Flowchart illustrating the idealised laboratory diagnosis of acute Q fever infection

Return to the NSW Control Guideline for public health units for Q fever.

Acute, clinically compatible illness

• PCR test:
• Detected
• Notification and public health follow-up
• Confirmed case
• Not detected
• Send for initial (acute) serology
• Initial (acute) serology:
• Ab¹ detected
• Notification and public health follow-up
• Possible case
• Obtain follow-up (convalescent) sera 2-3 weeks after initial specimens
• Ab¹ not detected
• Obtain follow-up (convalescent) sera 2-3 weeks after initial specimens
• Paired sera testing (after obtaining convalescent sera 2-3 weeks after initial specimens)
• Ab¹ detected (seroconversion) or 4-fold rise in titre
• Confirmed case (updated from possible)
• Ab¹ not detected or <4-fold rise in titre²
• Exclude²

References

1. Serological patterns and the detection of Q fever-specific antibody (Ab) is dependent on the time from onset of illness, assay completed (i.e. IFA, CFT, EIA) and past exposure to the organism. Refer to section 7 and Appendix 5 of the NSW Control Guidelines for detail.
2. Significant antibody titres may take 3-4 weeks from illness onset to appear in some cases. In cases not definitively confirmed by other means, a third sample is recommended, which should be collected 3-4 weeks after fever onset.