1. Rijksinstituut voor Volksgezondheid en Milieu (National Institute for Public Health and the Environment, RIVM), Bilthoven, The Netherlands
2. European Programme for Intervention Epidemiology Training (EPIET)
3. Gemeentelijke Gezondheidsdienst “Hart voor Brabant” (Municipal Health Service “Hart voor Brabant”), ’s Hertogenbosch, The Netherlands
4. Canisius Wilhemina Ziekenhuis, Nijmegen, The Netherlands
5. Voedsel en Waren Autoriteit (VWA), The Netherlands
6. Gezondheidsdienst voor Dieren (GD), The Netherlands
On 29 May 2007, a general practitioner (GP) from a rural village in the province of Noord-Brabant, in the south of the Netherlands, alerted the municipal health service about an unusual increase in pneumonia cases among adults in his practice. Cases presented with one or more of the following symptoms: fever, night sweating, muscle pain, cough and fatigue. A second GP from a nearby village reported a similar alert soon thereafter and this led to a further investigation of the cases. Earlier in the month, the same municipal health service received an alert by a regional medical microbiologist regarding an increase in severe pneumonias that did not respond well to antibiotics.
This first cluster of cases was initially attributed to Mycoplasma pneumoniae, but more in-depth diagnostics revealed that the majority of these patients had a positive serology for acute Coxiella burnetii infection. Also, six sporadic Q fever cases were reported from the same province through the mandatory notification system from January to April 2007. An investigation was launched to describe the outbreak, find the source and route of transmission, identify symptomatic and asymptomatic pregnant patients – who are more likely to contract chronic Q fever  – in the most affected area, and investigate possible links to animal reservoirs in the region in order to decide on appropriate control measures.
As Q fever is a rarely reported disease in the Netherlands, a broad case definition was used:
- a confirmed case of Q fever was defined as any inhabitant of the Netherlands presenting to a GP with clinical symptoms consistent with Q fever since 1 January 2007 and who had laboratory confirmed positive serology defined as a seroconversion or fourfold increase of antibody titer using a C. burnetii CFT (home-made complement fixation test using phase 1 and 2 antigen) in samples taken at least 14 days one after the other, or showing positive for phase 2 IgM antibodies in the C. burnetii IFA (Focus diagnostics) with a 1:64 or greater dilution.
- a probable case definition was also introduced only for an area in the east of the Noord Brabant region, where more cases were clustered, to better describe the outbreak there. Probable cases had clinical symptoms consistent with Q fever and either a less than fourfold increase in phase 2 IgM within 14 days, or a single serum sample positive for phase 2 IgM antibodies in a dilution of 1:20 or greater.
In all cases, Legionella
spp. was excluded.
Q fever is caused by Coxiella burnetii, an intracellular bacterium. It is an almost worldwide appearing zoonosis whereby goats, sheep and cattle have been described as the most common animal reservoir for human infections. Many Q fever outbreaks worldwide are temporally linked to the lambing season, as birth products from infected animals can be an important source of environmental contamination and transmission to humans via the aerosol route . At least three outbreaks of Q fever have been documented worldwide since January 2007: in the United Kingdom , Slovenia  and Australia .
In the Netherlands, 5-20 cases of Q fever have been reported annually between 2000 and 2006 . From 1 January until 2 August 2007, 63 confirmed and probable cases with Q fever have been reported to the municipal health services throughout the Netherlands. Fifty-nine of them were in the provinces of Noord Brabant and Gelderland, of which 36 were confirmed according to the used case definition. Among the 59 cases in these two provinces, 27 were living in a well defined area in the eastern part of Noord Brabant. It should be noted that retrospective active case finding was initiated in the latter area for patients with a GP consultancy after 15 May to better describe the cluster of cases there. The overall male to female ratio is 1.67 and the median age is 50 years. Date of symptoms onset is currently available for 47 of all patients. The peak of case occurrence was in week 21 of 2007. According to the data available including week 30, the last case had a symptoms onset in week 26 (Figure).
A trawling questionnaire was used to generate hypotheses about the possible source of the outbreak in eastern Noord Brabant area. The municipal health service undertook active case finding through the GP offices in this area, where about 11,500 inhabitants reside. The area is highly agricultural with a large population of ruminants (cattle, sheep and goats). The number of goats has been reported to be increasing during the last decade in this region, as has the degree of intensive goat farming ; moreover, there have been active reports of abortion waves due to C. burnetii infection among the goat population in 2006 and 2007. Meteorological factors may also have played a role in this outbreak setting, but this remains to be investigated. April was a very dry month; only 1.5 mm of precipitation fell in the nearby weather station of Eindhoven between 22 March 2007 and 6 May 2007, while the average precipitation value for April alone is 42 mm. Weather conditions, such as dry weather and wind, have been documented to play an important role in other Q fever outbreaks [8,9].
This is the first documented outbreak of Q fever in the Netherlands, and it is currently under investigation. So far, only sporadic cases and family clusters related to direct animal contact had been observed here. It is also an example of local GPs signalling an outbreak in the Netherlands, underlining their role in early warning of outbreaks, before laboratory-confirmed cases are reported to the health services. Further studies are planned.
We would like to thank the following for their contribution to the ongoing investigation: Rob Besselink and Franka Rijkens (Huisartspraktijk, Herpen), Sandra van Dam (GGD Hart voor Brabant, 's Hertogenbosch), Frederika Dijkstra (RIVM), Kees Groot (Ziekenhuis Bernhoven, Oss), Leslie Isken (RIVM), Rob van Kessel (GG en GD Utrecht), Jolanda Koel (GGD Hart voor Brabant, 's Hertogenbosch), Titia Kortbeek (RIVM), Merel Langelaar (RIVM), Chantal Lensen (Ziekenhuis Bernhoven, Oss), Jan Marcelis (Elisabeth Ziekenhuis, Tilburg), Daan Notermans (RIVM), Rob van Oosterom (VWA, Den Haag), Pierre Rutten (GGD Zuidoost Brabant), Ronald ter Schegget (GGD Zuidoost Brabant, Helmond), Peter Schneeberger (Jeroen Bosch Ziekenhuis, 's Hertogenbosch), Jim van Steenbergen (RIVM), Corien Swaan (RIVM), Aura Timen (RIVM), Ineke Weers-Pothoff (Jeroen Bosch Ziekenhuis, 's Hertogenbosch), Clementine Wijkmans (GGD Hart voor Brabant, 's Hertogenbosch).