Background
In developing countries, an estimated 863 million people live in slums, areas characterized by poor quality or informal housing, unhealthy living conditions, poverty, and marginalization from the formal health sector [
1]. Because slum dwellers represent a third of the urban population of low- and middle-income countries, addressing intra-urban health inequities is an important challenge facing cities in the developing world [
1,
2]. Little is known about the burden of disease in slums and low-income informal settlements because, due to their unofficial status and lack of resources, they are more frequently excluded from governmental epidemiologic surveillance and research studies. Additionally, health inequalities between slums and adjacent urban areas may be masked by their inclusion in a single surveillance catchment area, which has led to repeated calls for more robust intra-urban morbidity and mortality data [
2‐
6]. Drawing on social epidemiologic theory, a high prevalence of a range of noncommunicable diseases (cardiovascular and chronic respiratory disease, diabetes, mental illness, arthritis, and cancer) and related risk factors (overweight and obesity, poor nutrition, harmful drinking, smoking, and hypertension) is expected in a slum population due to the particularly adverse factors present within each component of the WHO conceptual framework of social determinants of health [
7]. This framework conceptualizes disease risk and risk behaviors as being influenced by three major components: the socioeconomic-political context, the structural determinants of socioeconomic position, and the intermediary determinants of health [
7]. Slums are characterized by urbanization, a lack of urban planning, overcrowding, and exclusion from social, health, and other services; such a socioeconomic-political context could be expected to have a higher prevalence of noncommunicable diseases due to the increased exposure to modifiable risk factors such as increased intake of fat and sugar associated with an urban lifestyle, few opportunities for physical activity due to limited space and insecurity, and a high prevalence of undiagnosed chronic conditions due to a lack of access to primary care services and health education. Slum dwellers also typically occupy a low socioeconomic position, and poverty and lower education levels are strongly linked to the development of NCDs [
8]. Primary intermediary factors that are expected to be prevalent in a slum setting and contribute to the development of noncommunicable disease include inadequate access to sanitation and other infrastructure [
5], insecure residential status [
5], and exposure to violence and crime. In informal settlements, chronic noncommunicable diseases are at particular risk of going undetected by formal health registries until presentation in a late stage of disease or death; this has been attributed to a lack of access to health services and inadequate or inappropriate care when services are sought [
4,
5]. This pattern of health-seeking behavior typically results in an undue human cost and financial burden on existing health systems [
3,
4], underscoring the need for noncommunicable disease (NCD) data to advise health interventions targeting the urban poor.
In Peru, a middle-income country with a growing burden of NCD [
9,
10], approximately forty percent of the population of the capital city, Lima, lives in low-income informal settlements. Limited research has investigated the epidemiology of NCD in populations living in informal settlements in Lima. The PERU-MIGRANT study was conducted in rural-to-urban migrants and lifelong urban residents living in a shantytown south of Lima [
11]; although not designed to yield population-based disease estimates, data from the shantytown segment of the PERU-MIGRANT cohort provided evidence of a significant risk of cardiovascular disease. The prevalence of overweight or obesity, hypertension, and diabetes were estimated to be 67-71%, 13-30%, and 2-5%, respectively [
12] and these results were similar to those of obesity and hypertension studies in other populations in peri-urban Lima [
13,
14]. A probable mood disorder (defined by a validated questionnaire) was identified in approximately a third (33-38%) of the PERU-MIGRANT shantytown cohort, suggesting an important burden of mental illness in these informal settlements [
15]. Although noncommunicable chronic respiratory disease has not been studied in an adult Peruvian shantytown population, research in adolescents indicates that this may additionally contribute to the NCD burden among adults living in these communities [
16]. Prior studies in informal settlements in Peru have identified gender and age as determinants of NCD and related risk behaviors. The prevalences of binge drinking and smoking were significantly higher among men [
17,
18], while women were more likely to be obese (assessed by either body mass index or waist circumference) and have metabolic syndrome [
13,
19,
20]. Increasing age was associated with hypertension in an adult shantytown population [
13]. As a part of a population-based health needs evaluation in a Peruvian shantytown, we aimed to measure the prevalence of NCD and related risk factors and to evaluate their associations with age and gender in order to inform the design of future interventions in this community.
Discussion
In the context of a community health needs evaluation, we investigated the prevalence and age and gender distribution of noncommunicable disease in a peri-urban shantytown in Peru. Overall, there was a low prevalence of self-reported, diagnosed noncommunicable disease, although the prevalences of depression (12%) and chronic respiratory disease in the population (8%) signal that these conditions may contribute significantly to the NCD burden. Perhaps most alarming was the high frequency of excess weight, particularly among women; our findings of a 53% prevalence of overweight/obesity overall and 54% prevalence of abdominal obesity in women indicate a major risk for development of a noncommunicable disease. With regard to other risk factors for NCD, inadequate fruit and vegetable consumption by the majority (92%) of participants and a 15% prevalence of hypertension—the majority undiagnosed—in this population demonstrate the importance of these risk factors as potential contributors to NCD risk in this community.
Our estimates of NCD morbidity are generally similar to those of prior studies conducted in informal settlements in Peru [
12,
15,
16]. However, our population prevalence of depression was substantially lower than the prevalence of probable mental illness estimated in the PERU-MIGRANT shantytown cohort (12 vs. 33-38%) [
15]. This difference could be explained by our definition of depression as having received a diagnosis of depression from a healthcare provider, which likely underestimated the prevalence of depression in our population. The difference also may be due to the fact that in the PERU-MIGRANT study, current rather than lifetime prevalence was measured; recall bias may have resulted in underreporting of lifetime depression diagnoses. The measure employed in the PERU-MIGRANT study may additionally have resulted in an overestimate of population depression prevalence due to its inability to distinguish between depression and anxiety [
15]. Our estimate of lifetime depression prevalence is, however, similar to that estimated for the adult population of metropolitan Lima (18%) [
30]. As compared to mental health research conducted in slum populations outside of Peru, the prevalence of depression in the present study is less than half of that measured in older adults [
31] and women [
32] living in slums in India, and is lower than the prevalence of self-rated poor or fair mental well-being measured in two Bangladeshi slum populations [
33,
34]. These differences are likely attributable in part to the fact that in other studies the definition of depression or poor mental health did not require having received a physician diagnosis.
The only other study to our knowledge to report on the prevalence of chronic respiratory disease in a adult slum population, conducted in India, found similar prevalences of asthma symptoms (10%) and chronic bronchitis (8.5%) [
35]. In this population, asthma symptomology, but not chronic bronchitis, was associated with female gender and increasing age. It is possible that the heterogeneity of conditions captured by our chronic respiratory disease measure obscured condition-specific gender and age differences that may have been present in our study population.
The prevalence of arthritis measured in the present study is slightly lower than the prevalence of osteoarthritis of the knees found in a Bangladeshi adult urban slum population [
36], which may be attributable to differences in the working conditions and physical demands of occupations, particularly for men, in these populations. Diabetes prevalences estimated in slum populations in Kenya [
37,
38] and India [
39] are similar to that of the present study while they are higher in Bangladesh (8%) [
40] and in an elderly Indian population (18%) [
41]. The paucity of cancer and myocardial infarction data from adult slum populations limits our ability to compare our findings regarding these outcomes.
Similarly to the prevalences of NCD conditions, the prevalences of risk factors for NCD estimated in this study are also comparable to those of prior studies in Peruvian informal settlements [
12,
13,
17,
18,
42]. Our population prevalences of hypertension, overweight status, and obesity are slightly lower than those estimated for the PERU-MIGRANT shantytown cohort, however, the age-specific prevalences of these conditions in our population suggest that this difference is due to the slightly younger age of our study population. The prevalence of overweight and obesity estimated in this study was similar to that of other slum populations in Nigeria [
43] and Kenya [
37] but greater than that of a different Kenyan slum [
44] and greater than Indian [
39] and Bangladeshi [
40] slum populations. These differences in the prevalence of overweight and obesity are likely due to a number of factors and may be related to the progress of the epidemiologic transition or characteristics specific to the particular slum setting. In contrast to the findings of the PERU-MIGRANT study [
19], women did not have a significantly greater prevalence of obesity defined by BMI, however, the greater prevalences of abdominal obesity in women in our study suggest that this finding may have been due to the limitations of our sample size rather than a true difference in results. Like the finding of the current study, research in Kenyan [
37,
45] and Indian [
39] slum populations found that women were more likely to have abdominal obesity while data from an Indian study provided evidence that abdominal obesity increased with age [
39]. Age and gender associations with abdominal obesity were not assessed in the Nigerian or Bangladeshi studies and the association with age was not assessed in the Kenyan studies. The association we observed between female gender and abdominal obesity may be the result of gender norms affecting individual health-related behaviors such as physical activity. The association of abdominal obesity with age likely reflects the cumulative effects of unhealthy diet and insufficient physical activity over the lifespan which we did not investigate in the current study but may further investigate in future NCD studies in this population.
Comparing to slum populations outside of Peru, our population prevalence of hypertension was similar to that of populations in Kenya [
45] and India [
39], but was considerably less than the prevalence of 38% measured in a Nigerian slum population [
43] and considerably greater than the approximately 2% prevalence measured in a Bangladeshi slum [
40]. As in the present study, hypertension was associated with increasing age in previous studies conducted in Peru [
13], India [
39], Kenya [
45] and Nigeria [
43]; this association was not evaluated in the Bangladeshi population. This age-related trend with hypertension likely reflects the stiffening of blood vessels through ageing, although it could also reflect uncontrolled confounding by factors that are associated both with age and hypertension.
Like other research in informal settlements in Peru, we found a greater prevalence of binge drinking and smoking among men [
17,
18], which is similar to patterns of hazardous drinking and tobacco use in the adult population of the Lima metropolitan area [
30] and which likely reflect differences in gender-based social expectations [
18]. Similar gender differences in hazardous drinking and tobacco use have been noted in non-Peruvian slum populations [
37,
39,
43,
45].
Because this study was conducted in the context of a broader health needs assessment, we designed our study instruments with the goal of balancing three objectives: 1) to capture a large number of health indicators on a broad spectrum of topics to describe the community burden of disease, 2) to collect valid measures of NCD-related variables, and 3) to limit participant burden. Although we did obtain an overall picture of the burden of communicable and noncommunicable disease in this population, we were unable to collect a number of NCD and NCD risk-related variables or to use more time-consuming, higher validity measures for each variable. The self-reported nature of the NCD variables, for example, likely led to underestimates of the prevalence of these diseases. With regard to NCD-related risk behaviors, only one aspect of unhealthy diet—adequate fruit and vegetable consumption—was measured, and we did not measure this variable using a high validity measure such as a food frequency questionnaire. Future investigations of diet-related NCD risk factors could additionally collect information regarding salt intake and saturated fat and trans-fat consumption, two other important aspects of diet-related NCD risk [
8]. Due to concerns about survey length, we also did not measure physical activity in our survey, and the inclusion of this risk factor will be important in future community surveys both as an important risk behavior related to NCD and to measure the impact of interventions and improvements in community infrastructure. The inclusion of biochemical measures would have allowed us to better measure certain NCDs and associated risk factors such as diabetes and high cholesterol and therefore should be included in future NCD studies in this community. Although our population estimates were weighted to account for the greater proportion of non-participation among males selected to participate in this study, the difficulty we encountered in contacting and in obtaining consent from potential male participants highlights the importance of coordinating the schedule of data collection with the availability of less accessible segments of the population and the potential need for participation incentives in order to reduce underrepresentation of men in the sampling of similar populations. Our relatively small sample size may have precluded the identification of other differences in NCD and risk factor prevalence by age and gender.
Despite these limitations, this study had a number of strengths. To our knowledge, this is the first population-based study to describe the burden of noncommunicable disease and related risk factors in a Peruvian shantytown. Aside from the randomized sampling and novel population of this study, other strengths include the objective measurement of BMI, abdominal obesity, and hypertension, and the use of a standardized questionnaire to assess NCD risk behaviors.
Acknowledgements
We would like to express our gratitude to our study participants and the Lomas de Zapallal community for their support of this study. We would also like to thank the Sociedad Cientifica de San Fernando, Omar and Carlos Maguiña, and José Viñoles for their valuable contributions to data collection and Thanh Ton for her insights regarding study design. This work was supported by the National Institutes of Health Office of the Director, Fogarty International Center, Office of AIDS Research, National Cancer Center, National Eye Institute, National Heart, Blood, and Lung Institute, National Institute of Dental and Craniofacial Research, National Institute On Drug Abuse, National Institute of Mental Health, National Institute of Allergy and Infectious Diseases, and National Institutes of Health Office of Women’s Health and Research through the Fogarty International Clinical Research Scholars and Fellows Program at Vanderbilt University (R24 TW007988) and the American Relief and Recovery Act.
Competing interests
The authors declare that they have no competing interests. Dr. Silvia Montano is an employee of the U.S. Government. This work was prepared as part of her official duties. Title 17 U.S.C. §105 provides that 'Copyright protection under this title is not available for any work of the United States Government'. Title 17 U.S.C. §101 defines a U.S. Government work as a work prepared by a military service member or employee of the U.S. Government as part of that person's official duties. The views expressed in this manuscript are those of the authors and do not necessarily reflect the official policy of position of the Department of the Navy, Department of Defense, nor the U.S. government.
Authors’ contributions
All authors participated in the design of the study. KH conceived of the study, supervised and participated in data collection, performed the statistical analysis and drafted the manuscript. SM and JA assisted in the coordination of the data collection. SM, SH, JA, and JZ provided critical feedback on drafts. All authors read and approved the final manuscript.