Indirect immunofluorescence antibodies to Legionella pneumophila: frequency in a rural community

Current and emerging Legionella diagnostics for laboratory and outbreak investigations

Legionnaires' disease (LD) is an often severe and potentially fatal form of bacterial pneumonia caused by an extensive list of Legionella species. These ubiquitous freshwater and soil inhabitants cause human respiratory disease when amplified in man-made water or cooling systems and their aerosols expose a susceptible population. Treatment of sporadic cases and rapid control of LD outbreaks benefit from swift diagnosis in concert with discriminatory bacterial typing for immediate epidemiological responses. Traditional culture and serology were instrumental in describing disease incidence early in its history; currently, diagnosis of LD relies almost solely on the urinary antigen test, which captures only the dominant species and serogroup, Legionella pneumophila serogroup 1 (Lp1). This has created a diagnostic "blind spot" for LD caused by non-Lp1 strains. This review focuses on historic, current, and emerging technologies that hold promise for increasing LD diagnostic efficiency and detection rates as part of a coherent testing regimen. The importance of cooperation between epidemiologists and laboratorians for a rapid outbreak response is also illustrated in field investigations conducted by the CDC with state and local authorities. Finally, challenges facing health care professionals, building managers, and the public health community in combating LD are highlighted, and potential solutions are discussed.

Legionella pneumophila serogroup 1 antibody kinetics in patients with Legionnaires' disease: implications for serological diagnosis

To evaluate current serological criteria for Legionella pneumophila serogroup 1 (Lp1), the antibody response was prospectively studied in all patients hospitalized for Legionnaires' disease in a Swedish county during 11 y (n = 62). A 4-fold or greater rise in antibody titre to > or = 128 (the minimum convalescent antibody level for diagnosis, as recommended by the Centers for Disease Control and Prevention), using the indirect immunofluorescence antibody test, was found in 21/52 (40%) of tested patients. By referring to the titre levels in healthy residents from the local population (World Health Organization criteria), 45/52 (87%) cases were confirmed serologically. In 21 patients followed longitudinally for 10 y, the median antibody titre fell from 256 (range 32-1024) to 16 (range 2-128) in 3 y. No booster reactions were observed in any patient. After 10 y, the geometric mean titre of this clinical cohort had reached the same level as observed in the background population 5 y earlier. Titre levels in subjects exposed to Legionella from a municipal water system indicate that only 1 out of 10 of all infections are identified clinically. Indirect immunofluorescent antibody testing with local reference sera is a sensitive method for laboratory confirmation of Lp1 in an unselected pneumonia population.

Polymerase chain reaction for detection of Legionellae DNA in urine samples from patients with community-acquired pneumonia

Polymerase chain reaction (PCR) was used for detecting Legionella DNA in water, sputum, tracheal aspirate and bronchoalveolar lavage fluid. There is paucity of data on the use of PCR for detection of Legionella in serum and urine samples. In 82 patients admitted with community-acquired pneumonia, urinary PCR was used in addition to urinary antigen assay for Legionella pneumophila serogroup 1 and serological tests (indirect immunofluorescence and ELISA) in paired sera. PCR was positive in urine samples from 21 patients (26%): in six of seven patients with acute legionellosis by CDC criteria, and 15 patients with negative urine antigen showing no fourfold rise in antibody titers in immunofluorescence test.

Hospital characteristics associated with colonization of water systems by Legionella and risk of nosocomial legionnaires' disease: a cohort study of 15 hospitals

OBJECTIVE

To investigate an increase in reports of legionnaires' disease by multiple hospitals in San Antonio, Texas, and to study risk factors for nosocomial transmission of legionnaires' disease and determinants for Legionella colonization of hospital hot-water systems.

SETTING

The 16 largest hospitals in the cities of San Antonio, Temple, and Austin, Texas.

DESIGN

Review of laboratory databases to identify patients with legionnaires' disease in the 3 years prior to the investigation and to determine the number of diagnostic tests for Legionella performed; measurement of hot-water temperature and chlorine concentration and culture of potable water for Legionella. Exact univariate calculations, Poisson regression, and linear regression were used to determine factors associated with water-system colonization and transmission of Legionella.

RESULTS

Twelve cases of nosocomial legionnaires' disease were identified; eight of these occurred in 1996. The rise in cases occurred shortly after physicians started requesting Legionella urinary antigen tests. Hospitals that frequently used Legionella urinary antigen tests tended to detect more cases of legionnaires' disease. Legionella was isolated from the water systems of 11 of 12 hospitals in San Antonio; the 12th had just experienced an outbreak of legionnaires' disease and had implemented control measures. Nosocomial legionellosis cases probably occurred in 5 hospitals. The number of nosocomial legionnaires' disease cases in each hospital correlated better with the proportion of water-system sites that tested positive for Legionella (P=.07) than with the concentration of Legionella bacteria in water samples (P=.23). Hospitals in municipalities where the water treatment plant used monochloramine as a residual disinfectant (n=4) and the hospital that had implemented control measures were Legionella-free. The hot-water systems of all other hospitals (n=11) were colonized with Legionella. These were all supplied with municipal drinking water that contained free chlorine as a residual disinfectant. In these contaminated hospitals, the proportion of sites testing positive was inversely correlated with free residual chlorine concentration (P=.01). In all hospitals, hot-water temperatures were too low to inhibit Legionella growth.

CONCLUSIONS

The increase in reporting of nosocomial legionnaires' disease was attributable to increased use of urinary antigen tests; prior cases may have gone unrecognized. Risk of legionnaires' disease in hospital patients was better predicted by the proportion of water-system sites testing positive for Legionella than by the measured concentration of Legionella bacteria. Use of monochloramine by municipalities for residual drinking water disinfection may help prevent legionnaires' disease.

Comparison of serologic tests with urinary antigen detection for diagnosis of legionnaires' disease in patients with community-acquired pneumonia

OBJECTIVE: To compare serologic methods and detection of urinary antigen in the diagnosis of community-acquired pneumonia. METHODS: Paired sera from 84 patients with community-acquired pneumonia were tested for Legionella pneumophila serogroup (LP SG) 1-7 and Legionella micdadei by use of the indirect immunofluorescence antibody test (IIF), enzyme-linked immunosorbent assay (ELISA) for LP SG 1-7 and complement-fixation (CF) test for LP SG 1. All patients were evaluated by ELISA urinary antigen detection for LP SG 1. RESULTS: Seven patients met the CDC criteria for acute Legionella infection, while in the rest of them we failed to detect urinary Legionella antigen. Thirty-three patients had non-diagnostic IIF antibody titers. Serum ELISA (IgG and/or IgM) was positive in 40 patients. Nine patients showed at least one CF titer of >/=1:32. The sensitivities of ELISA IgM for the first and the second serum samples compared with IIF were 42.8% and 46.6%, respectively, while the specificities were higher, i.e. 87% and 88.4%, respectively. The sensitivities of ELISA IgG for the first and the second samples were 42.8% and 53.3%, and the specificities were 77.9% and 76.8%, respectively. CONCLUSIONS: Although ELISA is simple to perform and easy to automate, we think that its advantages over indirect immunofluorescence and urinary antigen detection remain questionable.

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 greater than or equal to 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 less than 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.

A rural outbreak of Legionnaires' disease linked to visiting a retail store

Between May 7 and June 7, 1986, 27 residents of a rural county in Maryland developed legionellosis, and two died. Legionella pneumophila serogroup 1 was cultured from the sputum of two patients and identified in lung tissue of a third patient by direct fluorescent antibody staining. An additional 11 patients had four-fold rises in antibody titer to L. pneumophila, and 13 had single titers greater than or equal to 1:256. To determine risk factors for disease, we performed a case-control study. Twelve of 16 case-patients reported visiting store A in the two weeks before onset of illness compared with four of 28 control-patients. A serologic survey of employees showed that employees of store A were 3.63 times more likely than control employees to have titers of antibody to L. pneumophila greater than or equal to 1:256 (95% confidence intervals 0.8, 16.7). Cultures of soil specimens, samples of water from the hot water system of store A and from stagnant ponds near store A collected five weeks after the end of the outbreak were negative for Legionella species. Store A was adjacent to a site of excavation and construction during May 1986, when the community was experiencing an extended drought. This investigation suggests that exposure to excavation and construction activity may be a risk factor for legionellosis.

Prevalence of antibody to Legionella pneumophila in aborigines and non-aborigines in Western Australia

Three hundred and sixty-two sera were examined by the Legionella pneumophila indirect fluorescent antibody test, with serogroups 1 to 6 as antigens. Three age- and sex-matched population groups were tested: 200 non-aborigines from Perth; 100 aborigines from the Kimberley region; and 62 aborigines from Jiggalong Mission in the Pilbara region. Each population group was composed of 50% male and 50% female subjects, all within the age range of 20 to 40 years. The seropositivity rate for serogroup 1 (Philadelphia) was 13% for the Perth population group, 26% for the Kimberley group and 35.5% for the Jiggalong group. Seropositivity rates with the other 5 serogroups for the Perth population group were as follows: serogroup 2, 1%; serogroup 3, 5%; serogroup 4, 3%; serogroup 5, 3%; and serogroup 6, 9.5%. In both of the aboriginal population groups more subjects were seropositive to serogroups 3 and 5 than to serogroup 1. Multiple serogroup specificities and the occurrence of high titres were more common among the aboriginal groups. These findings indicate that there is considerable variation in the prevalence of L. pneumophila antibodies among ecologically distinct groups within Western Australia.

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 greater than or equal to 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 less than 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.

A note on legionellas in whirlpools

Water samples from 52 whirlpools (jacuzzi), water temperature 35-40 degrees C, and from 50 swimming pools, water temperature 8-30 degrees C, were investigated for the presence of Legionella pneumophila. This was isolated from 11 of 28 whirlpools with free available chlorine less than 0.3 mg/l. No legionellas were detected in 23 whirlpools with free available chlorine over 0.3 mg/l. Legionella pneumophila was found in two swimming pools. The results indicate that 0.3 mg/l of free available chlorine is sufficient to eliminate legionellas from whirlpools.

Sinusitis caused by Legionella pneumophila in a patient with the acquired immune deficiency syndrome

A patient with the acquired immune deficiency syndrome and Legionella pneumophila infection of the maxillary sinus is described. The organism was identified by direct immunofluorescence staining of sinus tissue. Because the Legionella species are intracellular pathogens, it is not surprising that this patient with a cellular immune defect was infected. However, no other site of Legionella infection was found. This appears to be the first reported case of upper respiratory tract infection by a Legionella species.

An outbreak of community-acquired Legionnaires' disease pneumonia

In October 1981, an outbreak of 29 cases of community-acquired pneumonia occurred among adult residents of Johnson County, Iowa. Retrospective study revealed 12 cases (41 per cent) had laboratory evidence of Legionnaires' disease (LD). No significant differences in clinical or epidemiological features were found between LD cases and the other pneumonias in the outbreak. All LD cases received erythromycin; one case died for a case-fatality rate of 8 per cent. The outbreak's focus could not be identified.

Factors influencing the reactivity of Legionella antigens in immunofluorescence tests

We examined several factors for their effects on the serological reactivity of Legionella antigens used for direct or indirect fluorescent-antibody tests. These factors included media, methods of killing, strain differences, and the nature of the reactivity with diverse human sera. The maximum serological reactivities were obtained with charcoal-yeast extract agar; the relative antigenicity of cells grown on a chemically defined medium could be fourfold less than those grown on the charcoal-yeast extract agar. Cells grown at 25 degrees C showed only small antigenic differences from those grown at 35 degrees C but had better morphological and staining characteristics. Cells killed by 1% Formalin or 37% Formalin vapors showed a 20% less relative antigenicity than those killed by heat, but their cell walls stained more clearly and they had fewer aberrations. As tested with several human sera, cells of Philadelphia 1 showed great variation in relative antigenicity with changes in media or methods of preparation; Bellingham 1 was quite stable under these same conditions. The data suggest that Bellingham 1 had serogroup 1-specific antigens, reactive with human sera, which were not present in Philadelphia 1.

Levels of antibody against Legionella pneumophila serotype 1 in healthy populations in five areas in New Zealand

Levels of antibody to Legionella pneumophila serogroup 1 in five areas of New Zealand were determined by indirect immunofluorescence. Both immunoglobulin G (IgG) and IgM levels were separately assessed. Of the 500 people studied, 2.8% had IgG titers of greater than or equal to 1:128 and 4.0% had IgM titers of greater than or equal to 1:128. Higher levels of IgG reactivity were noted in the southern part of New Zealand, but neither age nor sex appeared to be related to variations in antibody levels.