47-Environmental surveillance of Legionella pneumophila in two Italian hospitals

https://www.scielosp.org/pdf/aiss/2010.v46n3/274-278 

Ann Ist Super Sanità 2010 | Vol. 46, No. 3: 274-278 DOI: 10.4415/ANN_10_03_08

Environmental surveillance of Legionella pneumophila in two 

Italian hospitals 

Marina Tesauro, Annalisa Bianchi, Michela Consonni, Fabrizio Pregliasco and Maria Gabriella Galli Dipartimento di Sanità Pubblica, Microbiologia e Virologia, Università degli Studi di Milano, Milan, Italy

Summary. 

The aim of this study was to identify the most effective disinfection protocol to reduce the presence of Legionella pneumophila in the water system of two Italian hospitals. From 2004 to 2009, 271 samplings of hot water were carried out in 11 hospital units to detect the presence of L. pneumophila. Additionally, water samples collected from one boiler outlet and the hot water recirculation were tested. From 2004 to 2009, L. pneumophila was present in 37% of the samples. Of these, 68.3% and 18.8% were positive for serogroups 2-14 and 1, respectively. Furthermore, 12.9% of the samples were positive for both serogroups. Finally, a maximal count of 104 CFU/L was measured in the most distal sites. To reduce L. pneumophila colonization, a two-year long hyperchlorination (2004-2006) was carried out. Moreover, from June 2005 until now, continuous maintenance of boilers and tanks, substitution of the shower heads and increase of the boiler outlet temperature to 60 °C were performed. All these treatments led to a marked reduction of L. pneumophila colonization in the short but not in the medium-long term. Only the use of chlorine dioxide led, after four years, to a reduction of the loads of L. pneumophila to values below 100 CFU/L. However, in the distal sites a persistent degree of colonization (maximum value 700 CFU/L, average 600 CFU/L) was observed probably due to the presence of L. pneumophila in the stagnant water in dead legs. In conclusion, data show that long-term chlorination of hot water sources together with carefully aimed maintenance of water pipes can lead to an effective reduction of L. pneumophila concentration in hospital water systems. 

Key words: Legionella pneumophila, environmental surveillance, hospitals, disinfection, chlorine dioxide. Riassunto (Sorveglianza ambientale di Legionella pneumophila in due ospedali italiani). I

INTRODUCTION 

Legionella pneumophila is a Gram-negative bacterium that is normally found in water. It is known that L. pneumophila can persist for long periods of time in water and biofilms commonly found in manmade water systems, such as plumbing systems, air conditioning equipments or whirlpool spas. It is widely accepted that biofilms play a critical role in the persistence of these bacteria within water systems, providing shelter and nutrients and preventing disinfectants from gaining access to the bacteria through the exopolysaccharide matrix [1]. The strategies of L. pneumophila to adapt and resist to stressful environmental conditions include interaction with amoeba and biofilm localization and the ability to enter in a viable but nonculturable (VBNC) state [2]. Since 1977, it has been well documented that L. pneumophila is the etiological agent of severe pneumonia in humans commonly defined as Legionnaire’s disease (LD) [1-3]. Infection is normally caused by inhalation or aspiration of organisms from contaminated aerosol droplets. This process can then lead to sporadic cases as well as to severe outbreaks. In recent years, the increasing incidence of both nosocomial and community-acquired L. pneumophila infections has been a major public health concern. In Italy LD infections increased from 100 cases/year before 1998 to 869 cases in 2005, and in 2008 reached a total of 1189 cases. L. pneumophila serogroup (Sg) 1 was found to be responsible for 94.5% of these cases. Interestingly, 7.1% of those infections were acquired in healthcare settings in 2008 [4]. The increasing reports of LD cases probably depends on the greater awareness of clinicians and on improved diagnosis rather than on an overall increased incidence of the disease [5]. Furthermore, the fatality rate of hospital-acquired LD patients affected by chronic degenerative diseases, tumors, immunocompromised patients, or those undergone to organ transplantation, is much higher than the one observed in community-acquired LDs (33.3% vs 7.5%, respectively) [4]. Indeed, the degree of L. pneumophila colonization in hospital water supplies has been correlated with the incidence of nosocomial LD [6, 7]. While US Centers for Disease Control and Prevention (CDC) reports [8, 9], and Italian [10] and local [11] guidelines establish which type of intervention is best needed to reduce L. pneumophila colonization from hospital water supplies, there is conflicting evidence about the precise concentration of L. pneumophila that constitutes a risk factor for nosocomial LD. In addition, further studies are urgently needed to determine new guidelines for the prevention of L. pneumophila colonization in hospital water supplies based on the characteristics and complexity of the water system.

From 2004 to 2009 an environmental surveillance was performed in two private hospitals in Milan (Italy), housing more than 900 patients with physical and mental disabilities. In these hospitals: 1) the concentration of L. pneumophila was measured in the water system; 2) the extent of colonization after different methods of intervention was determined in order to identify an effective protocol to reduce the concentration of L. pneumophila in nosocomial water supplies. MATERIALS AND METHODS The two private hospitals under study are adjacent and located in the Milan area (Italy). The two structures have different buildings, reached by a municipal water supply and supported by two private wells. Hot water is produced from a series of boilers, collected in tanks and then distributed by a unique ring pipeline to both the structures. In recently built wards, pipes are made of polyethylene, whereas the old ones are made of galvanised steel material In 2002 L. pneumophila concentration was measured in 21 sites to monitor the entire water system of the two hospitals. However, from 2004 11 sites, located in medium-high risk wards, were selected. In these sites, every 3 months, L. pneumophila concentration was measured in hot water samples from 11 showers, one boiler outlet and water recirculation. In the same time, water temperature and residual free chlorine content were measured. In March 2009, since new local guidelines [11] were published, also cold water was sampled in one site. The samples were subsequently analyzed in laboratory, following Italian guidelines [10]. On positive samples, serogrouping, was performed using the Legionella latex test (Oxoid). Cold water from municipal water supply and wells was analyzed according to Italian Decree [12], detecting Escherichia coli, enterococci, coliforms at 37 °C, heterotrophic plate count at 22 °C and 36 °C, and Pseudomonas aeruginosa and Aeromonas hydrophila as additional parameters.

RESULTS To detect the presence of L. pneumophila in nosocomial water, from 2004 to 2009, a total of 271 samples of hot water from 11 units of two separate hospitals was analyzed as described in the “Materials and methods” section. In 2004-2009 L. pneumophila was present in 37% (99/271) of the samples and had a concentration equal or greater than 100 CFU/L, thus demonstrating that all units were colonized (Table 1). Serogroup 2-14 was the most frequent contaminant and, therefore, isolated from 68.3% of the positive samples. In contrast, serogroup 1 was found in 18.8% of the positive samples. Both serogroups were detected in 12.9% of the positive samples. In particular, hospital 1 was positive for L. pneumophila in 41% of the samples. Similarly, L. pneumophila was present in 37% of the samples taken from hospital 2. Lastly, 13% positive samples in the boiler outlet and 33% in the recirculation water were found. Both hospitals had similar levels of L. pneumophila concentration ranging from < 100 CFU/L (detection limit) to 104 CFU/L. The highest values were observed in the most distal points, indicated with R2 and R10, in both hospitals (Figure 1). Since these sites were found to be highly contaminated by L. pneumophila (103 to 104 CFU/L), the sanitation of the entire water system was performed and after a week the measurements repeated to observe the efficacy of the treatment. Hyperchlorination was performed five times from September 2004 to February 2006. During this process, free chlorine residual medium concentration was kept between 30 and 40 mg/L. To reduce L. pneumophila colonization, from June 2005 the hospital administrators decided to increase the water temperature from 50 °C to 60 °C at the boiler outlet. Furthermore, they improved the over-all maintenance of boilers and showers as described in the materials and method section. Moreover, they had dead end pipes localized and removed. All these measures are indicated as “continuous maintenance” in Figure 1. Despite these improvements to the water system, the overall levels of L. pneumophila colonization increased instead of diminishing. Indeed, from 2005 to 2006, 87% of the samples of hospital 1 were positive, compared to the 48% of the previous year (Table 1). Only the boiler outlet usually positive in 50% of cases, became negative when the temperature was raised to 60 °C. Lastly, while in year 2004-2005 water recirculation was found to be positive for L. pneumophila in 50% of the samples, in 2005-2006 it was positive in every measurement. Because of these discouraging results, another disinfection method was proposed: continuous exposure to chlorine dioxide. Following water treatment with 0.70 mg/L chlorine dioxide (April 2006), which was then gradually decreased to 0.2 mg/L, a dramatic reduction of L. pneumophila positive samples was observed in both hospitals (2% for values greater than 103 CFU/L). Moreover, a reduction of the count to low-range 100 CFU/L was noticed in all sampling sites, except in three units located in distal areas (maximum value of 700 CFU/L, average 600 CFU/L) with values always below the limits indicated in the new local guidelines [11]. Positive samples in the boiler outlet and recirculation water system that were respectively 27% and 73% before dioxide treatment reached 0% following dioxide exposure. For hospital 1, the colonization decreased from 68% to 8% and from 77% to 12% for hospital 2. Above all, L. pneumophila colonization has remained to acceptable levels up to present times. In this regard, in 2006-2007 hospital 1 and hospital 2 showed respectively 4% and 31% of positive samples, in 2007-2008 10% and 5% and in 2008-2009 8% and 0%. According to local guidelines (March 2009), L. pneumophila was searched in cold water in the last two samples and it was always found to be absent. The other values from the analysis on cold water from municipal water system and wells were always below the limits of Italian law [12].

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