Nygård Karin, Schimmer Barbara, Søbstad Øystein, Walde Anna, Tveit Ingvar, Langeland Nina, Hausken Trygve, Aavitsland Preben
Department of Infectious Disease Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
BMC Public Health. 2006 May 25;6:141. doi: 10.1186/1471-2458-6-141.
Giardia is not endemic in Norway, and more than 90% of reported cases acquire the infection abroad. In late October 2004, an increase in laboratory confirmed cases of giardiasis was reported in the city of Bergen. An investigation was started to determine the source and extent of the outbreak in order to implement control measures.
Cases were identified through the laboratory conducting giardia diagnostics in the area. All laboratory-confirmed cases were mapped based on address of residence, and attack rates and relative risks were calculated for each water supply zone. A case control study was conducted among people living in the central area of Bergen using age- and sex matched controls randomly selected from the population register.
The outbreak investigation showed that the outbreak started in late August and peaked in early October. A total of 1300 laboratory-confirmed cases were reported. Data from the Norwegian Prescription Database gave an estimate of 2500 cases treated for giardiasis probably linked to the outbreak. There was a predominance of women aged 20-29 years, with few children or elderly. The risk of infection for persons receiving water from the water supply serving Bergen city centre was significantly higher than for those receiving water from other supplies. Leaking sewage pipes combined with insufficient water treatment was the likely cause of the outbreak.
Late detection contributed to the large public health impact of this outbreak. Passive surveillance of laboratory-confirmed cases is not sufficient for timely detection of outbreaks with non-endemic infections.
贾第虫在挪威并非地方病，报告病例中超过90%是在国外感染的。2004年10月下旬，卑尔根市报告实验室确诊的贾第虫病病例有所增加。于是展开调查以确定疫情的源头和范围，以便实施控制措施。
通过该地区进行贾第虫诊断的实验室来确定病例。所有实验室确诊病例均根据居住地址进行定位，并计算每个供水区域的发病率和相对风险。在卑尔根市中心居住的人群中开展了一项病例对照研究，对照从人口登记册中随机选取，年龄和性别与病例匹配。
疫情调查显示，疫情始于8月下旬，10月初达到高峰。共报告了1300例实验室确诊病例。挪威处方数据库的数据估计，约2500例接受贾第虫病治疗的病例可能与此次疫情有关。20至29岁的女性占主导，儿童和老年人较少。从为卑尔根市中心供水的水源取水的人感染风险显著高于从其他水源取水的人。污水管泄漏加上水处理不足可能是此次疫情的原因。
发现较晚导致了此次疫情对公众健康造成巨大影响。对实验室确诊病例的被动监测不足以及时发现非地方病感染的疫情。
