FIG 3.

Morning saliva or nasal swab specimen collection yields improved detection across infection stages and assay analytical sensitivities. For each 4-day time bin relative to symptom onset, pairs of sequentially collected morning-to-evening specimens were assessed. In each pair, the viral load in each specimen was used to predict a positive or negative result if tested by an assay with a given limit of detection (LOD) below or above the viral load, respectively. Bar plots show the fraction of pairs with a positive result in either the morning or evening specimen that would be detectable if the morning specimen (orange) or evening specimen (purple) were tested at a given LOD. Error bars indicate the 95% confidence interval. Bars are not shown (X) when fewer than 10 pairs had positive results at the given LOD during the infection time bin. Among LODs and infection time bins with more than 10 positive pairs, the percents detectable for morning versus evening specimens were compared by an upper-tailed McNemar exact test, applied to the 2 × 2 table shown below each comparison. Resulting P values are shown above each comparison. Boldfaced values indicate significantly higher detection with morning sampling than with evening sampling. Analysis was performed on saliva specimens (A) and nasal swab specimens (B). Equivalent analysis for evening-to-morning pairs is shown in Fig. S5 in the supplemental material. Pos, positive; Neg, negative.