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• Haemophilus


  • Nonmotile and facultatively anaerobic, ferment carbohydrates, are generally oxidase and catalase positive, reduce nitrates to nitrites, and are obligate parasites on the mucous membranes of humans and animals
• Haemophilus species associated with humans


  • H. influenzae
  • H. parainfluenzae
  • H. haemolyticus
  • H. parahaemolyticus
  • H. paraphrohaemolyticus
  • H. pittmaniae
  • H. aegyptius
  • H. ducreyi
• X factor


  Hemin or hematin, required for growth of Haemophilus
• V factor


  Nicotinamide adenine dinucleotide (NAD), required for growth of Haemophilus
• Satellitism


  Phenomenon where a Haemophilus isolate obtains V factor from a V factor-producing organism like Staphylococcus aureus, Streptococcus pneumoniae, or Neisseria spp.
• Approximately 10% of the normal bacterial biota in adults consists of Haemophilus spp., with most being H. parainfluenzae and non-encapsulated H. influenzae
• Nontypable H. influenzae (NTHi)


  H. influenzae strains that are not encapsulated
• Virulence factors of H. influenzae


  • Capsule
  • Immunoglobulin A (IgA) proteases
  • Adherence mechanisms
  • Outer membrane components
• Invasive disease caused by H. influenzae


  Septicemia, meningitis, arthritis, epiglottitis, tracheitis, pneumonia
• Localized infections caused by nontypable H. influenzae


  Conjunctivitis, sinusitis, otitis media with effusion
• Before the Hib vaccine, the other H. influenzae serotypes (a, c, d, e, f) rarely caused invasive disease in humans
• Capnocytophaga, Brucella, and Francisella are other fastidious, gram-negative bacilli discussed in this chapter
• Capsule


  • Of all the virulence factors, the capsule, if present, plays the most significant role
  • The serologic grouping of H. influenzae into six antigenically distinct types—a, b, c, d, e, and f—is based on differences in the capsular polysaccharide
• Before widespread use of a vaccine, most invasive infections were caused by the encapsulated strain H. influenzae serotype b (Hib) and occurred primarily in young children
• Serotype b strains are rarely seen now in children in countries using the vaccine; however, occasional serious invasive infections are seen in adults, especially in those over age 65 years
• In unvaccinated children, type b is a leading cause of meningitis
• Serotype b capsule


  A unique polymer composed of ribose, ribitol, and phosphate (polyribitol phosphate)
• Capsule


  • Evidence suggests that the antiphagocytic property and anticomplementary activity of the capsule contribute to the virulence of encapsulated strains
• Nontypable (non-encapsulated) strains are currently responsible for most H. influenzae diseases in the United States
• 70% of invasive H. influenzae infections were caused by nontypable strains
• Serotype f (18%) accounted for the majority of invasive infections, with 403 infections caused by nontypable strains
• The U.S. Centers for Disease Control and Prevention (CDC) estimates that 6100 invasive case of H. influenzae, and 1015 deaths occur annually
• In developing countries, where there is a lack of vaccination, serotype b is still a significant cause of bacterial pneumonia deaths and meningitis in children
• H. influenzae remains a problem in older and debilitated people who have not been vaccinated
• Infections caused by encapsulated H. influenzae strains


  • Septicemia
  • Meningitis
  • Septic arthritis
  • Osteomyelitis
  • Pericarditis
• Infections caused by non-encapsulated H. influenzae strains


  • Otitis media with effusion
  • Conjunctivitis
  • Sinusitis
  • Bacteremia
  • Cellulitis
  • Pneumonia
• Before widespread use of the Hib vaccine, in virtually all cases of meningitis caused by H. influenzae in children between the ages of 3 months and 6 years were caused by serotype b
• Bloodstream invasion and bacteremic spread follow colonization, invasion, and replication of this organism in the respiratory mucous membranes
• Headache, stiff neck, and other meningeal signs are usually preceded by mild respiratory disease
• Epiglottitis


  • Rapid onset, acute inflammation, and intense edema of the epiglottis that may cause complete airway obstruction, requiring an emergency tracheostomy
  • Peak incidence occurs in children between 2 and 4 years of age
  • Maintenance of a secure airway is the most important aspect of treatment
• Bacterial tracheitis


  • A serious life-threatening disease in young children
  • Can arise after an acute, viral respiratory infection
  • Initially there is mild to moderate illness for approximately 2 to 7 days, but it progresses rapidly
  • Use of broad-spectrum antimicrobial agents during the early stages of the disease is imperative because thick secretions can occlude the trachea, so the disease must be differentiated from epiglottitis
• Haemophilus aegyptius


  Genetically related to H. influenzae, associated with acute, contagious conjunctivitis, commonly referred to as "pinkeye"
• Haemophilus influenzae biogroup aegyptius


  • Can cause conjunctivitis, primarily in pediatric populations
  • Despite being non-encapsulated, a clone caused a severe systemic disease known as Brazilian purpuric fever (BPF) in Brazil in 1984
• Brazilian purpuric fever (BPF)


  • Characterized by recurrent or concurrent conjunctivitis, followed by a sudden onset of high fever, petechial/purpural rash, septicemia, shock, and vascular collapse
  • Mortality rate may reach 70% within 48 hours after onset
• Haemophilus ducreyi


  • The causative agent of chancroid, a highly communicable sexually transmitted genital ulcer disease (GUD)
  • Infects the mucosal epithelium, genital and nongenital skin, and regional lymph nodes
• Chancroid


  • Commonly referred to as soft chancre, in contrast to the hard chancre of syphilis
  • Facilitates the transmission of other STDs, so all patients who have GUD should also be tested for human immunodeficiency virus (HIV) along with syphilis and herpesvirus
  • After an incubation period of approximately 4 to 14 days, a nonindurated, painful lesion with an irregular edge develops, generally on the genitalia or perianal areas
  • Suppurative (pus-forming), enlarged, draining, inguinal lymph nodes (buboes) are common in most infected patients
  • Men have symptoms related to the inguinal tenderness and genital lesions, whereas most women are asymptomatic
• Although less than 15 cases of chancroid are reported in the United States annually, as with Neisseria gonorrheae and Chlamydia trachomatis, cases are probably underreported
• H. ducreyi is an important cause of GUD in Latin America, Africa, and Asia
• Haemophilus parainfluenzae


  Has a very low incidence of pathogenicity, may cause a few cases of otitis media and acute sinusitis, and has been rarely implicated as a causative agent of endocarditis
• Haemophilus parahaemolyticus


  In the absence of other pathogens, may be a cause of some cases of pharyngitis