Intralitter transmission of haemophilus influenzae type b in infant rats and rifampin eradication of nasopharyngeal colonization.

The dynamics of nasopharyngeal colonization, bacteremia, and transmission of infection due to Haemophilus influenzae type b in infant rats were studied. Intranasal inoculation resulted in nasal colonization in 99% and bacteremia in 88% of infant rats. H. influenzae type b was transmitted to 93% of exposed, uninoculated littermates. Pretreatment with burro antibody to H. influenzae type b prevented bacteremia but not nasal colonization. Rifampin, in a dose of 20 mg/kg twice daily for two days, was 97% and 100% effective in eradicating two strains of H. influenzae type b from the nasopharynx. Efficacies of 10 mg/kg twice daily and 5 mg/kg twice daily for two days were 86% and 6%, respectively. No rifampin-resistant isolates were encountered in animals still colonized after rifampin therapy. This model for haemophilus colonization and intralitter transmission could be used to evaluate other chemoprophylactic agents and may provide additional insight into the epidemiology and immunology of haemophilus infections.