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

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.

Carriage of Haemophilus influenzae serotype A in children: Canadian Immunization Research Network (CIRN) study

Background

Haemophilus influenzae serotype a (Hia) has recently emerged as an important cause of invasive disease, mainly affecting young Indigenous children. Carriage of H. influenzae is a pre-requisite for invasive disease and reservoir for transmission. To better understand the epidemiology of invasive Hia disease, we initiated a multicentre study of H. influenzae nasopharyngeal carriage among Canadian children.

Methods

With prior parental consent, we collected nasotracheal tubes used during general anaesthesia in healthy children following routine dental surgery in a regional hospital of northwestern Ontario and a dental clinic in central Saskatchewan. In northwestern Ontario, all children were Indigenous (median age 48.0 months, 45.8% female); in Saskatchewan, children were from various ethnic groups (62% Indigenous, median age 56.3 months, 43.4% female). Detection of H. influenzae and serotyping were performed using molecular-genetic methods.

Results

A total of 438 nasopharyngeal specimens, 286 in northwestern Ontario and 152 in Saskatchewan were analyzed. Hia was identified in 26 (9.1%) and 8 (5.3%) specimens, respectively. In Saskatchewan, seven out of eight children with Hia carriage were Indigenous.

Conclusions

The carriage rates of Hia in healthy children in northwestern Ontario and Saskatchewan are comparable to H. influenzae serotype b (Hib) carriage among Alaska Indigenous children in the pre-Hib-vaccine era. To prevent invasive Hia disease, paediatric conjugate Hia vaccines under development have the potential to reduce carriage of Hia, and thus decrease the risk of transmission and disease among susceptible populations. Addressing the social determinants of health may further eliminate conditions favouring Hia transmission in Indigenous communities.

Presence of Antibodies Against Haemophilus influenzae Serotype a in Alaska Before and After the Emergence of Invasive Infections

BACKGROUND

Haemophilus influenzae bacteria can cause asymptomatic carriage and invasive disease. Haemophilus influenzae serotype a (Hia) is an emerging cause of invasive disease in Alaska, with greatest burden occurring among rural Alaska Native (AN) children. The first case of invasive Hia (iHia) in Alaska was reported in 2002; however, it is unclear how long the pathogen has been in Alaska.

METHODS

We quantified immunoglobulin G antibodies against Hia (anti-Hia) in 839 banked serum samples from Alaska residents, comparing antibody concentrations in samples drawn in the decades before (1980s and 1990s) and after (2000s) the emergence of iHia. We also assessed serum antibody concentration by age group, region of residence, and race.

RESULTS

The anti-Hia was >0.1 µg/mL in 88.1% (348 of 395) and 91.0% (404 of 444) of samples from the decades prior and after the emergence of Hia, respectively (P = .17). No significant differences in antibody levels were detected between people from rural and urban regions (1.55 vs 2.08 µg/mL, P = .91 for age ≥5) or between AN and non-AN people (2.50 vs 2.60 µg/mL, P = .26).

CONCLUSIONS

Our results are consistent with widespread Hia exposure in Alaska predating the first iHia case. No difference in Hia antibody prevalence was detected between populations with differing levels of invasive disease.

Impact of Vaccination on Haemophilus influenzae Type b Carriage in Healthy Children Less Than 5 Years of Age in an Urban Population in Nepal

Background

Reduction in detection of asymptomatic carriage of Haemophilus influenzae type b (Hib) can be used to assess vaccine impact. In Nepal, routine vaccination against Hib in children at 6, 10, and 14 weeks of age was introduced in 2009. Before vaccine introduction, Hib carriage was estimated at 5.0% among children aged <13 years in Nepal, with higher rates among children under 5. Large-scale evaluation of Hib carriage in children has not been investigated since the introduction of the pentavalent diphtheria-tetanus-pertussis/Hib/hepatitis B (DTP-Hib-HepB) vaccine in Nepal.

Methods

A total of 666 oropharyngeal swabs were collected between August and December 2018 from healthy children between 6 months and 5 years of age attending the vaccination clinic at Patan Hospital, Kathmandu, Nepal. Of these 666 swabs, 528 (79.3%) were tested for Hib by culture. Demographic and vaccination data were collected.

Results

Among 528 swabs tested for Hib, 100% came from fully vaccinated children. No swabs were positive for Hib (95% confidence interval, .0–.7). The absence of Hib in 2018 suggests vaccine-induced protection against Hib carriage 9 years after vaccine introduction.

Conclusions

Following 3 doses of pentavalent DTP-Hib-HepB vaccine, Hib carriage in children under the age of 5 years in Nepal is no longer common. Ongoing high coverage with Hib vaccine in early childhood is expected to maintain protection against Hib disease in Nepal.

Australian vaccine preventable disease epidemiological review series: invasive Haemophilus influenzae type b disease, 2000-2017

Introduction

Invasive Haemophilus influenzae type b (Hib) disease is rare in Australia following vaccine introduction in 1993. Two deaths in vaccinated children in 2017, and the Hib booster dose moving from age 12 months to 18 months in 2018, prompted this review.

Methods

Hib Case Surveillance Scheme 2000-2017 data were used to calculate incidence, incidence rate ratios (IRR) and vaccine failure (VF) trends. We used denominators from the Australian Immunisation Register to calculate incidence in immunised and unimmunised children.

Results

All-age national invasive Hib disease incidence halved from 0.13 per 100,000 population in 2000 to 0.06 in 2017. Of 345 cases notified in 2000-2017, 153 were born post-2000, with 51 (33%) Aboriginal and Torres Strait Islander (Indigenous), and compared with non-Indigenous children IRR was 8.34 (95% CI: 5.83-11.79), with no evidence of decrease. Overall case fatality rate was 12.4% (19/153); 6 cases had underlying medical conditions. The overall incidence of invasive Hib disease was over 8 times higher (16.6 per 100,000) in children with no recorded doses than in children with ≥1 vaccine dose (1.9 per 100,000). VF criteria were met in 65/145 (45%) cases aged >8 weeks, of whom 7 (11%) were immunocompromised and 6 (9%) died, with no evidence of VF increase over time.

Conclusion

Overall, invasive Hib disease incidence declined by 55% from 2000 to 2017, but marked disparity persists between Indigenous and non-Indigenous children. Following moving the fourth dose from 12 to 18 months in 2018, monitoring of 3-dose VFs will be important, especially in Indigenous children.

The burden of Staphylococcus aureus among Native Americans on the Navajo Nation

INTRODUCTION

Native Americans in the southwestern United States have a higher risk for many infectious diseases and may be at higher risk for Staphylococcus aureus due to the high prevalence of risk factors for S. aureus. Recent data on invasive S. aureus infections among Native Americans are limited.

METHODS

Active population- and laboratory-based surveillance was conducted in 2016-2017 on the Navajo Nation to document the rate of invasive S. aureus. A case of invasive S.aureus infection was defined as a Native American individual with S. aureus isolated from a normally sterile body site whose reported community of residence was on or around the Navajo Nation.

RESULTS

One hundred and fifty-nine cases of invasive S. aureus from 152 individuals were identified. The median age of cases was 56.3 years and 35% were female. Thirty-five percent of cases had community-acquired infections. Ninety-three percent of cases had underlying medical conditions, including diabetes (60%) and obesity (42%), 28% of cases had a documented prior S. aureus infection, and 33% were infected with methicillin-resistant S. aureus. The annual incidence of invasive S. aureus and of invasive methicillin-resistant S. aureus was 64.9/100,000 persons and 21.2/100,000 persons, respectively.

CONCLUSIONS

This community has a high burden of invasive S. aureus infections. Further research is needed to identify prevention strategies and opportunities for intervention.

Mercury Exposure and Poor Nutritional Status Reduce Response to Six Expanded Program on Immunization Vaccines in Children: An Observational Cohort Study of Communities Affected by Gold Mining in the Peruvian Amazon

Background: Poor nutritional status combined with mercury exposure can generate adverse child health outcomes. Diet is a mediator of mercury exposure and evidence suggests that nutritional status modifies aspects of mercury toxicity. However, health impacts beyond the nervous system are poorly understood. This study evaluates antibody responses to six vaccines from the expanded program on immunization (EPI), including hepatitis B, Haemophilus influenzae type B, measles, pertussis, tetanus, and diphtheria in children with variable hair mercury and malnutrition indicators. Methods: An observational cohort study (n = 98) was conducted in native and non-native communities in Madre de Dios, Peru, a region with elevated mercury exposure from artisanal and small-scale gold mining. Adaptive immune responses in young (3–48 months) and older children (4–8 year olds) were evaluated by vaccine type (live attenuated, protein subunits, toxoids) to account for differences in response by antigen, and measured by total IgG concentration and antibody (IgG) concentrations of each EPI vaccine. Mercury was measured from hair samples and malnutrition determined using anthropometry and hemoglobin levels in blood. Generalized linear mixed models were used to evaluate associations with each antibody type. Results: Changes in child antibodies and protection levels were associated with malnutrition indicators, mercury exposure, and their interaction. Malnutrition was associated with decreased measles and diphtheria-specific IgG. A one-unit decrease in hemoglobin was associated with a 0.17 IU/mL (95% CI: 0.04–0.30) decline in measles-specific IgG in younger children and 2.56 (95% CI: 1.01–6.25) higher odds of being unprotected against diphtheria in older children. Associations between mercury exposure and immune responses were also dependent on child age. In younger children, one-unit increase in log₁₀ child hair mercury content was associated with 0.68 IU/mL (95% CI: 0.18–1.17) higher pertussis and 0.79 IU/mL (95% CI: 0.18–1.70) higher diphtheria-specific IgG levels. In older children, child hair mercury content exceeding 1.2 µg/g was associated with 73.7 higher odds (95% CI: 2.7–1984.3) of being a non-responder against measles and hair mercury content exceeding 2.0 µg/g with 0.32 IU/mL (95% CI: 0.10–0.69) lower measles-specific antibodies. Log₁₀ hair mercury significantly interacted with weight-for-height z-score, indicating a multiplicative effect of higher mercury and lower nutrition on measles response. Specifically, among older children with poor nutrition (WHZ = −1), log₁₀ measles antibody is reduced from 1.40 to 0.43 for low (<1.2 µg/g) vs. high mercury exposure, whereas for children with good nutritional status (WHZ = 1), log₁₀ measles antibody is minimally changed for low vs. high mercury exposure (0.72 vs. 0.81, respectively). Conclusions: Child immune response to EPI vaccines may be attenuated in regions with elevated mercury exposure risk and exacerbated by concurrent malnutrition.

Evaluation of Haemophilus influenzae type b carrier status among children 10 years after the introduction of Hib vaccine in Brazil

The aim of the present study was to assess the prevalence of Haemophilus influenzae type b (Hib) nasopharyngeal (NP) colonisation among healthy children where Hib vaccination using a 3p+0 dosing schedule has been routinely administered for 10 years with sustained coverage (> 90%). NP swabs were collected from 2,558 children who had received the Hib vaccine, of whom 1,379 were 12-< 24 months (m) old and 1,179 were 48-< 60 m old. Hi strains were identified by molecular methods. Hi carriage prevalence was 45.1% (1,153/2,558) and the prevalence in the 12-< 24 m and 48-< 60 m age groups were 37.5% (517/1,379) and 53.9% (636/1,179), respectively. Hib was identified in 0.6% (16/2,558) of all children in the study, being 0.8% (11/1,379) and 0.4% (5/1,179) among the 12-< 24 m and 48-< 60 m age groups, respectively. The nonencapsulate Hi colonisation was 43% (n = 1,099) and was significantly more frequent at 48-< 60 m of age (51.6%, n = 608) compared with that at 12-< 24 m of age (35.6%, n = 491). The overall resistance rates to ampicillin and chloramphenicol were 16.5% and 3.7%, respectively; the co-resistance was detected in 2.6%. Our findings showed that the Hib carrier rate in healthy children under five years was very low after 10 years of the introduction of the Hib vaccine.

Long-term trends in invasive Haemophilus influenzae type B disease among indigenous Australian children following use of PRP-OMP and PRP-T vaccines

BACKGROUND

Among indigenous populations with high incidence and early onset of invasive Haemophilus influenzae type b (Hib) disease, PRP-OMP vaccines are used in the United States and PRP-T vaccines in Canada. In Australia, PRP-OMP vaccines were exclusively used in indigenous children from 1993 until they were replaced by PRP-T between late 2005 and 2009.

METHODS

Analytic descriptive study of 20 years of enhanced surveillance data (1993-2013) for invasive Hib disease in Australian children <10 years of age was conducted.

RESULTS

Of 579 Hib cases under 10 years of age reported from vaccine introduction in 1993 to 2013, 78 (13%) were in indigenous children, 47 (60%) of whom lived in regions with high prevaccine incidence. In this population, incidence per 100,000 declined from 18.1 (95% confidence interval [CI]: 10.4, 29.4) in the early PRP-OMP period (1993-1996) to 6.2 (95% CI: 4.0, 9.2) and 4.7 (95% CI: 1.7, 10.3) in the later PRP-OMP (1996-2009) and PRP-T periods (2009-2013), respectively. The indigenous:nonindigenous incidence rate ratio increased to 43 (95% CI: 16, 145) and 58 (95% CI: 7, 2660) in the later PRP-OMP and PRP-T periods, respectively, more than 10-fold higher than in lesser-incidence Australian regions.

CONCLUSIONS

We found no change in Hib incidence among indigenous Australian children living in high-incidence regions in the first 4 years following a change to PRP-T-containing combination vaccines. This may be of relevance to North American indigenous populations characterized by suboptimal living conditions and young age of onset for whom PRP-OMP continues to be recommended, such as Alaska Natives.

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.

A prospective study of agents associated with acute respiratory infection among young American Indian children

BACKGROUND

Native American children have higher rates of morbidity associated with acute respiratory infection than children in the general US population, yet detailed information is lacking regarding their principal clinical presentations and infectious etiologies.

METHODS

We pursued a comprehensive molecular survey of bacteria and viruses in nasal wash specimens from children with acute respiratory disease collected prospectively over 1 year (January 1 through December 31, 2009) from 915 Navajo and White Mountain Apache children in their second or third year of life who had been enrolled in an efficacy study of a respiratory syncytial virus monoclonal antibody in the first year of life.

RESULTS

During the surveillance period, 1476 episodes of disease were detected in 669 children. Rates of outpatient and inpatient lower respiratory tract illness were 391 and 79 per 1000 child-years, respectively, and were most commonly diagnosed as pneumonia. Potential pathogens were detected in 88% of specimens. Viruses most commonly detected were respiratory syncytial virus and human rhinovirus; the 2009 pandemic influenza A (H1N1) illnesses primarily occurred in the fall. Streptococcus pneumoniae was detected in 60% of subjects; only human rhinovirus was significantly associated with S. pneumoniae carriage. The presence of influenza virus, human rhinovirus or S. pneumoniae was not associated with increased risk for lower respiratory tract involvement or hospitalization.

CONCLUSIONS

Acute lower respiratory illnesses occur at disproportionately high rates among young American Indian children and are associated with a range of common pathogens. This study provides critical evidence to support reducing the disproportionate burden of acute respiratory disease among young Native Americans.

The continuing role of Haemophilus influenzae type b carriage surveillance as a mechanism for early detection of invasive disease activity

Prior to the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, Hib was the leading cause of bacterial meningitis in children under five years of age worldwide. In countries that have adopted Hib vaccination schedules, invasive disease has reduced markedly. Oro-naso pharyngeal carriage is recognized as the most significant source of infection. Hib carriage is significantly associated with poverty, such as overcrowding, poor ventilation in houses, lack of running water, and high smoking rates. Additionally, many Indigenous minority groups report high rates of Hib carriage. A resurgence of Hib disease among Alaskan children in the 1990s, lead to a change in approach to eliminate Hib disease and carriage in high-risk populations. This new approach identifies strategies for eliminating Hib disease focusing on the reservoirs of colonization within families and communities. Monitoring Hib carriage continues to offer an early warning system, whereby intervention could prevent invasive disease resurgence.

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

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

Haemophilus influenzae infections in the H. influenzae type b conjugate vaccine era

The widespread use of Haemophilus influenzae type b (Hib) conjugate vaccines has nearly eradicated invasive Hib disease where the vaccines are used. This success was accompanied by a shift in capsular serotypes of invasive H. influenzae disease, with nontypeable strains replacing type b strains as the most common bloodstream isolate, but there is no convincing evidence of a true increase in the incidence of non-serotype b invasive infections. H. influenzae causes predominantly mucosal infections. The introduction of vaccines for otitis media and global shifts in antimicrobial susceptibility emphasize the importance of continued surveillance of H. influenzae colonization and disease patterns.

Poor clinical outcome for meningitis caused by Haemophilus influenzae serotype A strains containing the IS1016-bexA deletion

Since the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, meningitis caused by serotypes other than Hib has gained in importance. We conducted active hospital-based surveillance for meningitis over an 11-year period in Salvador, Brazil. H. influenzae isolates were serotyped and analyzed by polymerase chain reaction, pulsed-field gel electrophoresis, and DNA sequencing to identify strains with a specific deletion (IS1016) in the bexA gene (IS1016-bexA). We identified 43 meningitis cases caused by non-type b H. influenzae: 28 (65%) were caused by type a (Hia), 9 (21%) were caused by noncapsulated strains, and 3 (7%) each were caused by types e and f. Hia isolates clustered in 2 clonal groups; clonal group A strains (n = 9) had the IS1016-bexA deletion. Among children <5 years of age, meningitis caused by Hia from clonal group A had higher case-fatality than meningitis caused by clonal group B. Despite small numbers, these results indicate that the presence of the IS1016-bexA deletion is associated with enhanced virulence in non-type b H. influenzae.

Haemophilus influenzae type b carriage in Indigenous children and children attending childcare centers in the Northern Territory, Australia, spanning pre- and post-vaccine eras

This paper investigates Haemophilus influenzae type b (Hib) carriage in Indigenous children and children attending childcare centres in the Northern Territory of Australia, 1992-2005. More than 10 years after the introduction of the Hib conjugate vaccine, Hib carriage persists in Indigenous children (3.4%, 2003-2005) and children attending childcare centres (0.2%, 2004). This is the first Australian study to examine Hib carriage spanning the pre- and post-vaccination eras. Increasing carriage rates contribute to Hib disease resurgence especially in those with higher disease burdens, such as remote Indigenous Australians, ongoing carriage surveillance provides a sentinel warning system for invasive disease.

BACKGROUND

Following the introduction of H. influenzae type b (Hib) conjugate vaccine to Australia in 1993 as a three dose (2, 4, 12 month) schedule, the incidence of Hib disease decreased dramatically in children, especially in those aged under 5 years. We investigate Hib carriage in Indigenous children and children attending childcare centres from the Northern Territory (NT) of Australia between 1992 and 2005. We report Hib carriage rates in this well vaccinated population, with previously documented high rates of invasive disease.

METHODS

Hib carriage was reviewed in nasopharyngeal or nasal swabs collected between 1992 and 2005; from over 2000 children (61% Indigenous) aged 0-6 years enrolled in 7 otitis media or carriage surveillance studies in the NT.

RESULTS

More than 10 years after the introduction of the Hib conjugate vaccine, Hib carriage persists at low levels, but at a higher rate in Indigenous children (3.4%, 2003-2005) than children attending childcare centres (0.2%, 2004), in the NT of Australia.

CONCLUSIONS

This is the first Australian study to examine Hib carriage spanning the pre- and post-vaccination eras. Ongoing carriage surveillance provides a sentinel warning system for invasive disease. This notifies public health professionals of potential invasive disease, creating early warning systems for intervention if Australian Indigenous children or children attending childcare centres are to follow current international trends associated with high rates of carriage preceding invasive disease-despite high vaccination rates. Internationally there is growing concern that increasing carriage rates are the driving force behind Hib disease resurgence especially in those with higher disease burdens, such as remote Indigenous Australians. Changes to the vaccination schedule from PRP-OMPC (PedvaxHIB(®)), to PRP-T (2, 4, 6, 12 months) from January 2010-may affect carriage and in time, invasive disease rates. This work is important for national and International comparisons as well as feeding back information to vaccine policy makers of the Hib carriage environment throughout this period.

Invasive Haemophilus influenzae Disease, Europe, 1996-2006

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

Vaccine preventable diseases and vaccination policy for indigenous populations

There are many similarities regarding the health status of Indigenous people in the 4 English-speaking developed countries of North America and the Pacific (United States, Canada, Australia, New Zealand), where they are all now minority populations. Although vaccines have contributed to the reduction or elimination of disease disparities for many infections, Indigenous people continue to have higher morbidity and mortality from many chronic and infectious diseases compared with the general populations in their countries. This review summarizes the available data on the epidemiology of vaccine-preventable diseases in Indigenous populations in these 4 countries in the context of the vaccination strategies used and their impact, with the aim of identifying successful strategies with the potential for wider implementation.

Haemophilus influenzae colonization and its risk factors in children aged <2 years in northern India

The disease burden and the age group of children most affected by Haemophilus influenzae remain controversial particularly in many countries of South Asia. Nasopharyngeal carriage of H. influenzae can indicate the transmission dynamics in these settings. In a prospective population-based study, nasopharyngeal swabs from 1000 children aged <2 years, belonging to various socioeconomic groups from rural and urban areas of northern India were taken. The prevalence of H. influenzae carriage was found to be 11·2%. Among these isolates, 69% belonged to type b and the rest were non-typable. The age group most affected was 18–21 months. The carriage rate was influenced by age and socioeconomic factors namely type of housing, overcrowding, and season. Hib carriage is quite common in northern India and it is associated with age, type of housing, overcrowding, and season. Since carriage gets established early, Hib vaccination should target children in early infancy.

Epidemiology of Haemophilus influenzae serotype a, North American Arctic, 2000-2005

Serotype a is now the most common seen in the North American Arctic; highest rates occur in indigenous children.

Before the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, rates of invasive H. influenzae disease among indigenous people of the North American Arctic were among the highest in the world. Routine vaccination reduced rates to low levels; however, serotype replacement with non–type b strains may result in a reemergence of invasive disease in children. We reviewed population-based data on invasive H. influenzae in Alaska and northern Canada from 2000–2005; 138 cases were reported. Among 88 typeable isolates, 42 (48%) were H. influenzae type a (Hia); 35 (83%) occurred in indigenous peoples. Among Hia patients, median age was 1.1 years; 62% were male; 1 adult died. Common clinical manifestations included meningitis, pneumonia, and septic arthritis. Overall annual incidence was 0.9 cases per 100,000 population. Incidence among indigenous children <2 years of age in Alaska and northern Canada was 21 and 102, respectively. Serotype a is now the most common H. influenzae serotype in the North American Arctic; the highest rates are among indigenous children.

Genetic variation in the response to vaccination

Vaccines are the most powerful means to prevent and diminish the burden of infectious disease. However, there are limitations to their use: vaccines are not yet available for all infectious diseases (including human immunodeficiency virus and respiratory syncytial virus), they sometimes lack efficacy, the response to vaccination is limited by maternal antibodies in very young infants, and the response to vaccination is variable or may even be absent in some individuals. This review focuses on genetic factors that determine the variable response to vaccination. The highly polymorphic human leukocyte antigen system, which is involved in antigen presentation, has been researched most in this aspect, and clearly affects the response to vaccination. Other, but less polymorphic pathways involved are the Toll-like receptor pathway, which is involved in antigen recognition and stimulation of the immune system, and the cytokine immunoregulatory network. The heritability, or the proportion of total variance that is due to additive genetic factors, appears to be particularly large for vaccine-induced antibody responses in young infants compared with cell-mediated responses and antibody responses in older, immunologically more mature individuals. Both antibody and cell-mediated responses are not only affected by loci within, but also strongly by loci outside the human leukocyte antigen system. Because most genes that are important in influencing immune responses to vaccination are still unknown, clearly more work is required. A better understanding of the factors that determine an effective response to vaccination may lead to the identification of specific genes and pathways as targets for the development of novel more uniformly effective vaccines.

Contributions of Native Americans to the global control of infectious diseases

For over a half of a century, Native American populations have participated in numerous studies regarding the epidemiology, prevention and treatment of infectious diseases. These studies have resulted in measures to prevent morbidity and mortality from many infectious diseases. The lessons learned from these studies and their resultant prevention or treatment interventions have been applied around the world, and have had a major impact in the reduction of global childhood morbidity and mortality.

Higher pertussis hospitalization rates in indigenous Australian infants, and delayed vaccination

This ecological study aimed to identify possible reasons for higher pertussis hospitalization rates in indigenous Australian infants. Two national datasets were analysed: the Hospital Morbidity Database and the Australian Childhood Immunisation Register (ACIR). Most (52%) pertussis hospitalizations in indigenous infants occurred at 0-2 months of age, and rates in these indigenous infants were significantly higher in remote areas. Indigenous infants had higher hospitalization rates and more frequently delayed vaccination than non-indigenous infants of the same age. These data suggest that residence in a remote area, as a proxy for poorer living conditions for indigenous people, and delayed vaccination, both contribute to higher pertussis hospitalization rates in indigenous infants.

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.

Frequent Haemophilus influenzae type B colonization in rural Thailand

In Asia, there is uncertainty regarding whether the burden of Haemophilus influenzae type b (Hib) disease is great enough to warrant vaccination. In this nasopharyngeal carriage study in rural Thailand, 7% of children younger than 5 years of age carried Hib, a prevalence similar to that found in countries with high rates of Hib disease before vaccine introduction.

Genotyping of type b Haemophilus influenzae strains, comparison of strains collected before and during vaccine availability

OBJECTIVE AND METHOD

Five hundred and seventy-eight strains of type b Haemophilus influenzae (521 isolated in children, and 57 in adults) were compared using pulsed-field gel electrophoresis (PFGE) to assess strain evolution and to study the impact of the generalization of anti-Haemophilus b (anti-Hib) vaccination in France. Among these strains, 398 (including 342 from meningitis) were isolated in 1985-1992 (pre-vaccination era), 39 (including 31 from meningitis) in 1993 (year of the generalization of anti-Hib vaccination), and 141 (including 50 from CSF) in 1994-2001 (vaccination era).

RESULTS

A total of 102 PFGE patterns (patterns for 1-101 isolates) were obtained after SmaI restriction of the 578 strains. The strains isolated in children were distributed in 96 patterns, and those isolated in the adult in 34 patterns. The strains isolated during the pre-vaccination era presented 94 patterns. During the vaccination era, 50% of the patterns disappeared and 12 new patterns (11.7%) including 15 strains were observed. The strains belonging to the new patterns (including the two observed in 1993) were isolated in adults (n=7) from blood culture and bronchial secretions, and children (n=9) from CSF, blood culture, and bronchial secretions. In children, among the strains associated to vaccination failure, two presented with a new pulsotype.

CONCLUSION

There is no evidence that the vaccination program brought about any drastic modifications in the type b strains causing meningitis or in the other type b strains in circulation whether in adults or children.

Lower respiratory tract infections among american Indian and Alaska Native children and the general population of U.S. Children

BACKGROUND AND OBJECTIVE

Lower respiratory tract infections (LRTIs) cause substantial childhood morbidity. This study characterizes and compares LRTI-associated morbidity among American Indian/Alaska Native (AI/AN) children and the general population of U.S. children.

METHODS

Hospitalization and outpatient records with a diagnosis indicating LRTIs were evaluated for children aged younger than 5 years during 1990-2001.

RESULTS

For 1999-2001, the LRTI-associated hospitalization rate was significantly higher for AI/AN children than for U.S. children (116.1 versus 63.2/1000, respectively), with the disparity being greater for infants than for 1- to 4-year-old children. Also the rate of LRTI-associated outpatient visits among AI/AN infants was higher than that for all U.S. infants (737.7 versus 207.2/1000, respectively). LRTI hospitalization and outpatient visit rates were highest in the Alaska and Southwest Indian Health Service regions. During 1990-2001, the LRTI hospitalization rate among AI/AN infants in the Alaska region and among the general U.S. infant population increased. Bronchiolitis-associated hospitalization rates increased for AI/AN and U.S. infants, whereas the pneumonia-associated hospitalization rate decreased among AI/AN infants and remained stable among U.S. infants.

CONCLUSIONS

LRTIs continue to be an important cause of morbidity in children, especially among AI/AN infants in the Alaska and Southwest regions. Strategies to reduce LRTI hospitalizations and outpatient visits are warranted for all infants, but the greatest potential impact would be among AI/AN infants.

Epidemiology of invasive Haemophilus influenzae type A disease among Navajo and White Mountain Apache children, 1988-2003

BACKGROUND

Before the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, rates of H. influenzae disease among Navajo and White Mountain Apache (WMA) children were among the highest reported worldwide. Routine Hib vaccination has significantly reduced rates of Hib disease in these populations. As Hib disease rates decrease to very low levels, there are concerns that non-type b strains of H. influenzae may emerge as more prevalent causes of invasive disease in children.

METHODS

We reviewed population-based, active laboratory surveillance data from the period of 1988-2003 for invasive H. influenzae type a (Hia) disease among Navajo and WMA children aged <5 years. Clinical information on cases was collected by chart review. A sample of Hia isolates from Navajo children was typed by pulsed-field gel electrophoresis (PFGE).

RESULTS

During 1988-2003, a total of 76 reported cases of invasive Hia disease occurred among Navajo and WMA children. The overall annual incidence was 20.2 cases per 100,000 population aged <5 years. There was no increase in Hia disease rates after Hib vaccination was introduced. The median age of patients was 12 months. Meningitis (50% of cases) was the most common presentation, followed by pneumonia (27.6%). Two children with Hia disease died. PFGE analysis revealed a limited genetic diversity of Hia strains in this population.

CONCLUSIONS

Active surveillance data showed high rates of invasive Hia disease among Navajo and WMA children but no increase in the incidence after Hib vaccination was introduced. The presentation of Hia disease is similar to that of Hib disease in the prevaccine era.

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.

Effects of sample collection and storage methods on antipneumococcal immunoglobulin A in saliva

Saliva contains components of both the mucosal and systemic immune systems. Variable flow rates, immunoglobulin proteases, and variation in collection and storage methods all introduce differences in the estimated concentrations of antibodies. We evaluated the effect of four collection methods and three storage protocols on the concentrations of immunoglobulin A (IgA) antibodies to pneumococcal capsular antigens 1, 5, 6B, and 14 and to pneumococcal surface adhesin A (PsaA) in saliva. Specimens were collected from 30 healthy Kenyan adults by collecting drool, by pipette suction, and with two commercial kits, OraSure and Oracol. Aliquots from each specimen were snap-frozen with glycerol in liquid nitrogen or stored for 4 to 8 h at +4 degrees C either with or without the addition of protease enzyme inhibitors prior to storage at -70 degrees C. Anticapsular IgA concentrations were not significantly different with different collection methods, but snap-freezing the specimens in liquid nitrogen led to concentrations 41 to 47% higher than those of specimens stored by the other methods (P < 0.0005).

Infectious disease hospitalizations among American Indian and Alaska native infants

OBJECTIVE

To describe the burden and trends in hospitalizations associated with infectious diseases among American Indian and Alaska Native (AI/AN) infants.

METHODS

First-listed infectious disease hospitalizations and hospitalization rates among AI/AN infants and infants in the general US population from 1988-1999 were analyzed by using Indian Health Service/tribal hospital discharge data and the National Hospital Discharge Survey data, respectively.

RESULTS

Infectious disease hospitalizations accounted for 53% of all AI/AN infant hospitalizations and approximately 43% of all US infant hospitalizations during 1988-1999. The annual hospitalization rate for infectious diseases among AI/AN infants declined from 27,486 per 100,000 infants in 1988 to 14,178 per 100,000 infants in 1999. However, the rates for AI/AN infants within the Alaska, Southwest, and Northern Plains regions remained higher than that for the general US infant population at the end of the study period. Lower respiratory tract infection hospitalizations accounted for almost 75% of AI/AN infant infectious disease hospitalizations, and the lower respiratory tract infection hospitalization rate for AI/AN infants was twice that for US infants.

CONCLUSIONS

Although infectious disease hospitalization rates for AI/AN infants have declined, AI/AN infants continue to have a higher infectious disease burden than the general US infant population.