Table 1.
Conditional probability for the diagnosis of SARS-CoV-2 infection depending on the prevalence in different settings presuming a sensitivity of 89% and a specificity of 99%, LR +/- 89/0.11 (RT-PCR)[5] and sensitivity of 56% and a specificity of 99%, LR +/- 56/0.44 (Ag-RDT) [10].
| Prevalence in 2020 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 1% | 2% | 5% | 10% | 15% | 25% | 35% | 50% | ||
| Population screenings in the Basque Country [15] | Primary Care Centres in Valencia [16] |
Staff members | Residents | Hospital Emergency Service | |||||
| Nursing Homes in Barcelona [17] | HUA Vitoria-Gasteiz [18] | ||||||||
| Sensitivity/ Specificity (%) |
If positive (+) result | Post-test probability (%) | |||||||
| 89/99 (RT-PCR) | Infection P (PPV) No infection P (1-PPV) |
47 (8-90) 53 (10-92) |
64 (19-93) 35 (6-81) |
82 (41-97) 17 (3-59) |
91 (60-98) 9 (1.5-40) |
94 (70-99) 6 (1-30) |
97 (81-99.5) 3 (0.5-19) |
98 (86-100) 2 (0.3-14) |
99 (90-99.9) 1 (0.1-10) |
| 56/99 (Ag-RDT) | Infection P (PPV) No infection P (1-PPV) |
36 (4-88) 64 (12-96) |
53 (11-91) 47 (9-89) |
75 (29-95) 25 (4-71) |
86 (48-98) 14 (2-52) |
91 (59-98) 9 (1.5-41) |
95 (72-99) 5 (0.7-28) |
97 (79-100) 2 (0.3-14) |
98 (85-100) 1.8 (0.2-15) |
| If negative (-) result | Post-test probability (%) | ||||||||
| 89/99 (RT-PCR) | Infection P (1- NPV) No infection P (NPV) |
0.1 (0-4) 99.9 (96-100) |
0.2 (0-4) 99.8 (96-100) |
0.6 (0.1-5) 99.4 (95-100) |
1.2 (0.2-6) 98.8 (94-99.8) |
1.9 (0.5-7) 98.1 (92-99.5) |
3.6 (1-10) 96.4 (90-99) |
6 (2-14) 94 (86-98) |
10 (4-21) 90 (79-95) |
| 56/99 (Ag-RDT) | Infection P (1- NPV) No infection P (NPV) |
0.4 (0-5) 99.6 (95-100) |
0.9 (0.1-5) 99.1 (95-100) |
2.3 (0.7-8) 97.7 (92-99) |
5 (2-11) 95 (89-98) |
7 (3-14) 93 (85-96) |
13 (7-22) 87 (78-93) |
19 (12-29) 81 (71-88) |
31 (21-42) 69 (58-79) |
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). In bold, 1-NPV < 5% (threshold for ruling out infection). HUA: Araba University Hospital, Vitoria-Gasteiz.