Molecular epidemiology of Legionella pneumophila infection at a Canadian tertiary care institution

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.

Persistence of Legionella pneumophila in a hospital's water system: a 13-year survey

OBJECTIVE

To describe the molecular epidemiology of Legionella pneumophila infections in the University of Iowa Hospitals and Clinics (UIHC).

DESIGN

Molecular epidemiological study using pulsed-field gel electrophoresis (PFGE).

SETTING

A large university teaching hospital. ISOLATES: All surviving isolates obtained from culture-proven nosocomial L. pneumophila infections and all surviving isolates obtained from the University of Iowa Hospital and Clinics' water supply between 1981 and 1993.

RESULTS

Thirty-three isolates from culture-proven nosocomial cases of L. pneumophila pneumonia were available for typing. PFGE of genomic DNA from the clinical isolates identified six different strains. However, only strain C (16 cases) and strain D (13 cases) caused more than 1 case. Strain C caused clusters of nosocomial infection in 1981, 1986, and 1993 and also caused 4 sporadic cases. Strain D caused a cluster in 1987 and 1988 plus 4 sporadic cases. Of the six strains causing clinical infections, only strains C and D were identified in water samples. PFGE identified three strains in the water supply, of which strains C and D caused clinical disease and also persisted in the water supply during most of the study period.

CONCLUSION

Specific strains of L. pneumophila can colonize hospital water supplies and cause nosocomial infections over long periods of time.