Table 2. COVID-19 cases associated with households or clusters during the third and fourth disease waves, Kyoto, Japan*.

Variables	Third wave	Fourth wave
Date	2020 Dec–2021 Feb	2021 Apr–May
Total no. cases (mean no./d)	4,592 (51.0)	4,181 (68.5)
Total no. (%) secondary cases among households	1,228 (26.7)	1,208 (28.9)
Total no. (%) cases associated with clusters	849 (18.5)	449 (10.7)
Median no. cases associated with each cluster (IQR)	11 (9–20.5)	7 (6–9)
Total no. clusters (mean no./day)	50 (0.56)	43 (0.70)
Median test positivity of each cluster, % (IQR)†	18 (9.7–37)	34 (15.6–66.3)

*IQR, interquartile range. †Calculated by using epidemiologic data available for 48 clusters in the third wave and 35 clusters in the fourth wave.