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Journal of Clinical Microbiology, July 2000, p. 2738-2739, Vol. 38, No. 7
Department of Medical
Microbiology1 and Department of
Infectious Diseases, Tropical Medicine and
AIDS,3 Academic Medical Center, University of
Amsterdam, Amsterdam, and the Laboratory of Public Health,
Haarlem,2 The Netherlands
Received 19 January 2000/Returned for modification 3 March
2000/Accepted 17 April 2000
A new immunochromatographic assay for rapid qualitative detection
of Legionella pneumophila serogroup 1 antigen in urine
specimens was used during an outbreak of legionellosis in The
Netherlands. The assay seems of the utmost value in providing a rapid
diagnosis of Legionnaires' disease in patients with severe
community-acquired pneumonia in an outbreak setting.
Legionellosis, an infection due to
Legionella species, presents in two different forms: Pontiac
fever, an acute self-limiting flu-like illness, and pneumonia or
Legionnaires' disease. Legionella pneumophila serogroup 1 is the cause of more than 80% of the cases of legionellosis in The
Netherlands. Patients with Legionnaires' disease have a variety of
signs and symptoms, but none of the clinical features is sufficiently
specific to establish the diagnosis. Because the rate of mortality from
untreated Legionnaires' disease ranges from 10 to 50%, rapid
diagnosis and early antibiotic treatment are required (3, 5, 6,
7). Detection of L. pneumophila serogroup 1 antigen in
urine specimens by radioimmunoassay and enzyme-linked immunosorbent
assay methods has long been used as a tool for the diagnosis of
Legionnaires' disease (1, 2, 4, 8, 9). Assays for the
detection of L. pneumophila serogroup 1 antigen in urine
have a sensitivity of 70% and a specificity that approaches 100%
(7). Recently, an immunochromatographic assay for the rapid
qualitative detection of L. pneumophila serogroup 1 antigen
(Legionella NOW; Binax, Portland, Maine) in urine specimens has become
available. This assay uses rabbit anti-L. pneumophila serogroup 1 antibody as the capture component and rabbit anti-L. pneumophila serogroup 1 antibody conjugated to colloidal gold as
the detection component. The assay provides a test result in 15 min and
is intended to aid in the presumptive diagnosis of Legionnaires'
disease caused by L. pneumophila serogroup 1 in conjunction
with culture and other methods. Preliminary performance data for the
immunochromatographic assay report a sensitivity of 95% and a
specificity of 95% (N. Moore and D. Gentile, Abstr. 99th Gen. Meet.
Am. Soc. Microbiol. 1999, abstr. C-19, p. 108, 1999).
The immunochromatographic assay was extensively used during a recent
outbreak of legionellosis in The Netherlands. An outbreak became
apparent on 11 March 1999, when an investigative team from the Academic
Medical Center, Amsterdam, detected L. pneumophila serogroup
1 antigen in urine specimens from seven patients admitted to a regional
hospital in Hoorn because of severe community-acquired pneumonia (CAP).
Simultaneously, L. pneumophila serogroup 1 antigen was also
detected in urine specimens from two patients with severe CAP at the
Laboratory of Public Health, Haarlem. Both patients were transferred
from the regional hospital in Hoorn to a Haarlem hospital for
respiratory support. A subsequent epidemiological investigation
revealed that the nine patients had been among the 80,000 visitors of
the Westfriese Flora, a flower show held annually in Bovenkarspel, The
Netherlands, from 19 to 28 February 1999. On 12 March, L. pneumophila serogroup 1 antigen was detected in urine specimens
from two additional patients admitted to the regional hospital in Hoorn
and four patients admitted to hospitals in the Amsterdam area. In
addition, the presumptive diagnosis of Legionnaires' disease was
confirmed on that day by a positive direct immunofluorescence assay
result for L. pneumophila in lung tissue acquired from one patient postmortem. On the same day, the National Health Department informed the general public of the outbreak through a nationwide television broadcast. In the following days, we cultured L. pneumophila serogroup 1 from sputum and lavage specimens from four
patients. No other pathogens were cultured.
Subsequently, several institutions provided their services to other
hospitals and family physicians for rapid identification of
outbreak-associated cases by the immunochromatographic assay. At the
Academic Medical Center, urine specimens from 86 visitors of the flower
show were subjected to the immunochromatographic assay. Visitors were
stratified into five patient groups according to clinical presentation.
Group 1 included patients admitted to an intensive care unit because of
severe pneumonia with need for respiratory support (n = 17); group 2 included patients hospitalized because of pneumonia
without need for respiratory support (n = 40); group 3 included nonhospitalized patients treated for mild pneumonia
(n = 8); group 4 included nonhospitalized patients who suffered or who had suffered an acute, self-limiting flu-like illness
(n = 12); group 5 included patients hospitalized for
reasons other than pneumonia (n = 3; carcinoma of the
lung, fever of unknown origin, heart failure), hospitalized patients
for whom additional clinical data were not available (n = 3), and visitors without objective symptoms (n = 3).
L. pneumophila serogroup 1 antigen was present in 40 of 86 (47%) urine specimens (Fig. 1). The
immunochromatographic assay provided a presumptive diagnosis of
Legionnaires' disease for 40 of 65 (62%) patients who presented with
pneumonia. The immunochromatographic assay was negative for 25 of 65 (38%) patients with pneumonia. On the basis of their clinical
presentations and the epidemiological timing, it was suspected that
these 25 patients could have had Legionnaires' disease. The percentage
of positive test results for the three pneumonia patient groups
increased with the clinical severity of the pneumonia, presumably
representing increased shedding of antigen from lung to urine via the
blood compartment in those with more severe disease. No positive test
results were obtained for the group of patients who presented with an
acute, self-limiting flu-like illness.
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Rapid Diagnosis of Legionnaires' Disease Using an
Immunochromatographic Assay for Legionella pneumophila
Serogroup 1 Antigen in Urine during an Outbreak in The
Netherlands
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ABSTRACT
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FIG. 1.
Test results obtained by the immunochromatographic assay
for detection of L. pneumophila serogroup 1 antigen in urine
specimens from 86 visitors of the flower show in Bovenkarspel, The
Netherlands. Visitors were stratified into five patient groups
according to clinical presentation, as described in the text.
In order to study the specificity of the immunochromatographic assay, we tested corresponding urine and sputum specimens from 30 successive patients who were suspected of having serious pneumonia and who were admitted to the intensive care unit or department of pulmonology of our hospital but who had not visited the flower show. Urine specimens were tested by the immunochromatographic assay, while sputum specimens were subjected to routine bacteriological examination and were inoculated onto buffered charcoal yeast extract agar and buffered charcoal yeast extract agar with antibiotics. For this group of patients, L. pneumophila serogroup 1 antigen was not detected in urine specimens and Legionella species were not cultured from sputum specimens. Identification of pathogens cultured from the sputum specimens revealed Streptococcus pneumoniae (three samples), Haemophilus influenzae (two samples), Pseudomonas aeruginosa (three samples), Neisseria meningitidis (one sample), species of the family Enterobacteriaceae (five samples), Candida species (three samples), and Chryseobacterium meningosepticum (one sample). No bacterial pathogen was isolated from 12 patients.
Although sensitivity per se was not assessed in this setting, our findings, in conjunction with the clinical and epidemiological data for patients from this outbreak, justify the conclusion that the immunochromatographic assay for the detection of L. pneumophila serogroup 1 antigen in urine specimens is a specific assay which is of the utmost value in providing a rapid diagnosis of Legionnaires' disease, especially in patients with severe CAP in an outbreak setting. However, our data also show that clinicians and clinical microbiologists should not rely on the immunochromatographic assay as the sole test for the diagnosis of Legionnaires' disease. Furthermore, isolation and characterization of the responsible strain remain essential for epidemiological studies and identification of the source of an outbreak.
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FOOTNOTES |
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* Corresponding author. Mailing address: Department of Medical Microbiology L1-104, Academic Medical Center, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands. Phone: 31 (0)20 566 9111. Fax: 31 (0)20 697 9271. E-mail: p.c.wever{at}amc.uva.nl.
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