Disease Description (Cause and Symptoms)

Cause: A zoonotic infectious disease caused by Coxiella burnetii. It is transmitted mainly through contact with infected livestock (cattle, sheep, and goats), inhalation of contaminated secretions, placenta, or dust (aerosols), consumption of contaminated dairy products, and ticks. Person-to-person transmission is rare.
Pathophysiology: As an intracellular pathogen, it multiplies within host macrophages. During the acute phase, it mainly causes pulmonary and systemic symptoms (fever, respiratory symptoms, liver injury, etc.); in some cases, hematogenous dissemination followed by chronic infection can cause involvement of specific organs, such as endocarditis and vascular infection. In the antibody response, phase II antibodies are associated with the acute phase, while high phase I IgG is associated with the chronic phase, particularly endocarditis.
Main symptoms: The incubation period is usually 2–3 weeks. Fever, chills, headache, muscle pain, fatigue, dry cough, and sore throat. Gastrointestinal symptoms (vomiting and diarrhea), hepatomegaly and signs of hepatitis, and rash (rarely) may occur. When the infection becomes chronic, endocarditis (fever, weight loss, heart murmur, etc.) and vascular infection are the main concerns.

Treatment

Acute Q fever
- First-line: Doxycycline 100 mg orally every 12 hours, usually for 14 days (may be extended depending on the clinical condition).
- When doxycycline is contraindicated, such as in pregnancy or children: Trimethoprim-sulfamethoxazole (TMP-SMX) may be considered during pregnancy (especially the first trimester) and breastfeeding, but drug selection requires consultation with obstetrics and gynecology and infectious disease specialists.
Chronic Q fever (endocarditis or persistent tissue involvement)
- Recommended regimen: Combination therapy with doxycycline + hydroxychloroquine (the treatment period is generally at least 12–18 months; longer in cases of endocarditis, with antibody monitoring required during treatment).
- In addition to antimicrobial treatment, surgical valve replacement may be necessary if endocarditis has caused heart valve damage.
Supportive treatment: Control of fever and pain, fluid replacement, and monitoring of liver function abnormalities.
Precautions:
- Coxiella culture is a high-risk (BSL-3) test, so laboratory safety requirements must be followed.
- The treatment duration and drug selection are adjusted according to the patient's condition (pregnancy, underlying diseases, immune status, and presence of a prosthetic valve).

Items and records to prepare
- List of medications currently being taken (prescription drugs, OTC medications, and supplements)
- Record of drug allergies
- Date symptoms began and their progression (duration of fever and changes in respiratory or systemic symptoms)
- History of animal contact (type of animal and whether there was recent contact with animals that had given birth or miscarried), and occupational history (livestock farming, slaughterhouse work, veterinarian, etc.)
- Whether you are pregnant or breastfeeding
- Previous heart disease (valvular disease or a prosthetic valve) and presence of vascular prostheses
- Previous test results (liver function tests, blood tests, chest X-ray/CT, antibody tests, etc.)
Tests that may be performed at an outpatient visit
- Serology (Phase I/II IgG, IgM), PCR (blood or tissue), basic blood tests (LFT, CBC), chest imaging, and transesophageal echocardiography (TEE) if endocarditis is suspected

Example questions (to confirm with the doctor):

Have you recently had contact with animals, especially livestock that had given birth?
If you are pregnant: How many weeks pregnant are you currently?

What are the side effects of this medication? (Especially those related to doxycycline and hydroxychloroquine.)
How long will treatment last, and how long should I be followed with antibody testing?
What criteria are used to determine whether there is a risk of chronic infection (endocarditis)?
If I must continue occupational exposure, what preventive measures should I take?
What are the treatment options and risks during pregnancy or breastfeeding?

I have a prosthetic valve (or congenital valvular disease), and my current phase I IgG level is high on antibody testing. How likely is chronic Q fever (endocarditis), and what additional tests or measures are needed?
I was recently exposed at an event involving livestock giving birth and have a fever. If acute Q fever is suspected, which tests should be performed first, and are there any antibiotics that should be started urgently?

(Summary for Reference)

Prevention: Proper handling of birth products from infected animals, pasteurization and sterilization of dairy products, tick control, use of personal protective equipment (PPE) by workers in high-risk occupations, and vaccination for high-risk groups in some countries (antibody testing is required before vaccination).
Complications: Hepatitis, myocarditis, nephritis, aseptic meningitis, chronic endocarditis and vascular infection, and chronic fatigue syndrome may occur.
Assessment through testing: During the acute phase, an increase in phase II antibodies (especially IgM/IgG); during the chronic phase, high phase I IgG is the key indicator.