Chapter 139. Haemophilus Infections (Kỳ 4) Prevention Vaccination (See also Chap. 116) The development of conjugate vaccines that prevent invasive infections with Hib in infants and children has been a dramatic success. Three such vaccines are licensed in the United States. In addition to eliciting protective antibody, these vaccines prevent disease by reducing rates of pharyngeal colonization with Hib. The widespread use of conjugate vaccines has dramatically reduced the incidence of Hib disease in developed countries. Even though the manufacture of Hib vaccines is costly, vaccination is cost-effective. The Global Alliance for Vaccines and Immunizations has recognized the underuse of Hib conjugate vaccines. The disease burden has been reduced in developing countries that have implemented routine vaccination (e.g., The Gambia, Chile). An important obstacle to more widespread vaccination is the lack of data on the epidemiology and burden of Hib disease in many developing countries. All children should be immunized with an Hib conjugate vaccine, receiving the first dose at ~2 months of age, the rest of the primary series at 2–6 months of age, and a booster dose at 12–15 months of age. Specific recommendations vary for the different conjugate vaccines. The reader is referred to the recommendations of the American Academy of Pediatrics (Chap. 116 and www.cispimmunize.org). Currently, no vaccines are available for the prevention of disease caused by nontypable H. influenzae. Chemoprophylaxis The risk of secondary disease is greater than normal among household contacts of patients with Hib disease. Therefore, all children and adults (except pregnant women) in households with at least one incompletely immunized contact <4 years of age should receive prophylaxis with oral rifampin. When two or more cases of invasive Hib disease have occurred within 60 days at a child-care facility attended by incompletely vaccinated children, administration of rifampin to all attendees and personnel is indicated, as is recommended for household contacts. Chemoprophylaxis is not indicated in nursery and child-care contacts of a single index case. The reader is referred to the recommendations of the American Academy of Pediatrics. Haemophilus influenzae Biogroup Aegyptius H. influenzae biogroup aegyptius was formerly called Haemophilus aegyptius because of phenotypic characteristics distinct from those of H. influenzae. However, later studies involving DNA hybridization and DNA transformation demonstrated that H. aegyptius and H. influenzae are members of the same species. H. influenzae biogroup aegyptius has long been associated with conjunctivitis. Moreover, this strain is now known to be the cause of Brazilian purpuric fever (BPF), which was first recognized in 1984 in the rural Brazilian town of Promissão. The sharing of many phenotypic and genotypic characteristics by the various strains of H. influenzae biogroup aegyptius that cause BPF indicates that these strains represent a clone of H. influenzae that has acquired specific virulence factors, several of which are associated with a pathogenicity island. The age of peak incidence of BPF is 1–4 years, with a range of 3 months to 8 years. The illness can occur sporadically or in outbreaks. Typically, after an episode of purulent conjunctivitis, high fever occurs in association with vomiting and abdominal pain. Within 12–48 h after onset, the patient develops petechiae, purpura, and peripheral necrosis and experiences vascular collapse. The characteristic laboratory features are thrombocytopenia, prolonged prothrombin time, uniformly unrevealing CSF findings, and blood cultures positive for H. influenzae biogroup aegyptius. Initial reports cited high mortality (70%), but subsequent studies have indicated that milder forms of the illness exist. Most patients have resolved or resolving purulent conjunctivitis, and culture of the conjunctiva is positive in approximately one-third of cases. BPF has been seen in several towns in Brazil and on two occasions in Australia. Haemophilus ducreyi Haemophilus ducreyi is the etiologic agent of chancroid (Chap. 124), a sexually transmitted disease characterized by genital ulceration and inguinal adenitis. H. ducreyi poses a significant health problem in developing countries. Although this infection is less common in the United States, its incidence has increased dramatically in the past several years. In addition to being a cause of morbidity in itself, chancroid is associated with HIV infection because of the role played by genital ulceration in HIV transmission. Microbiology H. ducreyi is a highly fastidious coccobacillary gram-negative bacterium whose growth requires X factor (hemin). Although, in light of this requirement, the bacterium has been classified in the genus Haemophilus, DNA homology and chemotaxonomic studies have established substantial differences between H. ducreyi and other Haemophilus species. Taxonomic reclassification of the organism is likely in the future but awaits further study. The histology of the genital ulcer of chancroid is characterized by perivascular and interstitial infiltrates of macrophages and of CD4+ and CD8+ T lymphocytes. The appearance is consistent with a delayed-type hypersensitivity, cell-mediated immune response. The presence of CD4+ T cells and macrophages in the ulcer may explain, in part, the facilitation of HIV transmission in patients with chancroid. Epidemiology and Prevalence Chancroid is a common cause of genital ulcers in developing countries. In the United States, chancroid is now endemic in some regions, and several large outbreaks have occurred since 1981. Recurring epidemiologic themes have been apparent in these outbreaks: (1) transmission has been predominantly heterosexual; (2) males have outnumbered females by ratios of 3:1 to 25:1; (3) prostitutes have been important in transmission of the infection; and (4) chancroid has been strongly associated with illicit drug use. . Chapter 139. Haemophilus Infections (Kỳ 4) Prevention Vaccination (See also Chap. 116) The development of conjugate vaccines that prevent invasive infections with Hib. towns in Brazil and on two occasions in Australia. Haemophilus ducreyi Haemophilus ducreyi is the etiologic agent of chancroid (Chap. 1 24), a sexually transmitted disease characterized by. recommendations of the American Academy of Pediatrics. Haemophilus influenzae Biogroup Aegyptius H. influenzae biogroup aegyptius was formerly called Haemophilus aegyptius because of phenotypic characteristics