Rifampicin prophylaxis for throat carriage of Haemophilus influenzae type b in patients with invasive disease and their contacts.

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Abstract
OBJECTIVE--To determine rates of colonisation with Haemophilus influenzae type b among household contacts of children with invasive H influenzae type b disease; compliance among medical staff with recommendations for use of rifampicin prophylaxis; and effects of rifampicin treatment in H influenzae type b colonisation of patients and contacts. DESIGN--Prospective study of patients and their household contacts. SETTING--Royal Children's Hospital (the major paediatric hospital) in Victoria, Australia, with catchment population of 4.2 million, including 300,000 children aged under 5 years. SUBJECTS--234 patients (age range 6 weeks to 8 years) with 235 episodes of all types of invasive H influenzae type b disease admitted during 1988-9 and their contacts. MAIN OUTCOME MEASURES--Positive cultures of H influenzae type b from throat swabs taken at admission and six weeks subsequently; recording of rifampicin prophylaxis. RESULTS--The percentage of patients with positive throat cultures fell from 69% (33/48) on day 1 of admission to 9% (4/47) after three days' treatment; at six weeks' follow up 32% (32/99) of patients who had not received rifampicin and 8% (5/61) who had, had positive throat cultures. Among household contacts, 33% (62/190) of children and 7% (25/359) of adults were colonised, and the colonisation rates were similar in contacts of patients with all types of H influenzae type b disease. Rifampicin prophylaxis was indicated in 85 families; in 34% it was not prescribed at all for contacts and in 41% not as recommended. The colonisation rates at follow up were significantly less in siblings given rifampicin (12%, 9/78), particularly in families in which all members were treated (3%), than in those in which they were not (36%) (odds ratio 21.5; 95% confidence interval 3.0 to 103.4). CONCLUSIONS--The rate of throat colonisation with H influenzae type b was similar among siblings of children with all types of invasive H influenzae type b disease. Colonisation in contacts can be reduced by rifampicin prophylaxis, but some contacts remained colonised or were recolonised by the time of follow up. Medical staff complied poorly with current recommendations for rifampicin prophylaxis, which reduces its intrinsically limited value in preventing H influenzae type b disease.