Low Incidence of Stroke in the Chiquitanos Tribe in the Bolivian Lowlands
To the Editor:
We read with great interest the article on stroke prevalence in rural Bolivia by Nicoletti et al.1 We greatly appreciate their study in this remote rural area in the Cordillera province of the Santa Cruz Department. The living conditions, the difficulties in primary health care, and the impact of stroke on this population are meticulously described. The results of the 2-phase study show a crude prevalence of first stroke of 174/100 000 in this area. In men the prevalence was more than twice as high. The authors conclude that the crude prevalence is lower than rates from developed countries and that it is similar to those reported from other surveys carried out in rural developing countries.1
Using the letter file of this journal, we would like to comment the article in some aspects. First, we feel that the description of the calculation of the prevalence is a little unclear. It is not clear enough to us exactly how the adjustment of the crude incidence rate for area and clustering was performed. We cannot follow in detail, for instance, how from 1 case in a observed population of 471 individuals a crude prevalence rate of 295 can be calculated. In addition, we suggest that it might have been useful to give the crude annual incidence figures alongside the prevalence data. This would make it easier, despite the valid difficulties reported by the authors, to draw comparisons with other studies in developed countries.
The crude annual incidence rate may be more useful in healthcare planning also, such as when assessing the need for acute stroke care. For instance, a recently published study in our area—Erlangen, in southern Germany—showed a crude annual incidence of first-ever stroke of 174/100 000 and was extremely helpful for planning and establishing our stroke unit.2 Second, the result in the study of Nicoletti et al that stroke was more than twice as prevalent in men than women is very interesting. In the Erlangen study mentioned above, the age-adjusted annual incidence rates were only slightly higher for men than women. It would be interesting to see the prevalence rate adjusted to the WHO standard, not only for both sexes but also separated for men and women.
Third, we would like to draw attention to a neuroepidemiological study3 with some similarities to that of Nicoletti et al,1 which we performed in another rural Bolivian region: the area of the indigenous tribe of the Chiquitanos. Some aspects of this study are interesting in comparison to the work of Nicoletti et al. The Chiquitano tribe lives in the southern Amazon region in Bolivia, in the northeast part of Santa Cruz Department, remote from larger towns (Figure⇓). Its population has an age and sex distribution similar to that of the study population.3 Our study covered a total population of 5652 individuals in 1995. The acute care for the whole region is provided by 1 hospital, including outpatient department (“consultorio”). Ambulatory care in the area is guaranteed by 7 specially trained nurses (“sanitarios”), who screen for neurological disease and refer the patient to the hospital if neurological disorder is suspected. If a patient dies before seen by professionals, the study general practitioner reviews the patient’s history to assess probable diagnosis. Because the hospital is supported by the Catholic church and Erlangen’s Medical Association for Bolivia, consultation and inpatient treatment are very cheap and available to everyone. Therefore, the rate of stroke patients not seen by professionals is assumed to be low. Over a 1-year period (April 1995 through March 1996), a total of 1514 individuals consulted the hospital staff or ambulatory care. One hundred thirty-nine patients suffered from neurological diseases (Table⇓). A first-ever stroke was possibly diagnosed in 2 patients (2 women, aged 71 and 62 years). Therefore, a crude annual incidence of 35/100 000 could be estimated. In contrast, cervical and lumbosacral pain syndromes were the most common neurological problems and were caused by sleeping in hammocks and by hard agricultural labor. Tropical pyomyositis was also very frequent and was the most common muscle disease. Epilepsy was found in 11 patients and extrapyramidal syndromes in 2. Although direct comparison with the study of Nicoletti et al is difficult, our findings seem to support their contention that stroke is uncommon in the indigenous population in Bolivia. The authors suggests in their conclusions that the low incidence of stroke among the inhabitants of Cordillera might be attributed to the age distribution, difficulties in reaching a hospital, and ethnic factors. Our study, interestingly, had a similar age distribution but good access to health care and a higher ethnic population. In our study, nearly all individuals (98%) are indigenous, whereas in the Nicoletti study only 30% are indigenous. This might indicate that ethnicity is perhaps the more important factor in the low stroke occurrence in rural and indigenous Bolivia.
Fourth, we agree with Nicoletti et al that neuroepidemiological studies are necessary for the organization and planning of health care in underprivileged areas. The department of Santa Cruz in Bolivia is particularly strongly marked by immigration from the highlands. The indigenous population of the Altiplano—where subsistence is increasingly perilous—are migrating to the Bolivian lowlands to build new lives. A zone with great problems is the “Brecha Casarabe” area near the capital Santa Cruz, where new settlers daily join the 25 000 population and where until now no sufficient infrastructure, including health care, has been in place. Fifth, in addition, the phenomenon of “transicion epidemiologica” should be considered. This refers to the new health problems associated with increasing life expectancy and urbanization: the treatment of older and chronically diseased people, the rehabilitation of stroke-handicapped patients, and the care of patients with socially caused diseases (AIDS, drug addiction, consequences of violence).4 5
We would like to conclude that the issues of neurological morbidity in underprivileged areas are an important and underresearched field and that the work by Nicoletti et al is an important step with regard to stroke epidemiology in this area. At our university we have reacted to this challenge by introducing the field of “Tropical Neurology and Neurology of the Underprivileged” into our neurology training program, by preparing teaching posters at our yearly German neurological meeting, and by directly supporting aid organizations in underprivileged areas.
- Copyright © 2000 by American Heart Association
Nicoletti A, Sofia V, Giuffrida S, Bartolini A, Bartalesi F, Lo Bartolo ML, Lo Fermo S, Cocuzza V, Gamboa H, Salazar E, Reggio A. Prevalence of stroke, a door-to-door survey in rural Bolivia. Stroke.. 2000;31:882–885.
Kolominsky-Rabas PL, Sarti C, Heuschmann PU, Graf C, Siemonsen S, Neundoerfer B, Katalinic A, Lang E, Gassmann KG, von Stockert TR. A prospective community-based study of stroke in Germany: the Erlangen Stroke Project (ESPro): incidence and case fatality at 1, 3, and 12 months. Stroke.. 1998;29:2501–2506.
Jitapunkul S, Bunnag S, Ebrahim S. Health care for elderly people in developing countries: a case study of Thailand. Age Ageing.. 1993;22:377–381.
First and foremost, we very much appreciated the interest and the comments of Dr Heckmann and colleagues, and we enjoyed reading data on neurological patients observed in hospitals and ambulatory facilities in another area of the Santa Cruz Department.
Concerning the question raised by Heckmann and colleagues about the calculation of the prevalence, as reported in our survey: to select the sample of about 10 000 inhabitants from the 10 areas of the Cordillera Province, a cluster sampling method was used, with the 10 areas acting as strata. Within each stratum, communities were selected at random, and each constituted 1 cluster.R1 The complex sampling methods, as random cluster sampling, result in additional variability in the sample estimate. The effect of the design on the variability of a sample estimate is measured by the ratio of the variance of estimates from the design used to the variance that could come from the same sample size if simple random sampling were used; it is called “design effect.” To account for the additional variability at the different stages of complex designs, the sample size and sample estimates were adjusted by the design effect. The design effect for each estimate is reported in the Table. As previously reported, our estimates were calculated by using the csample module of the EPI-INFO 6.R2
Our survey was designed and carried out to determine the point prevalence of the major neurological diseases (epilepsy, stroke, peripheral neuropathy, parkinsonism).R3 Therefore, it is not possible to provide incidence data. As stressed in our article, because of the lack of census data, death certificates, and hospital registers, the way to assess the true incidence in this rural population should be a follow-up of the population for a long period of time, implying high cost and organization problems.
Regarding the hypothesis of a possible effect of the ethnic group on the low prevalence rate, other types of analytic epidemiological design are necessary to test it, but at any rate we believe that the most important factors to explain our low prevalence rates could be case-fatality rates, low hospitalization rates, and the age structure of our population.
Concerning the higher prevalence found in men, as reported in our article, it is in agreement with data reported in literature.
World Health Organization. Epi Info 6. Atlanta, Ga: Centers for Disease Control & Prevention (CDC); 1994.
Nicoletti A, Reggio A, Bartoloni A, Failla G, Sofia V, Bartalesi F, Roselli M, Gamboa H, Salazar E, Osinaga R, Paradisi F, Tempera G, Duamas M, Hall AJ. Prevalence of epilepsy in rural Bolivia: a door-to-door survey. Neurology.. 1999;53:2064–2069.