Streptococcus pneumoniae in community-acquired respiratory tract infections in Spain: the impact of serotype and geographical, seasonal and clinical factors on its susceptibility to the most commonly prescribed antibiotics

Resistance of Streptococcus pneumoniae to antimicrobial agents shows geogra phical variation and also depends on serotype, patient age and sample origi n. Factors affecting antibiotic resistance in S. pneumoniae were studied fr om results of a multicentre susceptibility study of 12 antimicrobial agents , carried out in 14 Spanish hospitals between May 1996 and April 1997. The most frequent serotypes were serotypes 6 (14.8%), 19 (11.8%), 23 (10.5%), 3 (9.9%), 9 (8.0%), 14 (8.0%), 15 (3.9%) and 11 (3.2%); 9.6% of isolates wer e not typeable. The remaining 25 serotypes constituted 20.2% of strains. Pe nicillin resistance was more prevalent in serotypes 14 (88%), 23 (66%), 9 ( 62%) and 6 (57%), whereas erythromycin resistance was snore prevalent in se rotypes 6 (68.5%), 15 (61.4%), 14 (49.5%), 19 (42.7%) and 23 (39.3%). Serot ypes 6 and 19 were the serotypes most commonly isolated from both children and adults, although with different proportions (24.0% and 19.2% of isolate s from children were serotype 6 and 19, respectively, with the correspondin g figures for isolates from adults being 13.6% and 11.5%, respectively). Th e rates of resistance of pneumococcal strains to penicillin and cefuroxime were significantly higher in strains from children than in those from adult s (resistance to penicillin, 50.4% in children and 37.0% in adults; resista nce to cefuroxime, 62.4% in children and 45.6% in adults). There was signif icantly more resistance to erythromycin ire middle ear isolates (48.9%) tha n in blood isolates (27%). The prevalence of resistance to beta -lactams sh owed a seasonal pattern, with higher rates in summer and winter, proportion al to the magnitude of resistance. Susceptibility to macrolides did not var y seasonally. Our results stress the relative importance that geographical, temporal (seasonality), patient (sample type, origin, age group) and bacte rium-related (serotype) factors have on the variations in susceptibility ob served among different pneumococcal clinical isolates.