Nosocomial Legionnaires Research Articles

Nosocomial legionnaires' disease: Aspiration as a primary mode of disease acquisition

purpose: Nosocomial Legionnaires' disease remains a significant problem with many unresolved questions regarding transmission of legionella organisms to patients. We performed a case-control and environmental study to identify risk factors and modes of transmission of Legionella infection during an outbreak of nosocomial Legionnaires' disease in a military medical center. patients and methods: During the calendar year 1989, 14 cases of nosocomial Legionnaires' disease were identified by active surveillance following the discovery of 2 culture-proven cases among organ transplant recipients. Four control patients were matched to each case by age, sex, and date of admission. Cases and controls were compared with respect to past medical history and hospital exposure variables. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for matched variables. Environmental culturing of air and water supplies in and around the medical center was also performed. results: The case-control study revealed the following significant risk factors for the acquisition of nosocomial Legionnaires' disease: immunosuppressive therapy (OR = 32.7, CI = 4.5 to 302.6), nasogastric tube use (OR = 18.4, CI = 2.6 to 166.2), bedbathing (OR = 10.7, CI = 2.2 to 59.0), and antibiotic therapy (OR = 14.6, CI = 2.9 to 84.4). Shower use (OR = 0.1, CI = 0 to 0.4) appeared to be a negative risk factor. Water cultures revealed Legionella pneumophila serogroup 1, monoclonal antibody subtype Philadelphia (identical to all patient isolates) in the ground-water supply to the hospital, 1 hotwater tank, and 15% of 85 potable water sites tested. Air sampling of cooling towers, hospital air intakes, and medical air and oxygen supplies were negative for Legionella organisms. conclusions: This study confirms the importance of potable water in transmitting nosocomial Legionnaires' disease and suggests that the organism gains access to the hospital via external water supplies. The risk factors identified in this case-control study provide evidence that Legionnaires' disease may act as a superinfection in a nosocomial setting and is likely acquired by aspiration, similar to other nosocomial pneumonias.

Each water outlet is a unique ecological niche for Legionella pneumophila.

We determined the natural history of the colonization of our hospital's potable water by culturing water approximately biweekly from 20 sites throughout the hospital for 4 years. Overall, 545 (24.7%) of the 2200 samples grew Legionella pneumophila. During hyperchlorination, 11.7% of the samples were positive while 41.6% were positive in the absence of chlorination. There was no seasonal trend towards positivity, but there was marked inter-site variation in the semi-quantitative culture results. However, a single strain of legionella (as defined by plasmid profiling) tended to persist at a site. Such a site was a unique ecological niche in that different sites in the same wing were populated by distinct strains. The two wings of our hospital had a significantly different distribution of strains of legionella-plasmid profile type III predominated in the Victoria Wing while types II and VI predominated in Centennial Wing. Twenty-four of our 28 cases of nosocomial Legionnaires' disease occurred in the Centennial Wing. Three of the four cases in the Victoria Wing were caused by plasmid profile type III while 18 of the 24 isolates from patients who acquired their infection in the Centennial Wing were type II. We conclude that each water outlet serves as its own ecological niche of L. pneumophila.

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.

Control of endemic nosocomial Legionnaires' disease by using sterile potable water for high risk patients

In a setting where potable water is contaminated with Legionella pneumophila serogroup 1, we performed two case control studies. The first case control study consisted of 17 cases of nosocomial Legionnaires' disease (LD) and 33 control (the patients who were admitted to the ward where the case was admitted immediately before and after the case) subjects. Cases had a higher mortality rate 65% vs 12% (P less than 0.004); were more likely to have received assisted ventilation (P less than 0.00001); to have nasogastric tubes (P less than 0.0004) and to be receiving corticosteroids or other immunosuppressive therapy (P less than 0.0001). Based on the results of this study, sterile water was used to flush nasogastric tubes and to dilute nasogastric feeds. Only 3 cases of nosocomial LD occurred during the next year compared with 12 the previous year (P less than 0.0001). Nine cases subsequently occurred and formed the basis for the second case-control study. Eighteen control subjects were those patients admitted to the same unit where the case developed LD, immediately before and after the case. The mortality rate for the cases was 89% vs 6% for controls (P less than 0.00003). The only other significant difference was that cases were more likely to be receiving corticosteroids or other immunosuppressive therapy 89% vs 39% (less than 0.01). We hypothesized that microaspiration of contaminated potable water by immunocompromised patients was a risk factor for nosocomial Legionnaires' disease. From 17 March 1989 onwards such patients were given only sterile potable water. Only two cases of nosocomial LD occurred from June 1989 to September 1990 and both occurred on units where the sterile water policy was not in effect. We conclude that aspiration of contaminated potable water is a possible route for acquisition of nosocomial LD in our hospital and that provision of sterile potable water to high risk patients (those who are receiving corticosteroids or other immunosuppressive drugs; organ transplant recipients or hospitalized in an intensive care unit) should be mandatory.

Radiographic appearance of nosocomial legionnaires' disease after erythromycin treatment.

Radiographic features of 71 patients (48 men, 23 women) with nosocomial Legionella pneumophila pneumonia were assessed and compared with those of other nosocomial series of L pneumophila pneumonia. Sixteen patients were assessed retrospectively and 55 prospectively. Chest radiographs were assessed at the onset of the illness, 10 days later, and at 3 months. Erythromycin was given to 67 patients at the time of the diagnosis and to the remaining four at a later stage. Forty eight patients were over the age of 60. On the initial chest radiograph 53 of the 71 patients had unilateral shadowing (23 of them in the right lung); 35 had unilobar shadowing and the remaining 36 had more than one affected lobe. Pleural effusion was present in 24 cases and cavitation in 2. One patient had evidence of a pericardial effusion. At 10 days 21 patients had evidence of radiographic progression (14 ipsilateral), but 28 had improved. At 3 months 36 patients had an abnormal radiograph, 30 showing residual scarring, 15 loss of volume, six pleural shadows and two cavitation. Our series shows a lesser incidence of unilateral shadowing and pleural effusion than other nosocomial series and a lesser tendency to progression, but more patients had radiographic abnormalities at long term follow up.

Nosocomial Legionnaires’ Disease: Clinical and Radiographic Patterns

From 1981 to 1991, 55 patients (33 males, 22 females, mean age 58.6 years) with nosocomial Legionnaires' disease were studied. The mortality rate was 64%. One-half of the patients developed nosocomial Legionnaires' disease within three weeks of admission. A surprising clinical feature was the low rate of findings of consolidation on physical examination, despite the fact that 52% of patients had this finding on chest radiograph. More than one-half of patients had pre-existing lung disease, rendering a radiographic diagnosis of pneumonia due to Legionella pneumophila impossible in 16% of cases despite microbiological confirmation. Nineteen per cent of patients who had blood cultures done had a pathogen other than L pneumophila isolated, suggesting dual infection in at least some of the patients. When the clinical and radiographic findings were combined it was noted that 40% of patients had one of three patterns suggestive of nosocomial Legionnaires' disease: rapidly progressive pneumonia, lobar opacity and multiple peripheral opacities. However, in 60% of patients there were no distinctive features.

An outbreak of nosocomial Legionnaires' disease in a renal transplant unit in São Paulo, Brazil

From June 1989 to March 1990 there were eight cases of Legionnaires' disease caused by Legionella pneumophila serogroup 1 in a renal transplant unit. There were seven cases of pneumonia and one case of pleural effusion. A study was conducted to identify the source of the outbreak. Legionella anisa was cultured from tap water. Twenty-seven staff members of the unit were serologically tested and antibody titres were positive in two. The probable source of infection was the potable water system. Control measures were hyperchlorination and heating of the water, after which there were no further cases during 5 months' follow up. We believe this is the first reported Legionnaires' disease outbreak in Latin America.

Nosocomial legionnaires' disease: Lessons from a four-year prospective study

We studied all cases of nosocomial pneumonia at our 800-bed tertiary care hospital from September 1983 to September 1987. Of the 813 cases of nosocomial pneumonia, 31 (3.8%) were definite (isolation of organism or fourfold rise in titer) and 21 (2.5%) were possible cases (single or stable antibody titer of ⩾ 1:256) of legionnaires' disease. The definite cases involved a more severe form of pneumonia and a significantly higher mortality rate—64% versus 14% ( p < 0.0009) compared with the possible cases. Despite attempted comprehensive surveillance, only four (13%) of the definite cases of legionnaires' disease were found that would not have been diagnosed if the study were not ongoing. The yield from adequate (4- to 6-week convalescent serum samples) serologic testing was 5%, whereas the yield from sputum culture was 11%. We conclude that targeted surveillance of immunosuppressed patients with nosocomial pneumonia by culture of respiratory tract secretions for Legionella pneumophila is adequate for monitoring for the presence of legionnaires' disease in a hospital.

Control of Nosocomial Legionnaires' Disease through Hot Water Flushing and Supplemental Chlorination of Potable Water

Control of Nosocomial Legionnaires' Disease through Hot Water Flushing and Supplemental Chlorination of Potable Water

Nosocomial legionnaires disease in a children's hospital

Between August 1982 and December 1985, seven patients at a children's hospital developed hospital-acquired pneumonia caused by Legionella pneumophila. Demographic data included the following: mean age 12.3 years (range 9 months to 20.5 years); male/female ratio 5:2; all patients were white. Some previously identified risk factors present in our patients included high-dose corticosteroid therapy (five patients), other immunosuppressive therapy (four), and chronic lung (five) or kidney (three) disease. Symptoms and signs included rapid onset, fever, cough, pleuritic chest pain, dyspnea, abdominal pain, diarrhea, and headache. Rhinitis, myalgia, and neurologic abnormalities were not noted. Chest roentgenograms revealed single-lobe consolidation in three patients, diffuse bilateral alveolar infiltrates in three, and pleural effusion in three. All patients were treated with erythromycin; three patients also received rifampin. Tracheal intubation and mechanical ventilation were required by four patients. Six patients improved after therapy. One child died of persistent lung disease 1 month after the onset of legionnaires disease. L. pneumophila was isolated from potable water in the hospital. Aerosol equipment cleansed with tap water and the showers were implicated as means of exposure by patients to contaminated potable water. No new nosocomial cases were seen after immunocompromised children were prohibited from taking showers, and sterile water was used to cleanse equipment for administering aerosol medications.

Nosocomial legionnaires' disease (LD): Ten years' experience and report of an outbreak among surgical patients

Nosocomial legionnaires' disease (LD): Ten years' experience and report of an outbreak among surgical patients

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.

Nosocomial Legionnaires' disease: a global perspective

Nosocomial Legionnaires' disease is a worldwide problem. The lack of prospective surveys using sensitive diagnostic means, such as culture, has resulted in ignorance about the exact magnitude of the problem except at a handful of individual hospitals. Contaminated hospital hot water systems, cooling towers, and non-sterile tap water used for respiratory therapy may all cause disease. Culture diagnosis is the preferred method of case ascertainment, and provides bacterial isolates which can be used to implicate specific environmental sites using molecular epidemiologic techniques. Environmental culture surveys, done in the absence of known disease, are probably not indicated, but there remains concern that wards housing very high risk patients should be legionella-free. Use of monoclonal antibody typing of environmental isolates of L. pneumophila serogroup 1 may be useful in this regard, as it can possibly detect strains most likely to cause disease. Control of nosocomial disease requires centralized management and consultation by expert engineers, epidemiologists, and microbiologists.

Routine Culturing for Legionella in the Hospital Environment May Be a Good Idea: A Three-Hospital Prospective Study

The source for nosocomial Legionnaires’ disease is the water distribution system. However, the implications for legionella contamination in a hospital without known Legionnaires’ disease is unclear. Therefore, culturing for Legionella pneumophila in the environment has not been routinely recommended. The authors conducted a prospective pneumonia study in three hospitals, none of which was known to have a major problem with endemic legionellosis. The water system of Hospital 1 was colonized with L. pneumophila, serogroup 1; Hospital 2 was colonized by L. pneumophila, serogroup 5 (which is rarely associated with disease); Hospital 3 was essentially free of L. pneumophila. Sputum culture on selective legionella media, direct fluorescent antibody testing, and serology were performed for all nosocomial pneumonias regardless of clinical impression. At the end of the study the incidence of nosocomial legionnaires’ disease was found to be 9%, 0%, and 0% in Hospitals 1,2, and 3, respectively. In Hospital 1, monoclonal antibody subtyping confirmed that the patient isolates were identical to the environmental isolates. The authors conclude that environmental culturing, despite the absence of known Legionnaires’ disease, is useful. Positive cultures from the hospital water supply would mandate the introduction of legionella testing into the laboratory and stimulate physicians to consider Legionnaires’ disease when encountering nosocomial pneumonias.

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.

Nosocomial outbreak of Legionnaires' disease: molecular epidemiology and disease control measures.

Molecular laboratory techniques were used to study the epidemiology of an outbreak of nosocomial Legionnaires' disease. All patient isolates were Legionella pneumophila serogroup 1 and showed identical plasmid profiles and reactions with serogroup-specific monoclonal antibodies. L pneumophila was also cultured from four of five cooling tower water samples; however, the isolate from only one tower was serogroup 1 of the same subtype as patient isolates. Since the cases were temporally clustered and epidemiologically associated with exposure to cooling tower aerosols, the single cooling tower implicated by molecular analysis was the most likely source of the outbreak. Chlorination of cooling tower ponds has eradicated the epidemic strain. Since potable water also harbored the infecting organism and was the probable source for cooling tower contamination, decontamination of the hospital water system was also undertaken. Superchlorination of hot water holding tanks to 17 ppm on a weekly basis has effectively eradicated L pneumophila from the potable water system and appears to be a reasonable, simple, and relatively inexpensive alternative to previously described methods of control.

Are health care workers at risk for infection during an outbreak of nosocomial Legionnaires' disease?

We studied data from 500 health care workers to answer the question: Are health care workers at risk for infection during an outbreak of nosocomial Legionnaires' disease? These workers were employed at a hospital where eight cases of nosocomial Legionella pneumophila serogroup 1 pneumonia occurred over a 4-week period. The source was potable water. Acute-phase blood samples were collected on the day the water supply was decontaminated, convalescent samples were collected 4 to 6 weeks later from 373 subjects, and a single serum sample was obtained from an additional 127 subjects. Antibody titers to L. pneumophila were determined by an indirect immunofluorescent antibody (IFA) technique and by a microagglutination assay with the epidemic strain as the test antigen. Subjects who had an IFA titer of ⩾ 1:256 were retested with an anti-human IgM conjugate. None of the 373 health care workers had a fourfold rise in antibody titer. The geometric mean antibody titer of 73.8 for the 500 health care workers was significantly higher than that of 68.1 for 976 blood donors (p < 0.01). Only 2.4% had recent infection as evidenced by a microagglutination test, despite the fact that 84% were susceptible. We conclude that in the setting of a short-term outbreak of Legionnaires' disease caused by contaminated potable water the risk of infection among health care workers is low: 2.4% or less.

Control of Legionella in hospitals

Legionellas are present in water distribution systems and cooling towers of many hospitals. No firm data are available regarding the need for prophylactic disinfection of these contaminated systems. Disinfection of water systems and cooling towers is an accepted and effective means of ending nosocomial Legionnaires' disease, but it should be performed in conjunction with good epidemiological and microbiological studies to pinpoint environmental reservoirs and disseminators. Chlorination, pasteurization, or both, are the only means of disinfection found to be effective in disease outbreaks. Prospective surveillance of immunocompromised patients with pneumonia is probably the most effective means to determine if a hospital is a source of Legionnaires' disease and, therefore, requires further investigations and disinfection.

Potential in-hospital modes of transmission of legionella pneumophila. Demonstration experiments for dissemination by showers, humidifiers, and rinsing of ventilation bag apparatus

The mode of transmission of nosocomial legionellosis remains uncertain. Aerosolization of Legionella pneumophila by showers, humidifiers, and respiratory equipment rinsed in tap water was evaluated using plate-settling culture and air aspirator methods. All protocols simulated the actual hospital setting including use of humidifier equipment used in hospital patient rooms and water from faucets and showerheads in hospitals with nosocomial Legionnaires' disease. Protocols for humiditier and shower experiments mimicked the procedure actually used in hospitals by health care personnel. Showering failed to produce aerosols of L. pneumophila; however, portable humidifiers readily generated aerosols of L. pneumophila that disseminated throughout a two-bed patient room. Intensity of aerosolization directly correlated with the degree of L. pneumophila contamination of the tap water used to fill the humidifier. Rinsing of ventilation bag apparatus with tap water led to isolation of L. pneumophila from culture plates after the ventilation bags were squeezed. Thus, L. pneumophila could be aerosolized or directly instilled into a patient's bronchial tree following routine measures for cleaning ventilation bag apparatus with tap water. On the basis of these results, the use of humidifiers filled with tap water has been discontinued and sterile water is recommended for rinsing ventilation bag apparatus and tubing.

Nosocomial Legionnaires' disease. Epidemiologic demonstration of cooling towers as a source.

Investigation of a recent outbreak of nosocomial legionnaires' disease--initially thought to be due to the documented presence of Legionella pneumophila in the hospital potable water--showed that aerosols from one or more cooling towers were the actual source of infection. From June 27 to Aug 25, 1983, nosocomial legionnaires' disease developed in 15 persons at a hospital in Rhode Island. Twelve (80%) of 15 case-patients occupied rooms in building 1, unit B, compared with eight (28%) of 29 control patients (odds ratio = 10.8; 95% confidence interval = 1.4 to 85.6). Subsequent investigation demonstrated that water in a cooling tower located 100 ft upwind of unit B was heavily contaminated with L pneumophila, serogroup 1, subgroup 1, 2, 4, 5. The same strain was isolated from nine of the patients and from the make-up water for the tower. Active surveillance during the ten months following decontamination of the cooling tower identified no additional cases of nosocomial legionnaires' disease, although the hospital potable water had not been treated. While recommendations have been made for controlling nosocomial legionnaires' disease by heating or hyperchlorination of hospital potable water, this outbreak demonstrates the importance of an adequate epidemiologic-environmental investigation in choosing the appropriate control strategy.