Table 1

Distribution of disease-causing and nasal carriage isolates within clonal complexes (see Fig. 1). A 4 by 2 Fisher's exact test comparing the distribution within the ancestral clones, single-locus variants, double-locus variants, and satellite strains of community-acquired disease with the distribution in nasal carriage isolates is highly significant (P < 0.0001). However, there is no statistical difference between isolates recovered from community- and hospital-acquired disease (P = 0.86).

Position within clonal complexDisease isolatesOdds ratio (95% CI) for disease, relative to ancestral clones*
Nasal carriage isolates [n(%)]Communityacquired [n(%)]Hospitalacquired [n (%)]
Ancestral clone39 (22)45 (74)69 (73)1.00
Single-locus variant68 (38)9 (15)18 (19)0.11 (0.05 to 0.29)
Double-locus variant31 (17)4 (6)3 (3)0.11 (0.03 to 0.38)
Satellite 16 (9)0 (0)1  (1)0.00
Singleton (not within a clonal complex)25 (14)3 (5)3 (3)0.10 (0.03 to 0.41)
  • * This analysis includes only community-acquired disease and nasal carriage isolates, as these are epidemiologically directly comparable; hospital-acquired disease isolates are excluded.

  • A satellite is any isolate that is a member of a clonal complex, but is not a member of an ancestral clone or a single or double-locus variant (these exclude the strains within the three minor clonal complexes shown in Fig. 1 in which it is not possible to assign an ancestral clone; these are included in “singletons”).