Table 2 Association of physical, chemical, and microbiological water characteristics with Legionella spp. concentration of hot and cold water samples on ferries water distribution systems

Legionella spp.

pH

Sample Temp

pH ≥7.8 (%)

pH <7.8 (%)

RR

P

≥ 55°C (%)

< 55°C (%)

RR

P

Legionella spp.

32 (32.0)

40 (27.2)

1.17

0.25

7 (14.9)

74 (35.7)

0.41

0. 003

L. pneumophila sg 1

17 (17.0)

25 (17.0)

0.99

0.5

2 (4.3)

40 (19.3)

0.22

0.006

L. pneumophila sg 2–14

22 (22.0)

14 (9.5)

2.30

0.005

3 (6.4)

41 (19.8)

0.32

0.01

Legionella non pneumophila

1 (1.0)

7 (4.8)

0.21

0.09

2 (4.3)

7 (3.4)

1.25

0.5

Free chlorine

Total plate count

≥ 0.2 mg/L (%)

< 0.2 mg/L (%)

RR

P

≥400 CFU/L (%)

<400 CFU/L (%)

RR

P

Legionella spp.

8 (12.5)

10 (34.5)

0.36

0.01

26 (53.1)

56 (25.7)

2.09

0.0002

L. pneumophila sg 1

6 (9.4)

6 (20.7)

0.45

0.1

13 (26.5)

30 (13.8)

1.92

0.02

L. pneumophila sg 2–14

2 (3.1)

4 (13.8)

0.22

0.07

13 (26.9)

31 (14.2)

1.86

0.03

Legionella non pneumophila

0 (0.0)

2 (6.9)

0.00

0.09

3 (6.1)

6 (2.8)

2.22

0.2