In the period of 1999-2002 there has been investigated the sensitivity to 10 antibiotics in 286 strains of Haemophilus influenzae (Hi) isolated from the blood or cerebrospinal fluid of patients within the program of surveillance of invasive infections. The series overwhelmingly comprised Hib isolates - H. influenzae b (83.6 %) of which the majority (94.1 %) were isolated in children up to 6 years of age, suffering epiglottitis or meningitis; untypable isolates comprised 14.7 % and represented 2/3 of strains isolated in subjects of over 15 years of age; the remaining 1.7 % of strains belonged to serotypes e (1 strain) and f (4 strains). All Hib isolates and untypable Hi were sensitive to cefuroxim, cefotaxim, rifampicine, ofloxacin, and levofloxacin; and flve isolates of other serotypes (e and f) were sensitive to all 10 antibiotics under investigation. Resistance to ampicillin in invasive strains in our series regardless of serotype was caused exclusively by the production of p-lactamase. ©erall in our series of 286 strains collected in the course of four years there has been found an almost threefold higher resistance to ampicillin in Hib isolates (12.1 %) than in untypable Hi isolates (4.8 %); resistance to tetracycline and to chloramphenicol occurs sporadically and independently of the origin of the sample and serotype of the isolate. Strains resistant to ampicillin are more frequently resistant to tetracycline, chloramphenicol and co-trimoxazol than strains sensitive to ampicillin. Resistance to co-trimo-xazol that has been found in 14.3 % of invasive untypable strains is tenfold higher than the resistance of Hib isolates (1.3 %) and is almost identical with resistance to that antibiotic found previously in Hi isolates coming from samples from the lower respiratory tract. In the course of our follow-up there has been observed a decline in the occurrence of Hib strains resistant to ampicillin from 15.5 % in the year 2000 down to 7.3 % in 2002. This favorable trend can be attributed to the broad, independent campaign which began in 1999 with the aim of reducing the appearance of resistance by appropriate antibiotics application. The reduction of the number of invasive infections caused by Hib and of the occurrence of antibiotics resistant strains may also be a manifestation of the vaccination against Hib that has begun mid-2001. These favorable qualitative changes require further follow-up and a detailed analysis.

        Key words: Haemophilus influenzae - invasive infection - antibiotics resistance.