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The distribution of the L. pneumophila load in the analyzed samples did not display differences among the various analyzed locations (p > 0.05 all comparisons, Table 3). The L. pneumophila serotypes 2–14 were found more frequently than serotype 1. Finally, in 134 of 160 water samples, the presence of L. pneumophila and its load have been compared to the total bacterial load (Table 4). The HPC at 22 °C did not correlate with L. pneumophila in the analyzed samples (p > 0.05). However, the high (>103 CFU/mL) and intermediate (101–103CFU/mL) total bacterial load of the HPC at 37 °C is generally correlated to a higher frequency of positivity for L. pneumophila (p < 0.005 vs total bacterial load >103 CFU/mL and 101–102CFU/mL).

Table 4

HPC load (22 °C and 37 °C) related to the presence of L. pneumophila detected using culture

HPC 22 °CNumber of samplesNumber of samples positive for L. pneumophilaHPC 37 °CNumber of samplesNumber of samples positive for L. pneumophila
CFU/mLNumberNumber (%)CFU/mLNumberNumber (%)
>103 28 5 (17.8) >103 36 14 (38.9) 
102–103 10 4 (40) 102–103 18 5 (27.8) 
101–102 19 7 (36.8) 101–102 21 12 (57.1) 
<10 77 21 (27.3) <10 59 7 (11.8)* 
p-valuea  0.4049 p-valuea  0.0009 
HPC 22 °CNumber of samplesNumber of samples positive for L. pneumophilaHPC 37 °CNumber of samplesNumber of samples positive for L. pneumophila
CFU/mLNumberNumber (%)CFU/mLNumberNumber (%)
>103 28 5 (17.8) >103 36 14 (38.9) 
102–103 10 4 (40) 102–103 18 5 (27.8) 
101–102 19 7 (36.8) 101–102 21 12 (57.1) 
<10 77 21 (27.3) <10 59 7 (11.8)* 
p-valuea  0.4049 p-valuea  0.0009 

aChi-square test for all groups’ comparison.

*p <0.005 (Fisher's exact test) for subgroup <10 vs 101–102 and <10 vs >103.

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