Combined plasmid and peptide analysis of clinical and environmental Legionella pneumophila strains associated with a small cluster of Legionnaires' disease cases

Assessing risk of health care-acquired Legionnaires' disease from environmental sampling: the limits of using a strict percent positivity approach

BACKGROUND

Elevated percent positivity (≥30%) of Legionella in hospital domestic water systems has been suggested as a metric for assessing the risk of health care-acquired Legionnaires' disease (LD).

METHODS

We examined the validity of this metric by analyzing data from peer-reviewed studies containing reports of Legionella prevalence in hospital water (ie, percent positivity) and temporally matched reports of patients with health care-acquired LD.

RESULTS

Our literature review identified 31 peer-reviewed publications reporting matched data. We abstracted a total of 206 data points, representing 119 hospitals, from these articles. We determined that the proposed 30% positivity metric has 59% sensitivity and 74% specificity (ie, a 41% false-negative rate and a 26% false-positive rate). These notable error rates could have significant implications, given that we identified 16 peer-reviewed articles and 6 government guidance documents that referenced the 30% positivity metric as a risk assessment tool.

CONCLUSIONS

Environmental sampling of hospital water distribution systems for Legionella can be an important component of risk management for LD. However, the possible consequence of using a percent positivity metric with low sensitivity and specificity is that many hospitals might fail to mitigate when a true risk is present, or might unnecessarily allocate limited resources to deal with a negligible risk.

Nosocomial Legionnaires' disease caused by Legionella pneumophila serogroup 6: Implication of the sequence-based typing method (SBT)

Sequence-based typing (SBT) was used to determine the allelic profiles of 3 sporadic clinical isolates as well as 7 environmental isolates of Legionella pneumophila serogroup 6, isolated at the Karolinska Hospital during 2004. The clinical isolates were cultured from patients with nosocomial Legionnaires' disease (LD), while the environmental isolates were cultured from potable water sources of the hospital wards in the close vicinity of the 3 patients being investigated. The genes sequenced for the construction of the SBT profile included flaA, pilE, asd, mip, mompS and proA, in this pre-determined order and the allelic profile of the 10 isolates was identical (3, 13, 1, 28, 14, 9). Furthermore, 2 of the isolates, 1 clinical and 1 environmental, were analysed using the amplified fragment length polymorphism analysis (AFLP). The AFLP genotype of both isolates was congruent. Eight of 9 control L. pneumophila serogroup 6 isolates had the same SBT profile as the study isolates. We conclude that the environmental strain isolated from our hospital's drinking water is indistinguishable genotypically from the 3 clinical isolates of Legionella. However, this genotype of L. pneumophila is geographically widespread. Thus, results of genotyping must be evaluated in conjunction with the clinical and epidemiological data.

Legionella and Legionnaires' disease: 25 years of investigation

There is still a low level of clinical awareness regarding Legionnaires' disease 25 years after it was first detected. The causative agents, legionellae, are freshwater bacteria with a fascinating ecology. These bacteria are intracellular pathogens of freshwater protozoa and utilize a similar mechanism to infect human phagocytic cells. There have been major advances in delineating the pathogenesis of legionellae through the identification of genes which allow the organism to bypass the endocytic pathways of both protozoan and human cells. Other bacteria that may share this novel infectious process are Coxiella burnetti and Brucella spp. More than 40 species and numerous serogroups of legionellae have been identified. Most diagnostic tests are directed at the species that causes most of the reported human cases of legionellosis, L. pneumophila serogroup 1. For this reason, information on the incidence of human respiratory disease attributable to other species and serogroups of legionellae is lacking. Improvements in diagnostic tests such as the urine antigen assay have inadvertently caused a decrease in the use of culture to detect infection, resulting in incomplete surveillance for legionellosis. Large, focal outbreaks of Legionnaires' disease continue to occur worldwide, and there is a critical need for surveillance for travel-related legionellosis in the United States. There is optimism that newly developed guidelines and water treatment practices can greatly reduce the incidence of this preventable illness.

Effect of monochloramine disinfection of municipal drinking water on risk of nosocomial Legionnaires' disease

BACKGROUND

Many Legionella infections are acquired through inhalation or aspiration of drinking water. Although about 25% of municipalities in the USA use monochloramine for disinfection of drinking water, the effect of monochloramine on the occurrence of Legionnaires' disease has never been studied.

METHODS

We used a case-control study to compare disinfection methods for drinking water supplied to 32 hospitals that had had outbreaks of Legionnaires' disease with the disinfection method for water supplied to 48 control-hospitals, with control for selected hospital characteristics and water treatment factors.

FINDINGS

Hospitals supplied with drinking water containing free chlorine as a residual disinfectant were more likely to have a reported outbreak of Legionnaires' disease than those that used water with monochloramine as a residual disinfectant (odds ratio 10.2 [95% CI 1.4-460]). This result suggests that 90% of outbreaks associated with drinking water might not have occurred if monochloramine had been used instead of free chlorine for residual disinfection (attributable proportion 0.90 [0.29-1.00]).

INTERPRETATION

The protective effect of monochloramine against legionella should be confirmed by other studies. Chloramination of drinking water may be a cost-effective method for control of Legionnaires' disease at the municipal level or in individual hospitals, and widespread implementation could prevent thousands of cases.

Combined monoclonal antibody typing, multilocus enzyme electrophoresis, soluble protein profiles and plasmid analysis of clinical and environmental Legionella pneumophila serogroup 1 isolated in a Portuguese hospital

Sixteen strains of Legionella pneumophila serogroup 1 isolated from patients and the environment at Santa Cruz Hospital were examined using four typing methods. Monoclonal antibodies showed that all the isolates belonged to subgroup Pontiac and mainly to subtype Allentown. With multilocus enzyme electrophoresis nine subtypes (ETs) were revealed; each strain had the same profile with electrophoresis of soluble proteins, and plasmid analysis revealed that only two of the strains studied contained plasmids. Among these methods, multilocus enzyme electrophoresis was the most discriminative as a single epidemiological marker. Problems concerning the microbiological examination of environmental specimens and correlation with clinical strains confirmed the difficulty of investigating an outbreak source of legionellosis and the need for careful evaluation of the results.

Molecular fingerprinting of Legionella species by repetitive element PCR

Repetitive element PCR (rep-PCR) uses outward-facing primers to amplify multiple segments of DNA located between conserved repeated sequences interspersed along the bacterial chromosome. Polymorphisms of rep-PCR amplification products can serve as strain-specific molecular fingerprints. Primers directed at the repetitive extragenic palindromic element were used to characterize isolates of Legionella pneumophila and other Legionella species. Substantial variation was seen among the rep-PCR fingerprints of different Legionella species and serogroups. More limited, but distinct, polymorphisms of the rep-PCR fingerprint were evident among epidemiologically unrelated isolates of L. pneumophila serogroup 1. Previously characterized Legionella isolates from nosocomial outbreaks were correctly clustered by this method. These results suggest the presence of repetitive extragenic palindromic-like elements within the genomes of members of the family Legionellaceae that can be used to discriminate between strains within a serogroup of L. pneumophila and between different Legionella species. rep-PCR appears to be a useful technique for the molecular fingerprinting of Legionella species.

Application of numerical systematics to the phenotypic differentiation of legionellae

A total of 163 strains, including 106 strains of Legionella pneumophila, 28 strains of Tatlockia micdadei, and 29 strains of other legionellae (including members of the proposed genus Fluoribacter), were studied. Ten tests which together could distinguish the genera previously proposed were identified. These tests included catalase-peroxidase, gelatinase, hippurate hydrolysis, starch hydrolysis, medium browning, acetoin production, oxidase, medium fluorescence, colony fluorescence, and the bromcresol purple spot test. T. micdadei strains were strongly catalase positive and bromcresol purple spot test positive and produced acetoin but otherwise were usually inert in the other tests. L. pneumophila and Fluoribacter species could usually be distinguished by strength of catalase activity, blue-white colony fluorescence (if present), and differences in frequency of hippurate hydrolysis, starch hydrolysis, yellow-green medium fluorescence, and, to a lesser extent, oxidase activity. With a simple algorithm and computer program, the overall accuracy was 98.8%.

Subtyping of Legionella pneumophila serogroup 1 isolates by monoclonal antibody and plasmid techniques

A group of environmental and clinical Legionella pneumophila serogroup 1 isolates was subtyped by monoclonal antibody dot immunoblotting and plasmid analysis. Monoclonal antibody analysis defined seven subtypes within three major groups. Plasmid analysis (including restriction endonuclease digestion) revealed 10 subtypes. By combining plasmid and monoclonal techniques, all 16 strains were shown to be distinct. Plasmid profiles and monoclonal antibody reactivities of selected strains were stable despite serial passage (greater than 100 times). No plasmid-associated antigen was defined by this panel of monoclonal antibodies. The observed dissociation of plasmid profiles and monoclonal antibody reactivity patterns suggests that accurate epidemiologic typing of L. pneumophila serogroup 1 strains will require use of both techniques.

Diversity of plasmids in Achromobacter xylosoxidans isolates responsible for a seemingly common-source nosocomial outbreak

Achromobacter xylosoxidans, an uncommon yet highly resistant opportunistic pathogen, was isolated from nine hospitalized patients during an 8-month period. It had been isolated from only seven patients with either nonfatal infection or colonization from 1981 to 1984. From June 1985 to January 1986, A. xylosoxidans was isolated 18 times from seven different sites (sputum, 7 times; urine, 4 times; blood, 3 times; and lung, pleural fluid, wound tissue, and tracheal aspirate, 1 time each). Four patients died, including the three with bacteremia. All but two patients had nosocomial infections and either were on the same ward or were cared for by the same staff members. Eleven A. xylosoxidans strains yielded eight distinct plasmids (8, 21, 23, 26, 38, 50, 51, and 64 megadaltons). Whole-cell peptide patterns of 10 of these strains were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Isolates from the same patient contained the same plasmids and had identical peptide patterns but differed from other strains in both parameters. Plasmids were absent from the two community-acquired isolates. Although nosocomial strains showed similar antibiotic resistance patterns (only moxalactam and ticarcillin-clavulanic acid were uniformly active) and cross-contamination was strongly suggested epidemiologically, results of plasmid and peptide analyses did not support the possibility of a single-strain outbreak.

Plasmid profiles of Legionella spp. isolates, Italy

Plasmid analysis and restriction-endonuclease digestion were used to study 54 clinical and environmental Legionella strains. Plasmids with approximate molecular masses of 40, 50, 70, and 90 megadaltons (Mdal) have been isolated from L. pneumophila serogroup 1 strains. One L. jordanis strain contained two plasmids of 25 and 70 Mdal. Restriction analysis of clinical and related hospital-environmental isolates resulted in identical patterns. Geographic diversity is shown for strains of different origin.