US soldiers in high-tuberculosis areas face new epidemic: false positives

May 30, 2008

U.S. Army service members are increasingly deployed in regions of the world where tuberculosis (TB) is rampant, such as Iraq and Afghanistan, and the military now faces a growing medical problem. But it is not TB itself that is on the rise—instead, the problem lies with the growing number of “pseudoepidemics,” or clusters of false-positives for TB that are the result of universal testing with a notoriously inaccurate tuberculin skin test (TST) and inconsistent procedures for interpreting those tests in low-risk populations.

These false positives tests have become more than a mere institutional inconvenience or a momentary medical scare for Soldiers being tested. They are a real financial and medical burden because they inappropriately diverting limited funds and resources.

A recent study, published in American Thoracic Society’s first issue for June of the American Journal of Respiratory and Critical Care Medicine, describes eight outbreaks of false-positive TB tests between 1983 and 2005. The study was led by U.S. Army Major James Mancuso, M.D., of the Uniformed Services University of the Health Sciences.

Recent deployments to Iraq and Afghanistan, which are reported to have among the highest rates of active TB in the world, have raised concerns about TB exposure. However, many service members do not have sufficient contact with locals to raise their risk of contracting TB. As a consequence, “testing after recent deployments to the endemic and hyperendemic areas has occasionally resulted in large numbers of U.S. Army service members with [positive tests] and massive efforts aimed at preventing active TB,” wrote Dr. Mancuso.

Because the positive-predictive value of a test—that is, the likelihood of a positive result indicating an actual case—is dependent on the prevalence of disease in a population. The lower the prevalence of a disease, and the higher the variability in the test and testing procedures, the less the positive-predictive value of a test will be. “This may dramatically reduce the positive-predictive value of the test to below 50 percent,” said Dr. Mancuso.

Dr. Mancuso and his colleagues conducted outbreak investigations in deployed locations such as the Balkans and Afghanistan, where they collected and reviewed medical records of reported active and latent TB cases in deployed U.S. Army service members. They then obtained the medical histories of these soldiers, including prior diagnoses and treatments, determined current symptoms and interviewed the subjects to identify other possible risk factors. Finally, they retested all available skin test converters.

“Repeat testing of converters (positives) found that 30 to 100 percent were negative on retesting,” wrote Dr. Mancuso. In one case, 95 percent of positive TB tests (38 of 40 tests) from Army National Guard servicemen in Kosovo were subsequently found to be negative, and the pseudoepidemic was primarily attributed to variability with the test administration and reading, as well as to the specific type of test used.

“The testing of [a] predominantly low-risk population leads to false-positive results in individuals and pseudoepidemics of false-positive TST conversions in U.S. Army populations,” Dr. Mancuso concluded, recommending three actions to reduce the occurrence of false positive skin tests and these apparent outbreaks: test only truly high-risk personnel; standardize testing procedures; and use the more reliable of the TST tests, Tubersol, in lower-risk populations such as the U.S. Army.

“As always, an individualized assessment of each patient’s risk of tuberculosis should be used to target testing and treatment of latent tuberculosis infection. In the absence of other risk factors, clinicians and public health officials should interpret reported skin test conversions after deployment with caution,” he added.

Source: American Thoracic Society

Explore further: Testing for specific proteins significantly improves sensitivity of stool-based colorectal cancer screening

Related Stories

Testing for specific proteins significantly improves sensitivity of stool-based colorectal cancer screening

November 20, 2017
Testing for novel protein biomarkers in stool finds significantly more colorectal cancers (CRC) and advanced adenomas (precursors to cancer) compared to testing for hemoglobin alone. The proteins can be detected in a small ...

Use of Prostate Health Index test reduces unnecessary biopsies

November 20, 2017
The Prostate Health Index (phi) is a cost-effective tool used by urologists to detect prostate cancer. It reduces the risk of over diagnosis, and cuts down on the need to send men for unnecessary and often uncomfortable biopsies. ...

Mainstreaming genetic counselling for ovarian cancer could support screening, in Malaysia and beyond

November 20, 2017
A study that looked at mainstreaming genetic counselling for ovarian cancer to support screening programmes in Malaysia was presented at the ESMO Asia 2017 Congress. The preliminary results of the MaGiC study show that most ...

Vibrating sensors could identify blood biomarkers, improve early-stage detection, treatment of numerous diseases

November 20, 2017
Purdue University researchers have found a method of identifying biological markers in small amounts of blood that they believe could be used to detect a myriad of diseases, infections and different medical conditions at ...

Cell-weighing method could help doctors choose cancer drugs

November 20, 2017
Doctors have many drugs available to treat multiple myeloma, a type of blood cancer. However, there is no way to predict, by genetic markers or other means, how a patient will respond to a particular drug. This can lead to ...

Clinical trial suggests new cell therapy for relapsed leukemia patients

November 20, 2017
A significant proportion of children and young adults with treatment-resistant B-cell leukemia who participated in a small study achieved remission with the help of a new form of gene therapy, according to researchers at ...

Recommended for you

Rainfall can indicate that mosquito-borne epidemics will occur weeks later

November 22, 2017
A new study demonstrates that outbreaks of mosquito-borne viruses Zika and Chikungunya generally occur about three weeks after heavy rainfall.Researchers also found that Chikungunya will predominate over Zika when both circulate ...

Alcohol consumption and metabolic factors act together to increase the risk of severe liver disease

November 22, 2017
A new study provides insights into the interaction between alcohol consumption and metabolic factors in predicting severe liver disease in the general population. The findings, which are published in Hepatology, indicate ...

Gastric acid suppressant lansoprazole may target tuberculosis

November 21, 2017
A cheap and widely used drug, used to treat conditions such as heartburn, gastritis and ulcers, could work against the bacteria that cause tuberculosis (TB), according to new research from UCL and the London School of Hygiene ...

Improving prediction accuracy of Crohn's disease based on repeated fecal sampling

November 21, 2017
Researchers at the University of California San Diego Center for Microbiome Innovation (CMI) have found that sampling the gut microbiome over time can provide insights that are not available with a single time point. The ...

Anti-malaria drug shows promise as Zika virus treatment

November 17, 2017
A new collaborative study led by researchers at Sanford Burnham Prebys Medical Discovery Institute (SBP) and UC San Diego School of Medicine has found that a medication used to prevent and treat malaria may also be effective ...

Decrease in sunshine, increase in Rickets

November 17, 2017
A University of Toronto student and professor have teamed up to discover that Britain's increasing cloudiness during the summer could be an important reason for the mysterious increase in Rickets among British children over ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.