Legionella detection by culture and qPCR: Comparing apples and oranges

Figures & data

Table 1. Comparison of published studies from 2003 to 2013 using qPCR and culture enumeration of Legionella spp. from environmental samples.

	Detection method
Source	qPCR	Culture	Comments	Reference
United Kingdom 100 environmental samples (68 from various hospitals, 32 from private domestic water supplies and 4 from external sites). 20 hospital and environmental water samples known to be L. pneumophila culture-positive.	4/100 (4%) were positive for L. pneumophila. 14/20 (70%) were positive for L. pneumophila.	14/100 (70%) were positive for L. pneumophila. All previously tested positive for L. pneumohila (however, this was not done concurrently).	All 10 samples positive for L. pneumophila by culture and not qPCR contained ≤200CFU/L. Also one culture negative sample was repeatedly qPCR-positive.	Levi et al. (2003)
USA and Canada 114 Water and biofilm samples from both warm and colder groundwater.		29/87 (33.3%) were positive for Legionella spp.	40/87 (46.0%) were positive for Legionella spp. using PCR. 61/87 (70.6%) samples were observed to contain PCR inhibitors.	Brooks et al. (2004)
Belgium 46 water samples (25 shower water, 12 industrial water, 4 natural water, 5 tap water).		19/46 (41%) were positive for Legionella spp.	26/46 (56%) and 45/46 (98%) of samples were positive for Legionella spp. using PCR with LEG 225-LEG 858 and JFP-JRP primer, respectively.	Devos et al. (2005)
Italy 124 tap water samples from hospitals and private residence.	111/124 (90%) were positive for Legionella spp. using TaqMan qPCR method.	77/124 (62%) were positive for Legionella spp.	88/124 (71%) were positive for Legionella spp. using nested PCR method.	Fiume et al. (2005)
Spain Water samples 40 water samples (spas, hotels, hospitals, residential tap water.)	17/40 (43%) were positive for Legionella spp. using qPCR. 15/40 (38%) were positive for Legionella spp. using PMA-qPCR.	12/40 (30%) were positive for Legionella spp.	qPCR and PMA-qPCR (propidium monoazide pre-treatment) compared.	Yáñez et al. (2005)
France Hot water system 128 samples tested in laboratory 1. 92 samples tested in laboratory 2. 36 Cooling tower samples.	117/128 (91.4%) were positive for Legionella spp. and of these 89/128 (69.5%) were quantifiable. 94/122 (77%) were positive for L.pneumophila and 55/122 (45.1%) were quantifiable. 76/92 (82.6%) were positive for Legionella spp. and of these 56/92 (60.9%) were quantifiable. 57/91 (62.6%) were positive for L. pneumophila and of these 31/91 (34.1%) were quantifiable. 36/36 (100%) were positive for Legionella spp. and 35/36 (97.2%) of these were quantifiable. 31/33 (93.9%) were positive for L. pneumophila and 19/33 (57.6%) were quantifiable.	55/128 (43%) were positive for Legionella spp. and 27/128 (21.1%) of these had ≥250 CFU/L 41/92 (44.6%) were positive for Legionella spp. and 24/92 (26.1%) of these had ≥250 CFU/L 9/36 were positive for Legionella spp. (25%) and of these 8/36 had ≥250 CFU/L (22.2%)		Joly et al. (2006)
The Netherlands 68 commercial bottled mineral waters.		0/68 were positive for L. pneumophila	6/68 (9%) were positive for L. pneumophila using PCR.	Klont et al. (2006)
The Netherlands 16 surface water samples, 97 treated surface and ground water samples.	14/16 (86%) were positive for Legionella spp. 97/97 (100%) were positive for Legionella spp.	0/16 were positive for Legionella spp. 0/97 were positive for Legionella spp.		Wullings & van der Kooij (2006)
Belgium 30 tap water samples (showers taps, eyewash stations, fire sprinklers and recirculation loops).	14/30 (46.7%) were positive for L. pneumophila at concentrations ranging from 4.4 × 10^3 to 3.1 × 10^5 GU/L.	10/30 (33%) were positive for L. pneumophila at concentrations ranging from 4.0 × 10^2 to 9.0 × 10^3 CFU/L.	12/30 (40%) contained qPCR inhibitors.	Behets et al. (2007)
Brazil River water.		Legionella spp. was not identified by culture.	24 sequences were identified as more closely related to Legionella spp. than any other genera. Some colonies present on Legionella selective medium had the typical “ground glass” appearance of Legionella but the results of the latex test kit and fluorescent antibody assay were negative for Legionella spp.	Carvalho et al. (2007)
The Netherlands 357 water samples from 250 public buildings.	311/357 (87.1%) were positive for Legionella spp.	8/357 (2.2%) were positive for Legionella spp.		Diederen et al. (2007)
Spain 25 potable water. 30 cooling tower samples.	21/25 (84%) were positive for Legionella spp. 28/30 (93%) positive for Legionella spp.	13/25 (52%) were positive for Legionella spp. 22/30 (73%) positive for Legionella spp.	19/25 (76%) of potable water samples and 30/30 (100%) cooling tower samples were positive for Legionella spp using PCR.	Yáñez et al. (2007)
France 136 hot water system samples collected form 55 sites. 46 cooling tower water samples collected from 20 sites.	87/132 (65.9%) L. pneumophila positive and of these 50/132 (37.9%) were quantifiable (>25 GU/reaction). 28/46 (60.9%) L. pneumophila positive and of these 20/46 (43.5%) were quantifiable (>25 GU/reaction).	59/132 (44.7%) were positive for L. pneumophila and of these 40/132 (30.3%) were quantifiable (>250 CFU/L). 15/46 (32.6%) were positive for L.pneumophila and of these 9/46 (19.6%) were quantifiable (>250 CFU/L)	4 hot water system samples and 3 cooling tower samples contained inhibitors which would not be removed using dilution and were not used for the study.	Yaradou et al. (2007)
Japan 130 Hot water samples from 40 public buildings (hotels, offices, schools, stores, assembly halls).	24/130 (18%) were positive for Legionella spp. In 21 of these samples concentrations of Legionella ranged from 1.7 × 10^5 to 2.6 × 10^11 GU/L	5/130 (4%) were positive for Legionella spp. Concentration of Legionella ranged from 1.8 × 10^2 to 8.3 × 10^3 CFU/L	17 of the 40 sites were positive by qPCR	Edagawa et al. (2008)
Kuwait 263 swabs from hospital faucets and showerheads. 20 water samples from hospital water storage facility.		61/263 (23%) were positive for Legionella spp. 0/20 (0%) were positive for Legionella spp.	61/263 (23%) were positive for Legionella spp. using PCR. 6/20 (30%) were positive for Legionella spp. using PCR.	Qasem et al. (2008)
France 120 Hot water samples collected a hospital (including hot water tanks, showers and taps).	57/120 (47.5%) were positive for L. pneumophila (only 35/120 (29.1%) were quantifiable).	31/120 (25.8%) were positive for L. pneumophila	Samples taken from six different distribution systems within the hospital.	Morio et al. (2008)
USA 276 environmental water samples.	138/276 (50%) tested positive for L. pneumophila	99/276 (35.8%) tested positive for L. pneumophila	97/140 (69.3%) positive samples tested both culture and qPCR positive. 41/140 (29.3%) tested qPCR-positve only. 2/140 (1.4%) tested culture-positive only.	Nazarian et al. (2008)
Switzerland 46 brands of potting mix.	41/46 (89.1%) tested positive for Legionella spp.	21/46 (45.7%) tested positive for Legionella spp.		Casati et al. (2009)
Japan 25 water samples (9 public spas and 16 from model spa systems).	16/25 (64%) tested positive for Legionella spp. 10/25 (40%) tested positive for Legionella spp after pre-treatment with 20 µg/ml of Ethidium monoazide (EMA).	14/25 (56%) were positive for Legionella spp.	Results with pre-treatment of 1, 5 and 10 µg/ml of Ethidium monoazide (EMA) are also presented.	Chang et al. (2009)
Taiwan 34 samples from 13 spring resorts (source water, facility water and waste water).	5/34 (15%) tested positive for Legionella spp.	5/34 (15%) tested positive for Legionella spp.	No samples test both qPCR and culture positive. Therefore a total of 10/34 samples were positive by any method.	Hsu et al. (2009)
Italian 76 water samples cold water tap, boiler room, shoers, hot water recycling) from 19 hotels.	56/76 (74%) were positive for Legionella spp. 37/76 (49%) were positive for L. pneumophila.	32/76 (42%) were positive for Legionella spp. 19/76 (25%) were positive for L. pneumophila.		Bonetta et al. (2010)
Spain 20 cooling tower water samples. 30 hot water system samples.	10/20 (50%) were positive for L. pneumophila using mip Primers 9/20 (45%) were positive for L. pneumophila using dot primers 19/30 63%) were positive for L. pneumophila using mip Primers 20/30 (67%) were positive for L. pneumophila using dot primers	8/20 (40%) were positive for L. pneumophila 14/30 (46.7%) were positive for L. pneumophila		Fittipaldi et al. (2010)
Canada 101 samples from 95 whirlpool spas in semi-public establishments.	72/101 (72%) were positive for Legionella spp. 42/101 (42%) could be enumerated with concentrations ranging from 1000 (limit of detection) to 6.1 × 10^7 GU/L.	27/101 (27%) were positive for Legionella spp 14/101 (14%) could be enumerated with concentrations ranging from 250 to 3.5 × 10^5 CFU/L.		Guillemet et al. (2010)
France Water samples from the Tech River.	72/72 (100%) were positive for Legionella spp.	15/72 (20.8%) were positive for Legionella spp.	qPCR inhibitors were present in all non-diluted DNA extracts.	Parthuisot et al. (2010)
Indonesia 9 cooling tower water samples (from 9 cooling towers).	7/9 (78%) were positive for Legionella spp.	0/9 were positive for Legionella spp.		Yasmon et al. (2010)
China 51 samples from recreation spring facilities (source water, waste water and facility water).		3/51 (5.9%) were positive for Legionella spp.	5/51 (10%) were positive for Legionella spp. using PCR. 11/51 (22%) were positive using free living amoeba (FLA) culture method.	Huang et al. (2011a)
Taiwan 47 Carbonate springs. 17 Mud springs. 4 Sodium bicarbonate spring.		7/47 (15%) were positive for Legionella spp. 0/17 were positive for Legionella spp. 1/4 (25%) were positive for Legionella spp.	10/47 (21%) were positive for Legionella spp. 5/17 (29%) were positive for Legionella spp. 1/4 (25%) were positive for Legionella spp. Using PCR method.	Huang et al. (2011b)
Denmark 84 Hot water samples.	84/84 (100%) were positive for Legionella spp. 75/84 (89%) were positive for L. pneumophila.	43/84 (51%) were positive for Legionella spp.		Krøjgaard et al. (2011)
6 European Countries 232 cooling tower water samples. 506 hot and cold water samples.	221/232 (95%) were positive for Legionella spp. and 114/232 (49%) were positive for L. pneumophila. 495/506 (98%) were positive for Legionella spp. and 417/506 (82%) were positive for L. pneumophila.	73/232 (31%) were positive for Legionella spp. and 62/232 (27%) were positive for L. pneumophila. 278/506 (55%) were positive for Legionella spp. and 249/506 (49%) were positive for L. pneumophila.	7 laboratories from 6 countries participated in this study. This study also discussed the potential of qPCR results predicting culture results.	Lee et al. (2011)
France 185 water samples from 9 cooling water systems at 4 different sites.	181/185 (98%) were positive for Legionella spp. and 111/185 (60%) were positive for L. pneumophila.	102/165 (62%) were positive for Legionella spp. and 101/164 (63%) were positive for L. pneumophila		Touron-Bodilis et al. (2011)
Spain 25 samples from hotel potable hot water systems. 35 cooling tower water samples.	15/25 (60%) were positive for Legionella spp. 28/35 (80%) were positive for Legionella spp.	13/25 (52%) were positive for Legionella spp. 22/35 (63%) were positive for Legionella spp.	Regression analysis showed that average concentration of Legionella spp determined by qPCR were 20-fold higher that the culture determined concentrations.	Yáñez et al. (2011)
The Netherlands Two un-chlorinated drinking water supplies (water and Biofilm samples).	Legionella spp detected at ranges of 7.6 × 10^1 to 3.9 × 10^2 GU/L.	No Legionella spp. were detected from culture in any of the water or biofilm samples.		Wullings et al. (2011)
Kuwait Domestic water samples. 82 samples from bathroom faucets and showerheads. 51 from kitchen taps. 71 from hot/cold water tanks.	45/82 (55%) were positive for Legionella spp. 19/51 (37%) were positive for Legionella spp. 21/71 (30%) were positive for Legionella spp.	27/82 (33%) were positive for Legionella spp. 15/51 (29%) were positive for Legionella spp. 6/71 (8.5%) were positive for Legionella spp.		Al-Matawah et al. (2012)
China 216 cooling tower water. 132 piped water samples. 90 hot spring water samples.	67/216 (31%) were positive for Legionella spp. 32/132 (24%) were positive for Legionella spp. 84/90 (93%) were positive for Legionella spp.	57/216 (26%) were positive for Legionella spp. 25/132 (19%) were positive for Legionella spp. 49/90 (93%) were positive for Legionella spp.	43/216 (20%) cooling tower samples, 27/132 (20%) piped water and 64/90 (71%) of hot spring samples were positive for Legionella spp. using PCR.	Qin et al. (2012)
USA Chloraminated potable water distribution systems.	27/90 (30%) of water samples were positive for Legionella spp. at average concentration of 186.6 ± 458.2 GU/L and 4/90 (4%) were positive for L. pneumophila at average concentrations of 9.8 ± 4.4 GU/mL.	1/56 (2%) were positive for Legionella spp. at density of 2 CFU/mL.		Wang et al. (2012)
Taiwan Puzih River water samples.	59/150 (39%) were positive for Legionella spp. and 3/150 (2%) were positive for L. pneumophila.	14/150 (9%) were positive for Legionella spp. and 14/150 (9%) were positive for L. pneumophila.		Tung et al. (2013)

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