Diphyllobothrium latum Outbreak from Marinated Raw Perch, Lake Geneva, Switzerland

ER. Animal-based national surveillance for zoonotic disease: quality, limitations , and implications of a model system for monitoring rabies. To the Editor: Diphyllobothrium latum, a fi sh tapeworm, has a complex cycle including copepods and freshwater fi sh as intermediate hosts. Humans are infected by eating raw or undercooked fi sh meat. Clinical consequences of human infection are generally absent or mild, although anemia due to vitamin B12 defi ciency was described in Scandinavia (1). Freshwater fi sh host the parasite in some lakes of Switzerland, Italy, Scandinavia, northeastern Canada, and South America (1–4). Lake Geneva, in Switzerland, harbors perch, pike, and char, which are considered to be food delicacies and may act as secondary intermediate hosts. Perch are heavily infested (5,6). To date, D. latum has reportedly caused only sporadic cases in western Europe. One outbreak has previously been described in South Korea after 5 persons ate raw redlip mullet. Identification of the Diphyllobothrium species in that outbreak was uncertain (7). Since 2001, medical centers in the lake region have reported an increasing number of human cases. We report, to our knowledge, the fi rst outbreak of D. latum infections in this region, which occurred after a wedding party in June 2006. The menu included raw, mari-nated perch fi llets caught the same day in Lake Geneva. After D. latum infection was diagnosed in 2 guests, all those who attended (n = 32) were contacted within 4 months after the wedding. Information was collected with a standardized questionnaire on personal characteristics; past infection with D. latum; consumption of raw perch during the wedding, raw freshwater fi sh in the last 5 years, or both; and symptoms or visible proglottids in stools. All participants who ate the raw perch dish during the wedding had a stool sample examined for ova and proglottids at the Laboratory of Parasitology of the Geneva University Hospitals. Species identifi cation relied on egg and proglottid morphologic characteristics and epidemiologic factors. A confi rmed case-patient was de-fi ned as a case in a guest who ate raw perch at the wedding and had characteristic eggs or proglottids in stool. A probable case-patient was defi ned as a person who ate raw perch during the wedding and reported a " tagliatelle-like " worm of varying length in stools, without a history of consumption of raw beef, pork, or other raw fi sh in the previous 5 years …