Occurrence of mucoid M-18 Streptococcus pyogenes in a central Ohio pediatric population.

During a 1-year period from October 1986 through September 1987, we recovered 116 mucoid, hemolytic Streptococcus pyogenes isolates from clinical specimens collected from patients seen at our pediatric institution. A total of 102 isolates were from throat cultures (101 for pharyngitis, 1 for acute rheumatic fever), 13 were from other superficial body sites, and 1 was from pleural fluid. All of 40 mucoid isolates tested to date were determined to be M-type 18 strains. A direct latex agglutination test for group A carbohydrate antigen in throat swab specimens was equally sensitive in detecting M-18 mucoid and nonmucoid strains (45 of 77 [58%] and 795 of 1,186 [67%], respectively; not significant, P greater than 0.05). Antimicrobial susceptibility tests performed with 40 mucoid and 40 nonmucoid isolates against penicillin and nine other antimicrobial agents showed all strains to be susceptible, with no difference in MICs. All isolates tested were also considered fully susceptible to the bactericidal activity of penicillin. Further studies are needed to establish the relative virulence of M-18 strains and their possible association with the resurgence of acute rheumatic fever in central Ohio and other areas of the United States.