Trimethoprim and rifampin in combination for chemoprophylaxis of household contacts of patients with invasive infections due to Haemophilus influenzae type b

Rifampin alone or with trimethoprim for contacts of children with Haemophilus influenzae type b infections

We carried out a nonrandomized, unblinded study to compare the efficacy of rifampin alone with that of rifampin in combination with trimethoprim in the eradication of the Haemophilus influenzae type b (HIB) carrier state among contacts of patients with invasive HIB infection. The study population comprised 17 index patients admitted to hospital with severe HIB infections and 233 contacts, 43 of whom had nasopharyngeal colonization with HIB of the same biotype as that of the index patient. Rifampin in a daily dose of 20 mg/kg (maximum 600 mg) for 4 days eradicated the carrier state in 86% of cases, as did the combination of rifampin at the same dosage and trimethoprim in a daily dose of 5 mg/kg (maximum 160 mg) for 4 days.

Pathogenicity of a rifampin-resistant cerebrospinal fluid isolate of Haemophilus influenzae type b

Two children in a day care facility developed Haemophilus influenzae type b meningitis. The second child was enrolled in the facility after rifampin had been administered to the other attendees. The isolate from the first child was susceptible to rifampin, but the isolate from the second was resistant. Both isolates had identical outer membrane protein PAGE profiles. To investigate the virulence of these isolates, we inoculated infant rats intranasally with either the rifampin-resistant or rifampin-susceptible CSF isolate. The rates of nasal colonization (14 of 20 and eight of eight animals inoculated with the rifampin-resistant and rifampin-susceptible isolates, respectively) did not differ significantly. However, bacteremia occurred less frequently in pups inoculated with the rifampin-resistant strain than in animals inoculated with the susceptible strain (four of 20 vs eight of eight, P less than 0.0001). Nasal washings, blood, and CSF obtained from animals inoculated with the rifampin-resistant isolate were divided and plated on media containing rifampin (1 microgram/ml) or without rifampin. Except for those from one animal, organisms isolated from blood and CSF grew only on medium lacking rifampin, whereas H. influenzae type b growing from nasal washings was frequently found on both media. We conclude that mutation of H. influenzae to rifampin resistance is a hazard of rifampin chemoprophylaxis. Rifampin-resistant isolates have the potential to cause disease in patients and experimental animals, although they may be relatively less pathogenic than the parent, susceptible organism.

Chemoprophylaxis for the prevention of bacterial meningitis

Close contacts of index patients with Neisseria meningitidis or Haemophilus influenzae type b meningitis show higher nasopharyngeal carriage rates and are at an increased risk of contracting the disease. The key issue in the management of such contacts remains close and careful surveillance, because prophylaxis will never result in the absolute prevention of secondary cases. Adequate chemoprophylaxis with rifampin eradicates nasopharyngeal colonization in more than 90% and may prevent both co-primary and secondary diseases. Routine chemoprophylaxis for close contacts of systemic meningococcal diseases is recommended. However, there are several factors inherent in rifampin prophylaxis for the prevention of H. influenzae type b meningitis which exclude its use as a routine measure.