Question

You have just been accepted to nursing school. As a requirement, you have to have a tuberculosis (TB) test as well as a hepatitis B recombinant vaccine. The nurse who administers the TB skin test explains that if significant swelling occurs around the injection site, you will need to have chest x-rays to determine if you are infected with Mycobacterium tuberculosis. On the morning of the second day after the skin test, you awake to find your arm red and swollen in an area about the size of a quarter around the site of the test. It is also tender to the touch. Now you are really worried. Could you have TB?

1. Why does the reaction to the skin test take 36-48 hours to show up? Explain.

2. If you have a tuberculosis infection, why doesn’t the whole body, or at least the respiratory tract, react when the antigen is injected during this diagnostic test? After doing a chest x-ray, your doctor says the results are inconclusive. So, you are put on a six-month course of isoniazid to be safe. About six months later, while sitting in your medical microbiology class during a lecture on tuberculosis, you suddenly realize why you had that positive reaction to the skin test six months earlier. It had nothing to do with being infected, but was because you were born in Norway and your family moved to the United States when you were four years old.

3. What is going on here? Discuss in detail.

4. A while later, you told a friend of yours who is HIV-positive about your TB scare. She said that her doctor doesn't typically use the TB skin test on her, even though people with HIV are more susceptible to TB. Why is the skin test not always a reliable TB test for those with HIV?

Answer 1

Tuberculosis is a highly contagious disease , and it is caused by an infection of bacteria called Mycobacterium Tuberculosis . Exposure to mycobacterium bacteria can result in either the active TB disease or the latent TB infection . The latent TB means that the person infected but have no sign and symptoms . Latent TB can also eventually become active disease . Active TB disease is treated with a combination of medication for 6 to 9 months . Latent TB is usaully treated as well to prevent future active disease .

Here our patient is also on the latent phase of TB , there is no sign and symptom she haven't look on if she didn't go for the Skin test for TB because there is no symptoms come over Thats why our patient has no symptoms even of any respiratory tract when antigen has injected during teh diagnostic test ..

A TB skin test is also known as Mountoux Tuberculin skin test (TST) . Well this test is uasually well - tolerated and people rarely have negative reactions to it .

First phase of test ;- During the TB skin test , a tiny amount of tuberculin is injected under the skin , usually in the forearm . Tuberculin is the sterile extract purified protein derivative (PPD) that made from the bacteria . that cause TB . After receiving the injection , a small , pale bump will form at the site .

Second phase of test ;- This phase take place 48 to 72 hours later . At that time , the skin reaction means that how it reacted to the tuberculin this helps in determining whether the person is infected or not .

If the test is negative the person skin return in one to three weeks for a repeat test to ensure the result are the same .

But if the person is infected as like our patient above , the skin around the site of the injection should start to swell and harden by 48 to 72 hours . this bump or induration as it's referred to clinically , will also turn red . but the size of the induration . not the redness , is used to determine the person's results . The induration should be measured across the forearm , perpendicular to the axis between the paerson hand and elbow ,

Size of induration	Result
Less than 5 mm	negative for Tb
at least 5 mm	positive if ;- the person had recent contact with someone with TB The person is HIV- positive The person have had an organ transplant the person are taking mmunosupressants The person have previously had TB
at least 10 mm	positive if ;- the person recently immigrated from a country with a high incidence of TB The person live in a high - risk environment The person work in a hospital ., medical laboratory or other high risk setting The person is child under the age 4 the person have used injected drugs .
15 mm or more	positive

Yes , our patient get this TB from the Norway , the immigrants from Norway leads to cahin of transmission of TB ..Among more than 70 % of the patients diagnosed with TB in Norway in 1999 to 2001 which one had a foreign background, while the proportion in 1994 to 1998 was 53% . their was the significant clusters of strain at that time of M.Tuberculosis . which leads to outbreak and then many people wre miggrants to different country also carry   along with the strains of bacteria with them , our patient is also one of them .

The tuberculin skin testing is a reliable tool for the detection of tuberculous infection and its eventual prevention. False negative test may occur in indiviual with a compromised immune system , including those with human immunodeficency virus (HIV) infection , person taking immunosuppresive drugs (e.g . corticosteroid ) , severly malnourished and elderly . Nevertheless it is still useful in detectng infection in those who are in close contact of patient with tuberculosis disease . Once a skin test is found to be reative further diagnostic studies should be done to rule out tuberculosis disease , Once ruled out preventive therapy with isoniazid or a combination of drugs should be instituted . A TB cannot be eliminated until the importnace of preventive therapy is recognized by all.