Legionella pneumophila serogroup 1 subgrouping by monoclonal antibodies--an epidemiological tool

Distribution of lag-1 Alleles, ORF7, and ORF8 Genes of Lipopolysaccharide and Sequence-Based Types Among Legionella pneumophila Serogroup 1 Isolates in Japan and China

Approximately 85% of cases of Legionnaires' disease are caused by Legionella pneumophila serogroup 1. In this study, we analyzed the distribution of lag-1 alleles, ORF 7 and ORF 8 genes of lipopolysaccharide (LPS) and sequence-based types of 616 L. pneumophila serogroup 1 strains isolated in Japan (206 clinical, 225 environmental) and China (13 clinical and 172 environmental). The lag-1 gene was harbored by significantly more of the clinical isolates compared with the environmental isolates (90.3 vs. 19.1% and 61.6 vs. 3.0%, respectively; both P < 0.001). ORF 7 genes were detected in 51.0% of Japanese clinical and 36.0% of Japanese environmental (P = 0.001) isolates, as well as 15.3% of Chinese clinical and 9.9% of Chinese environmental isolates (P = 0.544). ORF 8 genes were detected in 12.1% of Japanese clinical and 5.8% of Japanese environmental (P = 0.017) isolates, as well as 7.7% of Chinese clinical and 3.4% of Chinese environmental isolates (P = 0.388). The Japanese and Chinese isolates were assigned to 203 and 36 different sequence-types (ST), respectively. ST1 was predominant. Most isolates with the same ST also had the same lag-1, ORF 7, and ORF 8 gene subgroups. In conclusion, the lag-1 was present in most of the clinical isolates, but was absent from most of the environmental isolates from both China and Japan, regardless of the water source and SBT type. PCR-based serotyping and subgrouping methods can be used to define a hierarchy of virulence genotypes that require stringent surveillance to prevent human disease.

Distribution of lag-1 alleles and sequence-based types among Legionella pneumophila serogroup 1 clinical and environmental isolates in the United States

Approximately 84% of legionellosis cases are due to Legionella pneumophila serogroup 1. Moreover, a majority of L. pneumophila serogroup 1 clinical isolates react positively with monoclonal antibody 2 (MAb2) of the international standard panel. Over 94% of the legionellosis outbreaks investigated by the Centers for Disease Control and Prevention are due to this subset of L. pneumophila serogroup 1. To date, there is no complete explanation for the enhanced ability of these strains to cause disease. To better characterize these organisms, we subtyped 100 clinical L. pneumophila serogroup 1 isolates and 50 environmental L. pneumophila serogroup 1 isolates from the United States by (i) reactivity with MAb2, (ii) presence of a lag-1 gene required for the MAb2 epitope, and (iii) sequence-based typing analysis. Our results showed that the MAb2 epitope and lag-1 gene are overrepresented in clinical L. pneumophila serogroup 1 isolates. MAb2 recognized 75% of clinical isolates but only 6% of environmental isolates. Similarly, 75% of clinical isolates but only 8% of environmental isolates harbored lag-1. We identified three distinct lag-1 alleles, referred to as Philadelphia, Arizona, and Lens alleles, among 79 isolates carrying this gene. The Arizona allele is described for the first time in this study. We identified 59 different sequence types (STs), and 34 STs (58%) were unique to the United States. Our results support the hypothesis that a select group of STs may have an enhanced ability to cause legionellosis. Combining sequence typing and lag-1 analysis shows that STs tend to associate with a single lag-1 allele type, suggesting a hierarchy of virulence genotypes. Further analysis of ST and lag-1 profiles may identify genotypes of L. pneumophila serogroup 1 that warrant immediate intervention.

The Presence of a Specific Genotype of Legionella pneumophila Serogroup 1 in a Hospital and Municipal Water Distribution System over a 12-year Period

The genotypic distribution of Legionella pneumophila serogroup 1 was investigated in the water distribution system of a 450-bed Swedish hospital and the surrounding community. A single genotype identified by amplified fragment length polymorphism (AFLP) analysis, was found in all 34 hospital isolates and in 18 out of 20 community isolates over a 12-y surveillance period. All isolates were either monoclonal antibody subtypes Benidorm or Bellingham. In a geographical comparison, the hospital genotype was also identified in 2 out of 6 Swedish hospitals, both located within 100 km of the studied community. In all, 70 isolates originating from 7 Swedish communities clustered in 4 groups, each also containing 1 AFLP type as defined by the European Working Group on Legionella Infections (EWGLI). It was concluded that a single Legionella pneumophila serogroup 1 genotype may colonize a large water distribution system over a long period of time, and that certain clones seem to be widely spread in the environment. Results from molecular typing of isolates originating from a limited geographical area must, therefore, be interpreted cautiously in epidemiological investigations of Legionnaires' disease.

Comparison of clinical and environmental isolates of Legionella pneumophila obtained in the UK over 19 years

Between January 1980 and December 1998, 3458 cases of Legionnaires' disease were reported to the national surveillance scheme in England and Wales. Of these, 463 (13.4%) were reported as proven by culture and isolation of Legionella spp., with 96.3% being Legionella pneumophila. Serogroup (Sgp), monoclonal antibody (mAb) subgrouping and restriction fragment length polymorphism (RFLP) analysis data were obtained for 321 (69.3%) of these, of which 284 were classified as being unrelated to any other isolate in the study. Typing data were also available for 117 unrelated environmental isolates of L. pneumophila obtained from England and Wales, giving a total of 401 unrelated isolates in the study. Of the clinical isolates, 88.0% were Sgp1, compared with only 42.7% of environmental isolates (p <0.001); 79.6% of clinical isolates were subgrouped as mAb2+, compared with only 12.8% of environmental isolates (p <0.001). RFLP typing identified 67 types among the 401 isolates, with clinical isolates showing significantly less diversity than environmental isolates (index of diversity (IOD) 0.944 vs. 0.958; p <0.05), with three RFLP types (1, 5 and 14) accounting for 40.0% of all clinical isolates. Combining the phenotypic and genotypic data resulted in 173 distinct phenons, with clinical isolates showing significantly less diversity than environmental isolates (IOD 0.964 vs. 0.996; p <0.01). Three phenons accounted for 30% of all clinical isolates. These data strongly suggest that some strains of L. pneumophila are more likely to cause human infection than would be expected from their distribution in the environment.

A hospital-associated outbreak of Legionnaires' disease caused by Legionella pneumophila serogroup 1 is characterized by stable genetic fingerprinting but variable monoclonal antibody patterns

An outbreak of 18 pneumonia cases caused by Legionella pneumophila serogroup 1 occurred at a Swedish university hospital 1996 to 1999. Eight clinical isolates obtained by culture from the respiratory tract were compared to 20 environmental isolates from the hospital and to 21 epidemiologically unrelated isolates in Sweden, mostly from patients, by using pulsed-field gel electrophoresis (PFGE), amplified fragment length polymorphism analysis (AFLP), and monoclonal antibody (MAb) typing. All patients and most environmental isolates from the outbreak hospital belonged to the same genotypic cluster in both PFGE and AFLP. This genotype was distinctly different from other strains, including a cluster from a second hospital in a different part of the country. The MAb subtype of the outbreak clone was Knoxville except for three isolates that were Oxford. A variation in the MAb reactivity pattern was also found in a second genotypic cluster. These changes in the MAb reactivity pattern were due to the absence or presence of the lag-1 gene coding for an O-acetyltransferase that is responsible for expression of the lipopolysaccharide epitope recognized by MAb 3/1 of the Dresden Panel. In all MAb 3/1-positive strains, the lag-1 gene was present on a genetic element that was bordered by a direct repeat that showed a high degree of sequence homology. Due to this homology, the lag-1 gene region seemed to be an unstable element in the chromosome. MAb patterns are thus a valuable adjunct to genotyping methods in defining subgroups inside a genotypic cluster of L. pneumophila sg 1.

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.

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.

Epidemiological and environmental investigations of Legionella pneumophila infection in cattle and case report of fatal pneumonia in a calf

A fatal pneumonia due to Legionella pneumophila was diagnosed in a young calf reared in a dairy herd located in northern Italy. Clinical symptoms consisted of watery diarrhea, hyperthermia, anorexia, and severe dyspnea. The pathological and histological findings were very similar to those observed in human legionellosis. Legionella pneumophila serogroup 1 (SG1) and SG10 were isolated from the calfs lung, and L. pneumophila SG1 was isolated from the calfs liver. L. pneumophila SG1 was also demonstrated in the lung tissue by immunofluorescence and immunohistochemical examinations. Nine of 10 L. pneumophila SG1 isolates belonged to the Olda subtype, and 1 belonged to the Camperdown subtype. A very low prevalence of antibodies to Legionella was detected in cows and calves reared in the same herd. Cultures of aqueous sediment of an old electric water heater which supplied hot water for the feeding of the calves yielded L. pneumophila SG1. Four of the colonies tested belonged to the Olda subtype. Ten clinical and four environmental isolates were examined for the presence of plasmids. Nine of them were also examined by pulsed-field gel electrophoresis assay, and the same patterns were found for L. pneumophila SG1 Olda strains isolated from the calf and from the electric heater. This is the first report of a documented case of a naturally occurring Legionella pneumonia in an animal. Cattle probably act as accidental hosts for legionellae, much the same as humans.

Molecular epidemiology of an outbreak of Legionnaires' disease associated with a cooling tower in Genova-Sestri Ponente, Italy

Fatty acid profile analysis, monoclonal antibody (MAb) subtyping, pulsed-field gel electrophoresis (PFGE), arbitrarily primed polymerase chain reaction (AP-PCR), and ribotyping were used to compare clinical and environmental Legionella pneumophila serogroup 1 isolates from an outbreak of Legionnaires' disease presumptively associated with cooling towers. According to the Oxford subtyping scheme, the MAb subtype of patients' isolates and of two strains originating from a cooling tower was Pontiac, whereas the other isolates were subtype Olda. The strains showed no intrinsic strain-to-strain difference in fatty acid profiles, and ribotyping and length polymorphism of the 16S-23S rDNA intervening regions failed to reveal any differences between the isolates. Conversely, PFGE and AP-PCR appeared to be more discriminatory, as the same genomic profile was found for the clinical and some environmental strains. Meteorologic and epidemiological data and the results of molecular analysis of the Legionella pneumophila serogroup 1 isolates support the hypothesis that the infection was transmitted from one of the cooling towers to the indoor environment of the same building, to homes in proximity that had open windows, and to the streets. In fact, the outbreak diminished and later ended after a part in the tower was replaced. This investigation demonstrates the utility of combined molecular methods (i.e., phenotypic and genomic typing) in comparing epidemiologically linked clinical and environmental isolates. Finally, the outbreak confirms the risk of Legionnaires' disease posed by cooling towers, mainly when atmospheric thermal and humidity inversions occur. This finding emphasizes the need to determine whether the source of infection is in the living or working environment or somewhere else.

Relationship between Legionella spp. and antibody titres at a therapeutic thermal spa in Portugal

The presence of Legionella spp. in the water of a Portuguese spa was ascertained during the spa season, between May and November. Simultaneously the prevalence of anti-legionella antibodies in people attending the spa was also investigated. The antibody titres of 172 randomly selected patients and 42 therapists were determined, and compared with a control group of 503 blood donors. Legionellae were present in the spa water at low concentrations, generally lower than 10(3) c.f.u./l. A total of 92 strains representing eight different species or serogroups were isolated; the predominant isolates belonged to Legionella pneumophila serogroup 6 and to L. londiniensis. During the study, no clinical cases of Legionnaires' disease were observed, and the antibody titres were generally low in the groups studied. However, the antibody titres of the patients increased slightly during their stay at the spa, approaching the values for the therapists. Mean antibody titres in the groups related with the spa were significantly higher than those in the blood donors against five of the seven legionella antigens tested. The largest number of elevated antibody titres in the exposed groups were to the L. pneumophila sg 5 and sg 6 antigens.

Molecular characterization of a virulence-associated epitope on the lipopolysaccharide of Legionella pneumophila serogroup 1

For identification of lipopolysaccharide (LPS)-associated epitopes of Legionella pneumophila serogroup 1, LPS of strain Philadelphia 1 was investigated using monoclonal antibodies (MAbs). The O-specific chain of LPS is a homopolymer of 5-acetamidino-7-acetamido-8-O-acetyl-3,5,7,9-tetradeoxy-D-glycero- L-galacto- nonulosonic acid. At least four immunoaccessible epitopes were recognized by different MAbs on the intact LPS. After O-deacetylation of LPS, the reactivity of one of the MAbs (MAb 3/1) was lost, indicating thus that the corresponding epitope is associated with the 8-O-acetyl group. Since the reactivity pattern of the MAb 3/1 is identical with those of the MAb 2 which was considered as a virulence marker for serogroup 1, this epitope may be involved in mediating virulence in L. pneumophila. Four MAbs specific to strains of serogroup 1 other than the monoclonal subtype Philadelphia recognized epitopes on the O-deacetylated LPS of strain Philadelphia 1 and, therefore, the virulence-associated epitope blocks recognition of the immunodeterminants that are accessible on the intact LPS of the strains lacking this epitope.

Analysis of Legionella pneumophila strains associated with nosocomial pneumonia in a neonatal intensive care unit

A premature child received continuous mechanical ventilation in a neonatal intensive care unit. On day 10 of his life he developed pneumonia due to Legionella pneumophila serogroup 1, monoclonal subtype Bellingham. The strain was cultured from a tracheal secretion taken on day 10 and detected by immunofluorescence using monoclonal antibodies on days 10, 12 and 17. Legionella pneumophila serogroups 1 and 6 (10(2)-4 x 10(4) cfu/l) were cultured from both central and peripheral hot water systems. Monoclonal antibody testing, macrorestriction analysis of the genomic DNA using pulse-field electrophoresis, and electrophoretic alloenzyme typing showed the isolate from the child to be identical to the serogroup 1 strains from the hot water system. Four unrelated Legionella strains of the same monoclonal subgroup Bellingham were studied for comparison. Legionellae were also isolated from two other incubators, but no clinical or microbiological indications of legionellosis were found in the neonates hospitalised there. Serogroup 1 strains isolated from the patient and from the hot water system and serogroup 6 isolates from the hot water supply were able to multiply in cultured Acanthamoeba castellanii cells and in guinea pigs. The serogroup 6 strain, although prevalent in the incubators, was not found in any of the clinical specimens by either culture of immunofluorescence.

Occurrence and distribution of Legionella species in composted plant materials

Legionellae were found in many samples of composted plant matter obtained from home gardeners and from facilities which undertook bulk composting. The predominant species isolated from these composts was Legionella pneumophila, the strains of which belonged to serogroups other than serogroup 1. Other Legionella species were present in many samples. Legionella longbeachae serogroup 1, which is implicated in human infections in South Australia, was present in samples obtained from two of six facilities composting large volumes of material and from 3 of 30 gardeners. Many of the species or strains isolated from composts have not been implicated as causative agents of legionellosis in South Austrailia, but some cause infection in healthy and immunosuppressed persons.

Fatal nosocomial Legionnaires' disease: relevance of contamination of hospital water supply by temperature-dependent buoyancy-driven flow from spur pipes

The investigation, epidemiology, and effectiveness of control procedures during an outbreak of Legionnaires' disease involving three immunosuppressed patients are described. The source of infection appeared to be a network of fire hydrant spurs connected directly to the incoming hospital mains water supply. Removal of these hydrants considerably reduced, but failed to eliminate, contamination of water storage facilities. As an emergency control procedure the incoming mains water was chlorinated continuously. Additional modifications to improve temperature regulation and reduce stagnation also failed to eliminate the legionellae. A perspex test-rig was constructed to model the pre-existing hospital water supply and storage system. This showed that through the hydraulic mechanism known as 'temperature buoyancy', contaminated water could be efficiently and quickly exchanged between a stagnant spur pipe and its mains supply. Contamination of hospital storage tanks from such sources has not previously been considered a risk factor for Legionnaires' disease. We recommend that hospital water storage tanks are supplied by a dedicated mains pipe without spurs.

Outbreak of Legionnaires' disease at University Hospital, Nottingham. Epidemiology, microbiology and control

Twelve patients in a large teaching hospital contracted Legionnaires' disease over a period of 11 months. The source was a domestic hot water system in one of the hospital blocks, which was run at a temperature of 43 degrees C. Five different subtypes of Legionella pneumophila serogroup 1 have been isolated from water in different parts of the hospital, over a period of time. Only one subtype, Benidorm RFLP 14, was implicated in disease. Circumstantial evidence suggested that the outbreak may have been due to recent colonization of the hot water system with a virulent strain of Legionella pneumophila. The outbreak was controlled by raising the hot water temperature to 60 degrees C, but careful surveillance uncovered two further cases in the following 30 months. Persistent low numbers of Legionella pneumophila were isolated from the domestic hot water of wards where Legionnaires' disease had been contracted, until an electrolytic unit was installed releasing silver and copper ions into this supply.

Legionella pneumophila in residential water supplies: environmental surveillance with clinical assessment for Legionnaires' disease

Although cases of community-acquired Legionnaires' disease have been epidemiologically linked to residential water supplies, the risk of acquiring Legionnaires' disease from exposure to Legionella pneumophila in residential water systems is uncertain. The residential water supplies of 218 members of the American Legion in six different geographical areas in Pittsburgh were cultured for L. pneumophila. Residents of the homes provided a recent medical history and a blood sample for detection of antibodies to legionella. A urine sample for legionella urinary antigen testing was also requested from individuals residing in legionella-positive homes and individuals with a positive antibody test. Six percent (14/218) of the homes yielded L. pneumophila (range within six areas 0-22%). Lower hot water tank temperature was significantly associated with legionella positivity (P less than 0.01). Analysis of water samples for mineral content showed no association between legionella positivity and concentrations of calcium and magnesium. Water samples from the area where 22% of the homes surveyed were positive for legionella had a higher iron content than water samples from the other areas tested. None of the individuals residing in legionella-positive homes showed elevated antibody titres to legionella or the presence of legionella antigen in urine. For the immunocompetent hosts, the risk of contracting Legionnaires' disease from exposure to contaminated household water supplies in the Pittsburgh area appears to be low.

Subtyping of Legionella pneumophila serogroup 1 strains isolated in Germany using monoclonal antibodies

Legionella pneumophila serogroup 1 (Lp1) strains isolated from patients and hot water supplies in different locations of Germany were subtyped using seven monoclonal antibodies (mabs) in the indirect immunofluorescence test (IFA) and in part, using a dot blot assay. Four of these mabs were produced in Dresden. Three mabs (mab 33G3, mab 32A12 and mab 144c2) were kindly supplied by J. Joly, Quebec, Canada. Altogether, seven antigenic variants were found among Lp1 strains isolated in Germany. Patient strains belonged to the Philadelphia, Benidorm, Knoxville, France, Olda-Heysham and Bellingham subgroups, whereas environmental isolates reacted like the Bellingham, Oxford, Philadelphia, Knoxville and France strains. The majority of patient strains (15 out of 26, 58%) reacted with our mab 3/1 (corresponding to mab 2 of the standard panel), but only 26 out of 118 environmental strains (22%) isolated from 4 of 15 hot water supplies did so (p less than 0.05). The majority of water-borne Lp1 strains reacted with a mab specific of the Bellingham subgroup. Three water systems under study were associated with human legionellosis. Two of them contained Bellingham-like strains, one Philadelphia-like legionellae.

Immunogold and fluorescein immunolabelling of Legionella pneumophila within an aquatic biofilm visualized by using episcopic differential interference contrast microscopy

Biofilms containing diverse microflora were developed in tap water on glass and polybutylene surfaces. Legionella pneumophila within the biofilms was labelled with monoclonal antibodies and visualized with immunogold or fluorescein isothiocyanate conjugates. Development of a differential interference contrast technique in an episcopic mode enabled simultaneous visualization of the total biofilm flora and gold-labelled legionellae. The legionellae occurred in microcolonies within the biofilm in the absence of amoebae, suggesting that the bacterial consortium was supplying sufficient nutrients to enable legionellae to grow extracellularly within the biofilm.

Transposon mutagenesis in Legionella pneumophila. II.--Mutants exhibiting impaired intracellular growth within cultured macrophages and reduced virulence in vivo

Transposon Tn5 mutants of L. pneumophila were isolated and screened for loss of virulence-associated characteristics. Three mutants were found with normal ability to produce putative pathogenicity determinants and to be endocytosed by guinea pig alveolar macrophages in vitro but with a greatly reduced ability to multiply within them. These mutants showed considerable loss of virulence in an authentic animal model of the pneumonia.

Legionellae isolated from clinical and environmental samples in Spain (1983-90): monoclonal typing of Legionella pneumophila serogroup 1 isolates

Legionella isolates recovered in 21 different Spanish provinces over 8 years from both clinical (67 isolates) and environmental (181) samples, mostly from case-associated buildings, are described; 92.5% of clinical isolates were L. pneumophila serogroup 1 (SG1), only five isolates belonging to other species or serogroups: two L. pneumophila SG6, two SG8 and one L. bozemanii SG1 not clearly related with clinical infection. L. pneumophila SG1 accounted for 53.6% of isolates from the environment, followed by SG8 (27.6%), SG3 (9.4%) and SG6 (7.2%). Three isolates were labelled as SG8/10. Subtyping of L. pneumophila SG1 by the standardized panel of monoclonal antibodies revealed 90.3% of clinical and 78.3% of environmental isolates as belonging to Pontiac subgroup. Pontiac isolates were further divided into 55.3% Philadelphia 1 or Allentown 1, 21.9% Benidorm 030E and 20.4% Knoxville 1. Characterization of samples from four outbreaks in which both clinical and environmental isolates had been recovered permitted the recognition of three Philadelphia 1 or Allentown 1 and one Knoxville 1 strains as the aetiological agents.

Differences in the respiratory burst of human polymorphonuclear leukocytes induced by virulent and avirulent Legionella pneumophila serogroup 1

Two strains of Legionella pneumophila of different virulence were examined for their influence on the metabolic oxidative activity of human polymorphonuclear leukocytes. The leukocytes exhibited decreased rates of oxygen consumption and diminished chemiluminescence activity following phagocytosis of a virulent strain of L. pneumophila serogroup 1. In contrast, phagocytosis of its multipassaged derivative rendered avirulent, was accompanied by increased rates of both oxygen consumption and chemiluminescence activity. Although no differences were observed in oxygen uptake induced by the virulent legionellae compared to leukocytes at rest, statistically significant differences were observed in the chemiluminescence responses. These observations were not unexpected, since the luminol-enhanced chemiluminescence assay, is more sensitive than the oxygen uptake assay. In spite of decreased metabolic activity of PMN in the presence of virulent legionellae, electron microscope studies showed higher numbers of intracellular L. pneumophila than the avirulent subtype. Thus, virulent and avirulent L. pneumophila can be differentiated on the basis of oxygen consumption and chemiluminescence assays.

Cefamandole-susceptible strains of Legionella pneumophila serogroup 1: implications for diagnosis and utility as an epidemiological marker

The standard selective Legionella medium that contains cefamandole failed to grow legionella pneumophila serogroup 1, subtype Bellingham, from a sputum sample from a patient with nosocomial Legionnaires' disease; the isolate did grow on a similar selective medium that substitutes vancomycin for cefamandole. Two Bellingham isolates from this patient's hospital environment also failed to grow when tested on the cefamandole medium. We tested 106 additional L. pneumophila serogroup 1 isolates that belonged to nine different monoclonal antibody subtypes and demonstrated that susceptibility to cefamandole was rare (10%) and limited to the Bellingham subtype. The diagnosis of Legionnaires' disease may be missed unless the culture protocol includes both a nonselective medium and a selective medium that does not contain cefamandole. In vitro susceptibility to cefamandole also provided an epidemiologic marker that linked a water source for a patient to nosocomial Legionnaires' disease.

Distribution of Legionella spp. in hydrothermal areas in continental Portugal and the island of São Miguel, Azores

Nineteen aquatic environment sites from three hydrothermal areas on continental Portugal and one area on the island of São Miguel, Azores, were examined for the recovery of Legionella spp. Physicochemical and bacteriological parameters were also determined for each site. Water temperatures varied between 22 and 67.5 degrees C, although the majority had temperatures above 40 degrees C; the pH varied between 5.5 and 9.2. The number of Legionella spp. recovered varied between 5.0 x 10(2) and 2.3 x 10(6) CFU/liter. A total of 288 isolates from 14 sites were identified by indirect immunofluorescence assay. The majority of the isolates belonged to Legionella pneumophila (74.3%), of which most belong to serogroup 1, but the relative proportion of L. pneumophila serogroups varied considerably. L. pneumophila serogroup 1 constituted 96.2% of the isolates in area 2 from central Portugal, but no isolates of this serogroup were recovered from São Miguel, where serogroup 6 strains were the predominant isolates. Ninety-six percent of the L. pneumophila serogroup 1 isolates belonged to monoclonal antibody subgroups OLDA and Bellingham. Other species identified were L. bozemanii serogroup 2, L. dumoffii, L. micdadei, L. moravica, L. oakridgensis, L. sainticrucis, and L. sainthelensi. Two undescribed species, which react by indirect immunofluorescence assay to antisera to "L. londoniensis" and "L. nautarum" and a group of isolates with strong cross-reaction to L. cincinnatiensis/L. sainticrucis/L. longbeachae by indirect immunofluorescence assay were also recovered. The latter were the only isolates recovered from area 3, in east central Portugal, over a period of 1 year.

An outbreak of Legionnaires' disease in Gloucester

Fourteen people living in or near the city of Gloucester fell ill with Legionnaires' disease caused by Legionella pneumophila serogroup (SG) 1 between 27 August and 27 October 1986. Another patient had fallen ill on 30 May. Nine of the 15 were diagnosed retrospectively during a case finding exercise. There were three deaths. Three cases of Pontiac fever were also diagnosed. The source was probably one or more wet cooling towers. Nineteen premises in the city with such towers were identified, and three just outside Gluocester. Samples from 11 of the 22 premises grew Legionella spp.; from nine of these L. pneumophila SG 1 (Pontiac) was isolated. The efficacy of regular addition of biocide in addition to hypochlorite added at the time of disinfection in inhibiting the growth of Legionella spp. was demonstrated. A survey of patients' movements during their likely incubation period showed that there was no single building that all patients had visited, but there were two areas of the city which nearly all had visited or passed through by car. A case-control study demonstrated an association with one of these areas. Cooling towers near both areas may have been sources but the evidence is insufficient to incriminate any single one. The unexpected finding of L. pneumophila SG 1 (Pontiac) in nine towers supports the hypothesis that there may have been multiple sources. Cooling towers may have been contaminated by mains water or by drift from other towers.

Legionella pneumophila serogroup 1 population in Italy by monoclonal subtyping

The Oxford panel of monoclonal antibodies was used to subtype 83 strains of Legionella pneumophila serogroup 1 of human and environmental origin. The International panel was also used to subtype 50 of them. All the 18 patients' isolates were of the Pontiac subgroup, and 40/43 of the environmental strains of the Pontiac subgroup were associated with human infection. The remaining environmental strains were subgroups Olda (15 strains), Camperdown (5 strains), and Bellingham (2 strains). The Philadelphia subgroup was the commonest among the environmental strains tested with the international MABs panel. This study confirms previous findings that L. pneumophila serogroup 1 isolates with the Pontiac (Oxford panel) or MAB-2 (international panel) reacting antigen marker seem to be more virulent than the other subgroups.

The Stafford outbreak of Legionnaires' disease

A large outbreak of Legionnaires' disease was associated with Stafford District General Hospital. A total of 68 confirmed cases was treated in hospital and 22 of these patients died. A further 35 patients, 14 of whom were treated at home, were suspected cases of Legionnaires' disease. All these patients had visited the hospital during April 1985. Epidemiological investigations demonstrated that there had been a high risk of acquiring the disease in the out patient department (OPD), but no risk in other parts of the hospital. The epidemic strain of Legionella pneumophila, serogroup 1, subgroup Pontiac 1a was isolated from the cooling water system of one of the air conditioning plants. This plant served several departments of the hospital including the OPD. The water in the cooling tower and a chiller unit which cooled the air entering the OPD were contaminated with legionellae. Bacteriological and engineering investigations showed how the chiller unit could have been contaminated and how an aerosol containing legionellae could have been generated in the U-trap below the chiller unit. These results, together with the epidemiological evidence, suggest that the chiller unit was most likely to have been the major source of the outbreak. Nearly one third of hospital staff had legionella antibodies. These staff were likely to have worked in areas of the hospital ventilated by the contaminated air conditioning plant, but not necessarily the OPD. There was evidence that a small proportion of these staff had a mild legionellosis and that these 'influenza-like' illnesses had been spread over a 5-month period. A possible explanation of this finding is that small amounts of aerosol from cooling tower sources could have entered the air-intake and been distributed throughout the areas of the hospital served by this ventilation system. Legionellae, subsequently found to be of the epidemic strain, had been found in the cooling tower pond in November 1984 and thus it is possible that staff were exposed to low doses of contaminated aerosol over several months. Control measures are described, but it was later apparent that the outbreak had ended before these interventions were introduced. The investigations revealed faults in the design of the ventilation system.

Legionnaires' disease and the sick-building syndrome

In October 1985, six cases of legionnaires' disease were associated with a police headquarters building. Four were amongst staff who worked in or visited the communications wing of the headquarters and two cases occurred in the local community. A case-control study implicated the operations room of the communications wing as the main area associated with infection. This wing was air-conditioned and smoke tracer studies showed that drift from the exhaust as well as from the base of the cooling tower entered the main air-intake which serviced the air-conditioning system. Legionella pneumophila serogroup 1 subgroup pontiac was isolated from water and sludge in the cooling tower pond. Contaminated drift from the top of the cooling tower was probably responsible for the two community cases. An additional discovery was that symptoms suggestive of the sick-building syndrome were associated with working in this wing.

Antigenic and genetic variation in Legionella pneumophila serogroup 6

Legionella pneumophila subsp. pneumophila serogroup 6 is second in importance only to L. pneumophila serogroup 1 as a cause of legionellosis. Monoclonal antibody (MAb) reactivity and multilocus enzyme electrophoretic analyses were used to subtype serogroup 6 isolates as a potential aid for epidemiologic and virulence studies. Forty-eight serogroup 6 isolates submitted to the Centers for Disease Control from 1980 to 1985 were examined by these methods. The isolates were divided into two groups based on differential reactivity with two MAbs. Thirty-two of the isolates were of a single electrophoretic type (ET) and were reactive with both MAbs. The remaining 16 isolates were distributed among 10 ETs and were reactive with one or both MAbs. The mean genetic diversity for serogroup 6, as determined from the degree of variability at 20 enzyme loci, was found to be essentially the same as that for L. pneumophila subsp. pneumophila as a whole. The ETs of serogroup 6 isolates were unique but closely related genetically to the ETs of L. pneumophila subsp. pneumophila serogroups 1 to 5, 7, and 8. The range of serogroup 6 subtypes distinguished by MAbs and enzyme electrophoresis suggests that the combination of these two methods can be useful as a typing system.

Taxonomic investigation of Legionella pneumophila using monoclonal antibodies

A panel of 19 monoclonal antibodies was used to produce patterns of immunofluorescent staining of 468 isolates of Legionella pneumophila. Twelve monoclonal antibodies were selected that divided L. pneumophila into 17 phenons which, in the majority of cases, conform to serogroup divisions. These phenons are more easily defined than the present serogroups, and isolates can be placed in them with little ambiguity. The standardized set of monoclonal antibodies was also used to define the subgroups of serogroup 1.

Legionella pneumophila in a hospital in Torino, Italy. A retrospective one-year study

Legionella pneumophila serogroup 1 was isolated from post mortem specimens from 13 out of 58 patients with pneumonia diagnosed at autopsy. The results of a study undertaken in the hospital environment showed that the water plumbing system was colonized with L. pneumophila serogroup 1 which could also be isolated from respiratory devices filled with tap water. Control measures instituted are described.

Differences in aerosol survival between pathogenic and non-pathogenic strains of Legionella pneumophila serogroup 1

A strain of Legionella pneumophila serogroup 1 known to be virulent for guinea-pigs was found to be least stable at a relative humidity (r.h.) of 60% when stored as a small particle aerosol. Three L. pneumophila serogroup 1 strains of different virulence for guinea-pigs were then tested at a r.h. of 60% at 20 degrees C. The most virulent strain was found to have the best survival and the avirulent strain was least stable. The strain of intermediate virulence did not survive as well as the virulent strain but was more stable than the avirulent strain. Strains of L. pneumophila serogroup epidemiologically associated with legionnaires' disease had better survival in small particle aerosols than strains which were not associated with disease. Subtyping with monoclonal antibodies also showed that the type more commonly associated with disease survived longer in aerosols than the other subtypes.

Nosocomial Legionnaires' disease--advances in diagnosis and typing

The impact of new methodologies on the routine diagnosis of legionella pneumonia has been limited but the potential for advance is considerable. Antigen detection immunoassays have not yet reached the stage where they are used in routine practice. Monoclonal antibodies have been successfully used for direct fluorescence of bronchial aspirates. Nucleic acid hybridization techniques have yet to find a role in diagnosis. Serology remains the most commonly used method in the diagnosis of Legionnaires' disease. Methods of typing Legionella pneumophila include monoclonal antibodies and isoenzyme, plasmid and nucleic acid analysis. Biotyping methods have not been found to be of value. The use of monoclonal antibodies has permitted the comparison of clinical and environmental isolates and allowed the separation of serogroup 1 into subgroups of differing virulence. The subgroup of serogroup 1 called Pontiac is responsible for the majority of sporadic and epidemic legionella pneumonia in the UK. An internationally accepted panel of monoclonal antibodies is used to define these strains. The extent to which other subgroups of serogroup 1 and other serogroups of L. pneumophila cause disease appear to reflect their environmental prevalence.

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.

Influence of growth temperature on virulence of Legionella pneumophila

The effect of growth temperature on the virulence of a strain of broth-grown serogroup 1 Legionella pneumophila (Wadsworth F889) was examined by growing the bacterium at different temperatures and then infecting guinea pigs (by intratracheal injection) and guinea pig alveolar macrophages. The 50% lethal dose for guinea pigs infected with 25 degrees C-grown F889 was log10 5.0 CFU and that for 41 degrees C-grown F889 was log10 5.7 CFU, or a fivefold difference. Guinea pig alveolar macrophages were infected in quadruplicate with log10 3.8 CFU of F889 cells grown at either 25 or 41 degrees C. Counts of F889 in the alveolar macrophages infected with 25 degrees C-grown bacteria were 40% greater after 1 day of incubation (P = 2 X 10(-4)) than were counts in the alveolar macrophage suspensions inoculated with 41 degrees C-grown bacteria. However, the counts were not significantly different after 3 days of incubation. Examination of cover slip cultures of guinea pig alveolar macrophages infected with 25 degrees C-grown or 41 degrees C-grown bacteria showed that the bacteria grown at the lower temperature were twice as likely to be macrophage-associated after 1 h of incubation than were the bacteria grown at the higher temperature. Growth at the lower temperature was also associated with a change in reactivity with monoclonal antibodies, but not with a change in plasmid content. Thus, environmental temperature may play an important role in modulating the virulence of L. pneumophila, possibly by affecting bacterial adherence to host cells.

Legionella pneumophila: monoclonal antibody typing of clinical and environmental isolates

Forty-one clinical isolates of Legionella pneumophila from sporadic cases of legionella pneumonia were collected from laboratories throughout the United Kingdom and were compared with 300 routine environmental isolates using two panels of monoclonal antibodies, covering serogroups 1-10. Eighty-five per cent of the clinical isolates belonged to the subgroup Pontiac of serogroup 1, whilst only 13% of the environmental isolates did. Approximately half of the clinical isolates tested came from patients with a recent history of foreign travel, mainly to southern Europe.

Widespread Legionella pneumophila contamination of dental stations in a dental school without apparent human infection

Following isolation of Legionella pneumophila from a special dental station water circuit, used primarily to cool high-speed dental drills which produce fine aerosols, a case finding and environmental survey was undertaken. Widespread colonization of the dental stations was found and the results suggested that amplification of the background levels of L. pneumophila was taking place within the stations. However there was no evidence for transmission causing human infection.

Nosocomial legionellosis associated with use of oxygen bubble humidifiers and underwater chest drains

In 1 year 12 of 48 patients who developed fatal pneumonia following admission with non-respiratory disorders to the Hospital Molinette, Torino, yielded Legionella pneumophila serogroup 1 from lung at autopsy. Patients were hospitalized on seven different wards for different conditions; only two of the wards had air conditioning but legionellas were not isolated from these. All patients were in poor health or immunocompromised. Some patients had inhaled humidified oxygen from piped supplies and three had undergone surgery. Legionella pneumophila serogroup 1 was detected in the water of oxygen bubble humidifiers and an underwater chest drain. The contaminated devices had been filled with tap or distilled water and the hospital water supply was found to be contaminated with L. pneumophila serogroup 1. Our findings suggest that filling bubble humidifiers or underwater chest drains with tap water is a potential hazard and should be avoided.

Legionella pneumophila in a hospital water system following a nosocomial outbreak: prevalence, monoclonal antibody subgrouping and effect of control measures

Swabs and water samples from a hospital water system were cultured for legionellae over an extended period. Legionella pneumophila serogroup 1, including outbreak associated strains, were isolated in small numbers from approximately 5% of these samples despite implementation of the current DHSS/Welsh Office regulations. No cases of nosocomial legionnaires' disease were proven during the study. Physical cleaning and chemical sterilization of taps, and replacement of washers with 'approved' brands did not eradicate the organisms. Eradication of legionellae in hospital water supplies appears to be unnecessary in preventing nosocomial legionnaires' disease provided the current DHSS/Welsh Office recommendations are implemented.

Heterogeneity of antibody response in infection with Legionella pneumophila serogroup 1

The antibody response of patients infected with Legionella pneumophila serogroup 1 in a common source outbreak was investigated. Heat-killed antigens from L pneumophila serogroups 1-3 and 6-10, plus several other strains of L pneumophila, together with 13 other species of legionellas were used in an indirect fluorescence antibody test. Formolised yolk sac antigens made from L pneumophila serogroups 1, 6, and 7 were also used. Although antibodies were produced to several L pneumophila serogroups or Legionella species by individuals, there was no constant pattern, suggesting that the response is a characteristic of the infected individual and not of the infecting strain of Legionella. There is evidence that heat-killed antigen made from L pneumophila serogroup 7 may give unreliable results.

Immunohistological detection of Legionella pneumophila in lung sections

Immunohistology was used for the detection of Legionella pneumophila serogroup I in necropsy tissue. Study of pneumonic lung from the recent Stafford outbreak has shown that this technique has a high sensitivity. A retrospective postmortem examination showed that L pneumophila serogroup 1 was an unusual cause of pneumonia in Oxfordshire during the study period. L pneumophila serogroup 1 can be successfully subgrouped, using a panel of monoclonal antibodies on formalin fixed paraffin embedded sections. Immunohistological methods have a potentially useful role in the diagnosis of Legionellosis at postmortem examination and in the epidemiological investigation of individual cases and outbreaks.