A pair of Q fever studies:
Million, Matthieu, et al. “Thrombosis and Antiphospholipid Antibody Syndrome During Acute Q Fever: a Cross-sectional Study.” Medicine, vol. 96, no. 29, 2017, pp. e7578.
This is a cross-sectional study from the French National Referral Center for Q fever that sought to determine whether thrombosis in acute Q fever patients was associated with IgG anticardiolipin antibodies. As it turns out, during acute Q fever, these antibodies are prevalent in acute Q fever and are believed to be associated with the progression of the acute illness (i.e. pneumonia, hepatitis, and fever) towards the chronic phase (i.e. localized infection i.e. endocarditis. See later).
This was performed from 1/2007 to 12/2015. Primary outcome was occurrence of thrombosis during the acute Q fever episode (i.e. within 3 months of the onset of symptoms). Out of 664 patients with acute Q fever, 13 had thrombosis on presentation; 4 arterial, 7 venous, and 2 with both arterial and venous. IN 12/13 cases, IgG aCL antibody was positive with a median value of 310 GPLU (GPLU = G type phospholipid units, positive is >22).
So in some ways, IgG aCL levels predict the level of badness. From their investigations into other cases, this seems to be the case. In 21 other cases from the literature, they found that 87% of cases with thrombosis (23 venous, 10 arterial) had positive IgG aCL (though they did not give the degree of positivity). Further, most of those patients (62%) had prolonged aPTT, which is the hallmark of anti-phospholipid antibodies (i.e. they make you look like you’re going to bleed in the labs but in reality, you clot).
Melenotte, Cléa, et al. “Acute Q Fever Endocarditis: a Paradigm Shift Following the Systematic Use of Transthoracic Echocardiography During Acute Q Fever.” Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America, vol. 69, no. 11, 2019, pp. 1987-1995.
This one is a prospective study (from France, again) on the use of TTE for the evaluation of acute endocarditis in acute Q fever, rather than chronic Q fever. Acute Q fever was defined as symptoms (fever, hepatitis, or pneumonia) with serologic criteria (phase II IgG levels >200 and IgM >50 with serocoversion or positive PCR or blood cultures) within 3 months. They also obtained IgG aCL levels. They defined acute Q ever IE as follows:
In 2434 patients with positive serology and in 1302 of those with TTE done during the acute phase disease, 48 patients were diagnosed with endocarditis (17 with definite and 31 with possible). Of these, 35 had no prior valvulopathy. Further, they found that those with endocarditis tended to have significantly higher aCLs when compared to those without endocarditis:
The authors recommend pursuing TTE and aCLs in acute Q fever and if you see new valvular lesion, to treat with doxy + HCQ (oh look at that), for 18 months. IF negative, and if aCL >60 and age >40 for men, then do TEE. I do not really have much to add here; didn’t really know that anticardiolipin antibody was a thing for Q fever. Big take aways: always check aCL, may risk stratify these patients (if you end up finding them) and always get a TTE. Duration of therapy changes dramatically.