Epidemiology and Infection

Research Article

Capture–recapture estimation of underreporting of legionellosis cases to the National Legionellosis Register: Italy 2002

M. C. ROTAa1 c1, A. CAWTHORNEa1, A. BELLAa1, M. G. CAPORALIa1, A. FILIAa1, F. D'ANCONAa1 and on behalf of the Legionellosis Working Group

a1 Centro Nazionale di Epidemiologia, Sorveglianza e Promozione della Salute, Reparto Epidemiologia delle Malattie Infettive, Istituto Superiore di Sanità, Roma, Italy


The objective of this study was to evaluate the degree of underreporting to the Italian National Legionellosis Register (NLR). For the year 2002, all cases of Legionellosis notified to the NLR were compared with cases recorded in the hospital discharge record (HDR) database. The number of unreported cases and the total number of cases in the population were estimated using the capture–recapture method with two independent data sources. Seventeen out of 21 Italian regions participated in the study. Overall, underreporting was estimated to be 21·4% and was found to be significantly greater in the Centre-South (28·2%) than in the North (20·0%). However, even after taking into account the higher degree of underreporting, a significantly lower incidence of the disease is registered in central-southern Italy. The hypothesis, which needs to be verified, is that, in addition to underreporting, under-diagnosis of legionellosis is more widespread in this geographical area.

(Accepted October 24 2006)

(Online publication December 19 2006)


c1 Author for correspondence: Dr M. C. Rota, Centro Nazionale di Epidemiologia, Sorveglianza e Promozione della Salute, Istituto Superiore di Sanità, 00161 Rome, Italy. (Email: mariacristina.rota@iss.it)


† Members of the Legionellosis Working Group are listed in the Appendix.