Blood draw
Q Fever (Acute Coxiella burnetii)
Serology for acute Q fever.
€ 78,00
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Infections · Blood
Q fever phase II, Coxiella burnetii IgG
IgG antibodies against the phase 2 protein of the Q fever bacterium; they show contact with the bacterium and remain present for a long time.
At a glance
- Measured in blood
- In 1 test panel
- No special preparation
Explanation
Q fever phase II, Coxiella burnetii IgG: what is measured?
Q fever is caused by the bacterium Coxiella burnetii, which mainly comes from goats and sheep and is breathed in through the air. The outer layer of the bacterium occurs in two forms, phase 1 and phase 2. In an acute infection, the antibodies against phase 2 are highest; in a chronic infection, it is those against phase 1. This test measures IgG against phase 2. This is the antibody that appears after the first IgM response and can then remain detectable for years.
What can it detect?
- A past infection with Coxiella burnetii, even if it caused no symptoms
- Support for the diagnosis of acute Q fever, if the antibodies clearly rise between two blood samples
Result
What does the result mean?
Positive result
A positive phase 2 IgG means that your immune system has at some point been in contact with Coxiella burnetii. This can be an infection from a few weeks ago, but also one that went unnoticed years ago; about 60 in 100 infections cause no symptoms. According to the LCI guideline (RIVM), phase 2 antibodies can persist for a long time, so a single positive result does not distinguish between an acute and a past infection. For an acute infection, a clear rise between two blood samples is needed.
Negative result
A negative phase 2 IgG makes a past Q fever infection unlikely. In the first two weeks of illness, a negative result does not rule out an acute infection, because the antibodies only appear from about the seventh to fifteenth day of illness and IgG comes after IgM. If the suspicion remains, the guideline advises sending in a second blood sample after 14 days; in the first two weeks, a PCR on blood is the better test.
After an abnormal result
When an acute infection is suspected, the doctor compares the result with a second blood sample after about two weeks; if acute Q fever is confirmed, treatment with antibiotics follows, and then blood tests (serology) to detect chronic Q fever in time. Acute Q fever 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.
Reliability
How reliable is the test?
The LCI guideline (RIVM) on Q fever names the immunofluorescence test as the reference method, with a sensitivity and specificity for IgG of almost 100 percent. The test shows the immune response, not whether the bacterium is still present. A single positive result is not suitable for proving acute Q fever; this requires seroconversion or a clear rise in titer in a second sample. In people without symptoms, a positive result mainly says something about the past.
What can affect the result?
- Phase 2 antibodies can remain present for years; a single result does not distinguish between an acute and a past infection.
- Antibodies are only detectable from about the seventh to fifteenth day of illness (window period).
- Cross-reactions with antibodies against other bacteria, including Bartonella and Legionella, occur.
- The outcome depends on the test used; one year after infection, the immunofluorescence test finds more phase 2 IgG than an ELISA.
Who it is for
Who is the test useful for?
Useful for
Useful when acute Q fever is suspected, together with a second blood sample after about two weeks, and in people who have been exposed to goats, sheep or an infected farm. The result can also show whether someone has already had the infection, for example before a vaccination. Not useful as a general check-up in people without symptoms and without exposure: a positive result then usually means an old, harmless infection and does not change the management.
How common is it?
Q fever is rare in the Netherlands. Between 2007 and 2010 there was a large outbreak around dairy goat farms, with 2,354 reports in 2009. After vaccination of goats and sheep, this fell back to a few dozen reports a year, as before the outbreak. In a national study in 2006 and 2007, about 2.4 in 100 Dutch people had antibodies against the bacterium without being ill.
RIVM and the RIVM/LCI guideline on Q fever
Drawbacks and risks
- A positive result in someone without symptoms usually points to an infection long ago, but can still lead to worry and unnecessary further tests.
- The result says nothing about long-lasting tiredness after Q fever; that diagnosis is based on the course of the symptoms, not on this test.
Get tested
Q fever phase II, Coxiella burnetii IgG: test panels
Q fever phase II, Coxiella burnetii IgG is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and resultsMore explanations
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