11 September 2008
Authors reply: Q fever in the Netherlands – what matters is seriousness of disease rather than quantity
- Centrum Infectieziektebestrijding (Centre for Infectious Disease Control, CIb), Rijksinstituut voor Volksgezondheid en Milieu (National Institute for Public Health and the Environment, RIVM), Bilthoven,The Netherlands
- Gemeentelijke Gezondheidsdienst “Hart voor Brabant” (Municipal Health Service “Hart voor Brabant”), ’s Hertogenbosch, The Netherlands
- Jeroen Bosch Hospital, ’s Hertogenbosch, The Netherlands
Citation style for this article: Schimmer B, Morroy G, Dijkstra F, Schneeberger PM, Weers-Pothoff G, Timen A, Wijkmans C, van der Hoek W. Authors reply: Q fever in the Netherlands – what matters is seriousness of disease rather than quantity. Euro Surveill. 2008;13(37):pii=18976. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=18976
Date of submission:
08 September 2008
We thank G. Cilla, M. Montes and E. Pérez-Trallero for their comments on our article ‘Large ongoing Q fever outbreak in the south of the Netherlands, 2008’ .
Since the publication the number of Q fever notifications received at the National Institute for Public Health and the Environment has increased to 880 (data from 1 January to 3 September 2008). As we have already indicated in our article , increased awareness for Q fever has certainly led to more diagnoses and laboratory-confirmed cases. Clinicians were regularly informed about the epidemic and its medical consequences. Numerous reports published in the newspapers will have increased the awareness about the disease among medical doctors and patients. We think this has led to accurate diagnosis of acute Q fever cases that would otherwise have gone undetected. As we have pointed out the notification criteria in the Netherlands require clinical signs and symptoms that are consistent with Q fever infection. A positive laboratory result without clinical disease is not sufficient for notification. We are currently retrospectively collecting data from physicians to get a more precise idea of the severity and duration of clinical disease.
Cilla et al. rightfully point to the lack of standardisation in interpretation of serology results. Interpretation of cut-off values for immunofluorescence (IF) antibody titres to diagnose acute Q fever depends on the antigens used. "Moreover, IF can be used for surveillance purposes for which higher cut-off values may be more appropriate. For diagnosis of acute Q fever, serology must be matched with clinical signs and symptoms. In case of doubt, follow-up samples should be taken to confirm diagnosis. In our cases serology was only performed in a clinical setting with a differential diagnosis that included Q fever. All cases were examined clinically after notification, and all initially dubious serologic results had to be confirmed by follow-up serum samples to obtain significant rise in titers and thus confirm the diagnosis. A case control study was carried out in 2007 in a small cluster area  in the southeast of the Netherlands. For this study indeed higher cut-off values were used than in the present outbreak.
- Schimmer B, Morroy G, Dijkstra F, Schneeberger PM, Weers-Pothoff G, Timen A, Wijkmans C, van der Hoek W. Large ongoing Q fever outbreak in the south of The Netherlands, 2008. Euro Surveill. 2008;13(31):pii=18939. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=18939
- Karagiannis I, Morroy G, Rietveld A, Horrevorts AM, Hamans M, Francken P, Schimmer B. A Q fever outbreak in the Netherlands: a preliminary report. Euro Surveill. 2007;12(32):pii=3247. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=3247
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