Multiple Types of Legionella pneumophila Serogroup 6 in a Hospital Heated-Water System Associated with Sporadic Infections

Abstract

Five sporadic cases of nosocomial Legionnaires’ disease were documented from 1989 to 1997 in a hospital in northern Italy. Two of them, which occurred in a 75-year-old man suffering from ischemic cardiopathy and in an 8-year-old girl suffering from acute leukemia, had fatal outcomes. Legionella pneumophila serogroup 6 was isolated from both patients and from hot-water samples taken at different sites in the hospital. These facts led us to consider the possibility that a single clone of L. pneumophila serogroup 6 had persisted in the hospital environment for 8 years and had caused sporadic infections. Comparison of clinical and environmental strains by monoclonal subtyping, macrorestriction analysis (MRA), and arbitrarily primed PCR (AP-PCR) showed that the strains were clustered into three different epidemiological types, of which only two types caused infection. An excellent correspondence between the MRA and AP-PCR results was observed, with both techniques having high discriminatory powers. However, it was not possible to differentiate the isolates by means of ribotyping and analysis of rrnoperon polymorphism. Environmental strains that antigenically and chromosomally matched the infecting organism were present at the time of infection in hot-water samples taken from the ward where the patients had stayed. Interpretation of the temporal sequence of events on the basis of the typing results for clinical and environmental isolates enabled the identification of the ward where the patients became infected and the modes of transmission of Legionellainfection. The long-term persistence in the hot-water system of different clones of L. pneumophila serogroup 6 indicates that repeated heat-based control measures were ineffective in eradicating the organism.

Genotypic variability and persistence of Legionella pneumophila PFGE patterns in 34 cooling towers from two different areas

“…In this study we recovered a minimum of one of the PFGE patterns observed in nearly 80% of the cooling towers after at least 6 months; this is very important and indicates that the same PFGE pattern may persist in the same cooling tower over long periods of time and may persist for more than 5 years in some cooling towers. The persistence of Legionella PFGE patterns in water distribution systems has been previously described in hospitals (Visca et al, 1999;Garcia-Nuñez et al, 2007) and other facilities (Garcia-Nuñez et al, 2006). Recently, our group has described PFGE pattern persistence in cooling towers during a 1-year period .…”

Detection and occurrence of indicator organisms and pathogens

“…Legionella of the same serogroups as those isolated from patients were present in each hospital water supply. Visca et al (1999) compared clinical and environmental strains of Legionella pneumophila serogroup 6 associated with a hospital in northern Italy by monoclonal subtyping, macrorestriction analysis (MRA), and arbitrarily primed PCR (AP-PCR). Environmental strains that antigenically and chromosomally matched the infecting organism were present at the time of infection in hot-water samples taken from the ward where the patients had stayed.…”

A hospital‐associated outbreak of Legionnaires' disease caused by Legionella pneumophila serogroups 4 and 10 with a common genetic fingerprinting pattern

“…In Scandinavia the high percentage of non‐sg 1 strains, especially amongst hospital‐associated cases, was even more pronounced than in the southern parts of Europe. Although these figures might be biased because relatively few Legionella pneumonia cases were culture‐proven in relation to the total number of cases, it is evident that the non‐sg 1 strains can cause outbreaks, especially in hospitals (10–15).…”

“…Relatively few studies describe epidemiological subtyping of L. pneumophila non‐sg 1 strains by serological and genotypic methods (10–15). Though MAb subgrouping has been useful in some instances (10, 11, 14), such strains are often only assigned to a serogroup, the potential of serological subgrouping being limited. Thus, genotypic methods are even more important for investigating L. pneumophila non‐sg 1 outbreaks than those caused by sg 1.…”