Table 2. Estimations of initial and residual infestation for treatment phase of a Chagas disease vector control program, Arequipa, Peru, 2003–2011*.

Treatment received	No. households	Initial prevalence, %			Estimated residual infestation
		Observed	Estimated		Prevalence, %	No. (%) infested households
I and II	35,207	20.1	35.6		0.006	2 (0.3)
I only	7,521	7.0	12.2		0.16	14 (2.1)
II only	4,169	4.0	6.9		0.09	4 (0.5)
Not treated	9,594	ND	6.9†		6.9	666 (97.1)
Total	56,491	16.2	25.8		1.2	686 (100)

*Estimates are calculated by using equations in Table 3 (estimated sensitivity of inspectors p = 57% [range 46%–66%] and probability of clearing households of infestation through 1 treatment c = 98.7% [range 98.4%–98.9%]). ND, no data. 
†Extrapolation of the prevalence in households participating only in the second treatment to households that were never treated.