Diagnostic accuracy and cost-efficiency of pooled sputum testing for tuberculosis among people deprived of liberty in Northeast Brazil
A cross-sectional study in Northeast Brazil demonstrates that four-sample sputum pooling with Xpert Ultra offers high diagnostic accuracy and significant cost-efficiency for tuberculosis screening among people deprived of liberty, supporting its scale-up to expand TB detection in prison settings.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Tuberculosis is an ancient disease that still claims more lives today than any other single infectious agent. It spreads through the air when people with the disease cough or speak, making crowded and poorly ventilated spaces like prisons particularly dangerous ground for transmission. To stop the spread, doctors must find infected individuals quickly and start treatment, but the tools to do this are often expensive and require complex machinery. One such tool is a molecular test that looks for the genetic fingerprint of the tuberculosis bacteria in a person's sputum. While this test is highly accurate, it uses a special cartridge for every single person tested, which can be too costly for health systems to afford when screening large groups of people. This financial barrier has led researchers to ask a simple question: if they mix sputum from four different people into one sample, can they still find the disease accurately while using far fewer cartridges?
In a study conducted across seven prison units in the state of Sergipe, Brazil, researchers put this idea to the test under real-world conditions. They gathered sputum samples from 336 people who were suspected of having tuberculosis because they reported symptoms like a persistent cough, fever, or night sweats. Instead of testing each person individually right away, the team took the leftover sputum from four different individuals within the same prison unit and combined them into a single mixture. They then ran this mixture through the molecular testing machine just once. If the mixed sample came back negative, the researchers knew all four people were clear. If the mixed sample came back positive, they would then go back and test each of the four individuals separately to find the specific person who was sick. This approach was compared against the standard method of testing every single person individually to see if the results matched.
The results showed that this pooling strategy works with remarkable precision. Out of 84 mixed samples tested, the results agreed with the individual tests in 82 cases, a match rate of nearly 98 percent. The method correctly identified almost all the people who had the disease, missing only two cases where the bacteria were present in such tiny amounts that they were barely detectable even in a single sample. When the mixed sample was negative, the researchers could be certain that none of the four people in that group had the disease. The few times the test missed a case, it was because the bacteria were so sparse that diluting them in a mixture pushed them below the machine's ability to see them. Despite these rare misses, the overall agreement between the two methods was so high that the researchers described it as nearly perfect.
Beyond the accuracy, the study revealed a dramatic improvement in efficiency and cost. By mixing the samples, the team reduced the number of expensive test cartridges needed by nearly 60 percent. In financial terms, this saved the health system over 1,500 US dollars for the 336 people tested, bringing the cost per person down from nearly 8 dollars to less than 3 dollars. The savings were not just about money; the machine also ran for significantly less time. Testing everyone individually would have kept the machine busy for more than 372 hours, but the pooling strategy cut that time down to about 154 hours. This freed up the laboratory to process many more samples without needing new equipment or extra staff.
These findings offer a practical solution for a setting where tuberculosis spreads easily and resources are often scarce. The study suggests that health officials can screen far more people in prisons using the same budget, potentially catching cases earlier and stopping the chain of transmission. While the method is not perfect for every single type of infection, particularly those with extremely low levels of bacteria, the evidence from this Brazilian prison system indicates that pooling sputum is a safe, accurate, and highly efficient way to expand access to life-saving diagnosis. The researchers concluded that this approach could be scaled up to help Brazil meet its goals for eliminating tuberculosis, proving that a simple change in how samples are handled can make a profound difference in public health.
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