TABLE 1.

Classification of 37 confirmed flavivirus infections^a

Infection type	No. of patients	S1-S2 interval (days)	IgM/IgG OD ratio range (S1 sample)	S2 sample
				IgM/IgG OD ratio range	IgG titer (log10t50) range
Classical
Acute primary infection	2	8	3.17-3.67	2.21-2.30	<2.00
Acute secondary infection	16	6-14	0.31-1.00	0.27-1.03	5.18-6.85
Low S2 IgG acute secondary infection	3	9-10	0.40-0.80	0.59-0.69	3.73-4.21
Probable acute secondary infection	6	18-52	0.63-1.15	0.24-0.88	5.44-6.65
Nonclassical
High S1 IgG acute primary infection	1	7	1.20	1.88	<2.00
High S1 IgM acute secondary infection	5	7-13	1.39-1.75	0.80-0.99	5.13-6.27
High S1 IgM and low S2 IgG acute secondary infection	2	9-13	2.04-2.55	0.77-1.41	4.18-4.38
High S1 IgM probable acute secondary infection	2	27-28	2.33-2.52	0.98-1.15	4.93-5.70

^aTwenty-seven serologically classical and 10 serologically nonclassical infections.