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You are here: Home Clinical Topics Tuberculosis Clinical Pearl: Compliance with INH Prophylaxis for Tuberculosis

Clinical Pearl: Compliance with INH Prophylaxis for Tuberculosis

Author(s): Elinor A. Graham, MD; J. Carey Jackson, MD
Date Authored: March 01, 1997

Have you ever wondered why you often get a reaction of questioning disbelief when you tell a patient from a developing country with a positive PPD that their chest x- ray is normal, but we now recommend that they take medicine for 6 months for tuberculosis. What you have just said makes very little sense to them from their past experience of tuberculosis in their native country. In most areas of Asia, Africa and Central America children are given BCG vaccine at birth and may be boosted later on in life. The BCG produces a positive PPD up to 4 years. In addition, conversion to a +PPD from exposure to TB occurs at a rate of 2-3%/year. By age 20, the majority of population is PPD positive. In these circumstances, the PPD loses its effectiveness as a screening test for TB and is not used in developing countries.

In developing countries, if people become sick or if tuberculosis is suspected for other reasons, they will have a chest x-ray done. If the chest x-ray is normal they are not put on any medication. If the chest x-ray is abnormal and shows evidence of tuberculosis pulmonary disease they then will be treated with medications. When providers in the United States tell them that they have a normal chest x-ray but still should take medicine for tuberculosis they are confused. To take medicine for tuberculosis in their experience means that they have tuberculosis pulmonary disease, yet we have just told them that their chest x-ray looks normal.

To help the patient make sense of this seeming contradiction, the provider needs to back up several steps and explain the differences between medical practices in the United States and in developing countries. We also find that it sometimes helps to differentiate between tuberculosis infection and tuberculosis disease or illness in the lungs. If they have tuberculosis infection without evidence of disease in the lungs we recommend that they take a single medicine for 6 months to prevent tuberculosis disease later on in life. If they did indeed have evidence of tuberculosis disease in the lungs we would then recommend that they take 3 - 4 medications for 6 - 9 months and we would be concerned about the possibilities of them spreading the disease to other individuals. Usually with this type of explanation the recommendation makes more sense to the patient and they will accept taking prophylactic INH.

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