No 4 - 2012

Hantavirus 2010-2011

Hantavirus is transmitted to humans from rodents, primarily through inhalation of aerosols from urine and faeces, but also via bites and other types of contact.

In Denmark, the vastly predominant variant is Nephropatia Epidemica (NE) which is of low virulence. NE is caused by Puumala hantavirus, the reservoir of which is red mice (Clethrionomys glareolus). Red mice are common across Denmark, but Puumala hantavirus is most frequently found in red mice on Funen, where NE also occurs more frequently than in other parts of Denmark. The population of mice - and NE occurrence - peaks in the autumn and early winter and varies from year to year.

Very seldomly, infection with Saaremaa hantavirus is observed, the reservoir of which is the striped field mouse (Apodemus agrarius). The striped field mouse is found on Lolland-Falster and was recently observed in great numbers in Central Jutland where it was previously believed to have been extinct for more than 100 years. In other countries, hantavirus may cause more serious types of haemorrhagic fever. Haemorrhagic fever with renal syndrome may be caused by Hantaan (Asia) or Dobrava hantavirus (South and East Europe). Hantavirus pulmonary syndrome may e.g. be caused by Sin Nombre, Andes or Bayou hantavirus (North and South America).

Hantavirus is not routinely monitored. Hantavirus test results were extracted from the microbiological database (MiBa), which comprises all national microbiological test results as from 1 January 2010.

In the 2010-2011 period, a total of 429 patients were tested for hantavirus at the three laboratories which diagnose hantavirus in Denmark: DCM in Odense and Skejby and the Department of Virology, Statens Serum Institut.
A total of 30 cases were IgM positive for hantavirus, 23 of these also tested positive for IgG antibodies. No PCR-positive specimens were found.

Case

In the autumn of 2011, a man residing in a rural district close to the town of Svendborg presented with proteinuria and impaired renal function. Prior to symptom onset, he had cleared up a garden shed. PCR for Puumala hantavirus was negative, but IgM and IgG were positive. The patient recovered without hospitalisation or treatment.

Symptoms and treatment

Following a 1-6-week incubation period, the most frequently occurring symptoms are fever, headache, abdominal and lower back pain, nausea and vomiting.

Serum creatinine is typically increased and thrombocytopaenia occurs. Kidney symptoms are frequent: often as proteinuria and haematuria, and occasionally oliguria followed by polyuria.

Haemorrhagic manifestations and visual disturbances may occur. The course is milder in children than in adults.

There is no specific treatment.

Diagnosis

The diagnosis is made serologically and/or by blood or urine PCR. Negative PCR testing does not exclude hantavirus infection. In case of IgM detection of hantavirus without concomitant IgG detection, the diagnosis should be confirmed by subsequent detection of IgG antibodies against hantavirus. If the patient was presumably infected abroad, this should be stated when ordering the test.

Commentary

Diagnosis should be considered in patients with acutely occurring fever, headache, abdominal pain, nausea, proteinuria/haematuria, renal impairment and relevant exposure.
Infection reservoirs are found both on Funen, Lolland-Falster and in Jutland, but the disease is mainly observed in South Funen.
The period 1987-2000 saw an average of ten annual cases, which is in line with the number recorded in 2010-2011.

(C. Bjerre, P. Valentiner-Branth, M. Voldstedlund, Dept. of Epidemiology, K.T. Franck, A. Fomsgaard, Dept. of Virology, S. Ellermann-Eriksen, Aarhus University Hospital, T.G. Jensen, Odense University Hospital)

Outbreak of salmonella Strathcona

Towards end of September 2011, the SSI Enteropathogenic Laboratory-identified several cases of the very rare salmonella serotype S. Strathcona which had not previously been diagnosed in Denmark. An outbreak investigation was initiated by the Dept. of Epidemiology and the Central Outbreak Group. A request via the EU agency for infectious diseases, ECDC, showed that Germany and to a lesser extent Austria and Italy had also diagnosed cases of S. Strachcona in the same period.

A total of 43 Danes fell ill due to S. Strathcona between 4 September and 26 October 2011. The patients were living in a number of different locations across most parts of Denmark. A total of 26 females and 17 males aged 083 years were affected. Initial interviews identified no obvious food sources, but did show that nearly all patients had been shopping with the Rema 1000 supermarket chain. Subsequently, an investigation was initiated in cooperation with Rema 1000 and selected patients. Detailed information on relevant purchases was extracted from the supermarket chain's computer system. Comparison of the purchases made by ten affected families showed that eight had bought the same type of small oblonged "Datterino" tomatoes. Next, a case-control study was performed, contributing to establish the tomatoes as a probable source. When the tomatoes were identified as the outbreak source, they were no longer on sale. Follow-up by the Danish Veterinary and Food Administration showed that the tomatoes were Italian. Italian follow-up showed that the same tomatoes had also been sold in Germany and Austria.

Commentary

This outbreak was one of only two acknowledged salmonella outbreaks in 2011, and to our knowledge the largest S. Strathcona outbreak ever recorded. Fresh tomatoes have previously been the source of salmonella outbreaks, but this is the first major salmonella outbreak caused by tomatoes observed in Denmark.

(L. Müller on behalf of the Outbreak Team, Department of Epidemiology)

EPIET

Again, it is possible to apply for the two-year field epidemiologist European training programme EPIET (European Programme for Intervention Epidemiology Training). Participants will build skills related to the monitoring and control of infectious diseases, outbreak tracing and management, applied research, communication, etc. The programme starts in September 2012 and is completed during a two-year placement in another European country. Deadline for application: 5 February 2012. Further information: www.ecdc.eu or contact Kåre Mølbak, Dept. of Epidemiology.

25 January 2012