## 3 Results  
In general, and for both quantitative methods (incubation conditions: 42 and 37 \({}^{\circ}\)C) the counts ranged from 1.20 log CFU to 3.50 log CFU. In most cases where a species was isolated from more than one tissue, the counts in skin samples were slightly higher (but not significantly) than the counts from pectoral muscle samples which were also slightly higher than the ones in the liver and the visceral cavity. In total 18 _Campylobacter_ species were isolated by the four different analytical methods, 16 being common for all methods, while _C. rectus_ was isolated at 42 \({}^{\circ}\)C by both isolation methods (quantitative and qualitative characterization) and _C. hominis_ was isolated only by the qualitative method at 37 \({}^{\circ}\)C. By far, _C. jejuni_ was the most abundant species, followed by _C. coli_. These two species accounted for more than 61% of the total isolated _Campylobacter_ strains (Tables 2 and 3). \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & & & & & & \\ \cline{3-5}  & **Species** & **Quantitative** & **Qualitative** & **Quantitative** & **Qualitative** \\  & **42 \({}^{\circ}\)C** & **42 \({}^{\circ}\)C** & **37 \({}^{\circ}\)C** & **37 \({}^{\circ}\)C** \\ \hline
1 & _C. coli_ & 64 & 64 & 63 & 63 \\
2 & _C. rectus_ & 1 & 1 & - & - \\
3 & _C. hominis_ & - & - & - & 1 \\
4 & _C. helveticus_ & 1 & 1 & 1 & 1 \\
5 & _C. upsaliensis_ & 2 & 2 & 2 & 2 \\
6 & _C. jejuni_ & 97 & 98 & 96 & 97 \\
7 & _C. avium_ & 17 & 21 & 18 & 21 \\
8 & _C. fetus_ & 19 & 19 & 19 & 19 \\
9 & _C. hepatitis_ & 10 & 11 & 10 & 11 \\
10 & _C. lari_ & 23 & 24 & 24 & 24 \\
11 & _C. sputporum_ & 4 & 4 & 4 & 4 \\
12 & _C. mucosalis_ & 1 & 1 & 1 & 1 \\
13 & _C. gracilis_ & 2 & 2 & 2 & 2 \\
14 & _C. showae_ & 1 & 1 & 1 & 1 \\
15 & _C._ & _hyointestinalis_ & 4 & 4 & 4 \\
16 & _C. concisus_ & 2 & 2 & 2 & 2 \\
17 & _C._ & 1 & 1 & 1 & 1 \\
18 & _C. ureolyticus_ & 5 & 6 & 6 & 6 \\  & Total & 256 & 264 & 256 & 262 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Number of strains for every _Campylobacter_ species isolated by the four different methods. Table 4 presents the birds (_Gallus domesticus_) found positive for any _Campylobacter_ strain in any of the examined tissues. From a total of 600 birds, the positivity score varied between 40.33% and 41.50% depending on the method, with the qualitative method at 42 \({}^{\circ}\)C detecting the highest prevalence rate (41.50%). Interestingly, only 6 birds (1%) showed mixed infection by two _Campylobacter_ species. Multilinear regression revealed that for all methods the size of the flock and the presence of small ruminants were decisive factors very strongly correlated to the prevalence of _Campylobacter_ spp. (R \(>\) 0.943, \(p\) \(<\) 0.001). Particularly, the small size of the flock (3-15 birds) acted as a protective factor, while the larger size (more than 40 birds) was correlated with increased prevalence. \begin{table}
\begin{tabular}{l l c c c c} \hline \hline  & & \multicolumn{5}{c}{**Method**} \\ \cline{3-6}  & **Group** & **Qt 42 \({}^{\circ}\)C** & **Qt 42 \({}^{\circ}\)C** & **Qt 37 \({}^{\circ}\)C** & **Qt 37 \({}^{\circ}\)C** \\ \hline
1 & A (1), B(no), C(no), D (a) & 5 & 5 & 3 & 2 \\
2 & A (1), B (yes), C (no), D (a) & 9 & 9 & 9 & 8 \\
3 & A (1), B (no), C (yes), D (a) & 9 & 9 & 9 & 9 \\
4 & A (1), B (yes), C (yes), D (a) & 9 & 9 & 9 & 9 \\
5 & A (1), B (yes), C (yes), D (b) & 7 & 7 & 7 & 7 \\
6 & A (2), B (no), C (no), D (a) & 13 & 13 & 15 & 12 \\
7 & A (2), B (yes), C (no), D (a) & 12 & 12 & 12 & 12 \\
8 & A (2), B (no), C (yes), D (a) & 14 & 16 & 14 & 17 \\
9 & A (2), B (yes), C (yes), D (a) & 22 & 22 & 22 & 22 \\
10 & A (2), B (yes), C (yes), D (b) & 18 & 18 & 18 & 18 \\
11 & A (3), B (no), C (no), D (a) & 18 & 18 & 18 & 18 \\
12 & A (3), B (yes), C (no), D (a) & 21 & 27 & 27 & 27 \\
13 & A (3), B (no), C (yes), D (a) & 26 & 25 & 26 & 26 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Number of positive birds per experimental group for every different method.