Appendix 5. Q fever laboratory result interpretation

Typical serological respo​nse in acute Q fever

Typical serological respo​nse in acute Q fever , text alternative follows

Infection:

  • IgM and then IgG antibodies develop to phase II antigens in 10 to 14 days from symptom onset. 
  • Seroconversion or a fourfold rise in phase II IgG or CFT titre in convalescent serum is diagnostic of Q fever.

Abbreviations:

  • CFT - complement fixation test
  • EIA - enzyme immunoessay
  • IFA - immunofluorescence assay
  • PCR- polymerase chain reaction
  • Ph - phase

*by IFA​

Reproduced with permission of the copyright owners and authors Dr Jenny Robson, Sullivan Nicolaides Pathology and Dr Alex Chaudhuri, Director of Infectious Diseases, The Prince Charles Hospital, Chermside QLD 4032 and Senior Lecturer, University of Queensland School of Medicine.

Source: Medicine Today April 2013; 14(4): 54-59.

Serological patterns and PCR results for acute Q fever and chronic Q fever

Acute resolving Q fever

PCR

​​Symptoms onset ​<7 days ​14-21 days ​3 months ​6 months ​12 months
​Serum ​positiv​e ​Negative ​​Negative ​​Negative ​​Negative

 EIA

Symptoms onset ​<7 days ​14-21 days ​3 months ​6 months ​12 months
IgM - Phase 2​ ​+- Positive ​Positive ​​Equivocal* ​​Negative ​​Negative​
​IgG - Phase 2​ Negative ​Positive ​Positive ​​Positive ​​Positive​**

CFT

Symptoms onset ​<7 days ​14-21 days ​​3 months ​​6 months ​12 months
​CFT - Phase 2 ​<8 ​64 ​512 ​256 ​64
CFT - Phase 1 ​​<8 ​<8 ​16​​ ​32 ​16

IFA

Symptoms onset ​<7 days ​14-21 days ​​3 months ​​6 months ​12 months
​IgM - Phase 2​ 10-80 ​320 640 ​160 ​64
IgG - Phase 2​ <10 ​320 ​640 ​1280 ​640
​IgA - Phase 2​** ​<10 ​<10 ​<10 ​40 ​20
​IgM - Phase 1 ​<10 ​80 ​320 ​160 ​<10
​IgG - Phase 1 ​<10 ​<10 ​320 ​160 ​160
​IgA - Phase 1** ​<10 ​<10 ​<10 ​<10 ​<10​

*May persist for months to years and not clinically significant
**May become undetectable over a long period of time
***Not always performed - clinical relevance uncertain

Reproduced with permission of the copyright owner and author Dr Jenny Robson, Sullivan Nicolaides Pathology.
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Serology compatible with evolving Chronic Q fever

PCR

​​Symptoms onset ​<7 days ​14-21 days ​3 months ​6 months ​12 months
Serum/tissue ​Positive ​+-Positive* +-Positive* ​​Nil. ​​Nil.

CFT

Symptoms onset ​<7 days ​14-21 days ​​3 months ​​6 months ​12 months
​CFT - Phase 2 ​<8 ​64 ​512 ​1028 ​512
​​CFT - Phase 1 ​​<8 ​<8 ​512 ​1028 ​1028

IFA

Symptoms onset ​<7 days ​14-21 days ​​3 months ​​6 months ​12 months
​IgM - Phase 2​ 10-80 ​320 640 ​160 ​<10
IgG - Phase 2​** <10 ​320 1024 ​2560 ​10240
​IgA - Phase 2​ ​<10 ​<10 ​<10 ​40 ​20
​IgM - Phase 1 ​<10 ​160 640 ​160 ​<10
​IgG - Phase 1** ​<10 ​<10 ​1024 ​2560 ​20480
​IgA - Phase 1*** ​<10 ​<10 ​<10 ​160 ​160
*Poor sensitivity in serum ~50%
**Persisting pahse 1 and to a lesser extent phase 2 IgG (CFT and IFA)
***Elevated phase 1 IgA > 160 may be present in chronic infection​

Reproduced with permission of the copyright owner and author Dr Jenny Robson, Sullivan Nicolaides Pathology.
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