Volume 27, Number 3—March 2021
Dispatch
Familial Clusters of Coronavirus Disease in 10 Prefectures, Japan, February−May 2020
Reiko Miyahara
, Naho Tsuchiya, Ikkoh Yasuda, Yura K. Ko, Yuki Furuse, Eiichiro Sando, Shohei Nagata, Tadatsugu Imamura, Mayuko Saito, Konosuke Morimoto, Takeaki Imamura, Yugo Shobugawa, Hiroshi Nishiura, Motoi Suzuki, and Hitoshi Oshitani
, Naho Tsuchiya, Ikkoh Yasuda, Yura K. Ko, Yuki Furuse, Eiichiro Sando, Shohei Nagata, Tadatsugu Imamura, Mayuko Saito, Konosuke Morimoto, Takeaki Imamura, Yugo Shobugawa, Hiroshi Nishiura, Motoi Suzuki, and Hitoshi Oshitani
Table 2
Characteristics of primary cases in households and SAR categorized for households of familial clusters of coronavirus disease in 10 prefectures, Japan, February−May, 2020*
| Variable | No. (%) primary cases | No. family contacts | No. secondary infected cases | No. symptomatic secondary infected cases | No. asymptomatic secondary infected cases | SAR, % (95% CI) | Risk ratio (95% CI) |
|---|---|---|---|---|---|---|---|
| Overall |
306 (100) |
775 |
147 |
103 |
39 |
19.0 (16.3–21.9) |
|
| Sex | |||||||
| F | 152 (49.7) | 408 | 68 | 50 | 14 | 16.7 (13.2–20.6) | Referent |
| M | 153 (50.0) | 366 | 79 | 53 | 25 | 21.6 (17.5–26.2) | 1.29 (0.97–1.73) |
| Unknown |
1 (0.3) |
1 |
1 |
0 |
1 |
NA |
NA |
| Age, y | |||||||
| <1–19 | 10 (3.6) | 42 | 10 | 7 | 3 | 23.8 (12.1–39.5) | Referent |
| 20–29 | 48 (15.7) | 135 | 18 | 15 | 2 | 13.3 (8.1–20.3) | 0.56 (0.28–1.12) |
| 30–39 | 36 (11.8) | 103 | 21 | 15 | 6 | 20.4 (13.1–29.5) | 0.85 (0.44–1.66) |
| 40–49 | 58 (19.0) | 139 | 14 | 9 | 5 | 10.1 (5.6–16.3) | 0.42 (0.20–0.88) |
| 50–59 | 57 (18.6) | 155 | 25 | 13 | 9 | 16.1 (10.7–22.9) | 0.68 (0.35–1.30) |
| 60–69 | 43 (14.1) | 85 | 31 | 20 | 10 | 36.5 (26.3–47.6) | 1.53 (0.83–2.81) |
| 70–79 | 31 (10.1) | 53 | 11 | 10 | 1 | 20.8 (10.8–34.1) | 0.87 (0.41–1.85) |
| >80 |
22 (7.2) |
63 |
17 |
14 |
3 |
29.4 (23.2–36.2) |
1.13 (0.58–2.23) |
| Contact history with nonfamilial COVID-19 cases | |||||||
| No | 146 (47.7) | 357 | 91 | 64 | 24 | 25.4 (21.0–30.3) | 1.90 (1.4–2.57) |
| Yes | 159 (52.0) | 417 | 56 | 39 | 15 | 13.4 (10.3–17.1) | Referent |
| Unknown |
1 (0.3) |
1 |
0 |
0 |
0 |
NA |
NA |
| No. household contacts per primary case | |||||||
| 1 | 88 (28.8) | 88 | 17 | 15 | 2 | 19.3 (11.7–29.1) | Referent |
| 2 | 75 (24.5) | 150 | 26 | 16 | 8 | 17.3 (11.6–24.4) | 0.90 (0.52–1.56) |
| 3 | 82 (26.8) | 246 | 47 | 32 | 13 | 19.1 (14.4–24.6) | 0.90 (0.60–1.63) |
| 4 | 35 (11.4) | 140 | 36 | 27 | 8 | 25.7 (18.7–33.8) | 1.33 (0.80–2.22) |
| >5 |
26 (8.5) |
151 |
21 |
13 |
8 |
13.9 (8.8–20.5) |
0.72 (0.40–1.29) |
| Symptoms | |||||||
| Symptomatic | 271 (88.6) | 661 | 136 | 98 | 33 | 20.6 (17.6–23.9) | Referent |
| Asymptomatic | 28 (9.2) | 93 | 11 | 5 | 6 | 11.8 (6.1–20.2) | 0.57 (0.32–1.02) |
| Unknown |
7 (3.6) |
21 |
0 |
0 |
0 |
NA |
NA |
| Time from symptom onset to diagnosis, d, n = 271 | |||||||
| 0–2 | 30 (11.1) | 65 | 4 | 3 | 1 | 11.6 (5.1–21.6) | Referent |
| 3–7 | 130 (48.0) | 319 | 63 | 42 | 21 | 19.8 (15.5–24.5) | 3.21 (1.21–8.51) |
| 8–14 | 94 (34.7) | 230 | 51 | 40 | 8 | 22.2 (17.0–28.1) | 3.60 (1.35–9.6) |
| >14 |
17 (6.3) |
45 |
18 |
9 |
9 |
40.0 (25.7–55.7) |
6.50 (2.36–17.93) |
| Confirmed date of primary case | |||||||
| Feb 22–Apr 16 | 179 (58.5) | 448 | 78 | 57 | 16 | 17.4 (14.0–21.3) | Referent |
| Apr 17–May 31 |
127 (41.5) |
328 |
69 |
46 |
23 |
21.0 (16.8–25.9) |
1.21 (0.90–1.61) |
| Policy of testing for asymptomatic contacts | |||||||
| No testing, 2 prefectures | 54 (17.6) | 138 | 16 | 12 | 1 | 11.6 (6.8–18.1) | Referent |
| Testing for asymptomatic contacts, 8 prefectures | 252 (82.4) | 637 | 131 | 91 | 38 | 20.6 (17.5–23.9) | 1.77 (1.09–2.88) |
*COVID-19, coronavirus disease; NA, not applicable; SAR, secondary attack rate.
Page created: December 29, 2020
Page updated: February 21, 2021
Page reviewed: February 21, 2021
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.