Weil Felix Test

Your doctor may order the Weil-Felix test if you have symptoms suggestive of rickettsial infection and a recent history of possible exposure to rickettsial agents. The test is performed five to seven days after the onset of symptoms to detect antibodies, which are mainly of the IgM (immunoglobulin M) type. IgM antibodies are the first antibodies produced by the body to fight an infection.

Rickettsial disease may present as a mild illness or a life-threatening condition, causing jaundice, pneumonia, myocarditis (inflammation of heart muscle), multi-organ failure and shock.

Symptoms of rickettsial infection are nonspecific and mimic viral infections or bacterial infections. They usually appear about one to two weeks after exposure to infection and may differ slightly based on the type of rickettsial infection, but generally include:

• Severe headache
• High-grade fever
• Chills
• Painless ulcer (eschar) at the site of tick or mite bite
• Enlarged lymph glands
• Rash 
• Vomiting
• Nausea
• Lack of appetite
• Muscle pain
• Abdominal pain
• Enlarged liver
• Increased respiratory rate

If diagnosed early, the infection can be readily treated with antibiotics. Certain features that can help the doctor make an early diagnosis include:

• A history of tick bite
• Recent travel to areas where the infection is prevalent
• Similar illness in family members, colleagues or pets

 You do not need any special preparation before the Weil-Felix test.

A blood test is ordered to check for rickettsial antibodies. The following procedure is used to collect a blood sample:

• A laboratory technician will tie a tourniquet (a tight band) around your upper arm and ask you to tighten your fist. This helps to make the veins in your arm more prominent.
• The site for needle insertion will be cleaned with an antiseptic wipe.
• The technician will then insert a sterile needle into a vein and collect a blood sample in a container.
• Once the sample is collected, he/she will release the tourniquet and remove the needle.
• The sample will be labelled and sent to the laboratory for testing. 

You may feel a slight pricking sensation when the needle is inserted, it subsides soon. Temporary bruises at the puncture site are also common after a blood test. Please talk to your doctor if you notice an infection at the blood withdrawal site.

Normal results:

If no agglutination is seen in the test, it indicates the absence of rickettsial antibodies in the given blood sample and may suggest that you do not have a rickettsial infection. The symptoms may be attributed to another condition.

However, since agglutinating antibodies are detectable only during the second week of infection, the result may also be negative in the early stages of the disease. Treatment in early stages of the disease may also delay or mask the immune response.

Abnormal results:

Presence of agglutinating antibodies in the given sample indicates a positive result and suggests that you have rickettsial infection.

Antibody test results are usually reported as less than or more than a certain titre. A single high titre of 1:320 or greater, or a fourfold rise in titre (starting from 1:50) between two samples taken two to four weeks apart is reported as a positive result. A single titre greater than 1:80 indicates possible infection.

Bacteria such as Salmonellae, Proteus and Streptococcus pyogenes may give false-positive results, which means that you get a positive result even though you do not have the infection.

Your doctor will interpret the results based on your symptoms, clinical history and results of other tests.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.