Haemophilus, Legionella, Bordetella

• Haemophilus influenzae, Bordetella pertussis, and Legionella pneumophila are discussed in terms of epidemiology, pathogenesis, clinical features, complications, laboratory diagnosis, antimicrobial treatment, and prevention
• Haemophilus influenzae b (Hib) causes respiratory tract infections in early childhood, including acute epiglottitis, pneumonia, meningitis, and septicaemia
• Haemophilus influenzae is NOT the cause of influenza
• Haemophilus influenzae b (Hib) is associated with untreated mortality as high as 90% and can lead to sequelae like deafness, seizures, and intellectual impairment
• Haemophilus influenzae, Bordetella pertussis, and Legionella pneumophila infections can be prevented through appropriate measures to prevent acquisition and spread
• Bordetella pertussis, causing whooping cough, is a highly contagious infection of the respiratory tract, most severe in infants with mortality rates estimated at 4%
• Problems with pertussis:

  • Reduced herd immunity due to lack of natural boosting and waning immunity
  • Poor long term protective efficacy of acellular pertussis vaccines
  • Reinfection can occur
  • Improved laboratory diagnosis
• An additional booster for pertussis is recommended for:

  • Children aged 11-14 years
  • Healthcare workers
  • Pregnant women
• Stages of Whooping Cough:

  • Catarrhal Stage (1-2 weeks): nonspecific symptoms
  • Paroxysmal Stage (1-6 weeks): paroxysmal cough, post-tussive vomiting
  • Convalescent Stage (3-4 weeks): gradual reduction in cough severity
  • Total duration of all three phases is around 3 months
• Pertussis is most infectious during the paroxysmal stage and lasts for around 3 weeks after the onset of the paroxysmal stage
• Diagnosis of Pertussis:

  • Clinical features
  • Microbiological tests like Nucleic Acid Amplification tests (NAAT) and culture
  • Serology (may be affected if recent vaccine)
  • Other supportive lab tests like increased white cell count with lymphocytosis
• Treatment of Whooping Cough:

  • Primarily supportive with fluid administration
  • Macrolides like Azithromycin or clarithromycin
  • Hospitalization & ICU care may be required in the very young
• Prevention of pertussis:

  • Universal infant immunization is recommended
  • Acellular pertussis vaccines are now generally used, containing antigens and causing fewer reactions than whole cell vaccines
  • Administered in combination with Diphtheria, Tetanus, and acellular Pertussis vaccines (DTaP)
• Legionella species:

  • Gram-negative bacillus
  • Flagellated
  • Non-capsulated
  • Strict aerobe
• Risk factors for legionellosis:

  • Warm temperatures (25-42°C), water stagnation, scale, and sediment enhance colonization
  • Infection arises following inhalation of aerosols from contaminated water
• Legionnaires’ Disease:

  • Clinical features: typically aged 50-60 years, abrupt onset of fever, chills, dry cough, headache
  • Risk factors for severe disease: old age, cigarette smoking, immunosuppression
• Legionnaires’ Disease diagnosis:

  • Urinary antigen detection is the most commonly used test
  • Sputum, tracheal aspirate, or BAL can also be used for diagnosis
• Legionnaires’ Disease treatment:

  • β-lactam agents are not effective
  • Drugs with good intracellular penetration are required, like respiratory fluoroquinolones or macrolides