Burden of non-communicable diseases (NCDs) in Africa

Chronic NCDs such as diabetes, cardiovascular diseases (CVD), and cancers are emerging as leading causes of mortality and morbidity in Africa. In this region, with a population of around 1.1 billion, there were an estimated 28 million adults living with diabetes in 2015 [1, 2]. It is anticipated that in sub-Saharan Africa (SSA) alone, the number of people living with the disease will rise to 34.2 million by 2040 [2]. Similarly, in 2015, a projected 1.6 million deaths were attributable to CVD in Africa [3]. This figure is expected to rise by another 1 million by 2030 [3]. Cancer-related deaths are also anticipated to double to 1.2 million by 2030 [3]. Close to one-third of NCD-related deaths in low- and middle-income countries (LMICs) are premature and occur before the age of 60 [4]. Thus, NCDs already present a major health burden for the African continent and are expected to be the most common cause of death, exceeding the number of deaths from communicable, maternal, perinatal, and nutritional diseases combined, by 2030 [5].

Risk factors for NCDs in Africa

Because of the diverse social, environmental, and biological settings within Africa, the distributions of known and other potentially novel risk factors, and their determinants, are likely to differ from those of European populations or those of African descent living outside Africa [Reference Gurdasani6]. The higher incidence of certain cancers, such as liver, cervical and oesophageal, in Africa compared with high-income countries (HICs) may reflect underlying differences in their risk factors in these regions [Reference Ferlay7]. Population growth and the concomitant rise in life expectancy are likely to only partly explain the increase in NCDs. Many of the known risk factors for NCDs in HICs are the same for LMICs, including smoking, alcohol, diet, obesity, raised cholesterol and blood pressure [Reference Yusuf8, Reference Murphy9]. However, the distribution and relative contribution of these risk factors to the burden of NCDs in Africa are unclear. We also have only a limited understanding of the social, environmental and biological drivers of these risk factors within African populations. Rapid urbanisation and globalisation, and the associated trends towards unhealthy lifestyles, contribute to the burden of NCDs [Reference BeLue10]. Small increases in urbanisation are associated with lower levels of physical activity and higher body mass index [Reference Riha11–Reference Sobngwi13]. Globalisation has increased the availability of cheap, nutrient-poor, and energy-dense foods, which are likely to increase the risk of obesity and associated cardiometabolic risk factors [Reference Hawkes14]. Notably, the high burden of NCDs in rural areas, as well as urban centres, suggest there may be additional contributing or distinct factors [Reference Kavishe15].

Impact of maternal and childhood health on NCDs in Africa

Maternal and neonatal health and risk of NCDs are interrelated. The prevalence of overweight and obesity in adult women in Africa has been rising; between 1980 and 2013, the burden of overweight and obesity in females increased by an average of 10% [Reference Ng16]. Maternal obesity increases the risk of developing gestational diabetes [Reference Torloni17], and is associated with poor maternal and neonatal outcomes [Reference Yu, Teoh and Robinson18–Reference Wendland20]. Women who develop diabetes and hypertension during pregnancy have an increased risk of type 2 diabetes (T2D), CVD, and metabolic syndromes [Reference Yogev and Visser19, Reference Ben-Haroush, Yogev and Hod21–Reference Kaul23]. Children of obese or diabetic mothers also have a higher risk of metabolic disease in later life [Reference Boney24]. By contrast, under-nutrition in utero or in early life may also result in an increased risk of T2D and CVD in adulthood [Reference Uauy, Kain and Corvalan25–Reference Gluckman, Hanson and Beedle28]. Adaptive responses to exposures in utero are thought to prepare the foetus for the postnatal environment [Reference Uauy, Kain and Corvalan25]. Rapid changes in the nutritional environments, as seen in many LMICs, could lead to an increase in NCDs [Reference Uauy, Kain and Corvalan25–Reference Barker27]. These maternal and developmental risk factors may have a social, environmental, or biological basis, and are intergenerational – highlighting the complexity of the epidemiological transitions across the African continent, and in other LMICs [Reference Gluckman, Hanson and Beedle28, Reference Barker29, Reference Barker, Bagby and Hanson30].

Changing burden of infectious disease in Africa

Substantial progress has been made in reducing the burden of many types of infectious diseases, including those in early childhood. However, tuberculosis (TB), malaria, and HIV, as well as hepatitis B and C, remain endemic across the region. Africa has the highest burden of HIV in the world, with approximately 26 million prevalent cases and 1.3 million new infections recorded in 2014 [31]. TB and HIV co-infection is a growing issue in many LMICs [Reference Pawlowski32]; as such, it is the most common cause of death for people with AIDS [33]. Anti-retroviral therapy (ART) coverage in Africa has rapidly increased over the past decade; 51% of known cases in SSA received treatment in 2012 [34]. Expanding use of ART has led to a notable decline in HIV-associated morbidity and mortality in Africa; HIV is rapidly becoming a chronic disease, requiring long-term treatment and management. This and the emergence of drug resistant strains of HIV, malaria, TB, and other pathogens pose a major challenge for the continent's infectious disease control and management programmes, which may also have implications for the burden of NCDs [35, Reference Okeke36].

Interrelationship between non-communicable and infectious disease in Africa

The interrelated risk factors for infectious and non-communicable diseases are likely to have an important impact on the spectrum and distribution of chronic diseases in Africa, and other LMICs undergoing similar epidemiological transitions. The immune and metabolic systems are closely integrated, with each system's response dependent on the other for normal function [Reference Hotamisligil37]. Evolving from a common antecedent organ, they have shared and overlapping signalling pathways [Reference Hotamisligil37]. Chronic inflammation has been unequivocally linked to obesity, insulin resistance, T2D, and an increased risk of malignancy [Reference Hotamisligil37, Reference Crusz and Balkwill38]. Likewise, several infectious diseases and their treatments are associated with an increased risk of NCDs [Reference Young39]. HIV and ART may increase the burden of cardiometabolic risk factors, including lipid and glucose abnormalities [Reference Dillon40–Reference Triant43]. Hepatitis B and C infection may also increase the risk of developing T2D [Reference Shintani44–Reference Wang46], as well as chronic liver disease and hepatocellular cancers, in addition to other oncogenic pathogens [Reference Chen and Morgan47]. Similarly, insulin resistance and T2D may influence clinical outcomes in patients with hepatitis-associated liver disease and cancer [Reference Wang48]. Endemic infectious diseases may have also had an impact on selective adaptation and risk of NCDs – for example, renal function and African trypanosomiasis [Reference Genovese49]. Thus, the body's own immune response, endemic and chronic infections, and their treatments, may play an important role in the development and progression of NCDs in Africa, although the underlying mechanisms are not well understood.

The need for surveillance and prospective studies in Africa

Understanding the aetiology and determinants of NCDs in Africa is a fundamental step in developing strategies for disease prevention, management and control. Crucially, the impact of population and individual risk factors on disease susceptibility is largely unknown. Usually, chronic disease risk prediction models applied to African populations are based on regional comparisons of national indices, cross-sectional or case-control assessments, and the extrapolation of risk prediction algorithms developed in populations in Europe and elsewhere [Reference Gaziano50–Reference Crowther and Norris52]. Furthermore, those studies conducted in African populations often use varying methods and definitions, or only assess a small subset of potential risk factors, limiting comparative analysis [Reference Mensah53–Reference Murphy55].

Whilst research institutions in Africa have clearly developed research frameworks for assessing the epidemiological and clinical burden of chronic disease across the region, there is a need to integrate and scale up such efforts [Reference Gurdasani6, Reference Dillon40, Reference Motala51, Reference Kahn56]. The INDEPTH Network of health and demographic surveillance systems is an example of a pragmatic model for examining disease burden across different settings [57–Reference Ng59]. Utilizing such established surveillance systems and analogous research initiatives to implement high quality and comparable large-scale population-based studies across the spectrum of chronic diseases and their risk factors will be crucial to understanding the aetiology and burden of chronic diseases in Africa. Likewise, implementation of standardised tools for the measurement of NCD risk factors in LMICs, such as those developed by the WHO, will enable comparability [60]. Importantly, establishing prospective studies in these settings will provide an invaluable framework to evaluate the utility of existing generic cut-off points or develop specific risk prediction algorithms for African populations, and provide the foundations for future aetiological and healthcare interventions.

The need for research into the implementation of integrated health services and the management of chronic diseases in Africa

Aligning epidemiological and implementation research will provide the most effective strategy to identify pragmatic solutions for delivering chronic disease health care. The emerging double burden of chronic infectious and non-communicable disease imposes a substantial strain on limited healthcare resources and has implications for health policy and planning. In many African countries, where health systems are fragile, under-resourced or targeted primarily to infectious diseases, the capacity to effectively deal with the burden of chronic NCDs and accompanying co-morbidities is severely limited [Reference Beran and Yudkin61, Reference Maseko, Chirwa and Muula62]. These health system challenges will only become more apparent as the prevalence of NCDs increases.

Chronic infectious and non-communicable disease programmes in Africa have traditionally been distinct at all levels of healthcare provision. However, emerging evidence suggests that an integrated approach to the broad spectrum of chronic diseases may provide the most cost-effective mechanism for disease treatment and control due to the related underlying pathogenesis and strategies for management [Reference Janssens63, Reference Atun64]. Integrating NCD management with existing HIV/AIDS/TB, malaria, and maternal and child health programmes would utilise existing infrastructure, and allow for more rapid implementation of NCD health care [Reference van Olmen65]. Ideally these services would be placed within a strengthened and well-resourced primary health care system that can provide pro-active, patient-centric and long-term community-based care [66]. However, a more complete understanding of the broad range of risk factors, and their interrelation, will be critical in designing such integrated health care systems – and provide mechanisms for broader preventative strategies. In these contexts, it is vital to conduct public health implementation research to fully explore the most effective and economic strategies to deliver accessible and integrated health care for chronic diseases [Reference Beaglehole67–Reference de-Graft Aikins, Boynton and Atanga70]. Universal implementation of existing low cost interventions for the diagnosis and management of NCDs and infectious diseases would be a pivotal first phase [66].

Likewise, it will be important to identify the most effective strategies for chronic disease management for the African context; reliable information on the efficacy of drug treatments for NCDs and infectious diseases, and their adverse reactions in African populations is limited [Reference Aminkeng71, Reference Ramos72]. Harnessing and integrating existing health and pharmacovigilance systems could also facilitate drug efficacy trials and monitoring. Evaluation of current and novel chronic disease diagnostics, treatment and management strategies, including point of care testing and low-cost technology-based interventions within resource-limited settings, will be vital to implementing efficient mechanisms for integrated chronic disease research and care across the region, and in translating research findings into health care policy and services [Reference Drain73, Reference Pai74].

An integrated approach to chronic disease research and care in Africa

NCDs and infectious diseases should not be viewed as distinctive fields within global health research [Reference Horton75]. There is a critical need to combine research efforts across both acute and chronic infectious diseases and NCDs to better understand their interrelation and to develop more effective health systems to provide long-term management and care. Research and implementation partnerships will need to adopt innovative multidisciplinary research agendas that both strengthen and integrate existing infrastructure and advance implementation science. Combined, such structures could allow the formation of large-scale population health resources that would enable comprehensive studies into the diagnosis, prevention and management of chronic diseases, and their complex interactions, over diverse settings [Reference Collins76].