Infections
Hantavirus IgM
Antibodies that develop shortly after a hantavirus infection; the main test with sudden fever and kidney symptoms.
Everything about this testWhat it measures
Hantaviruses (officially orthohantaviruses) are carried by mice and rats. People become infected by breathing in dust particles containing virus from droppings, for example when cleaning a shed or cellar. In the Netherlands it is almost always Puumala virus from the bank vole. This test measures IgM antibodies: the type of antibody that the immune system makes first. In most patients, IgM is positive about ten days after the start of the illness.
- A recent hantavirus infection with sudden fever, headache, abdominal pain and reduced kidney function
- The milder European form, nephropathia epidemica, caused by Puumala virus
Positive
According to the LCI guideline (RIVM), a positive IgM result points to a hantavirus infection if there are also matching symptoms, such as sudden fever, headache, abdominal pain, low blood pressure and worsened kidney function. The test cannot reliably tell which hantavirus it is, because the different types react strongly to each other's tests. In the Netherlands it is almost always Puumala virus; most people recover from it within two to three weeks.
Negative
A negative IgM result does not rule out an infection in the first days of illness, because in most patients IgM only becomes positive around the tenth day of illness. If the suspicion remains, the test can be repeated after a few days to weeks, or the doctor can check whether the IgG antibodies clearly rise in two samples taken at least fourteen days apart. Without symptoms and without contact with rodents or their droppings, a negative result adds little.
If your result is abnormal
With a positive result and matching symptoms, the doctor assesses kidney function and the platelet count and, if needed, refers to the hospital; there is no specific medicine, and treatment is supportive. Orthohantavirus infection is a notifiable disease in group C of the Dutch Public Health Act and must be reported to the GGD (municipal public health service) within one working day, after which source tracing follows.
Reliability
According to the LCI guideline (RIVM), serology is the appropriate method for diagnosing hantavirus infections, using immunofluorescence tests and ELISAs. How often the test misses an infection or is falsely positive has not been well established. The biggest problem is cross-reactivity: the different hantaviruses react strongly to each other's tests, so the result can show an infection but not reliably which virus it was. In people without symptoms and without exposure to rodents, the chance of this rare infection is so small that a positive result is more often false than true.
Limitations
- In the first days of illness, IgM is often still negative; only around the tenth day is it positive in most patients.
- There is extensive cross-reactivity between the different hantaviruses; determining the type requires a neutralization test in a specialized laboratory.
- IgM can remain detectable for months after the infection and then wrongly look like something very recent.
- About 90 in 100 infections with Puumala virus cause no symptoms, so a positive result does not have to mean illness.
How common is this
Orthohantavirus infection is rare in the Netherlands: between 2018 and 2023 an average of 31 cases per year were notified, ranging from 10 to 49. Almost all cases involve Puumala virus and come from the east and southeast of the country. In a national study in 2006 and 2007, about 1.7 in 100 people in the Netherlands had antibodies against Puumala virus; in Enschede this was 3.2 in 100.
Who is this useful for
Useful with sudden fever with headache, abdominal pain and signs of reduced kidney function, in someone who may have come into contact with mouse or rat droppings in the preceding weeks, for example when cleaning a shed or cellar or when working in wooded areas. Also in people who keep pet rats or feeder rats. Not useful as a general check-up in people without symptoms: the infection is rare, and an abnormal result then does not change the management.
Downsides and risks
- A positive result without matching symptoms can lead to a notification to the GGD and to unnecessary testing, while the infection usually clears up on its own.
- The test cannot reliably tell which hantavirus it is, which can cause confusion about how serious the infection is.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results