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Sporadic and epidemic community legionellosis: two faces of the same illness

¹ University of Lyon 1, UMR CNRS 5558, Villeurbanne, ² Infection Control Unit, Edouard Herriot Hospital, and ³ Unit of Prevention and Genetic Epidemiology, Centre Léon Bérard, Lyon, France.

To the Editors:

We read with interest the article of Sopena et al. 1 on the comparisons of risk factors, presentation and outcome of community-acquired Legionella pneumophila pneumonia in 138 sporadic-case patients (1994–2004) and 113 outbreak-case patients (2002). As suggested by the authors, a limitation of comparison on the clinical severity between the two populations could be related to the delay in diagnosis. In other words, in the case of an outbreak, many exposed patients were screened for legionellosis using urinary antigen assays so that patients with mild symptoms could be diagnosed and treated. Conversely, sporadic cases were more frequently diagnosed, such as when the patients were hospitalised due to the severity of their symptoms. This corresponds to a more typical presentation and detection of the disease. A means to test this hypothesis would be to calculate the delay between the onset of the disease and the time of Legionella urinary antigen detection within the two groups of patients, and then compare the severity of the symptoms adjusted with these delays. It would be reasonable to suppose that for a similar delay in diagnosis, the clinical features would be the same for sporadic and outbreak cases. If differences persisted after adjustment for delays in diagnosis, then specific determinants would need to be identified in relation to the severity of the legionellosis within these two populations.

Similarly, as demonstrated in some studies performed among patients with cancer 2, this investigation would face a bias due to the earlier time of diagnosis associated with a screening procedure called "lead-time" and would possibly lead to over-diagnosis.

REFERENCES

1. Sopena N, Force L, Pedro-Botet ML, et al. Sporadic and epidemic community legionellosis: two faces of the same illness. Eur Respir J 2007;29:138–142.[Abstract/Free Full Text]
2. Zackrisson S, Andersson I, Janzon L, Manjer J, Garne JP. Rate of over-diagnosis of breast cancer 15 years after end of Malmö mammographic screening trial: follow-up study. BMJ 2006;332:689–692.[Abstract/Free Full Text]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Permissions Request Permissions Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Vanhems, P. Articles by Lasset, C. Search for Related Content PubMed PubMed Citation Articles by Vanhems, P. Articles by Lasset, C.