Examining the effect of session duration on step count in the Step it UP! Game.

Multimorbidity, the presence of two or more concurrent diseases or health conditions in a single individual, is an emerging global public health challenge []. As populations age and healthcare advances prolong life expectancy, large numbers of people have multiple diseases or health conditions, known as comorbidities, simultaneously. Non-communicable disease multimorbidity is estimated to affect one-in-three people in low- and middle-income countries (LMICs) []. This phenomenon complicates treatment strategies, amplifies healthcare costs, and worsens the outcomes of those affected, particularly within resource-constrained health systems []. Tuberculosis (TB), the leading infectious cause of death worldwide, presents a unique challenge within the context of comorbidities and multimorbidity []. While TB is preventable and curable, it continues to affect millions globally, particularly in LMICs, and is associated with a substantial and persistent burden of post-TB disability []. The World Health Organization (WHO) defines five key comorbidities for TB: diabetes, human immunodeficiency virus (HIV), smoking, undernutrition and disorders due to alcohol use []. In 2020, these five WHO-defined key comorbidities were estimated to account for 4·5 million (45%) new and relapse TB episodes globally []. In South Africa, the leading natural cause of death from 2016-2018 was TB, recently superseded by diabetes in 2019 []. However, the interaction between TB, diabetes and other comorbidities including HIV is poorly described, as are sex differences. There are complexities in applying the concept of multimorbidity to TB disease, which have resulted in divergent case definitions and a subsequent inability to meaningfully compare data from different settings. Most notably, when defining multimorbidity as “the presence of two or more concurrent diseases or health conditions in a single individual”, there is inconsistency as to whether TB is included as one of these two diseases, or whether multimorbidity in the context of TB disease is defined as TB plus two or more concurrent diseases or health conditions. To address this, the WHO proposed the following definitions; “Comorbidity: A concurrent disease or health condition in a person with tuberculosis (TB)”, and, “Multimorbidity: The presence of two or more concurrent diseases or health conditions in a person with TB” []. Applying these definitions to existing and future datasets enables harmonised international research and evidence synthesis.