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==Overview==
==Overview==
'''Q fever''' is caused by infection with ''[[Coxiella burnetii]]''. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs.
Laboratory findings consistent with the diagnosis of Q fever include [[Serology|positive serology]] for [[antibodies]] (especially [[Immunofluorescence|indirect immunofluorescence (IIF),]] positive [[PCR]], and [[Liver enzymes|elevated liver enzymes]].
 
==Laboratory Findings==
Because the signs and symptoms of Q fever are not specific to this disease, it is difficult to make an accurate diagnosis without appropriate laboratory testing. Results from some types of routine laboratory tests in the appropriate clinical and epidemiologic settings may suggest a diagnosis of Q fever.  For example, a platelet count may be suggestive because persons with Q fever may show a transient [[thrombocytopenia]].  Confirming a diagnosis of Q fever requires serologic testing to detect the presence of [[antibodies]] to Coxiella burnetii antigens. In most laboratories, the indirect immunofluorescence assay (IFA) is the most dependable and widely used method. Coxiella burnetii may also be identified in infected tissues by using [[immunohistochemical]] staining and DNA detection methods.
 
''Coxiella burnetii'' exists in two antigenic phases called phase I and phase II. This antigenic difference is important in diagnosis. In acute cases of Q fever, the antibody level to phase II is usually higher than that to phase I, often by several orders of magnitude, and generally is first detected during the second week of illness.  In chronic Q fever, the reverse situation is true.  Antibodies to phase I antigens of C. burnetii generally require longer to appear and indicate continued exposure to the bacteria.  Thus, high levels of antibody to phase I in later specimens in combination with constant or falling levels of phase II antibodies and other signs of inflammatory disease suggest chronic Q fever. Antibodies to phase I and II antigens have been known to persist for months or years after initial infection.


Recent studies have shown that greater accuracy in the diagnosis of Q fever can be achieved by looking at specific levels of classes of antibodies other than [[IgG]], namely [[IgA]] and [[IgM]].  Combined detection of IgM and IgA in addition to IgG improves the specificity of the assays and provides better accuracy in diagnosis.  IgM levels are helpful in the determination of a recent infection. In acute Q fever, patients will have IgG antibodies to phase II and IgM antibodies to phases I and II.  Increased IgG and IgA antibodies to phase I are often indicative of Q fever [[endocarditis]].
==Laboratory tests==
 
Tests that may be done include:
===Serologic testing for Q fever===
 
* Blood tests to check for antibodies to Coxiella burnetti
*[[Immunofluorescence|Indirect immunofluorescence (IIF)]] is the method of choice for [[antibody]] detection and is preferred over [[ELISA]] and [[complement fixation]].<ref name="urlDiagnosis of Q Fever">{{cite web |url=http://jcm.asm.org/content/36/7/1823.short |title=Diagnosis of Q Fever |format= |work= |accessdate=}}</ref><ref name="pmid7496944">{{cite journal |vauthors=Dupont HT, Thirion X, Raoult D |title=Q fever serology: cutoff determination for microimmunofluorescence |journal=Clin. Diagn. Lab. Immunol. |volume=1 |issue=2 |pages=189–96 |year=1994 |pmid=7496944 |pmc=368226 |doi= |url=}}</ref>
* Liver function test
*[[Antibodies]] start to be detected after 7-14 days of infection, with most patients testing positive by the third week.
* Complete blood count (CBC)
*[[Antibodies|Anti phase II antibodies]] are tested first. If positive, [[Antibodies|anti phase I antibodies]] are tested.
* Tissue staining on infected tissues to identify the bacteria
*After acute infection, [[Serology|serologic]] follow-up for serum [[Antibodies|anti phase I IgG antibodies]]. The test is done twice every 3 months for 2 years. If it's positive, a [[Transesophageal echo cardiography|transesophageal echo]] should be done to rule out [[endocarditis]].<ref name="pmid6622891">{{cite journal |vauthors=Derrick EH |title="Q" fever, a new fever entity: clinical features, diagnosis and laboratory investigation |journal=Rev. Infect. Dis. |volume=5 |issue=4 |pages=790–800 |year=1983 |pmid=6622891 |doi= |url=}}</ref>
*All [[Serology|serologic]] test results should be used in the context of clinical data because false positive test results are seen in many other diseases (e.g. [[leptospirosis]]).   
===Polymerase chain reaction (PCR)===
   
*[[PCR]] can be used to detect ''[[Coxiella burnetii|C.]] [[Coxiella burnetii|burnetii]]'' [[DNA]] in [[Culture medium|cultures]] and clinical samples.
*[[PCR]] is positive in the first week of infection, thus it can be used to diagnose Q fever in patients who are [[Serology|serologically]] negative in the early stages of the disease.<ref name="pmid10515901">{{cite journal |vauthors=Maurin M, Raoult D |title=Q fever |journal=Clin. Microbiol. Rev. |volume=12 |issue=4 |pages=518–53 |year=1999 |pmid=10515901 |pmc=88923 |doi= |url=}}</ref>
*Quantitative [[PCR]] also can be used in patients whose [[Immunoglobulin G|anti phase II IgG antibodies]] are persistently positive in order to detect [[chronic]] Q fever.
===Cultures===
*''[[Coxiella burnetii|C.]] [[Coxiella burnetii|burnetii]]'' doesn’t grow on ordinary [[blood cultures]] but can be cultivated on special media as embryonated eggs or [[cell culture]].
*''[[Coxiella burnetii|C.]] [[Coxiella burnetii|burnetii]]'' is extremely infectious and samples should be handled with caution.
===Liver function tests===
*A two-to-three fold increase in [[AST]] and [[ALT]] is seen in most patients.


==References==
==References==
{{Reflist|2}}
{{Reflist|2}}


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Latest revision as of 23:55, 29 July 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Ahmed Younes M.B.B.CH [2]

Overview

Laboratory findings consistent with the diagnosis of Q fever include positive serology for antibodies (especially indirect immunofluorescence (IIF), positive PCR, and elevated liver enzymes.

Laboratory tests

Serologic testing for Q fever

Polymerase chain reaction (PCR)

Cultures

Liver function tests

  • A two-to-three fold increase in AST and ALT is seen in most patients.

References

  1. ↑ "Diagnosis of Q Fever".
  2. ↑ Dupont HT, Thirion X, Raoult D (1994). "Q fever serology: cutoff determination for microimmunofluorescence". Clin. Diagn. Lab. Immunol. 1 (2): 189–96. PMC 368226. PMID 7496944.
  3. ↑ Derrick EH (1983). ""Q" fever, a new fever entity: clinical features, diagnosis and laboratory investigation". Rev. Infect. Dis. 5 (4): 790–800. PMID 6622891.
  4. ↑ Maurin M, Raoult D (1999). "Q fever". Clin. Microbiol. Rev. 12 (4): 518–53. PMC 88923. PMID 10515901.
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