanta, Georgia.

DESIGN, SETTING, AND PARTICIPANTS

A population-based surveillance study with a cohort substudy and descriptive epidemiological analysis identified adults aged 18 years or older with invasive NTHi infection (isolation of NTHi from a normally sterile site) between January 1, 2008, and December 31, 2018 (final date of follow-up).

EXPOSURES

Time period, HIV status, and genetic relatedness (ie, cluster status) of available NTHi isolates.

MAIN OUTCOMES AND MEASURES

The primary outcome was incidence of invasive NTHi infection (from 2008-2016 and 2017-2018) among persons with HIV and compared with NTHi infection from 2008-2018 among those without HIV. The secondary outcomes were assessed among those aged 18 to 55 years with invasive NTHi infection and included epidemiological, clinical, and geographic comparisons by cluster status.

RESULTS

Among 553 adults with invasive NTHi infection (median age, 66 years [Q1-Q3, 48-78 years]; 52% male; and 38% black), 60 cases occurred among persons with HIV. Incidence of invasive NTHi infection from 2017-2018 among persons with HIV (41.7 cases per 100 000) was significantly greater than from 2008-2016 among those with HIV (9.6 per 100 000; P < .001) and from 2008-2018 among those without HIV (1.1 per 100 000; P < .001). Among adults aged 18 to 55 years with invasive NTHi infections from 2017-2018 (n = 179), persons with HIV (n = 31) were significantly more likely than those from 2008-2018 without HIV (n = 124) to be male (94% vs 49%, respectively; P < .001), black (100% vs 53%; P < .001), and have septic arthritis (35% vs 1%; P < .001). Persons with HIV who had invasive NTHi infection from 2017-2018 (n = 31) were more likely than persons with HIV who had invasive NTHi infection from 2008-2016 (n = 24) to have septic arthritis (35% vs 4%, respectively; P = .01). Pulsed-field gel electrophoresis of 174 of 179 NTHi isolates from 18- to 55-year-olds identified 2 genetically distinct clonal groups: cluster 1 (C1; n = 24) and cluster 2 (C2; n = 23). Whole-genome sequencing confirmed 2 clonal lineages of NTHi infection and revealed all C1 isolates (but none of the C2 isolates) carried IS1016 (an insertion sequence associated with H influenzae capsule genes). Persons with HIV were significantly more likely to have C1 or C2 invasive NTHi infection from 2017-2018 (28/31 [90%]) compared with from 2008-2016 among persons with HIV (10/24 [42%]; P < .001) and compared with from 2008-2018 among those without HIV (9/119 [8%]; P < .001). Among persons with C1 or C2 invasive NTHi infection who had HIV (n = 38) (median age, 34.5 years; 100% male; 100% black; 82% men who have sex with men), 32 (84%) lived in 2 urban counties and an area of significant spatial aggregation was identified compared with those without C1 or C2 invasive NTHi infection.

CONCLUSIONS AND RELEVANCE

Among persons with HIV in Atlanta, the incidence of invasive nontypeable H influenzae infection increased significantly from 2017-2018 compared with 2008-2016. Two unique but genetically related clonal strains were identified and were associated with septic arthritis among black men who have sex with men and who lived in geographic proximity.

Haemophilus influenzae Type b Invasive Disease in Amish Children, Missouri, USA, 2014

During 5 months in 2014, three Amish children in Missouri, USA, were diagnosed with invasive Haemophilus influenzae type b infection. Two were rural neighbors infected with a genetically similar rare strain, sequence type 45. One child had recently traveled, raising the possibility of maintenance of this strain among unvaccinated carriers in Amish communities.

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.

Differential association between HLA and diffuse panbronchiolitis in Northern and Southern Chinese

BACKGROUND

Diffuse panbronchiolitis (DPB) is a progressive inflammatory pulmonary disease that predominately affects East Asians. Genetic susceptibility to DPB is correlated with the human leukocyte antigens HLA-B54 in Japanese and HLA-A11 in Koreans. However, no systematic genetic study of DPB pathogenesis has been conducted in the Chinese population. The aim of this study was to investigate the possible association between HLA and disease susceptibility in Chinese patients with DPB.

METHODS

A literature review of both Chinese and English language studies on Chinese DPB patients, published between 1983 and 2010, was conducted. Seventy subjects met the inclusion criteria and were retrospectively analyzed for HLA gene frequency according to geographic region.

RESULTS

HLA-B54 frequency was significantly greater in DPB patients than in controls in the Northern Chinese group (35.7% vs. 4.6%, p=7.5×10(-7)). Although the HLA-B54 frequency was slightly increased in the Southern Chinese patients, the difference was not significant compared with control subjects (14.3% vs. 5.7%, p=0.28). The HLA-A11 frequency was significantly greater in DPB patients than controls in the Southern Chinese group (54.8% vs. 26.4%, p=0.009). Despite an increase of HLA-A11 frequency in the Northern Chinese group, no significant variation in HLA-A11 frequency was found compared with control subjects (42.9% vs. 30.8%, p=0.535). The HLA-A2 frequency was significantly decreased in DPB patients than in controls in the Southern Chinese group (22.9% vs. 66.0%, p=0.001). However, no significant difference in HLA-A2 frequency was found in the Northern Chinese group (50.0% vs. 46.9%, p=0.872).

CONCLUSION

HLA-B54 and HLA-A11 were positively associated with DPB in Northern and Southern Chinese, respectively. Population substructure may impact the genetic predisposition of DPB in China.

Effect of azithromycin on patients with diffuse panbronchiolitis: retrospective study of 51 cases

BACKGROUND

Patients with diffuse panbronchiolitis (DPB) are routinely treated with erythromycin, clarithromycin, and roxithromycin. The clinical effect of azithromycin on DPB has not been confirmed in a large cohort.

OBJECTIVE

The present study was undertaken to investigate the clinical effects of azithromycin on patients with DPB.

METHODS

Fifty-one patients with DPB treated with azithromycin in Shanghai Pulmonary Hospital, China, from July 2001 to April 2007 were analyzed retrospectively. Azithromycin (500 mg a day) was administrated intravenously in the first 1-2 weeks, taken orally (500 mg, once a day) for 3 months, and tapered to 3 times a week for 6-12 months. The patients were followed up until September 1, 2009. The therapeutic effect, according to their clinical and radiological findings, arterial gas analysis, lung function, and sputum bacterium before and after the therapy, was categorized into the following five grades: 1) cured; 2) improved; 3) no response; 4) aggravation, and 5) relapse.

RESULTS

With azithromycin therapy, 14 (27.5%) patients with DPB were completely cured. The symptoms were eliminated to certain degrees for the other 36 cases (70.6%) of DPB. Five-year survival in this cohort was 94.1%.

CONCLUSION

Azithromycin is effective and well tolerated for patients with diffuse panbronchiolitis.

Socioeconomic and racial/ethnic disparities in the incidence of bacteremic pneumonia among US adults

OBJECTIVES

We examined associations between the socioeconomic characteristics of census tracts and racial/ethnic disparities in the incidence of bacteremic community-acquired pneumonia among US adults.

METHODS

We analyzed data on 4870 adults aged 18 years or older with community-acquired bacteremic pneumonia identified through active, population-based surveillance in 9 states and geocoded to census tract of residence. We used data from the 2000 US Census to calculate incidence by age, race/ethnicity, and census tract characteristics and Poisson regression to estimate rate ratios (RRs) and 95% confidence intervals (CIs).

RESULTS

During 2003 to 2004, the average annual incidence of bacteremic pneumonia was 24.2 episodes per 100 000 Black adults versus 10.1 per 100 000 White adults (RR = 2.40; 95% CI = 2.24, 2.57). Incidence among Black residents of census tracts with 20% or more of persons in poverty (most impoverished) was 4.4 times the incidence among White residents of census tracts with less than 5% of persons in poverty (least impoverished). Racial disparities in incidence were reduced but remained significant in models that controlled for age, census tract poverty level, and state.

CONCLUSIONS

Adults living in impoverished census tracts are at increased risk of bacteremic pneumonia and should be targeted for prevention efforts.

The Alaska Haemophilus influenzae type b experience: lessons in controlling a vaccine-preventable disease

OBJECTIVE

Before 1991, Alaska Native children experienced one of the highest rates of invasive Haemophilus influenzae type b disease. H influenzae type b vaccine has led to a near-elimination of invasive H influenzae type b disease in the United States. We describe challenges encountered in controlling H influenzae type b disease in Alaska and update the current status of H influenzae disease and carriage in Alaska as lessons to other populations.

PATIENTS AND METHODS

We reviewed data from statewide H influenzae disease surveillance conducted during 1980-2004. Vaccine coverage data were based on audits from tribal facilities and the National Immunization Survey. H influenzae type b colonization data were based on 6 carriage studies.

RESULTS

After universal infant vaccination in 1991, H influenzae type b disease among Alaska Native and non-Native children < 5 years of age decreased by 94% and 96%, respectively. After a 1996 change in H influenzae type b vaccine from polyribosylribitol phosphate-outer membrane protein conjugate vaccine to H influenzae type b oligosaccharide-CRM197 vaccine, the incidence of H influenzae type b disease increased in rural Alaska Natives from 19.8 to 91.1 cases per 100000 per year < 5 years of age. During 2001-2004, with use of polyribosylribitol phosphate-outer membrane protein conjugate vaccine, the rate of H influenzae type b disease in Alaska Native and non-Native children aged < 5 years decreased to 5.4 and 0 per 100000 per year, respectively. In postvaccine studies, H influenzae type b carriage has decreased in Alaska Native children < 5 years of age.

CONCLUSIONS

H influenzae type b vaccination has resulted in a dramatic decrease in invasive H influenzae type b disease in Alaska; however, despite high rates of H influenzae type b vaccine coverage, H influenzae type b disease rates among rural Alaska Native children < 5 years of age remain higher than the rates among non-Native Alaska and other US children. Equity in disease rates may not be achieved in indigenous populations with the current vaccines unless other environmental and household factors contributing to disease transmission are addressed.

Toward elimination of Haemophilus influenzae type B carriage and disease among high-risk American Indian children

OBJECTIVES

This report describes the epidemiology of Haemophilus influenzae type b (Hib) invasive disease and oropharyngeal colonization among Navajo and White Mountain Apache children younger than 7 years in an era of widespread immunization.

METHODS

We conducted active surveillance for invasive H influenzae disease from 1992 to 1999 and an oropharyngeal carriage study from 1997 to 1999. The predominant vaccine used was PedvaxHib.

RESULTS

The average annual incidence of invasive Hib disease among children younger than 24 months was 22 cases per 100,000. Of 381 children younger than 7 years, only 1 (0.3%; 95% confidence interval = 0.0%, 1.3%) was colonized with Hib; 370 (97%) had received 2 or more doses of Hib conjugate vaccine.

CONCLUSIONS

Among Navajo and White Mountain Apache children, Hib conjugate vaccines have led to a sustained reduction in invasive Hib disease and a reduction in oropharyngeal Hib carriage. The disease incidence among children younger than 24 months remains 20 times higher than in the general US population. Hib elimination will require additional characterization of colonization and disease in these high-risk populations.

Experience with the prevention of invasive Haemophilus influenzae type b disease by vaccination in Alaska: the impact of persistent oropharyngeal carriage

OBJECTIVES

To report the epidemiology of invasive Haemophilus influenzae type b (Hib) disease in high-risk Alaska Native infants before and after universal infant Hib vaccination and evaluate an increase in invasive Hib disease in 1996 after changing Hib vaccine type.

STUDY DESIGN

Statewide laboratory surveillance for invasive Hib disease has been conducted since 1980. Three cross-sectional Hib carriage studies were conducted in 1997 and 1998.

RESULTS

The invasive Hib disease rate in Alaska Natives decreased from 332 cases per 100,000 children <5 years old in 1980-1991 to 17:100,000 in 1992-1995 but increased primarily in rural areas to 57.9:100,000 after a switch in Hib vaccine types. Carriage studies in 5 rural Alaska Native villages showed oropharyngeal Hib carriage as high as 9.3% in children aged 1 to 5 years; in contrast, carriage in urban Alaska Native children was <1%.

CONCLUSIONS

Although Hib disease has decreased in Alaska, the rate of Hib disease and carriage in rural Alaska Natives did not decrease to the same extent as in non-Natives and urban Alaska Natives. Use of polyribosylribitol phosphate-outer-membrane protein conjugate vaccine for the first vaccine dose is critical to disease control in this population with continued transmission in infants <6 months of age. The ability to eliminate Hib carriage and disease may be affected by population characteristics, vaccination coverage, and Hib vaccine type used. This may pose a challenge to global elimination of Hib.

Estimation of the indirect effect of Haemophilus influenzae type b conjugate vaccine in an American Indian population

BACKGROUND

Oropharyngeal carriage studies of Haemophilus influenzae type b (Hib) and the rapid drop in Hib invasive disease in countries with widespread Hib conjugate vaccine immunization programmes for infants have indicated there may be significant indirect effects (herd immunity) associated with these vaccines. Our goal was to quantify the magnitude of these effects in an American Indian population during its early years of Hib immunization.

METHODS

In a synthetic case-cohort study, we combined data from an efficacy trial, an immunization uptake records survey, and ongoing surveillance for Hib disease on the Navajo Nation from 1988 to 1992. Decline in the incidence of invasive Hib disease among children <2 years old was estimated via proportional hazards survival models as a function of individual immunization status and the proportion of immunized children in a community.

RESULTS

The predominant vaccine during the study period was Hib-OMPC (92% of immunizations). The effectiveness of receipt of at least one dose was 97.2%. Compared to communities with 0-20% coverage with at least one dose, residence in communities with 20-40% and 40-60% coverage was associated with risk reductions of 56.5% and 73.2%, respectively.

CONCLUSIONS

The results indicate substantial indirect effects of Hib-OMPC immunization may occur even at relatively low levels of immunization coverage. Countries that implement Hib immunization programmes may receive greater benefits at the community level than those due to the direct protection conferred to the individual through vaccination.

Pulsed-field gel electrophoresis used to investigate genetic diversity of Haemophilus influenzae type b isolates in Australia shows differences between Aboriginal and non-Aboriginal isolates

We used pulsed-field gel electrophoresis to study the epidemiology and population structure of Haemophilus influenzae type b. DNAs from 187 isolates recovered between 1985 and 1993 from Aboriginal children (n = 76), non-Aboriginal children (n = 106), and non-Aboriginal adults (n = 5) in urban and rural regions across Australia were digested with the SmaI restriction endonuclease. Patterns of 13 to 17 well-resolved fragments (size range, approximately 8 to 500 kb) defining 67 restriction fragment length polymorphism (RFLP) types were found. Two types predominated. One type (n = 37) accounted for 35 (46%) of the isolates from Aboriginals and 2 (2%) of the isolates from non-Aboriginals, and the other type (n = 41) accounted for 2 (3%) of the isolates from Aboriginals and 39 (35%) of the isolates from non-Aboriginals. Clustering revealed seven groups at a genetic distance of approximately 50% similarity in a tree-like dendrogram. They included two highly divergent groups representing 50 (66%) isolates from Aboriginals and 6 (5%) isolates from non-Aboriginals and another genetically distinct group representing 7 (9%) isolates from Aboriginals and 81 (73%) isolates from non-Aboriginals. The results showed a heterogeneous clonal population structure, with the isolates of two types accounting for 42% of the sample. There was no association between RFLP type and the diagnosis of meningitis or epiglottitis, age, sex, date of collection, or geographic location, but there was a strong association between the origin of isolates from Aboriginal children and RFLP type F2a and the origin of isolates from non-Aboriginal children and RFLP type A8b. The methodology discriminated well among the isolates (D = 0.91) and will be useful for the monitoring of postvaccine isolates of H. influenzae type b.

Haemophilus influenzae invasive disease in the United States, 1994-1995: near disappearance of a vaccine-preventable childhood disease

We analyzed national Haemophilus influenzae (Hi) surveillance data from 1994 and 1995 to describe the epidemiology of Hi invasive disease among persons of all ages. Serotype data were available for 376 (56%) of 669 reported Hi cases among children aged 4 years or younger; 184 (49%) were H. influenzae type b (Hib). Among children aged 4 or younger, incidence (per 100,000) of all Hi invasive disease was 1.8 in 1994 and 1.6 (p < 0.05) in 1995. Children aged 5 months or younger had the highest average annual incidence rate of Hib invasive disease (2.2 per 100,000); children aged 6 to 11 months had the next highest rate (1.2 per 100,000)(p < 0.05). Of 181 children with Hib invasive disease whose age in months was known, 85 (47%) were too young (aged 5 months or younger) to have completed a primary series with an Hib-containing vaccine. Of the 83 children with known vaccination status who were eligible to receive a primary series (aged 6 months or older), 52 (63%) were undervaccinated, and the remaining 31 (37%) had completed a primary series in which vaccine failed. Among persons aged 5 years or older with Hi invasive disease, the lowest average annual incidence was among those 20 to 39 years of age (0.15 per 100,000), and the highest was among those aged 80 years or older (2.26 per 100,000). Among persons aged 5 years or older, serotype data were available for 1,372 (71%) of the 1,940 Hi invasive disease cases; 159 (28%) of the 568 Hi cases with known serotype were due to Hib.

The immunogenicity of Haemophilus influenzae: meningococcal protein conjugate vaccine in Polynesian and non-Polynesian New Zealand infants

OBJECTIVE

To examine the comparative immunogenicity of the Haemophilus influenzae type b-meningococcal protein (PRP-OMP) conjugate vaccine in Polynesian and non-Polynesian New Zealand infants.

METHODOLOGY

Fifty-six Polynesian and 53 non-Polynesian infants aged 2-7 months recruited from primary health care settings in Auckland received a two-dose primary series of PRP-OMP. A sub-sample of 83 participants received a booster dose of PRP-OMP at 12-16 months of age. Anti-PRP antibody concentrations were measured in pre- and post-vaccination blood samples.

RESULTS

Antibody responses consistent with long-term protection (> or = 1.00 microgram/mL) were observed in 72, 85 and 95% of children following the first, second and booster doses.

CONCLUSIONS

Despite differences in disease epidemiology, PRP-OMP was highly immunogenic in Polynesian and non-Polynesian infants.

Nonencapsulated Haemophilus influenzae in Aboriginal infants with otitis media: prolonged carriage of P2 porin variants and evidence for horizontal P2 gene transfer

Aboriginal infants in the Northern Territory of Australia experience recurrent otitis media from an early age. Nonencapsulated Haemophilus influenzae (NCHi) colonization of the nasopharynx initially occurs within weeks of birth, persists throughout infancy and most of childhood, and contributes to otitis media. We established previously that the high carriage rates of NCHi in these infants result from concurrent and successive colonization with multiple strains, with sequential elimination of dominant strains. We have now sequenced loops 4, 5, and 6 of the NCHi P2 porin gene and characterized several strains with prolonged carriage times. Furthermore, despite a wide diversity of P2 gene sequences, we have four examples of P2 gene identity for strains with different genetic backgrounds as characterized by PCR ribotyping and randomly amplified polymorphic DNA typing, which leads us to suggest that the P2 gene has been transferred between strains. We also discuss the possibility that the paradoxical observation of cocolonization and prolonged carriage of P2-identical strains is related to immune suppression or tolerance in the host.

Upper airway carriage by Haemophilus influenzae and Streptococcus pneumoniae in Australian aboriginal children hospitalised with acute lower respiratory infection

When nasopharyngeal secretions from 171 Australian Aboriginal children hospitalized with acute lower respiratory tract infections (ALRI) were cultured selectively for Streptococcus pneumoniae and Haemophilus influenzae, 136 (79.5%) and 151 (88.3%) children yielded 166 and 254 isolates of S. pneumoniae and H. influenzae, respectively. In colonized subjects multiple populations of S. pneumoniae (20% of carriage-positive patients) and H. influenzae (55%) were common. Pneumococci belonging to 27 types or groups were identified. H. influenzae serotype b colonized 16.4% of all children studied. More than one half of 152 children tested were excreting antibiotics at the time of admission to hospital. Significantly fewer children with serum antibiotic residues were colonized with S. pneumoniae than were antibiotic free children. Antibiotic usage had no measurable impact on the isolation rate of H. influenzae.

Epidemiology of invasive Haemophilus influenzae infections in Cape Town, South Africa

The full spectrum of invasive Haemophilus influenzae disease has not been documented previously in Africa. This 1-year prospective study was designed to determine the epidemiology of invasive Haemophilus influenzae disease in Cape Town children. During this period, 142 children with invasive disease were hospitalized; 85 (59.9%) presented with meningitis, 35 (24.6%) with pneumonia and 22 (15.5%) with other diseases. No cases of epiglottitis were seen. Sixty per cent of cases were male and 40% female. The median age of the children was 9 months, with a range of 1-144 months, and 65.5% were aged < 12 months. Neurological dysfunction was noted in 40% and 18% of children with meningitis on admission and discharge, respectively. The overall case fatality rate (95% confidence intervals) was 9.2% (4.9-15.7), and for meningitis, pneumonia and septicaemia it was 4.7% (1.2-16.4), 14.3% (4.6-31.8) and 40% (8-78.1), respectively. Serotype b accounted for 86.5% of all cases, 97.3% of cases of meningitis, 71.4% of cases of pneumonia, 50% of cases of septicaemia, all cases of arthritis and cellulitis and none of mastoiditis. The incidence rates (95% confidence intervals) for all invasive type b infections were 169 (122-198) and 47 (39-57) per 100,000 population for children < 1 and < 5 years, respectively. For meningitis the rates were 112 (84-148) and 34 (25-40) per 100,000, respectively. Rates for mixed race and white children were similar, but those for black children were more than double those rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Children with Haemophilus influenzae bacteremia initially treated as outpatients: outcome in 85 American Indian children

Eighty-five American Indian children less than 16 years of age with Haemophilus influenzae bacteremia were retrospectively determined to have been treated as outpatients after their initial evaluation. We hoped to determine the proportion that developed new foci, the time interval to this development and whether age or temperature at presentation predicted outcome. Fifty-one (60%) presented with nonfocal findings. Seventy-two (85%) were treated with antibiotics at the initial visit. Although 49 (58%) of the patients were never hospitalized, a new focus was identified in 25 (29%), including 13 (15%) with a final diagnosis of meningitis. The new foci were identified within 6 days of presentation (median, 2 days). An additional 15 (18%) patients had no new focus but were febrile and/or ill at follow-up. All patients with meningitis or a second positive culture were hospitalized at the first follow-up visit. Age and temperature at presentation did not help predict outcome. All patients with H. influenzae bacteremia require prompt reevaluation and close follow-up by an experienced physician.

Invasive Haemophilus influenzae type b disease in children less than 5 years of age in Minnesota and in Dallas County, Texas, 1983-1984

During 1983 and 1984, 733 cases of invasive Haemophilus influenzae type b disease in children less than 5 years of age were identified in Minnesota and in Dallas County, Texas. The overall incidence of disease was lower in Minnesota than in Dallas County. However, among urban residents, the rates of disease for whites were similar in the two areas. A higher rate of disease among whites in urban Minnesota compared with rural Minnesota resulted from an increased rate of cases for diagnoses other than meningitis. Local practices might have affected the rate of certain diagnoses, since ascertainment of Hib disease other than meningitis is more dependent on diagnostic practices than is diagnosis of meningitis. These data suggest that the incidence of invasive H. influenzae type b disease is influenced by the racial composition of the population, the rates of disease in specific subgroups, and possibly by local medical practices. Understanding the factors that contribute to the incidence of disease is necessary to interpret variations in different populations and changes over time.

The epidemiology of invasive Haemophilus influenzae infections in children under five years of age in the Northern Territory: a three-year study

A survey of all episodes of invasive Haemophilus influenzae infections that were diagnosed over a three-year period in children seen at the regional hospitals of the Northern Territory has found a significantly (P less than 0.001) higher incidence in children in Central Australia (the Alice Springs and Barkly regions, and the Anangu Pitjantjatjara Lands) than in the Top End (the Darwin, East Arnhem and Katherine regions), and a greater incidence in Aboriginal than in non-Aboriginal children. Identified risk factors for Aboriginal children were infancy (more than 70% of cases occurred before 12 months of age), sex (with a predominance in girls) and residence in Central Australia; the estimated annual incidence for Central Australian Aboriginal children was 991 cases per 100,000 children. There was a significant correlation (r = 0.62) between the total number of cases diagnosed each month in Central Australia and the mean monthly temperatures recorded in Alice Springs. Whereas virtually all cases of invasive H. influenzae infection in non-Aboriginal children were caused by type b strains, strains other than type b caused 15% of the cases in Aboriginal children. The possibilities for prevention by immunization are discussed.

Epidemiology of invasive Haemophilus influenzae type b infections in Bedouins and Jews in southern Israel

We report the epidemiology of invasive Haemophilus influenzae type b disease requiring hospital intervention in Southern Israel, an area that contains two ethnic populations, Bedouins and Jews. The study is based on 107 blood or cerebrospinal fluid culture-positive cases during the years 1984 to 1988. The annual incidence rate among children younger than 5 years of age was 51/100,000 (48/100,000 for Jews and 58/100,000 for Bedouins). Thirty-nine percent of patients had meningitis, 32% had pneumonia and 31% had otitis media. Epiglottitis was present in only one case (less than 1%). The median age was 8 months. Twenty-six percent of the cases were 6 months old or younger, 75% were 1 year old or younger and 87% were 18 months old or younger. Ninety-five percent of all meningitis cases occurred during the first 18 months of life. A projected number of 2938 hospitalization days and 9.8 deaths/year for a population in which 100,000 births occur yearly was calculated. The major impact of invasive H. influenzae type b infections and the very young age involved justify initiation of H. influenzae vaccine studies in our region.

Global genetic structure and molecular epidemiology of encapsulated Haemophilus influenzae

A collection of 2,209 isolates of six polysaccharide capsule types of Haemophilus influenzae, including 1,975 serotype b isolates recovered in 30 countries was characterized for electrophoretically demonstrable allele profiles at 17 metabolic enzyme loci. Two hundred eighty distinct multilocus genotypes were distinguished, and cluster analysis revealed two primary phylogenetic divisions. The population structure of encapsulated H. influenzae is clonal. Currently, most of the invasive disease worldwide is caused by serotype b strains of nine clones. Strains producing serotype c, e, and f capsules belong to single divisions and have no close genetic relationships to strains of other serotypes. Serotype a and b strains occur in both primary phylogenetic divisions, probably as a result of transfer and recombination of serotype-specific sequences of the cap region between clonal lineages. A close genetic relatedness between serotype d isolates and some strains of serotypes a and b was identified. There are strong patterns of geographic variation, on an intercontinental scale, in both the extent of genetic diversity and the clonal composition of populations of encapsulated strains. The analysis suggests that the present distribution of clones is, in part, related to patterns of racial or ethnic differentiation and historical demographic movements of the human host populations.

Pharyngeal carriage and acquisition of anticapsular antibody to Haemophilus influenzae type b in a high-risk population in southwestern Alaska

Haemophilus influenzae type b disease in Alaskan Eskimos is characterized by greatly increased disease incidence at younger ages. This suggests that Eskimo infants have increased exposure to the disease. Exposure was studied in 1982-1983 in children less than age three years who lived in four Eskimo villages, as well as in a random sample of their family members (354 people from 132 households). During a 12-month period, up to four pharyngeal cultures and two serum specimens were obtained from each participant. Colonization with H. influenzae type b was relatively uncommon (overall 2.5% of cultures, 6.8% of individuals) and was not associated with age, sex, season, or prior incidence of disease in the village. Biotyping and outer-membrane-protein typing of H. influenzae type b isolates revealed homogeneity within villages, with differences between villages. Matched sera revealed a significant decline in H. influenzae type b capsular antibody in the course of the study year. However, pharyngeal carriage of H. influenzae type b was associated with increases in antibody for carriers and members of their households. Antibody levels were positively associated with age. Only one case of H. influenzae type b disease developed during the study. Low carriage of H. influenzae type b was coincident with low incidence of disease and declining levels of capsular antibody in these villages. Mechanisms for increased exposure which would not be reflected in high carriage rates may exist for these young children.