Table 1.

Average prevalence of NAb (titer of ≥1:20) by age in anonymous serum samples from Children's National Medical Center

Group	Age (yr)	No. of samples:		% prevalence	Relative prevalence	95% confidence interval	P value
		Tested	Positive
Infantsa	<1	175	31	15
Toddlers	1–<3	83	13	13.5	0.9	0.49, 1.64	0.72
Children Adolescents	3–18	350	96	21.5	1.43	0.99, 2.07	0.052

^aReference group for comparisons of relative prevalence.