[Legionnaire's disease: surveillance in France in 2005]

Legionnaire's disease is a recently described infection and surveillance in France was implemented in 1987. In 2005, 1,527 cases were notified corresponding to a population incidence rate of 2.5 per 100,000. The median age of cases was 61 years [5-100] and the male to female sex ratio was 3.0. The case fatality rate was 11%. One or more risk factors were identified for 1,084 (71%) cases. The majority of cases (91%) was diagnosed by urinary antigen detection and a strain was identified in 276 cases (18%). Legionella pneumophila serogroup 1 infection was confirmed in 95% of cases. A specific exposure during the incubation period was reported for 39% of cases. Travel exposure was reported for 17% and hospital exposure for 7%. Multiple clusters and outbreaks were investigated. The largest one reported was identified in the north Lyon with 34 cases. Since 1997 the incidence of LD has steadily increased. This probably suggests a better detection of cases and an improvement in the surveillance system. In recent years, several new measures concerning prevention and control were implemented. However these efforts must continue particularly in the research domain to improve knowledge of the disease, in order to limit its impact on exposed populations.

[Factors associated with mortality in Legionnaires' disease, France, 2002-2004]

Risk factors for Legionnaires' disease are well known (older age, smoking, or immunosuppression), however, the factors associated with mortality are less documented. A retrospective analysis based on cases notified between 2002 and 2004 was conducted in France to identify these factors.

METHOD

Cases were identified through mandatory notifications sent to the Institut de veille sanitaire, France. Factors associated with mortality were identified using a logistic regression analysis.

RESULTS

Three thousand two hundred sixty-seven cases of Legionnaire's disease were notified during the study period and the evolution was documented for 85% of the cases (2.791). Three hundred seventy-seven deaths (13.5%) were notified. 72.5% of the patients were men and the median age was 61. The multivariate analysis applied to patients under 60 years revealed that cancer or hemopathy (OR=6.4 CI95% 3.6-11.2), underlying renal disease (OR=3.2 CI95% 1.0-9.9), or alcohol abuse (OR=2.2 CI95% 1.1-4.4) were associated with mortality. For older patients (>60 years) factors linked to mortality were: cancer/hemopathy (OR=1.8 CI95% 1.2-2.6), underlying renal disease (OR=3 CI95% 1.4-6.4), underlying cardiac disease (OR=2.4 CI95% 1.4-4), alcohol abuse (OR=2.4 CI95% 1.2-5.2), immunosuppression (OR=1.7 CI95% 1.1-2.6), nosocomial acquisition of the disease (OR=2.0 CI95% 1.3-3), or infection acquired in nursing home residents (OR=2.4 IC 95% 1.6-3.6).

CONCLUSION

These preliminary results further describe Legionnaires' disease and its mortality. However, they should be confirmed by carefully conducted prospective analysis. The description of LD patients at high risk of death will contribute to better prevention measures.

[Principles of an outbreak investigation in public health practice]

An outbreak (or epidemic) is a higher number of cases of a given disease in a given population and time interval. A timely investigation has for aim to identify the source and vehicle of the outbreak and provides unique opportunities to better understand its occurrence and the role of contributing risk factors to implement the most appropriate measures to control it and prevent further recurrences. The investigation of an outbreak is based on a multidisciplinary approach (clinical, epidemiological, environmental, and microbiological) with a descriptive and analytical (hypothesis testing) phase. In this article, we describe the methodological approach of a field outbreak investigation illustrated by examples taken from our experience. The investigation includes the following steps: establishing the existence of the outbreak; defining the disease; finding cases; describing cases by time, place, and person characteristics; establishing a hypothesis related to the mode of occurrence; testing the hypotheses; conducting an environmental investigation; conducting a microbiological investigation; controlling the outbreak, preventing further occurrences, and writing an investigation report to share experience with the public health and scientific community. The investigation of an outbreak is an evolving process: information gathered or conclusions made at a given stage must be fully used for following steps. The social, institutional, and political background associated with outbreaks usually makes their investigation complex and should be taken into account. The earlier the outbreak is detected and investigated in close relation with public health authorities, the greater will be the potential preventive impact of control measures.