Table 1.

Serogroup distribution of U.S. ABCs isolates characterized in this study.

Serogroup	2000–2005 No. of isolates (%)	2006–2010 No. of isolates (%)	2011–2015 No. of isolates (%)	P value 2006–10 vs. 2011–15
A	1 (0.10)	0 (0)	0 (0)	N/A
C	277 (29.03)	173 (31.11)	88 (28.54)	0.43
Y	319 (33.43)	207 (37.22)	84 (27.25)	<0.0001
W	27 (2.83)	22 (3.96)	40 (12.97)	0.0029
B*	298 (31.26)	129 (23.22)	79 (25.72)	0.41
NG	29 (3.04)	19 (3.42)	17 (5.51)	0.14
Other	3 (0.31)	6 (1.08)	0 (0)	N/A
Total Isolates	954	556	308

Results for 2000–05 [17] and 2006–10 [18] were reported previously. Nongroupable isolates are abbreviated NG.

^*Serogroup B isolates are represented as weighted values. Serogroup B isolates from Oregon are assigned a value of 0.10, while isolates from all other states are assigned 0.90. The uncorrected total number of isolates collected in each time period are 1175 in 2000–05, 638 in 2006–10, and 349 in 2011–15.