GeneXpert or chest-X-ray or tuberculin skin testing for household contact assessment (GXT): protocol for a cluster-randomized trial

Table 1 Sample size required to detect superior initiation of tuberculosis preventive treatment (TPT) with either one of the experimental arms compared to standard arm

TPT initiation proportion among all HHC identified		Number required per group to detect significant difference^a, accounting for clustering by household
Standard	Experimental (GX or no TST)^b	N per arm—80% power	N per arm—60% power	Total N^c (3 arms)
40%	45%	3046	1901	9138
40%	50%	766	478	2298
35%	40%	2921	1823	8763
	42.5%	1311	818	3933
	45%	742	464	2226
	47.5%	477	298	1431
30%	35%	2734	1706	8202
	40%	703	439	2109
	42.5%	455	284	1365
	45%	318	199	954
25%	30%	2484	1551	7452
	35%	649	405	1947
	40%	297	186	891

^aAlpha = 0.05. The intra-class correlation coefficient (ICC) or clustering effect of HHC on TPT initiation was estimated from the ICC for completion in the adult trial comparing 4R with 9H [1], among study subjects who had at least one other family member in the study—i.e., from participants in families of size > 1. We expect the average number of household contacts to be 3 (based on our just completed ACT4 study[2, 3]
^bIn the Standard and GX arms, all children < 5 years and older HHC who are TST positive will be eligible to initiate TPT. We estimate this will be about 50% of all HHC, resulting in the lower overall expected initiation rate among all HHC—as cannot exceed the expected proportion eligible for TPT. In the no TST arm, we expect a higher proportion of HHC will start therapy, but we will estimate the number eligible based on prevalence of positive TST in the same age groups at the same centers in the other two arms; the number required in the no TST arm is therefore the same—based on this estimation
^cTotal is based on 80% power
Abbreviations: CXR chest X-ray, TST tuberculin skin testing, TB tuberculosis, TPT tuberculosis preventive treatment, ICC intra-class correlation coefficient, HCC household contacts, GX GeneXpert

ISSN: 1745-6215