<p>Chagas disease vector control campaigns are being
conducted in Latin America, but little is known about medi-
um-term or long-term effectiveness of these efforts, espe-
cially in urban areas. After analyzing entomologic data for
56,491 households during the treatment phase of a Triato-
ma infestans bug control campaign in Arequipa, Peru, dur-
ing 2003–2011, we estimated that 97.1% of residual infesta-
tions are attributable to untreated households. Multivariate
models for the surveillance phase of the campaign obtained
during 2009–2012 confirm that nonparticipation in the initial
treatment phase is a major risk factor (odds ratio [OR] 21.5,
95% CI 3.35–138). Infestation during surveillance also in-
creased over time (OR 1.55, 95% CI 1.15–2.09 per year). In
addition, we observed a negative interaction between non-
participation and time (OR 0.73, 95% CI 0.53–0.99), sug-
gesting that recolonization by vectors progressively dilutes
risk associated with nonparticipation. Although the treatment
phase was effective, recolonization in untreated households
threatens the long-term success of vector control.
Chagas disease, an often deadly disease widespread in
the Americas, is caused by the protozoan parasite Try-
panosoma cruzi (1,2) and transmitted by hematophageous
triatomine insects (3). In southern South America Triatoma
infestans bugs are the primary vector (2). In 1991, the na-
tions of this region created the Southern Cone Initiative to
coordinate control efforts against T. infestans bugs. During
the first decade of this initiative, 2.5 million households were
treated with insecticide (4), which led to disruption of trans-
mission of T. cruzi by T. infestans bugs in several countries
and states (2). However, vector control efforts have at times
failed unexpectedly, and repeatedly in some areas (5,6).
Across most of their range, T. infestans insects are
found predominantly in rural areas (2). However, the vec-
tor has become an urban problem in Arequipa, Peru, a city
of 850,000 inhabitants (7