Eurosurveillance - Volume 11, Issue 6, 01 June 2006

Four years ago, Henriette de Valk and colleagues determined both the need for and feasibility of a European network on Listeria infections in humans. The network was envisioned as a way to strengthen surveillance in individual countries by harmonising microbiological methods and providing epidemiologic tools for investigations. The results of their survey were clear: respondents felt that such a network would aid in the detection and investigation of outbreaks, and that it could be based on existing national surveillance systems. There has been considerable institutional support for developing a European Listeria network, and in response to planning efforts, Listeria surveillance has improved in several countries. However, the network has yet to be realised.

Mandatory notification of listeriosis began in France in 1999. Enhanced public health surveillance, including routine molecular characterisation of Listeria monocytogenes strains, epidemiologic follow up of cases, and collection of food samples, has improved the sensitivity of outbreak detection and response.

We analysed the surveillance data from listeriosis cases notified to the Finnish National Infectious Diseases Register between 1995 and 2004 and describe our recent experience in investigating clusters of listeriosis cases. The number of annual cases varied between 18 and 53 but no trends in incidence were identified (average annual incidence was 7 cases per million inhabitants).

Listeriosis has been a mandatorily notifiable disease in Germany since January 2001. Clinical cases with isolation of Listeria monocytogenes from sterile specimens or neonates are reported to the Robert Koch-Institut. Listeriosis incidence significantly increased from 0.26 per 100 000 inhabitants (217 cases) in 2001 to 0.62 per 100 000 (519 cases) in 2005.

An outbreak of listeriosis occurred in the Swindon area of the UK in autumn 2003. Five cases were detected in pregnant women. Four of these women were thought to have eaten prepacked sandwiches from a retail outlet in one particular hospital. Sampling at the supplier detected Listeria monocytogenes, which was indistinguishable on molecular testing from the patients’ isolates. Recent changes in UK food legislation should help diminish the risk of further outbreaks/cases such as ours occurring.

During an eight week period in spring 2005, 10 cases of listeriosis were reported in a small area of northwest Switzerland (150 000 inhabitants). Eight cases were in older immunocompromised patients who became ill with bacteraemia (three deaths), and two cases were in pregnant women who had septic abortion.