Up to 60% of people infected with Coxiella burnetii remain asymptomatic.[26]Anderson A, Bijlmer H, Fournier PE, et al. Diagnosis and management of Q fever - United States, 2013: recommendations from CDC and the Q fever working group. MMWR Recomm Rep. 2013 Mar 29;62(RR-03):1-23.
https://www.cdc.gov/mmwr/preview/mmwrhtml/rr6203a1.htm
http://www.ncbi.nlm.nih.gov/pubmed/23535757?tool=bestpractice.com
For those who experience symptoms, the majority will have a mild disease without need for hospitalisation. Hospitalised patients represent only 2% to 6% of infected individuals.[5]Parker NR, Barralet JH, Bell AM. Q fever. Lancet. 2006 Feb 25;367(9511):679-88.
http://www.ncbi.nlm.nih.gov/pubmed/16503466?tool=bestpractice.com
[38]Maurin M, Raoult D. Q fever. Clin Microbiol Rev. 1999 Oct;12(4):518-53.
https://cmr.asm.org/content/12/4/518.full
http://www.ncbi.nlm.nih.gov/pubmed/10515901?tool=bestpractice.com
Around 2% of people with acute infection die of the disease.[11]Dahlgren FS, McQuiston JH, Massung RF, et al. Q fever in the United States: summary of case reports from two national surveillance systems, 2000-2012. Am J Trop Med Hyg. 2015 Feb;92(2):247-55.
http://www.ajtmh.org/content/journals/10.4269/ajtmh.14-0503#html_fulltext
http://www.ncbi.nlm.nih.gov/pubmed/25404080?tool=bestpractice.com
Those who recover fully from infection may possess lifelong immunity against re-infection.
Prognosis of C burnetii endocarditis has much improved and mortality is as low as 5% at 5 years if diagnosis is timely, and if combination treatment with doxycycline and hydroxychloroquine is adequately prescribed and monitored.
Prognosis of C burnetii vascular infections is of concern if the patient does not undergo surgery to remove the infected vascular tissue or vascular prosthetic material; mortality is as high as 30%.[99]Eldin C, Mailhe M, Lions C, et al. Treatment and prophylactic strategy for Coxiella burnetii infection of aneurysms and vascular grafts: a retrospective cohort study. Medicine (Baltimore). 2016 Mar;95(12):e2810.
https://journals.lww.com/md-journal/fulltext/2016/03220/Treatment_and_Prophylactic_Strategy_for_Coxiella.1.aspx
http://www.ncbi.nlm.nih.gov/pubmed/27015164?tool=bestpractice.com
Mortality is reduced to around 7% with optimal management (i.e., routine surgery performed 3 weeks to 1 month after initiation of antibiotic treatment, and following an 18- to 24-month course of combination treatment with doxycycline plus hydroxychloroquine with close drug level monitoring).[99]Eldin C, Mailhe M, Lions C, et al. Treatment and prophylactic strategy for Coxiella burnetii infection of aneurysms and vascular grafts: a retrospective cohort study. Medicine (Baltimore). 2016 Mar;95(12):e2810.
https://journals.lww.com/md-journal/fulltext/2016/03220/Treatment_and_Prophylactic_Strategy_for_Coxiella.1.aspx
http://www.ncbi.nlm.nih.gov/pubmed/27015164?tool=bestpractice.com
In patients with cardiovascular-related C burnetii infections, treatment should be stopped at 18 months in those who have native valve or vascular infection without vascular prosthetic material, or at 24 months in those with prosthetic valve or vascular infection with vascular prosthetic material, only if serological outcome is favourable (i.e., two-fold decrease in dilution titre of phase I IgG, and absence of phase II IgM at 1 year).[84]Million M, Thuny F, Richet H, et al. Long-term outcome of Q fever endocarditis: a 26-year personal survey. Lancet Infect Dis. 2010 Aug;10(8):527-35.
http://www.ncbi.nlm.nih.gov/pubmed/20637694?tool=bestpractice.com
If serology is not favourable, antibiotic treatment should be continued, and observation and drug levels should be verified. An expert opinion should be obtained if therapeutic drug levels are achieved without improvement in serological outcomes.