Table 2. Incidence of CHIKV infections and seroprevalence of CHIKV PRNT in different age groups. ^a .

Age	Subjects, n	CHIKV PRNT ≥10, n (% of age group) b	Symptomatic CHIKV infection, n [n/100 person-yrs (95% CI)]	Subclinical CHIKV infection, n [n/100 person-yrs (95% CI)]	Total CHIKV infection, n [n/100 person-yrs (95% CI)]	Ratio of subclinical to symptomatic CHIKV infection
6 mos—5 yrs	148	1 (0.7)	5 [3.23 (1.23, 7.08)]	10 [6.46 (3.32, 11.47)]	15 [9.69 (5.66, 15.59)]	2:1
6–15 yrs	184	2 (1.1)	8 [4.23 (1.99, 7.98)]	24 [12.68 (8.33, 18.55)]	32 [16.91 (11.78, 23.56)]	3:1
16–30 yrs	168	34 (20.2)	2 [1.13 (0.23, 3.63)]	20 [11.32 (7.13, 17.14)]	22 [12.45 (8.02, 18.51)]	10:1
31–50 yrs	170	90 (52.9)	3 [1.8 (0.50, 4.81)]	21 [12.63 (8.05, 18.94)]	24 [14.43 (9.49, 21.12)]	7:1
>50 yrs	183	112 (61.2)	1 [0.55 (0.05, 2.59)]	12 [6.66 (3.64, 11.28)]	13 [7.21 (4.04, 11.98)]	12:1
All ages	853	239 (28.0)	19 [2.19 (1.36, 3.35)]	87 [10.03 (8.09, 12.31)]	106 [12.22 (10.06, 14.72)]	4.6:1

^aBased on 853 subjects with both enrollment and 12-month blood collections.

^bCHIKV PRNT titer at enrollment using 80% plaque reduction.

CHIKV = chikungunya virus; n = number; CI = confidence interval; PRNT = plaque reduction neutralization test.