Table 3.
Conditional probability of diagnosis of SARS-CoV-2 infection with assays targeting IgG depending on seroprevalence (sensitivity of 90% and a specificity of 99%, LR +/- 90/0.1) [13] or pre-test probability of total antibodies (IgG and IgM) among patients with varying degrees of clinical suspicion for COVID-19 and either negative RT-PCR throughout the course of their illness, presuming a sensitivity of 91% and a specificity of 99.8%, LR +/- 455/0.09 at week 3 after onset and a sensitivity of 94.3% and a specificity of 99.8%, LR +/- 471/0.06 at week 5 after onset [13].
| Seroprevalence [19] | Pre-test probability [22] | |||
|---|---|---|---|---|
| 5% | 10% | 40% | 10% | |
| Seroprevalence study ENE-COVID, 27 April - 11 May 2020 |
Unvaccinated old patient with diabetes presents with low-grade fever and mild cough 15 days prior, beginning 5 days after attending a family reunion | Young patient previously healthy and vaccinated presents with 5 weeks of debilitating fatigue and difficulty concentrating. The patient informs 2 days of a mild sore throat shortly before the onset of current symptoms. | ||
| If positive (+) result | Assays targeting IgG alone sensitivity 90%, specificity 99% |
Total antibodies, sensitivity 91%, specificity 99.8% (week 3 after onset) |
Total antibodies, sensitivity 94.3%, specificity 99.8% (week 5 after onset) |
|
| Infection P (PPV) No infection P (1-PPV) |
83 (41-97) 17 (3-59) |
91 (60-98.5) 9 (1.5-39) |
99.7 (90-100) 0.3 (0-10) |
98.1 (69-100) 1.9 (0.1-31) |
| If negative (-) result | ||||
| Infection P (1- NPV) No infection P (NPV) |
0.5 (0.1-5) 99.5 (95-100) |
1 (0.2-6) 99 (94-100) |
6 (2-14) 94 (86-98) |
0.6 (0.1-5) 99.4 (95-100) |
P: probability; PPV: positive predictive value; NPV: negative predictive value. LR +/-: Positive/negative likelihood ratio. The probability of having the infection whether the result is positive, or negative is expressed in % (95% CI).