Características epidemiológicas de las infecciones invasoras por Haemophilus influenzae tipo b, en el área norte de Santiago

In order to study factors associated with ihe occurrence of Haemophilus mlluenzae ripe b [Hib) invasive infections, and lo assess the risk of secondary cases in the northern metropolitan area of Santiago, Chile, a controlled study was conducted on 100 households of patients admited to the local children's hospital with Hib diseases and on 100 control households of the same community bearing a child that matched the corresponding case with respect to age, gender and geographic origin. The families were consecutively enrolled between april 1989 and december 1991; all 200 households were followed along a period of 1 2 month, and arrangements wore made to pfovide immediate medical care lo children wiih febrile episodes. Mean attack rale of Hib invasive disease was 1 9.9 x 1 O5 subjects under age 5 years, without differences among the populations sewed by the fourteen ambulatory care facilities of the involved area. No significant differences were delected among the study and control household groups regarding to age, gender, socioeconomical level and attendance to school or day care centers, but both groups differed from the population of the area regarding the proportion on adult members, and the mean number of household members was significantly higher in the study group than in controls [6.9vs 5.5). Both Hib colonization rate (7.4 vs 2.2%), and the proportion of households with at least one colonized member, (30 vs 9%), were higher among household of palienls than in controls (p < 0,0001, and < 0,028, respectively). None of the patients had a previous contact with a case of Hib disease, nor secondary cases were observed among tneir 1 1 7 potentially susceptible contacts. On the basis of a conservative risk estimate 500 times higher than the local attack rale, the risk of secondary Hib disease in that area of the city is significantly different from that reported in the literature (p < 0,0008). (Key wordci Hemophilvs influenzoe, household contacts, secondary cases, contact tracing, communicable disease, control, prevention.)