Understanding Q-detect: Coxiella burnetii exposure and the humoral and cellular immune response

Between 2007 and 2011 a large Q fever epidemic struck the Netherlands. Many
people still suffer from chronic disease that damages vessels and heart valves.
Other are suffering from long-term complaints such as chronic fatigue, myalgia,
arthritis and general malaise. To diagnose Q fever, serology is the main method
available in the clinic. Antibodies are often no longer measurable in people
with a past infection.
The Coxiella Induced Interferon-gamma test (Q-detect*) was designed at the
Radboudumc (Nijmegen) and further developed at Innatoss, The test was used in a
large study in Herpen. In the Q-Herpen-II study 1517 villagers were tested for
Q fever. The aim of the study was (i) early identification of chronic Q fever
patients and (ii) determining the prevalence of Q fever in a high incidence
area. One of the secondary aims was to compare Q-detect* with the indirect
immune fluorescence (IFA) test. In light of waning immunity, the hypothesis was
that a cellular immunity test could identify additional cases on top of
measuring antibodies.
This hypothesis was confirmed. On top of 461 individuals positive in IFA and
Q-detect*, 36 were positive in IFA only and 402 individuals were positive in
Q-detect* only. The discrepancy between the two laboratory tests was
unexpected. This triggered questions on specificity of Q-detect*. In the
current study we address this issue, in part to provide an answer to the 402
individuals that were only Q-detect positive and also to define specificity and
sensitivity of Q-detect*.

(i) to determine specificity of Q-detect* for registration purposes.
(ii) to design a decision tree for follow-up of patients with a positive
Q-detect* and

A random group (n=100) from a Dutch region minimally affected by Q fever will
be tested in Q-detect*, which measures the interferon-gamma production ex vivo
in whole blood after stimulation with heat-killed Coxiella burnetii (C.b.).
C.b. is cultured and processed at the Central Veterinary Institute in Lelystad.
Positive samples will be tested for anti-phase 1 and anti-phase 2 Coxiella
antibodies using indirect immune fluorescence (IFA). IFA-negative samples will
be tested in an in-house developed immunoblot that identifies antibodies
against different C.b. antigens. For comparison, 25 individuals with a history
of Q fever (IFA and Q-detect* positive), will be tested in the immunoblot as
well as cytokine test, that measures IFN-gamma as well as TNFalpha, IL1beta,
IL-2, and IL-10. The working hypothesis is that infected individuals will
resemble Q fever patients in immunoblot as well as cytokine profile.

Random participants donate one additional tube of blood (4 mL). The
venepuncture is performed by qualified personnel of Medlon and poses negligible
risk. Receiving information on the study and filling in the informed consent
form will take not more than 10 minutes.
Q-fever patients are informed in advance by Innatoss and will need to visit the
blood drawing post in Oss once. The venepuncture is performed by qualified
personnel of DC Bernhoven and poses negligible risk.

Personal benefit is negligible but participation will contribute to providing
better diagnostic options for Q-fever.

In the event that subjects have a positive Q-detect test (either true positive
or false positive) Innatoss will arrange for initial follow-up consisting of a
standard IFA test. In the extremely rare event that blood tests suggest
possible chronic Q fever, the GP will be informed immediately. The benefit for
the subject is that a timely diagnosis will facilitate adequate treatment.

Subjects who are positive in IFA without an indication of possible chronic Q
fever, will be notified through Medlon after the end of the study. If the
results of the study indicate that the likelihood is high that a positive
result is false positive, subject will be informed. At the request of the
subject his/her GP will be informed as well. The independent expert (a GP with
extensive Q fever experience) will provide professional advise.