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Infections, kidneyand cardiovasculardisease in AboriginalcommunitiesStephen McDonaldSenior Staff Specialist, Nephrology & TransplantationServicesExecutive Officer, Australia & New Zealand Dialysis andTransplant (ANZDATA) RegistryThe Queen Elizabeth HospitalThe parlous state of health among Aboriginal peoplein Australia has been extensively documented overthe past 20 years. Among the areas with the largestdifferentials in health status are those relating to kidneydisease, cardiovascular disease and infections. In thisarticle the published literature on rates of kidney diseaseand cardiovascular disease and infectious diseasesamong Aboriginal people will be briefly reviewed, andthen links between these conditions explored.Kidney diseaseHigher rates of all stages of kidney disease have beenshown among Australian Aboriginal people for sometime. Broadly speaking, rates of kidney disease areascertained in two ways. There are well-validatedmarkers of mild kidney disease. The earliest stages arereflected in abnormal levels of albumin (albuminuria)or protein in the urine (proteinturia), with more severestages reflected in abnormalities in serum creatinineor calculated glomerular filtration rate (GFR). Theprevalence of albuminuria has been studied in severalremote Aboriginal communities. Age-specific prevalencerates of over 50% have been described for some remoteNorthern Territory communities, with commensurateincreases in rates of reduced GFR. 1, 2 The pattern issimilar to other remote communities 3, 4 including onestudied in South Australia. 5 In these communities, as inother environments, these early markers strongly predictthe risk of later more serious disease. 6The most severe stage of kidney disease is end stagekidney disease (ESKD). This is the stage where formsof dialysis and kidney transplantation are required tomaintain life. In Australia, patients receiving thesetreatments are recorded in the Australia & New ZealandDialysis and Transplant (ANZDATA) Registry. Theincidence rate of Aboriginal people commencing dialysiseach year is substantially higher than non-Aboriginalpeople 7 . In addition there is an interaction with age,with the relative risk for ESKD for Aboriginal comparedto non-Aboriginal people substantially higher among the35-55 year age groups (Figure 1). As a methodologicalFigure 1. Age-specific incidence ratios for Aboriginal vsnon-Aboriginal ESKD in Australia, 1996-2001 (ANZDATARegistry).aside, this prevents calculation of a valid directly agestandardisedincidence ratio, as comparisons will varydepending on the structure of the reference population.Acute InfectionsAcute infectious illnesses are described at much higherrates among Aboriginal people. The actual relative riskvaries according to the type of infection studied andthe way the data is collected. The Australian Instituteof Health & Welfare report a two-fold increase in ratesof admission to hospital with infectious and parasiticdiseases. 8 These are nation-wide figures, and farhigher rates have been reported for remote and moredisadvantaged communities. For example, the pointprevalence of bacterial skin infections has been reportedto range from 10 to 70%. 9-12 Both upper and lower 8respiratory tract infections are also extremely common.Circulatory diseaseRates of circulatory (or cardiovascular) disease areextremely high among Aboriginal people, and this groupof diseases is a major contributor to the prematuremortality among Aboriginal people. 13 Age-specificrates of cardiovascular mortality are up to 10 times thenational average. 14 This situation is similar to that seenamong other indigenous groups. 15 The relative increasein hospital admission rates for circulatory disease amongAboriginal people is less marked that that of mortality,with rates 1.5-2 times that of non-indigenous peopleshown both in regional data 16 and national reports. 8 Thegreater relative risk for mortality than hospital admissionsuggests a number of possibilities, including greatercase-fatality rates, admission of sicker patients, ordifferences in practice patterns.12
Community-based reports of the prevalence ofcardiovascular disease (as opposed to risk factors)are more problematic. Earlier studies using restingECG-based criteria showed 10-20% of people in somecommunities had ECG changes of ischaemia. 17-19 Otherdata comes from a survey using exercise ECG testing, 20or surveys of case notes, 21 but these are difficult tointerpret in the absence of non-indigenous controls.When risk factors for circulatory disease (smoking,diabetes, obesity, hyperlipidaemia) are considered,there have been a large number of surveys with variabledegrees of increase in risk factors (for examples see 22-27).Are these problems related?This coexistence of high rates of infections, kidneydisease and circulatory disease raise questions abouthow they might be related. Links between thesediseases might occur through a number of possiblemechanisms.Strong links have been shown between kidneydisease and cardiovascular disease among nonindigenousgroups, and all stages of kidney diseasehave been shown to predict cardiovascular morbidityand mortality. 28-30 Although many community-basedstudies have examined risk factors for cardiovasculardisease among Australian Aboriginal people, few haveexamined the coexistence of cardiovascular and renaldisease. In one well-described cohort, the presence ofalbuminuria predicted cardiovascular mortality 31-32 ; inanother albuminuria and reduced GFR were associatedwith increased carotid intima-media thickness 2 . Othercross sectional studies of remote 4, 22, 23 and non-remote24,33Aboriginal communities have included assessmentsof risk factors, but not necessarily cardiovascular or renaldisease outcomes.There are some direct pathological links betweeninfections and kidney disease (and also infections andcardiac disease in rheumatic heart disease). The bestdescribed link between infection and kidney disease isthat of post-infectious glomerulonephritis (PIGN, alsoknown as post-streptococcal glomerulonephritis). Thisglomerulonephritis is triggered by an immunologicalreaction to infection, and one of the most important andmost common causes is Streptococcal skin infections.Epidemics of this disease have been described inNorthern Australia. 10-12 However, PIGN is responsibleonly for a very small number of the cases of ESKD inAustralia. 34 The situation underlying the increased ratesof kidney disease among Aboriginal people is likely tobe more complex than an increase in a single disease.Traditional dogma teaches that kidney function recoversfully after PIGN, however, there is evidence that PIGNamong Aboriginal people is not a benign process,and does predict later development of albuminuria /proteinuria. 35 A more likely theory is that a series ofinsults throughout life, beginning with smaller kidneyassociated with lower birthweight and progressingthrough higher rates of PIGN and thence diabetes andhypertension, explains the increased rate of kidneydisease among Aboriginal people. 36The list of risk factors for kidney disease andcardiovascular disease is very similar. Diabetes andhypertension are major risk factors for both diseases,and diabetes especially is prevalent at extremely highrates among some Aboriginal communities. Othershared risk factors extend beyond the traditional model.The presence of infection/inflammation is anotherobvious link. Very modest increases in C-reactive protein(a marker of inflammation) have been shown to be a riskfactor for cardiovascular disease in the non-Aboriginalpopulation 37 . Among Aboriginal people, greater increasesin CRP (consistent with those seen as a responseto bacterial infection) are well-described 38-40 and areassociated with the presence of albuminuria 38 andincreased carotid intima-media thickness. 41 It is likelythat these increases of CRP reflect shared associationswith bacterial infections rather than a direct causativerole of chronic bacterial role in atherosclerosis or kidneydisease. This is not to suggest repeated bacterial skin orlung infections cause cardiovascular or kidney diseasedirectly, but that they all share causal factors. Themost apparent of these are the living conditions, withovercrowding and other markers of poverty extremelycommon among Aboriginal people, particularly thoseliving in remote communities. Consistent with this isthe observation that rates of ESKD among AustralianAboriginal are particularly increased among those livingin remote areas. 42Increased rates of ESKD incidence in Australia havealso been associated inversely with markers of socioeconomicstatus among non-Aboriginal people. 43 Allthese observations are consistent with the paradigmexpounded by Marmot, where the influence of socioeconomicfactors is likely to be reflected in a numberof mediators, including increased household crowding,lower birth weight, higher rates of cigarette smoking andobesity. This relationship has been remarkably robustbetween different countries and cultures. 44ConclusionsLinks between renal and cardiovascular disease existat a number of levels among Australian Aboriginalpeople. In addition to the usual list of “traditional”cardiovascular risk factors, increased CRP over a rangeof CRP concentrations considerably greater than thatdescribed in non-indigenous settings is common, and isassociated with both renal and cardiovascular disease.These increased CRP concentrations are likely to reflectthe generalised burden of infection and thereby poor13
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