All clinical S. pneumoniae specimens isolated from patients with invasive or sterile-site infections admitted to one regional general hospital in southern Chile were collected during a 5-year period (February 1994 to September 1999). A total of 247 strains belonging to 50 serotypes were isolated in this survey: 69 in patients under 5 years of age, 129 in patients 5 to 64 years old, and 49 from patients 65 years and older. Eight serotypes were identified in all age groups, while all other serotypes were found exclusively in one age group or in patients over 4 years of age. Serotype 3 was never found in patients under 5 years old, and serotype 14 was not found in patients >64 years of age. There was no difference in the serotypes causing infection in each one of the 5 years of the survey. Our results suggest that both bacterial virulence factors and host factors play an important role in the selection of S. pneumoniae serotypes causing invasive infection. Possible host factors include age-related differences in the immune response. Comparative studies with other areas of the world may help to further understanding of our observations in southern Chile.

We compared the incidence of nasopharyngeal colonization byStreptococcus pneumoniae, the serotypes causing mucosal and invasive diseases, and the antibiotic resistance of these strains in patients admitted to three large hospitals and children attending day care centers in two Chilean cities (Santiago and Temuco). The populations in both cities were similar in ethnic background, socioeconomic status, family size, and access to medical care. Significant differences in nasopharyngeal colonization rates, in serotypes causing infections, and in antibiotic resistance were found between the two cities. In children 0 to 2 years of age, 42% were colonized with S. pneumoniae in Santiago compared to 14% in Temuco. A total of 41 serotypes were identified in both Chilean cities studied. Six serotypes were found only in Santiago; 14 serotypes were found only in Temuco. Antibiotic-resistant serotypes 6A, 6B, 14, 19F, and 23F were detected only in Santiago. We show that important differences in the incidence of nasopharyngeal carriage, infection, andS. pneumoniae serotypes can exist in similar populations in different areas of the same country. Our findings are relevant for prevention strategies, antibiotic usage, and vaccine design.