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Table 1 Dengue antibody detection by ELISA in serum and reconstituted filter paper blood of Vietnamese febrile patients, repeated tests and storage time of specimens.

From: Enzyme-linked immunoassay for dengue virus IgM and IgG antibodies in serum and filter paper blood

  Dengue tests in febrile patients
  Upon presentation (t0) After convalescence (t3)
  IgM IgG IgM IgG
Total cases tested 781
Storage time (days, median, range) 252 (57 – 751) days 228 (36 – 730)
No. positive sera (index value ≥1) 222 (28%) 673 (86%) 261 (33%) 679 (87%)
No. cases tested twice 73 74 73 73
Median storage time first test (days, range) 114 (57 – 283) 92.5 (36 – 253)
Median storage time second test (days, range) 280 (225 – 798) 259 (204 – 777)
No. positive first test 9 (12%) 59 (80%) 17 (23%) 56 (77%)
No. positive second tests 23 (32%) 63 (85%) 23 (32%) 61 (84%)
P value (Chi Square test) <0.001 <0.001 <0.001 <0.001
No. of combined sera and blood spots on filter paper tested 161
Median storage time (days, range) 283 (139 – 795) 262 (118 – 774)
No. positive sera 46 (29%) 121 (75%) 89 (55%) 128 (80%)
No. positive filter papers 8 (5%) 97 (60%) 55 (34%) 123 (76%)
P value (Chi Square test) <0.0001 < 0.0001 <0.0001 <0.0001
Kappa value 0.191 0.391 0.567 0.549
  1. t3: three weeks after t0.