TABLE. Cumulative frequency and conditional probability of SARS-CoV-2 detection or symptoms over time among household contacts who received positive SARS-CoV-2 test results or developed symptoms — Tennessee and Wisconsin, April–September 2020.
| Main analysis | No. of days from index patient's illness onset | No. of household contacts (% of total) |
Conditional probability of remaining asymptomatic with negative test results until day 14 % (95% CI)* | ||
|---|---|---|---|---|---|
| SARS-CoV-2 detected |
Symptomatic |
Symptomatic or SARS-CoV-2 detected |
|||
| n = 109 | n = 122 | n = 145 | |||
| All households and all household contacts included† |
5 |
68 (62) |
101 (83) |
119 (82) |
71 (57–81) |
| 7 |
83 (76) |
110 (90) |
130 (90) |
81 (67–90) |
|
| 10 |
94 (86) |
116 (95) |
138 (95) |
93 (78–98) |
|
| 14 |
104 (95) |
121 (99) |
141 (97) |
— |
|
|
Sensitivity analyses
| |||||
| Excluding households with possible co-primary patients§ |
—
|
n = 75
|
n = 84
|
n = 103
|
—
|
| 5 |
41 (55) |
68 (81) |
80 (78) |
74 (59–84) |
|
| 7 |
52 (69) |
74 (88) |
88 (85) |
80 (66–89) |
|
| 10 |
62 (83) |
79 (94) |
96 (93) |
93 (77–98) |
|
| 14 |
70 (93) |
83 (99) |
99 (96) |
— |
|
| Excluding household contacts that are possibly tertiary transmissions¶ |
—
|
n = 99
|
n = 118
|
n = 135
|
—
|
| 5 |
68 (69) |
99 (84) |
117 (87) |
76 (61–86) |
|
| 7 |
80 (81) |
108 (92) |
127 (94) |
87 (72–94) |
|
| 10 |
88 (89) |
113 (96) |
127 (94) |
95 (82–99) |
|
| 14 |
97 (98) |
118 (100) |
134 (99) |
— |
|
| Excluding households with possible co-primary patients and household contacts that are possibly tertiary transmissions** |
—
|
n = 66
|
n = 81
|
n = 94
|
—
|
| 5 |
41 (62) |
67 (83) |
79 (84) |
80 (64–89) |
|
| 7 |
50 (76) |
73 (90) |
86 (91) |
86 (71–94) |
|
| 10 |
57 (86) |
77 (95) |
86 (91) |
95 (81–99) |
|
| 14 | 64 (97) | 81 (100) | 93 (99) | — | |
* The conditional probability is the probability of remaining negative by reverse transcription–polymerase chain reaction and asymptomatic to day 14 after the index patient’s illness onset, given that the household contact has been negative and asymptomatic through day 5, 7, or 10. 95% CIs were estimated using Greenwood’s exponential CIs (Major Greenwood, Jr. [1926]. The Natural Duration of Cancer. Reports of Public Health and Related Subjects, Vol. 33, HMSO, London).
† Analysis included 104 households and 185 household contacts.
§ Analysis included 82 households and 141 household contacts. Households were excluded if any household contact had illness onset or positive test <2 days after the index patient’s illness onset.
¶ Analysis included 104 households and 175 household contacts. Household contacts were excluded if they had a positive test >2 days after another nonindex household contact became positive.
** Analysis included 82 households and 132 household contacts.