Haemophilus influenzae type b disease after rifampin prophylaxis in a day care center: possible reasons for its failure.

Five infants enrolled in a day care center (DCC) developed invasive disease due to Haemophilus influenzae type b during a 25-week period. The isolates from four patients had identical outer membrane proteins and were biotype 1. Although rifampin prophylaxis was recommended on two different occasions, retrospective surveys demonstrated that 39 and 60%, respectively, of infants failed to receive the agent for various reasons. Pharyngeal cultures were obtained from infants, their families and DCC staff after prophylaxis was given the second time. Forty-seven % of DCC infants had positive cultures, and 59% of their households had at least one carrier of the invasive strain. Rifampin prophylaxis administered a third time to infants and members of their households was unsuccessful in eradicating the invasive Haemophilus influenzae type b strain from DCC infants. The possible reasons for failure of rifampin in this DCC outbreak included incomplete understanding by physicians and health department officials of the factors affecting a DCC outbreak of Haemophilus influenzae type b disease and failure properly to implement rifampin prophylaxis to all contacts and the index cases.