More recent studies have found considerable genotypic and phenotypic heterogeneity among resistant isolates, suggesting resistant strains have now evolved from several phylogenetic lineages. Spread of resistance among pneumococcal strains is facilitated by horizontal transfer via transformation of genes coding for altered PBPs from resistant S. pneumoniae and oral a-hemolytic streptococci to susceptible pneumococcal strains. These newly resistant strains, in turn, become increasingly prevalent because of selective antibiotic pressure. The proportion of pneumococcal isolates resistant to commonly used antibiotics is generally highest among preschool-age children. Because young children are more often colonized with pneumococci and are more frequently given antibiotics that provide selective pressure for drug-resistant strains, it is not surprising to find resistant pneumococcal infections are more common in this age group.
Children attending day care are at particularly high risk of drug-resistant pneumococcal infection.
Data from active surveillance in metropolitan Atlanta during 1994 showed that, although the incidence of invasive pneumococcal infection was 3-fold higher among African Americans than whites, the proportion of isolates with decreased susceptibility to penicillin was greater among whites. Among African Americans, the rate of disease due to penicillin-nonsusceptible strains was more than doubled among suburban as opposed to urban residents. White race and suburban residence may be surrogates for higher socioeconomic status, easier access to medical care, and more frequent use of antibiotics among more affluent persons. Additional studies are needed to comprehensively assess the clinical impact and economic costs of drug-resistant pneumococcal infections. The American Academy of Pediatrics has issued guidelines for treating pneumococcal meningitis and other invasive pneumococcal infections.