Legionnaires' disease - Results of a multicentre Canadian study

BACKGROUND:

There has never been a cross-Canada surveillance project to determine the rate of Legionella species as a cause of community-acquired pneumonia requiring hospitalization and to determine whether there are any regional differences in the rates of Legionnaires'' disease in Canada. Anecdotally, Legionnaires'' disease is thought to be uncommon in Western Canada.

METHODS:

From January, 1996 through to October 31, 1997, a prospective study of the etiology of community acquired pneumonia requiring admission to 15 tertiary care hospitals in eight Canadian provinces was conducted. A urine sample from each patient was tested for Legionella pneumophila serogroup 1 antigen using a commercially available ELISA assay. A culture of sputum or other respiratory specimens for Legionellaceae was carried out at the discretion of the attending physician. Two hundred thirty-four patients had acute and 6-week convalescent serum samples tested for antibodies to L pneumophila serogroups 1 through 6 using an ELISA method.

RESULTS:

28 of the 850 patients (3.2%) had Legionnaires'' disease; 18 of 823 (2.1%) were positive for L pneumophila serogroup 1 by urinary antigen testing. The rate of Legionnaires'' disease, based on urinary antigen, at the Halifax site was higher than that at the other sites (seven of 163 patients versus 11 of 660 P=0.04]). Of the 28 cases of Legionnaires'' disease identified using all methods, 11 of 277 patients (3.9%) were enrolled from Western provinces versus 17 of 573 patients (2.9%) from Eastern provinces (P=nonsignificant).

CONCLUSIONS:

Legionnaires'' disease is just as common in Western as in Eastern Canada. L pneumophila serogroup 1 may be more common in Halifax than at the other sites studied.Key Words: Acquired pneumonia, Canada, Legionella, Legionella urine antigen, Legionnaires'' diseaseLegionnaires'' disease is an acute infectious disease of which the predominant manifestation is pneumonia (1). The most common cause is Legionella pneumophila serogroup 1, however, just under half of the over 40 recognized species in the Legionellaceae family can cause Legionnaires'' disease (2). A soluble antigen is present in the urine of patients with Legionnaires'' disease due to serogroup 1 (3-5). A commercially available enzyme immunoassay is available that detects this antigen with a specificity of 100% and a sensitivity of 94.6% (3). We used this test to determine the frequency with which L pneumophila serogroup 1 was a cause of community-acquired pneumonia (CAP) in Canada, and to determine whether there was any geographic clustering of the cases of Legionnaires'' disease. We tested a subset of the study population for Legionella species infection using a serological assay. Our objectives were to determine the rate of seroconversion among patients with a positive urinary antigen assay and to determine whether infection with serogroups 2 to 6 occurred in Canada.