Monitoring

Acute Q fever patients who do not have risk factors for persistent focalized infection should be serologically monitored at 3 and 6 months. Clinical and serologic monitoring should be stopped at 6 months if there is no clinical sign of persistent focalized infection and if phase I immunoglobulin G (IgG) is <1:800.

The monitoring recommendations for patients receiving treatment for C burnetii infection are as follows:

Acute infection:

  • A baseline transthoracic echocardiogram is recommended to assess the presence of vegetations or heart valve disease.

  • Serologies should be repeated at 3 and 6 months.

  • In the event that phase I IgG serologies persist ≥1:800 and/or with signs of bad clinical evolution, a PET/CT scan must be performed along with polymerase chain reaction serum test.[2]

Persistent focalized infections:

  • Serologies and drug level monitoring (i.e., maintaining doxycycline levels at 5-10 mg/L, and hydroxychloroquine at 0.8 to 1.2 mg/L) must be performed every month along with clinical follow-up while the patient is receiving antimicrobial therapy, and for the first 6 months after antibiotic discontinuation. Then every 6 months for 5 years. Indeed, relapses have been reported up to 5 years after Q fever endocarditis treatment.[86][104]

  • Cure is considered in a patient with good clinical outcome, a full 18- to 24-month treatment (in those with cardiovascular-related C burnetii infections), and a good serologic outcome (i.e., two-fold decrease in dilution titer of phase I IgG, and absence of phase II IgM at 1 year).[86] Phase I IgG ≤1:800 is no longer used as a cure criterion.[86]

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