[Incidence and distribution of Streptococcus pyogenes type M in patients treated at the Dr. Fran Mihaljević Infectious Disease Clinic in Zagreb from 1990 to 1996].

Aim: The aim of this study was to estimate the changes in the appearance and distribution of M types of Streptococcus pyogenes in different cultures from 78 patients treated during the 1990-1996 period at the Dr. Fran Mihaljević University Hospital for Infectious Diseases in Zagreb.

Materials And Methods: Isolates were characterized by the T-agglutination pattern and M type and/or opacity factor type using the standards recommended by two World Health Organization Collaborating Centers for Reference and Research on streptococci from Minneapolis and Prague.

Results: In this study, 19% (15/79) of isolates were recovered from normally sterile sites, 26.6% (21/79) came from skin and 54.4% (43/79) from throat swabs. In one patient isolates from the skin and blood culture were analyzed. Of all, 92.4% (73/79) of the isolates were typed by T-agglutination pattern and 73.5% (58/79) by M protein and/or OF typing. The results of M typing showed 14 M types: M1, M3, M4, M5, M6, M11, M12, M28, M57, M58, M60, M75, M76 and M78. The most commonly isolated types were M1 and M3 (13.8%, 8/58 each), followed by M28 found in 12.1% (7/58), and M6 and M12 in 10.3% (6/58) each. These five M types accounted for 60.3% (35/58) of all isolates. Analysis to changes in the distribution of M1 and M3 types during the 1990-1991 and 1992-1993 periods revealed a significantly greater proportion of M1 and M3 isolates in the former (Fisher's two-tailed exact test, p = 0.018). A significantly greater proportion of M1 and M3 isolates was also recorded in the 1990-1991, than in 1994-1996 period. (Fisher's two-tailed exact test, P = 0.021). It was investigated whether Streptococcus pyogenes M1 and M3 types were associated with toxic and invasive infection. There were 28.2% (22/78) of patients with toxic and invasive infection: 31.9% (7/22) of them with the diagnosis of scarlet fever, whereas 68.1% (15/22) of the strains were obtained from normally sterile sites. There were 45.5% (10/22) of M1 and M3 types from patients with toxic and invasive infections. Types M6, M28 and M76 were found in an equal proportion of 9.1% (2/22), and M4, M12 and M 60 of 4.5% (1/22) each. In three strains, M type could not be identified (T8/25 SOR+, T25 SOR+ and T11 SOR+). M1 and M3 types were isolated from 10.3% (6/56) of patients with other streptococcal infections. A significantly greater proportion of M1 and M3 types was recorded in patients with toxic and invasive infections than in those with other streptococcal infections (Fisher's two-tailed exact test, p = 0.004). A multivariate logistic regression model was used to assess whether the increased proportion of streptococcal M types 1 and 3 was associated with the 1990-1991 period, or with the infection characteristics.

Conclusions: The changes in the distribution of M types 1 and 3 were found to be significantly associated only with toxic and invasive infections (odds ratio 4.35, p = 0.025). Odds ratio suggests that patients with toxic and invasive infections had a 4.35--fold increased risk of infections caused by types M1 and M3 found in patients with other streptococcal infections. The increased proportion of M types 1 and 3 during the 1990-1991 period was more significantly associated with the characteristics of infection than with the study period.