Table 2.

Summary of reported secondary cases from 1 January 2015 to 30 April 2020, in Zanzibar

	2015	2016	2017	2018	2019	2020*
No of household members tested during index case investigation	11 601†	8479	7638	10 782	14 963	8511
Median age (years) of investigated index cases	–	15 (IQR: 7–25)	16 (IQR: 8–26)	16 (IQR: 7–25)	18 (IQR: 8–28)	17 (IQR: 8–26)
Fraction of index cases who are male (%)	49.7	41.6	43.7	47.4	48.5	53.0
No of positive investigated people (secondary cases) (%)	591† (5.1%)	365 (4.3%)	319 (4.2%)	445 (4.1%)	544 (3.6%)	267 (3.1%)
No of positive investigated people (secondary cases) performed from January to April (%)	169 (6.7%)	167 (4.9%)	74 (4.7%)	164 (4.8%)	177 (5.1%)	267 (3.7%)
Probability to find a secondary case during investigation (95% CI)	0.048† (0.045 to 0.052)	0.041 (0.037 to 0.045)	0.040 (0.036 to 0.044)	0.040 (0.036 to 0.043)	0.035 (0.032 to 0.038)	0.030 (0.027 to 0.034)

*Time period 1 January to 30 April.

†Data available from 1 January to 16 September.