Table 2 Serum neutralizing antibody titers and isolation of infectious virus from the respiratory tract.

From: Duration and key determinants of infectious virus shedding in hospitalized patients with coronavirus disease-2019 (COVID-19)

Serum neutralizing antibody titer

Total number samples

Number culture positive samples (%)

Number culture negative samples (%)

<1:20

31

27 (87%)

4 (13%)

1:20

10

4 (40%)

6 (60%)

1:40

7

2 (29%)

5 (71%)

1:80

2

0 (0%)

2 (100%)

1:160

4

0 (0%)

4 (100%)

1:320

11

0 (0%)

11 (100%)

1:640

9

0 (0%)

9 (100%)

1:1280

14

0 (0%)

14 (100%)

1:2560

16

0 (0%)

16 (100%)

  1. Serum neutralizing antibody titers against SARS-CoV-2 were determined using a plaque-reduction neutralization assay17. Neutralizing antibodies (titers of 1:20 or higher) were detected in 72.3% (81/112) of the serum samples. For six patients, infectious SARS-CoV-2 was isolated from the respiratory tract despite the presence of neutralizing SARS-CoV-2 antibodies in the serum sample pairs. In four of these six patients, infectious virus was not isolated in the consecutive respiratory tract samples obtained after a virus culture positive sample (sampled from day +1, +1, +4, and +4 in respect to virus culture positive sample). For one patient, infectious virus was not isolated in the respiratory tract sample obtained one day after the virus culture positive respiratory tract sample, while the respiratory tract sample obtained 2 days after the virus culture positive respiratory tract sample was positive for infectious SARS-CoV-2. All respiratory tract samples obtained thereafter tested negative for infectious virus. For one patient, no follow-up respiratory tract samples were available.
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