Chagas' disease among older adults: branches or mainstream of the present burden of Trypanosoma cruzi infection?

Mff Lima-Costaa,b, Sm Barretoa,b and Hl Guerraa

a Oswaldo Cruz Foundation René Rachou Research Center, Av. Augusto de Lima 1715. 30.190.002. Belo Horizonte, Minas Gerais, Brazil.
b Federal University of Minas Gerais Medical School, Brazil.

Sir—We have recently reported an important burden of Trypanosoma cruzi infection (the parasite which causes Chagas' disease [CHAD]) among older individuals (>=60 years of age) in an endemic area in Brazil where the transmission of the infection was interrupted around 20 years ago.1 These results have significant consequences for public health because they indicate that policy makers, due to the enduring consequences of T. cruzi infection, should continue worrying about CHAD for some time after interruption of transmission. This is the present scenario in Brazil, where the transmission of the infection has been substantially reduced or even interrupted in most endemic areas. This may also apply to other countries because the World Health Organization estimates that the eradication of the transmission of T. cruzi will be achieved in South America by 2010.2

Commenting on our work, Villar3 wrote that our findings do not capture the substantial part of the burden of the disease. Because we worked with older individuals, the ‘data reflect branches, rather than the mainstream, of the burden of CHAD and the past, rather than the current epidemiological scenario of the CHAD.’ However, the analysis of data on mortality and public hospitalizations due to this disease in Brazil shows that the scenario that we have pictured in our study is not the past, but the current epidemiological situation of CHAD in this country.

Figure 1Go presents Brazilian death rates from CHAD for the years 1980, 1985, 1990 and 1995 and shows: (1) a consistent decrease in mortality from this cause in the period and (2) a consistent increase of death rates with age, which peaks at age 60–69 years. Similar results were found when we analysed mortality rates by birth cohort. In all cohorts the mortality rates increase successively with age with the greatest risk of death being between 60 and 69 years. We also notice that mortality rates are higher in older cohorts (Table 1Go). Because mortality reflects only a part of the total burden to the disease we have also examined public hospitalization rates from CHAD in the country (around 80% of Brazilian people depend exclusively on the public health sector).4 Similar trends of increasing rates with age are seen for public hospitalizations with highest rates among individuals aged 60–69 or >=70 years of age (Figure 2Go).



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Figure 1 Death rates for Chagas' disease, according to age group. Brazil, 1980, 1985, 1990 and 1995

Source: Brazilian Ministry of Health.6,7

 

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Table 1 Age-specific death rates per million from Chagas' disease with birth cohort of 1981–1985, 1956–1960 and 1931–1935 indicated, according to year. Brazil, 1980, 1981 and 1995
 


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Figure 2 Hospitalization rates for Chagas' disease, according to age group. Brazil, 1992, 1994, 1996, 1998 and 2000

 
The population aged >=60 years is increasing very fast in Brazil and the leading causes of death in this group are cerebrovascular and ischaemic heart diseases (5181 and 5035 deaths per million, respectively). Chagas' disease is the second cause of death from infectious disease for older adults in this country (272 per million), following septicaemia (388 per million).5 The analysis of mortality and public hospitalization rates in Brazil show that a substantial toll of the present burden of T. cruzi infection affects older adults. With the continued success of the control programme in Brazil we can foresee that CHAD will be a problem only for this population.

References

1 Lima-Costa MFF, Barreto SM, Guerra HL, Firmo JOA, Uchoa E, Vidigal PG. Ageing with Trypanosoma cruzi infection in a community where the transmission has been interrupted: the Bambuí Health and Ageing Study (BHAS). Int J Epidemiol 2001;30:887–93.[Abstract/Free Full Text]

2 World Health Organization. Division of Control of Tropical Diseases. Chagas' Disease Elimination: Burden and Trends. WHO web page: www.who.int/ctd./html/chagburtre.html. 2000.

3 Villar JC. Commentary: Control of Chagas' disease: let's put people before vectors. Int J Epidemiol 2001;30:894–95.[Free Full Text]

4 PAHO/WHO. Basic Country Health Profiles for the Americas: Brazil: Health Systems and Services Country Profile. http://www.americas.health-sector-reform.org/english/brapren.pdf. 2000.

5 Lima-Costa MFF, Guerra HL, Barreto SM, Guimarães RM. Diagnóstico de saúde da população idosa brasileira: um estudo da mortalidade e das internações hospitalares públicas [Diagnosis of health condition of the elderly population in Brazil: a study of mortality and admissions in public hospitals]. Informe Epidemiológico do SUS 2000;9:23–41.

6 Brazilian Ministry of Health. Executive Secretary. Population Counts and Estimates. DATASUS web page: www.datasus.gov.br/cgi/deftohtm.exe?ibge/popbr.def. 2001.

7 Brazilian Ministry of Health. Executive Secretary. Information System on Mortality. DATASUS web page: www.datasus.gov.br/cgi/tabcgi.exe?sim/dxbr.def. 2001.

8 Brazilian Ministry of Health. Executive Secretary. Information System on Hospitalizations. DATASUS web page: www.datasus.gov.br/cgi/deftohtm.exe?sih/mbr.def. 2001.


 

Commentator's Response—Patient-based research in Chagas' disease should emerge, be comprehensive and built on the ground of vector control

Juan C Villarc

c Universidad Autónoma de Bucaramanga, Colombia and Population Health Institute, McMaster University, Canada.

Sir—In a paper recently published in the International Journal of Epidemiology, Lima e Costa et al. showed an important burden of Chagas' disease (CHAD) in Trypanosoma cruzi-seropositive subjects older than 60 and living in towns where disease transmission was stopped more than 20 years ago.1 In an accompanying commentary, I acknowledged the importance of their work, but expressed concern that those findings may underestimate the total burden of CHAD.2 The authors now provide supplementary data on CHAD-associated mortality and hospitalizations in Brazil, giving support to their contention that adults older than 60 represent a major source of burden. In principle, I do not see any conflict between my commentary's main point advocating more patient-based research on CHAD and a paper bringing to attention the need for extra care for the infected elderly living in these towns. What needs further debate is, however, whether the population studied by Lima e Costa et al. represents ‘the mainstream’ or ‘the branches’ of the burden of CHAD. Extending that metaphor further, I believe that both structures share the same roots, are largely complementary and must be grounded in a successful, continued vector control programme.

A controversy on where the hierarchies of the burden of CHAD are will be always context-relative and dependent on both resources and values of policy-makers. But is it necessary to re-orient the priorities for research and control policies in the future? In my commentary I listed the reasons why I believe control policy for CHAD needs a new direction following the undeniable achievements of the vector control campaigns in Southern South American countries. I advocate more patient-based research as the ultimate target for health care services, and the safest way to achieve and sustain long-term victory on the control of its burden. If exclusive attention is given to those lifelong residents in the areas of former vector transmission, I still maintain that a large proportion of the burden would remain uncovered.

Where is the important but hidden burden of CHAD? I believe it is likely to be found in young to middle-aged inhabitants of urban areas. First, take the rapid demographic changes in South America over the last decades, where the percentage of urban population has doubled (from 40% to 80%) since the 1950s, mainly due to internal migrations.3 For economic reasons, rural migrants typically moved to the cities at their most productive ages. Although some of them may have gone to the country capitals for more job opportunities, perhaps the immigration to those medium-size cities surrounding former or current areas of active transmission has more relative importance. That can be the case of Córdoba in Argentina, Santa Cruz de la Sierra in Bolivia, or Cúcuta in Colombia, where the prevalence of T. cruzi-infected blood units was above 7% in the late 1980s or early 1990s.4 While the interruption of vector transmission of T. cruzi programmes have been running, the migration of the work force to the cities has also been underway. Since T. cruzi vector transmission occurs mostly in the first decades of life,5 more infected subjects in their productive years have been moving to the cities. Conversely, old adults, lifelong residents in the endemic areas would have stayed in their towns. Therefore, those rural migrants who moved to the cities constitute a group with a high potential to prevent disability adjusted life years (DALY) lost. That is particularly important for a disease whose incidence rarely occurs after the fifth decade, such as CHAD. Provided the success of vector control remains, this potential tends to grow in the cities, while decreasing in the areas of former active transmission.

Let us take now the natural history of CHAD. From the Figures provided by Lima e Costa et al., one can confirm the expected reduction of the burden for CHAD in Brazil in the past decades, but also notice how the shape of the curves of mortality and hospitalization has remained unchanged. Those Figures strongly suggest that the natural history of the disease has been basically the same. Virtually no incidence of symptomatic CHAD occurs after the fifth decade of life.5–7 Indeed, most of the sudden, unexpected death in CHAD occurs before, whereas most deaths after the 50s occur in previously symptomatic individuals.8 Those lower mortality rates before the 60s are much more important in terms of DALY lost. The same argument applies for hospitalizations. For a chronic cardiomyopathy that is highly lethal once it becomes symptomatic,9–11 the rise in the number of deaths and hospitalizations after the fifth decade is not surprising. I would therefore interpret the excess of mortality at older ages as worsening of previously symptomatic disease. Likewise, the excess of hospitalizations after the 50s would be mostly due to re-admission of previously symptomatic patients. This information leads us to see CHAD as an entity with an unchanged, particularly high impact on premature death or disability.

I believe patient-based research on CHAD should emerge. Studies like Lima e Costa's make us aware that a substantial burden of disease remains in spite of the interruption of the transmission. On the basis of a continued vector control programme, I see a large common ground for answering research questions highly relevant for both infected individuals and their health care givers. Most of them would apply for both young and old patients living in either rural or urban settings. However, focusing on people over 60 living in towns of former active transmission would either miss most of the high-risk asymptomatic population, or tackle a burden of a disease that has already started. For a disease whose risk factors, or interventions with preventive capabilities have not been identified yet, including the infected, urban population in their productive years to be included in the control programmes would attain a more comprehensive impact.

References

1 Costa MF, Barreto SM, Guerra HL, Firmo JO, Uchoa E, Vidigal PG. Ageing with Trypanosoma cruzi infection in a community where the transmission has been interrupted: the Bambuí Health and Ageing Study (BHAS). Int J Epidemiol 2001;30:887–93.[Abstract/Free Full Text]

2 Villar JC. Commentary: Control of Chagas' disease: let's put people before vectors. Int J Epidemiol 2001;30:894–95.[Free Full Text]

3 Analysis of urban and rural population growth at the regional level. In: World Population Prospects: The 1999 Revision, Chapter III. United Nations Population Division, Department of Economic and Social Affairs (DESA). http://www.un.org/esa/population/publications/wup1999/wup99.htm2002. Accessed 3 January 2002.

4 Schmunis GA. Trypanosoma cruzi, the etiologic agent of Chagas' disease: status in the blood supply in endemic and nonendemic countries. Transfusion 1991;31:547–57.[CrossRef][ISI][Medline]

5 Puigbo JJ, Nava R Jr, Carcia BH, Gil YC. A 4-year follow-up study of a rural community with endemic Chagas' disease. Bull World Health Organ 1968;39:341–48.[ISI][Medline]

6 Laranja FS, Dias E, Nobrega G, Miranda A. Chagas' disease. A clinical, epidemiological and pathologic study. Circulation 1956;14:1035–60.[ISI]

7 Prata AR. Natural history of Chagasic cardiomyopathy. In: Pan American Health Organization (ed.). New Approaches in American Trypanosomiasis. Washington DC: PAHO, 1976.

8 Rassi A Jr, Rassi SG, Rassi A. Sudden death in Chagas' disease. Arq Bras Cardiol 2001;76:75–96.[Medline]

9 Pugliese C, Lessa I, Santos FA. Estudo da sobrevida na miocardite crônica de Chagas descompensada [Survival of decompensated chronic Chagas' myocardiopathy]. Rev Inst Med Trop Sao Paulo 1976; 18:191–201.[Medline]

10 Espinosa R, Carrasco HA, Belandria F et al. Life expectancy analysis in patients with Chagas' disease: prognosis after one decade (1973–1983). Int J Cardiol 1985;8:45–56.[CrossRef][ISI][Medline]

11 Mady C, Cardoso RH, Barretto AC, da Luz PL, Bellotti G, Pileggi F. Survival and predictors of survival in patients with congestive heart failure due to Chagas' cardiomyopathy. Circulation 1994;90:3098–102.[Abstract]





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