Secondary cases of invasive disease caused by spread of Haemophilus influenzae type b.

Three 6-year-old girls were admitted to hospital within a period of 9 days because of invasive disease caused by Haemophilus influenzae type b (Hib). Two days after the index case contracted bacterial meningitis, her twin sister developed septicemia. Nine days after onset of illness in the index case, a day-care contact developed a febrile illness. The antibiograms of the bacterial strains isolated from cerebrospinal fluid or blood in the first two cases were identical; in the third case, blood cultures were negative but Hib antigen could be detected in serum and in urine. These cases illustrate the contagiousness of Hib disease. All household contacts of a case should be informed about the risk and their protection with rifampicin considered.