2.2 Eligibility criteria
We defined the eligibility criteria for the studies according to the POS
(Population, Outcome, and Study) approach of the PRISMA (Preferred
Reporting Items for Systematic reviews and Meta-analysis) statement
(Liberati et al., 2009). In Table 1 are summarized the
definitions used. In brief, we included publications that met the
following inclusion criteria: 1) the studies reported the presence of
NTS in samples from poultry birds (included subpopulations such as
layers, broilers, and breeders at the individual or flock/collective
level), samples from products and subproducts of poultry, or
environmental samples from the ambient related to poultry production, 2)
the studies assessed the prevalence of NTS, the frequency and diversity
of the serovars, or the antimicrobial resistance profiles, and 3) the
studies were full text primary publications from the Americas published
in English, Spanish, or Portuguese in peer-reviewed journals from 1980
to March 2020. Reasons for exclusion were 1) reporting turkeys, ducks,
ostriches, pigeons, quails, or wild, song or, ornamental birds, 2) not
reporting any of the three types of samples defined, 3) reporting NTS
isolates previously obtained, 4) not reporting at least one of the
defined outcomes, 5) re-used data from a previous study, 6) study
outside the Americas. We did not include any grey literature (i.e.,
unpublished studies, thesis, conference proceedings, or reports) to
assure an adequate and comparable level of methodological quality among
the selected studies.