Table 1.

Characteristics of participants in community-based serologic study

Characteristic	Round 1	Round 2	Round 3	Round 4
Date range of sera collection	April 2 to April 29, 2009	August 29, 2009 to February 20, 2010	April 16 to May 15, 2010	August 19 to December 11, 2010
Median sample collection date	April 15, 2009	November 17, 2009	April 30, 2010	November 12, 2010
No. of participants	259	2057	703	1824
Age
≤18 years	77 (29.7%)	660 (32.1%)	214 (30.4%)	596 (32.7%)
19–50 years	159 (61.4%)	1217 (59.2%)	438 (62.3%)	1076 (59%)
>50 years	23 (8.9%)	180 (8.8%)	51 (7.3%)	152 (8.3%)
Sex
Male	117 (45.2%)	933 (45.4%)	315 (44.8%)	819 (44.9%)
Serum available in other rounds
Round 1		246 (12%)	172 (24.5%)	173 (9.5%)
Round 2	246 (95%)		698 (99.3%)	1798 (98.6%)
Round 3	172 (66.4%)	698 (33.9%)		676 (37.1%)
Round 4	173 (66.8%)	1798 (87.4%)	676 (96.2%)