Inequalities in multimorbidity in South Africa

Recently, there has been a renewed research interest in multimorbidity (i.e., the case where an individual suffers from two or more disease conditions at the same time) [1, 2]. However, this research area remains in its infancy [2]. Though its epidemiological pattern is similar to that of non-communicable diseases [3], very little is known about the socioeconomic distribution of multimorbidity. Is the usual reported socioeconomic gradient for ill-health also present for multimorbidity? Traditionally, studies on health inequalities have focused mainly on a single disease condition or different disease conditions in isolation [4‐6] but not multimorbidity per se. The dearth of studies relevant to this issue, even in industrialised countries, is surprising given that prevalence of multimorbidity is very high in these countries. Indeed, multimorbidity in industrialised countries is described as the rule rather than the exception, at least in primary care [2]. For instance in the United States, it is estimated that over 80 million people will be affected by multimorbidity by 2020 [2].

The prevalence of multimorbidity is generally associated with “increasing age, lower level of education, and public health insurance” [1] (p.367). Thus, its burden increases as a population ages [7]. This can have considerable impact on families, especially in settings where poverty is widespread and comprehensive health care is lacking [7]. However, in resource-poor countries, including those in Africa, research into inequalities in multimorbidity is even more limited. It is arguably true that, proportionately, the current burden of multimorbidity in these settings far outstrips that of developed and industrialised countries [8]. Multimorbidity is also noted to reduce quality of life significantly. This is “not only in terms of how people felt about their lives generally, but also in terms of the extent of their psychological distress” [9] (p.202). This will further increase the cost of treating multimorbidity. For instance in Australia, it was found that the cost of treating a person with multimorbidity is five times that for other people with only one illness [9].

In South Africa, inequalities in health have been extensively reported with the poor bearing a disproportionate burden [4, 10]. As noted earlier, such studies did not focus on multimorbidity but on either a specific group (e.g., children) or different disease conditions. In order to provide more pertinent empirical evidence, this paper explores inequality in multimorbidity generally in South Africa. Specifically, the paper examines socioeconomic inequality in multimorbidity in illness and disability between 2005 and 2008.

Over 50% of the population is female with an average age of 27 years (Table 1). The majority of the population is single/never married with only a few (<2%) divorced/separated. Only a few people (<3%) had attained tertiary level education. Over 45% of the population is educated up to the secondary level and slightly less than a quarter had no formal education. About 13% of the population reported at least an illness/injury in the past one month; most report flu or acute respiratory tract infection. Only a small population (<0.06%) are infected with STDs. Disability was reported by less than 4% of the population with physical disability dominating (Table 1).

Figure 1 uses the GHS 2008 data to show the number of individuals that are affected by multimorbidity in illness. Each bar indicates the number of people affected by the indicated condition in addition to at least one other illness. In 2008, as shown in Figure 1, multimorbidity in illness that combines BP and at least one other illness is the combination that affects the greatest number of individuals. Over 280,000 South Africans (representing 0.6% of the population) are estimated to report having high BP and at least one other illness. The number is also high for those that indicated a combination of diabetes and other condition(s). Close to 200,000 individuals (representing 0.4% of the population) are estimated to belong to this category. Multimorbidity in illness that combines STDs and other condition(s) has the least reported number of individuals, only about 9,000 (representing 0.02% of the population). Over 50,000 people are estimated to report one of depression, tuberculosis and diarrhoea and at least one other illness.

The results for disabilities also show that a substantial number of individuals suffered from multimorbidity in disability in 2008. As shown in Figure 2, about 35,000 people (representing 0.07% of the population) are estimated to have a physical disability in addition to another disability. Data from the same year also show that sight disability (with at least one other disability) was estimated to affect more than 28,000 people in South Africa. Similarly, about 15,000 people, representing 0.03% of South Africans, are estimated to be affected by multiple disabilities combining either emotional disability or hearing disability, with at least one other disability. Speech disability (with at least one other disability) was estimated to affect only about 6,000 individuals.

In order to show the intensity of multimorbidity, Figure 3 plots the proportion of individuals with multiple illnesses or disabilities that indicated only two conditions, three conditions and more than three conditions. Generally, as shown in Figure 3, multimorbidity conditions mainly involve only two conditions.

However, this is not the case with STDs and drug abuse. For STDs (drug abuse), 70% (35%) were estimated to report at least three other conditions in addition. These conditions, as shown in Figure 1, affected only a small number of people. For depression, for instance, about 50% reported only one illness in addition, while about 30% reported two other additional conditions. High blood pressure with a substantial number of people, as indicated in Figure 1, was only reported by 15% with at least two additional conditions.

As shown in Figure 3, similar patterns were observed for multimorbidity in disability. Most of the reported multimorbidity in disability occurs as two concurrent conditions. For speech disability, multimorbidity in disability relates to only two concurrent conditions (see also Table 2). For emotional disability, over 30% indicated two additional conditions.

A summary of results in Figure 3 is shown in Table 2. Generally, the average number of conditions suffered by those with multimorbidity (illness or disability), with the exception of trauma, drug abuse, depression, HIV, and STDs, is in the neighbourhood of two concurrent conditions.

Figures 4 and 5 show the distribution of multimorbidity by SES using indirectly standardised concentration indices. As indicated earlier, a positive (negative) index signifies a pro-rich (pro-poor) distribution of multimorbidity.

As indicated in Figure 4, between 2005 and 2008, multimorbidity in illnesses is more common among the poor than the rich. Individuals who suffer from diarrhoea and other illnesses are the ones most likely to be among the poorer socioeconomic groups (concentration index = −0.0013 in 2008). The same significant pattern is observed for tuberculosis (concentration index = −0.0017 in 2008) and BP (concentration index = −0.0018 in 2008). The other illnesses are not statistically significant at conventional levels. However, positive indices were sometimes recorded for diabetes and STDs. The last category “multiple illnesses” covers individuals who indicate at least two of the indicated illnesses within the recall period. It assesses multimorbidity in illness irrespective of the combination of illnesses. Apart from 2007, where the indirectly standardised concentration index (−0.0006) is not statistically significant at the 5% level, there is generally a negative and significant concentration of multimorbidity in illness among the poorer socioeconomic groups (concentration index = −0.0009 in 2005, -0.0016 in 2006 and −0.0006 in 2008).

The distribution of multimorbidity in disability in Figure 5 shows a heavy concentration among poorer socioeconomic groups. This relationship is more consistent for disabilities than for multimorbidity in illness. The “multiple disabilities” category in Figure 5, constructed in a similar way as the “multiple illnesses” category in Figure 4, shows a statistically significant greater concentration of multimorbidity in disability among the poor than among the rich between 2005 and 2008 (concentration index = −0.0006 in 2005, -0.0007 in 2006, -0.0007 in 2007 and −0.0006 in 2008).

This paper has shown that multimorbidity affects a substantial number of people in South Africa. It also shows that the poor bear a significantly greater burden of multimorbidity in illness and disability. With reference to the conditions considered in this paper, in 2008 between 0.02% and 0.6% of the population are burdened by multimorbidity in illness while between 0.01% and 0.07% are burdened by multimorbidity in disabilities. With a population of about 48 million people in 2008, this translates into substantial numbers. Most of the multimorbidity here relates to two conditions. However some individuals are affected by three or more disease conditions especially for multimorbidity combining STDs and other conditions. Concentration indices show the extent to which multimorbidity in illness and disability is concentrated among the poor. Though the extent of concentration varies for each multimorbidity condition between the years considered this ‘pro-poor’ distribution is present for both disabilities and illnesses. This conforms to the views expressed by Haveman and Wolfe [28] that in comparison with the nondisabled, “those with disabilities have substantially lower levels of economic well-being in spite of public income support programs” (p.996). These differences in the concentration indices for each multimorbidity condition between the years cannot directly be explained by the analysis. It may not be a reflection of worsening multimorbidity among the rich but differences in the proportion of individuals suffering from these diseases based on the GHS as shown in Table 1.

From the literature, as noted earlier, only a few studies, and limited to high income countries, have explored the relationship between multimorbidity and socioeconomic status [7, 9]. There is dearth of information for developing countries. Therefore, it is difficult to compare the results in this paper with any from other developing countries.

In Australia, Walker [9], applying a logistic regression on data from the Australian national surveys, showed that low socioeconomic status significantly increases the probability of having three or more chronic illnesses. In Scotland, Barnet et al.[7] found that multimorbidity increases with age, and is correlated with deprivation; where deprivation is an indicator of lower SES. These findings are similar to those obtained in this paper. Multimorbidity in South Africa is significantly associated with lower SES and this is more so for multimorbidity in disability.

The ‘pro-poor’ inequalities in multimorbidity were found generally to decline between 2005 and 2008. This signifies that the burden of multimorbidity is not only concentrated among the poor but also becoming prevalent among the non-poor. These results exhibit a different pattern from those of another study in South Africa that examines inequalities in single illness or disability conditions [4]. That study showed an increasing ‘pro-poor’ distribution for many illnesses and disabilities in South Africa. While it is difficult to explain the differences, it points to differences that may exist in the patterns of inequalities in single disease conditions and multimorbidity over time. Future studies are therefore needed to examine this in other contexts and to investigate the factors that underlie these differences.

Though there is no doubt about the existence of multimorbidity, most “health systems are largely configured for individual diseases rather than multimorbidity” [7] (p.37) thereby making it difficult to manage these conditions simultaneously. To address the issue of multimorbidity, however, requires more than the health system. Based on the Commission on Social Determinants of Health, to tackle the current socioeconomic distribution of multimorbidity in South Africa requires an integrated approach that goes beyond the health sector and which recognises the importance of the social determinants of health [29]. As argued elsewhere in the broad context of health inequality, this “requires a coherent intersectoral approach that will account for the interrelatedness of factors that are associated with health inequalities in South Africa” [30] (p.762). This strategy must recognise that the burden of diseases, including that of multimorbidity, is greater among the poor than among the rich.

This study has some limitations. The GHS data sets do not include all the likely disease conditions, e.g., cancers. However, the conditions included in the GHS account for most of the premature mortality, measured by years of life lost, in South Africa [4]. Further, the data were collected from general households and exclude institutions such as nursing homes and hospices that house people who are very likely to suffer multimorbidity. The data are self-reported measures of illnesses and disabilities but as argued elsewhere [4], the presence of most of these illnesses can only be known through medical diagnosis while, in the case of disabilities, they are more likely to be self-diagnosed or easily observed. While it is difficult to postulate about the nature of inequality, the burden and extent of multimorbidity in South Africa may thus be underestimated.

Multimorbidity affects a substantial number of South Africans. Its distribution shows that the poor bear a greater burden. This is more so for disability than for illness. The dearth of information on this distribution in many developed and developing countries can be attributed to the lack of data that link socioeconomic status with the incidence of multimorbidity. Based on the findings in this paper, there is a need to design policies that address multimorbidity in South Africa. These policies, with insights from the World Health Organisation’s Commission on Social Determinants of Health, should be coherent and involve more than the health sector. Further, there is a need to design national surveys that specifically assess multimorbidity.