Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. There are many Cochrane Reviews about the diagnosis and treatment of tuberculosis and those involved in managing this condition also need to know about its prognosis, especially in the presence of other illnesses. We can now help them in regard to diabetes and tuberculosis, with a new review published in August 2024. Here are two of the authors, Juan Franco and Yang Guo from the Institute of General Practice, Medical Faculty of the Heinrich-Heine-University Düsseldorf in Germany, to tell us more.

Juan: Worldwide, tuberculosis or TB caused an estimated 1.6 million deaths in 2022, with about 10.6 million new cases diagnosed in that year alone.
Diabetes is one of the important risk factors and, each year, the WHO provides a statistic, called the "population attributable fraction" (PAF) as an estimate of how much TB is due to diabetes. The PAF helps us understand what percentage of cases of a disease, in this case, TB, can be attributed to a specific risk factor, in this case, diabetes. It tells us how much of the TB burden could be avoided if diabetes were eliminated. It is based on the prevalence of TB and estimates for the risk posed by diabetes. This is where our own work comes into play and I’ll hand over to Yang, to summarise what we did for our Cochrane Review.

Yang: Thanks, Juan. In our review, we aimed to determine the prognostic value of diabetes in predicting TB in both children and adults, across all settings.
We searched for cohort studies in which adults, adolescents, and children from diverse settings were characterised by many baseline characteristics, including diabetes. Our primary outcome for this review was the incidence of TB disease among people with diabetes, which was defined by repeated measures of altered fasting plasma glucose and other standard criteria.

Juan: To put this in context, people can be infected with TB (and not have any symptoms), or they can present with symptoms, such as persistent cough, which may be bloody, weight loss, fever, and night sweats. After the diagnosis is made, this is called TB disease, and we were interested in the association between this outcome and diabetes.

Yang: To do this, we used data from a total of 48 cohort studies with more than 61 million participants. Our main analysis, based on data from about a quarter of these studies, indicated that having diabetes almost doubles the risk of TB disease. More precisely, in statistical terms, the hazard ratio for developing TB disease was 1.90 times higher in people with diabetes compared to people without.
A few of the studies presented their data in a different way, using the odds ratio or risk ratio for the development of TB. When we pooled these studies, they showed similar results to the hazard ratios, with a pooled odds ratio of 1.61 and a pooled risk ratio of 1.60.
It is important to add that most of the included studies had less than ten years of follow-up; but the very few studies with longer follow-up signalled an even higher risk for TB disease, although these results are uncertain.
We also found that the risk of TB disease was higher in people with poor glycemic control and complications due to diabetes, which highlights the importance of optimal care in this population.

Juan: Thanks for summarising the numbers so clearly, Yang. These estimates will inform future WHO Global TB Reports, which deliver state-of-the-art, annual updates on the TB epidemic and progress in TB prevention, diagnosis and treatment worldwide. The reports also update on the milestones achieved by the World End TB Strategy. This comprehensive global framework, launched in 2014, aims to eliminate TB-related deaths, TB incidence, and the catastrophic costs for families affected by TB. So, all in all, the Global TB Reports are vital for tracking the epidemic, guiding policies, and promoting research and innovation.
With that in mind, Yang would you like to say a little about how systematic reviews like ours might help the End TB Strategy?

Yang: In general, systematic reviews are crucial for policymakers. They provide valuable insights into prognosis, diagnosis, treatment and even prevention strategies. Concerning the End TB Strategy, systematic reviews may facilitate the design and implementation of effective TB control programs and, thereby, ease the enormous burden of TB.
In the case of our Cochrane Review, the prognostic information we provide allows the prediction of the proportion of TB cases that are attributable to diabetes. This may raise overall awareness on the importance of diabetes as a risk factor for TB and help health systems to design targeted interventions for populations at high risk of both TB and diabetes. The review could also support planning and prioritisation of resources as part of TB control efforts.
Finally, Juan, if people would like to read our review, how can they get hold of it?

Juan: It’s available free online at Cochrane Library dot com. A search for “diabetes and tuberculosis” will show it near the top of the list.