Social Epidemiology of a Large Outbreak of Chickenpox in the Colombian Sugar Cane Producer Region: a Set Theory-Based Analysis
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ARTIGO ARTICLE 1393 Social epidemiology of a large outbreak of chickenpox in the Colombian sugar cane producer region: a set theory-based analysis Epidemiología social de una gran epidemia de varicela en la región colombiana productora de caña de azúcar: un análisis basado en teoría de conjuntos Alvaro J. Idrovo 1 Cidronio Albavera-Hernández 1,2 Jorge Martín Rodríguez-Hernández 1 Abstract Introduction 1 Instituto Nacional de Salud There are few social epidemiologic studies on Chickenpox, or varicella, is a benign disease Pública, Cuernavaca, México. 2 Hospital General Regional, chickenpox outbreaks, although previous find- caused by infection with the varicella zoster vi- Instituto Mexicano del ings suggested the important role of social de- rus (VZV). In general, cases of chickenpox appear Seguro Social, Cuernavaca, terminants. This study describes the context of a among children between the ages of 1 and 14 1, México. large outbreak of chickenpox in the Cauca Valley and when the infection occurs in adolescents or Correspondence region, Colombia (2003 to 2007), with an em- adults the severity is higher than in children. In A. J. Idrovo phasis on macro-determinants. We explored the addition, it is potentially more frequent among Instituto Nacional de Salud 2 Pública. temporal trends in chickenpox incidence in 42 immunosuppressed individuals . Migration is an Avenida Universidad 655, municipalities to identify the places with higher important risk factor associated with the occur- Col. Sta Ma. Ahuacatitlán, occurrences. We analyzed municipal character- rence of chickenpox. When adults not exposed Cuernavaca, Morelos, 62100, México. istics (education quality, vaccination coverage, to VZV migrate to regions where chickenpox is [email protected] performance of health care services, violence- endemic, the risk of infection is high 3. This has related immigration, and area size of planted been described as occurring when an individu- sugar cane) through analyses based on set theory. al interacts with others in schools, homes and Edwards-Venn diagrams were used to present the shopping centers 4. main findings. The results indicated that three Studies from Serbia and Montenegro 5, Puer- municipalities had higher incidences and that to Rico 6, St. Lucia-West Indies 7, India, South- poor quality education was the attribute most east Asia 8, and Somalia 9, and with US Navy and prone to a higher incidence. Potential use of set Marine Corps recruits in island territories 10 re- theory for exploratory outbreak analyses is dis- port that chickenpox is a serious disease among cussed. It is a tool potentially useful to contrast adults in tropical climates, where seroprevalence units when only small sample sizes are available. is lower. However, a recent study in Australia re- ported that social and cultural characteristics are Chickenpox; Disease Outbreaks; Delivery of more significant than climate for VZV transmis- Health Care sion 4, suggesting overlaps with some of the de- terminants of chickenpox outbreaks, which un- fortunately are not known. In the Cauca Valley region of Colombia, a large outbreak of chickenpox was observed and documented between 2003 and 2007 11. This Cad. Saúde Pública, Rio de Janeiro, 27(7):1393-1402, jul, 2011 1394 Idrovo AJ et al. outbreak affected children and adults in similar from agricultural data contained in Cauca Valley proportions. However, the causes of this epidem- official statistics; and the last indicator was taken ic were not explored. The region involved in this from the Colombian registries of displaced indi- outbreak is located in western Colombia, which viduals. These indicators were selected as proxy includes the Pacific Ocean coast, between 3° 05’ variables related with our study hypothesis. and 5° 01’ latitude N, 75° 42’ and 77° 33’ longi- Vaccination coverage is an indicator based tude W. The geography of the Cauca Valley region on a mass immunization plan (Plan Ampliado de is varied, with coasts, mountains, jungles, and a Inmunización, PAI, in Spanish) 13. The outcome very fertile valley. In the plains region, sugar cane used for this indicator is the measles, mumps and constitutes the main crop, which is highly impor- rubella vaccine (MMR triple viral), which is con- tant since this relatively small region produces sidered to be a good indicator because it requires roughly 1.7% of the world’s sugar. only one dose at one year old, and it is adminis- The objective of this study was to describe tered after the child has had all previous vaccines the context of the large outbreak of chickenpox in in the vaccination scheme. This indicator reflects this region, with special emphasis on any macro- the performance of primary health care services determinants potentially related with incidence. since good health care coverage is reflected by Our a priori hypothesis was that the chickenpox a municipality having a high percentage of vac- outbreak was related to problems with the per- cinations. Previous studies have reported a de- formance of health care services, lower educa- crease in vaccination coverage over the last 15 tional levels among the population, the migration years 14,15,16. of vulnerable peoples, and/or changes in sugar The production function in a subsidized re- cane-related processes. Since only a small sam- gime is a composite indicator. It relates the eco- ple size was available, it was decided to explore nomic resources from all financial sources with the use of set-theory methods to contrast munic- the expenditure on health care personnel dedi- ipalities. With this approach a simple method to cated to identify and insure the most vulnerable link social epidemiology with field epidemiology families, or to carry out stewardship activities 13. was tested. Usual methods in social epidemiol- It was calculated as the ratio between individuals ogy include, for example, multilevel analysis or in a subsidized regimen/total municipal popu- complex multivariate analyses, so the analysis is lation x 100. The Colombian health system is usually performed by experts. based on managed care and, therefore, the sepa- ration of financing and the provision of health care functions are the principles used to promote Methods cost-efficiency 17. The system has two types of affiliation: contributory and subsidized regime. A case series study was conducted, with the 42 The former covers those who have the ability to Cauca Valley municipalities serving as observa- pay (people with full or partial employment) and tion units. Agency registries from the epidemio- the latter provides services to those who are not logical surveillance system were used to obtain able to pay the necessary contributions (indigent the number of clinical cases between 2003 and and unemployed people). In this context, good 2007. These data originated from the weekly re- performance in a subsidized regime theoretically ports of mandatory notification events. Accord- has a high percentage of enrollement 13. ing to the Colombian epidemiological surveil- Education quality is an indicator constructed lance program, a case of chickenpox is clinically using the percentage of students with medium, defined when a patient has mild to moderate fe- high or very high scores on the national exam ver with a few general symptoms associated with administered by the Colombian Institute for the maculopapular and vesicular lesions that form Development of Higher Education (Instituto Co- granulose crusts 12. lombiano para el Fomento de la Educación Su- perior, ICFES, in Spanish) 13. It is expressed as a Potential contextual determinants percentage and a municipality has better perfor- mance when a high percentage of students have To explore the social and physical environment, medium or high scores. The area size (hectares) five robust indicators were used: (i) vaccination of planted sugar cane is an indicator of the first coverage, (ii) production function in a subsi- process in the production of sugar and ethanol dized regime, (iii) education quality, (iv) area size to produce fuel. Data used in this analysis were of planted sugar cane, and (v) violence-related extracted from the Cauca Valley’s 2007 official immigration. The first three indicators were ex- statistics for agricultural assessment. Original tracted from the Cauca Valley’s 2006 Municipal data are collected by the Regional Agricultural Management Report 13; the fourth was derived Planning Unit (Unidad Regional de Planificación Cad. Saúde Pública, Rio de Janeiro, 27(7):1393-1402, jul, 2011 SOCIAL EPIDEMIOLOGY OF A LARGE OUTBREAK OF CHICKENPOX 1395 Agropecuaria, URPA, in Spanish), and these are and “necessary determinant” in a manner similar available at the official webpage (Evaluaciones to the Susser and Rothman’s causality frameworks agricolas 2000-2009. http://www.valledelcauca. were used 21,22. However, it is important to re- gov.co/agricultura/publicaciones.php?id=1966, member that our analysis does not establish cau- accessed on 25/Apr/2009). sality but, rather, contrasts contexts, which is one Violence-related migration in Colombia is a of the three proposed uses of small-N studies 23. complex demographic process. It is characterized In our case, when a determinant is required to as either a protracted internal displacement for be present it is a “sufficient determinant”, and which the processes of finding lasting solutions when without its presence the higher incidence have stalled and/or when displaced individuals doesn’t occur it is a “necessary determinant”. are marginalized as a consequence of violations These methods were considered appropriate or a lack of protection of human rights, includ- since there were few observations available for a ing economic, social and cultural rights 18. Ac- formal multiple statistical analysis. cording to some authors, threats by armed actors are the proximal cause of forced displacement and problems related to land possession are the Results distal cause 19. Said displacement increases the demand for basic services and infrastructure to The chickenpox outbreak is summarized in Fig- satisfy migrants’ needs in the reception munici- ure 1.