Sixteen-year tuberculosis notification trends, spatial heterogeneity, treatment outcomes and diagnostic delay in Khuzestan, Iran: a registry-based study

Tuberculosis is an ancient bacterial infection that primarily attacks the lungs, though it can spread to other parts of the body. For decades, health officials have relied on a simple count of new cases reported to clinics to track how the disease is moving through a population. This count, known as a notification, is not a perfect measure of how many people are actually sick, because it depends on whether people can reach a doctor, whether the disease is spotted quickly, and whether the paperwork is filed correctly. When researchers try to look at these numbers over many years, a new problem arises: the map changes. Administrative borders shift, counties merge or split, and populations grow or shrink. If a researcher compares the number of cases in a region from twenty years ago to today without accounting for these changes, the comparison is like weighing a person on a scale that has been recalibrated in the middle of the measurement. To understand the true story of a disease, scientists must first rebuild the map and the population counts so that the past and the present can be compared fairly.

In the southwestern province of Khuzestan, Iran, a team of researchers undertook this difficult task to understand the story of tuberculosis over a sixteen-year period. They gathered records for nearly nine thousand registration episodes, which represent individual instances where a person was diagnosed and entered into the health system's registry. Because the administrative boundaries of the province had changed over time, the team could not simply look at the raw numbers for every district. Instead, they reconstructed the population counts for years between official censuses and grouped the historical counties into twenty consistent units for a broad overview. For a deeper, more precise look at trends over time and space, they focused on ten specific areas where the boundaries and surveillance methods remained comparable throughout the entire sixteen years. This careful reconstruction allowed them to separate the noise of changing borders from the actual signal of the disease.

The researchers found that the number of new tuberculosis cases reported in these stable areas was steadily going down. After adjusting for changes in the age structure of the population, the rate of new cases dropped by roughly two and two-thirds percent every year. This decline was consistent across different age groups, from children to the elderly, and it held true even when the final year of the study was excluded, suggesting the trend was not a fluke caused by a single year of unusual events. However, the disease was not disappearing evenly across the landscape. When the team looked at the rates across the twenty historical county groups, they saw a wide gap: some areas reported fewer than two cases per one hundred thousand people, while others reported more than twenty-two. This geographic unevenness was real and significant, but when the researchers looked for specific "hotspots"—tight clusters of high rates that might indicate a local outbreak—they found something surprising. While the data showed a weak tendency for neighboring areas to have similar rates, no single small area stood out as a statistically confirmed hotspot once the researchers accounted for the fact that they were testing hundreds of locations at once. In other words, the high rates in specific spots were likely due to chance or local reporting differences rather than a distinct, spreading cluster of infection.

Beyond where the disease was found, the study also examined what happened to the patients once they were diagnosed. Of the nearly nine thousand people in the registry, about ten percent experienced an adverse outcome, meaning they either died, were lost to follow-up, or failed to respond to treatment. The data revealed that men were more likely to have a poor outcome than women, and people who had been treated for tuberculosis before were at higher risk than those being treated for the first time. Conversely, people with tuberculosis outside the lungs, known as extrapulmonary tuberculosis, had a lower observed risk of adverse outcomes, though the researchers noted this might reflect differences in how these cases are identified or treated rather than the disease itself being less dangerous.

Perhaps the most striking finding concerned the time it took for a patient to receive a diagnosis after first feeling sick. The median delay was fifty-five days, meaning half of the patients waited longer than this before getting a confirmed diagnosis. While fifty-five days is a long time, the researchers discovered that the situation was much worse for a smaller group of people. The distribution of wait times had a long tail, with five percent of patients waiting more than three hundred twenty-two days, and some waiting over two years. This delay was not random; it varied significantly based on the patient's situation. Men were diagnosed faster than women, and people who had been treated before were diagnosed faster than new cases. Interestingly, people who were currently in prison at the time of registration were diagnosed much faster, with a delay that was nearly eighteen days shorter on average. The researchers cautioned that this shorter delay likely reflected the intense screening and referral processes within the prison system rather than a benefit of being incarcerated, and they noted that they could not calculate the true rate of disease within prisons because they lacked population data for that group.

The study concluded that while the overall burden of tuberculosis notifications in Khuzestan was declining, the journey to a diagnosis remained frustratingly long for many, and the disease remained unevenly distributed across the region. The researchers emphasized that their work provided a clear picture of the trends and the delays, but it could not prove exactly why these patterns existed or what specific interventions would fix them. The absence of confirmed local clusters suggested that health officials should be careful not to label isolated high-rate areas as definitive outbreaks without further local investigation. Instead, the findings pointed toward a need for targeted reviews of diagnostic pathways, particularly for patients with extrapulmonary tuberculosis and those who have been treated before, to ensure that the long delays in diagnosis are shortened and that the geographic gaps in care are addressed. By successfully harmonizing the historical geography and population data, the team demonstrated a method that could be used in other regions facing similar administrative changes, turning a messy, fragmented history into a clear, comparable story of public health.