Baja mortalidad en un brote de enfermedad del legionario: correlación con el estudio de citopatogenicidad / Low mortality rate in an outbreak of Legionnaires’ disease: Correlation with the cytopathogenity study

Fundamento y objetivo: En el año 2001 tuvo lugar en Murcia un brote de enfermedad del legionario (EL) con una de las tasas de mortalidad más bajas conocidas. Los objetivos de este estudio fueron describir la presentación clínica y los resultados de los estudios molecular y de virulencia de los aislamientos clínicos de Legionella para correlacionar la baja mortalidad de la serie con la virulencia de la cepa. Pacientes y método: Estudio prospectivo y descriptivo de un brote de EL en un subgrupo de 86 pacientes. Se analizan datos demográficos, factores de riesgo y evolución clínica. Se ha practicado subtipificación molecular mediante electroforesis en campo pulsátil y estudio de citopatogenicidad de los aislamientos clínicos y se han comparado con los de aislamientos procedentes de otros brotes. Resultados: La edad media fue de 58,2 años, con predominio del sexo masculino (77,9%). El tabaquismo fue el factor de riesgo más frecuente (71,7%). El 70,2% de los pacientes presentaba enfermedades de base. Las manifestaciones clínicas, los datos de laboratorio y la radiología fueron compatibles con un cuadro de neumonía atípica. La mortalidad fue del 3,2%. Todos los aislamientos clínicos de Legionella pneumophila mostraron el mismo subtipo molecular. En el estudio de citopatogenicidad, las cepas de Legionella procedentes del brote se incluyeron dentro del grupo de menor virulencia. Conclusiones: En este subgrupo de pacientes predominaron el sexo masculino, el tabaquismo, la presentación clínica compatible con neumonía atípica y la baja mortalidad. La baja virulencia de este genotipo molecular de L. pneumophila podría ser causante, en parte, de la baja mortalidad observada en el brote de Murcia (AU)

Background: In 2001 an outbreak of Legionnaires’ diseases occurred in Murcia, Spain, with one of the lowest known rates of associated mortality. We describe the clinical data of a subgroup of patients, and present the results from molecular and virulence studies to correlate the lower mortality of the overall series with the strain virulence. Patients and methods: A subgroup of 86 patients from the outbreak of Legionnaires’disease was prospectively included. Demographic, risk factors and clinical evolution data were obtained. Moreover, we performed a pulsed field gel electrophoresis and cytopathogenicity assay of the Murcia outbreak that were compared with other unrelated Legionella isolates. Results: Sixty-nine (77.9%) patients were males. The mean age of the patients was 58.2 years (range: 32–87). Smoking was the most frequent risk factor in 62 patients (71.7%) and 61 patients (70.2%) had underlying diseases. Clinical, laboratory and radiological manifestations were compatible with the atypical pneumonia syndrome. The mortality rate was 3.2%. All the clinical L. pneumophila isolates analyzed by PFGE showed the same subtype. When analyzing theses strains together with other Legionella strains, they were included in the group with lower virulence in the cytopathogenicity study. Conclusions: The most outstanding data in this subgroup of patients were: male-sex, smoking, atypical clinical manifestations and low mortality. The low virulence of this molecular genotype of L. pneumophila may be responsible, in part, for the low mortality observed in the outbreak in Murcia (AU)

Legionnaires' disease: evaluation of a quantitative microbial risk assessment model.

BACKGROUND: The quantities of Legionella vary considerably from natural waters to water in contaminated domestic hot water supplies, whirlpool spas and cooling towers, with the risk for LD rising as the Legionella counts grow. We currently report the results from our Quantitative Microbial Risk Assessment (QMRA) model evaluation. We developed the LD QMRA model to better understand Legionella exposure risks. METHODS: Using an animal data derived model for LD, we calculated risks from estimated exposures for a whirlpool spa outbreak, two hot spring spa outbreaks and compared the results to the reported LD risks. RESULTS: The QMRA model shows agreement (generally less than an order of magnitude discrepancy) with the reported Legionnaires' disease sub-clinical severity infection, clinical severity infection, and mortality risks. CONCLUSIONS: The LD QMRA model may lead to risk based limits to supplement the current guidance on Legionella control in cooling towers, whirlpool spas and other potential exposure sources. The verification of QMRA for LD also suggests the techniques, given suitable animal model data, may be useful in quantifying human response to other airborne pathogens.

[Pathogenesis, diagnosis and therapy of Legionella infections]. / Pathogenese, Diagnostik und Therapie der Legionella-Infektion.

Legionella species are ubiquitous in aquatic environments. About 50 years ago they entered the engineered (technical) environment, i.e. warm water systems with zones of stagnation. Since that time they represent a hygienic problem. After transmission to humans via aerosols legionellae might cause Legionella pneumonia (legionnaires' disease) or influenza-like respiratory infections (Pontiac fever). Epidemiological data suggest that Legionella strains might differ substantially in their virulence properties. Although the molecular basis is not understood L. pneumophila serogroup 1 especially MAb 3/1-positive strains cause the majority of infections. The main virulence feature is the ability to multiply intracellularly. After uptake into macrophages legionellae multiply in a specialized vacuole and finally lyse their host cells. Several bacterial factors like surface components, secretion systems and iron uptake systems are involved in this process. Since the clinical picture of Legionella pneumonia does not allow differentiation from pneumoniae caused by other pathogens, microbiological diagnostic methods are needed to establish the diagnosis. Cultivation of legionellae from clinical specimens, detection of antigens and DNA in patients' samples and detection of antibodies in serum samples are suitable methods. However, none of the diagnostic tests presently available offers the desired quality with respect to sensitivity and specificity. Therefore, the standard technique is to use several diagnostic tests in parallel. Advantages and disadvantages of the diagnostic procedures are discussed. Therapeutic options for Legionella infections are newer macrolides like azithromycin and chinolones (ciprofloxacin, levofloxacin and moxifloxacin).

Outbreak of Legionnaires' disease on a cruise ship linked to spa-bath filter stones contaminated with Legionella pneumophila serogroup 5.

In January 2003, two cases of Legionnaires' disease associated with a ship's cruise were registered in the database of National Epidemiological Surveillance of Infectious Diseases. A 70-year-old male heavy smoker with mild emphysema contracted the disease during a cruise. Legionella pneumophila serogroup (sg) 5 was isolated from the patient's sputum and the ship's indoor spa. The isolate from the spa matched the patient's isolate by genotyping performed by pulsed-field gel electrophoresis (PFGE). The second case was in a 73-year-old female. During epidemiological investigation, a third case of Legionnaire's disease in a 71-year-old male was subsequently diagnosed among passengers on the same ship on the following cruise. Environmental investigation revealed that porous natural stones (Maifanshi) in the filters of the spas had harboured L. pneumophila, a phenomenon which has not been reported except in Japan. This is the first documented evidence of L. pneumophila sg 5 infection on a ship and of porous stones as a source of Legionella infection.

A nosocomial outbreak of Legionella pneumophila caused by contaminated transesophageal echocardiography probes.

A case-control study of three cases of Legionella pneumophila pneumonia identified transesophageal echocardiography (TEE) as a risk factor. Patient isolates and environmental strains from water used for rinsing TEE probes were identical by pulsed-field gel electrophoresis. This is the first report of endoscopy as a potential source of legionellosis.

Legionella pneumophila feoAB promotes ferrous iron uptake and intracellular infection.

In order to determine the role of ferrous iron transport in Legionella pathogenesis, we identified and mutated the feoB gene in virulent Legionella pneumophila strain 130b. As it is in Escherichia coli, the L. pneumophila feoB gene was contained within a putative feoAB operon. L. pneumophila feoB insertion mutants exhibited decreased ferrous but not ferric iron uptake compared to the wild type. Growth on standard buffered charcoal yeast extract agar or buffered yeast extract broth was unaffected by the loss of L. pneumophila FeoB. However, the L. pneumophila feoB mutant had a reduced ability to grow on buffered charcoal yeast extract agar with a reduced amount of its usual iron supplementation, a phenotype that could be complemented by the addition of feoB in trans. In unsupplemented buffered yeast extract broth, the feoB mutant also had a growth defect, which was further exacerbated by the addition of the ferrous iron chelator, 2,2'-dipyridyl. The feoB mutant was also 2.5 logs more resistant to streptonigrin than wild-type 130b, confirming its decreased ability to acquire iron during extracellular growth. Decreased replication of the feoB mutant was noted within iron-depleted Hartmannella vermiformis amoebae and human U937 cell macrophages. The reduced intracellular infectivity of the feoB mutant was complemented by the introduction of a plasmid containing feoAB. The L. pneumophila feoB gene conferred a modest growth advantage for the wild type over the mutant in a competition assay within the lungs of A/J mice. Taken together, these results indicate that L. pneumophila FeoB is a ferrous iron transporter that is important for extracellular and intracellular growth, especially in iron-limited environments. These data represent the first evidence for the importance of ferrous iron transport for intracellular replication by a human pathogen.

Disinfection kinetics of Legionella pneumophila by ultraviolet irradiation.

Disinfection kinetics of Legionella pneumophila by ultraviolet irradiation was investigated. The change in viable cell concentration with exposure time could be divided into three steps: lag step in which little change in viable cell concentration was observed, fast disinfection step and slow disinfection step. The slow disinfection step was not observed at the initial cell concentrations below about 10(6) cfu/mL. The disinfection kinetics were well described with two parameters; lag time and disinfection rate constant of the fast disinfection step. The effects of UV intensity, temperature and initial cell concentration in the kinetic parameters were investigated. With increasing initial cell concentration, the lag time decreased and the disinfection rate constant increased. The effects of initial cell concentration on the kinetic parameters were considered to be attributed to the decrease in the effective UV irradiation intensity due to the partial shield of UV light by the disinfected cells. The empirical correlations were presented for predicting the lag time and disinfection rate constant. Furthermore, UV disinfection of L. pneuophila in a model hot-tub connected with external irradiation chamber was also discussed.