Effect of monochloramine treatment on colonization of a hospital water distribution system by Legionella spp.: a 1 year experience study

Contamination of hot water distribution systems by Legionella represents a great challenge due to difficulties associated with inactivating microorganisms, preserving the water characteristics. The aim of this study was to examine over the course of 1 year in 11 fixed sites, the impact of monochloramine disinfection on Legionella, heterotrophic bacteria (36 °C), Pseudomonas aeruginosa contamination, and chemical parameters of a plumbing system in an Italian hospital. Three days after installation (T0), in the presence of monochloramine concentration between 1.5 and 2 mg/L, 10/11 sites (91%) were contaminated by L. pneumophila serogroups 3 and 10. After these results, the disinfectant dosage was increased to between 6 and 10 mg/L, reducing the level of Legionella by three logarithmic unit by 2 months postinstallation (T2) until 6 months later (T3). One year later (T4), there was a significant reduction (p = 0.0002) at 8/11 (73%) sites. Our data showed also a significant reduction of heterotrophic bacteria (36 °C) in 6/11 (55%) sites at T4 (p = 0.0004), by contrast the contamination of P. aeruginosa found at T0 in two sites persisted up until T4. The results of the present study show that monochloramine is a promising disinfectant that can prevent Legionella contamination of hospital water supplies.

Potable water as a cause of sporadic cases of community-acquired legionnaires' disease

BACKGROUND

The environmental sources of sporadic, community-acquired legionnaires' disease are largely unknown, and culturing of water sources after identification of a case is currently not recommended. We conducted a prospective study of sporadic cases of community-acquired legionnaires' disease to determine whether the environmental reservoirs could be identified.

METHODS

We cultured samples of potable water obtained from sources to which each of 20 patients with culture-confirmed, community-acquired legionnaires' disease had been exposed during the two weeks before the onset of symptoms. Monoclonal-antibody subtyping and restriction-endonuclease analysis were performed on the legionella isolates recovered from both the patients and the associated environmental cultures.

RESULTS

For 8 of the 20 patients, isolates of Legionella pneumophila with identical subtypes were identified in cultures from both the patient and the potable water to which the patient had been exposed. The environmental reservoirs linked to the infections were the water supplies of two private residences, two nursing homes, two hospital outpatient clinics, and an industrial plant.

CONCLUSIONS

Potable-water supplies that harbor L. pneumophila are an important source of community-acquired legionnaires' disease. Future studies should include attempts to identify the environmental sources of this infection.

Risk factors for contamination of domestic hot water systems by legionellae

To assess risk factors associated with the contamination of the domestic environment by legionellae, 211 houses in the Quebec City area were randomly selected and water samples were collected from the hot water tank, the shower heads, and the most frequently used faucet. After centrifugation, concentrated samples were seeded in triplicate on BCYE and GPV media. Data on the characteristics of the hot water system and plumbing in the house and on the personal habits of the occupants were collected for each house. Among these 211 houses, hot water was provided by either an oil or gas heater in 33 and by an electric heater in 178. Legionellae were isolated from none of the samples from houses with oil or gas heaters and from 39% (69 of 178) of those with electric water heaters (P less than 0.0001). This association remained highly significant after control for water temperature and other variables in a stratified analysis. In the 178 houses with an electric heater, 12% of the faucets, 15% of the shower heads, and 37% of the water heaters were contaminated. Legionella pneumophila serogroups 2 and 4 were the most frequently isolated strains. Logistic regression showed that factors associated with electric water heater contamination were (i) location of the house in older districts of the city (P less than 0.0001), (ii) old age of the water heater (P = 0.003), and (iii) low water temperature (P = 0.05). Contamination of the water heater was the only factor significantly associated with the contamination of peripheral outlets (P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)