Exploratory Temporal and Spatial Distribution Analysis of Dengue Notifications in Boa Vista, Roraima, Brazilian Amazon, 1999-2001†
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Exploratory Temporal and Spatial Distribution Analysis of Dengue Notifications in Boa Vista, Roraima, Brazilian Amazon, 1999-2001† by Maria Goreti Rosa-Freitas*, Pantelis Tsouris**#, Alexander Sibajev***, Ellem Tatiani de Souza Weimann**, Alexandre Ubirajara Marques**, Rodrigo Lopes Ferreira** and José Francisco Luitgards-Moura*** *Laboratório de Transmissores de Hematozoários, Departamento de Entomologia, Instituto Oswaldo Cruz, Av. Brasil 4365, Manguinhos, 21045-900 Rio de Janeiro, RJ, Brasil **Núcleo Avançado de Vetores – Convênio FIOCRUZ-UFRR BR 174 S/N - Boa Vista, RR, Brasil ***Centro de Ciências Biológicas e da Saúde, UFRR, BR 174 S/N - Boa Vista, RR, Brasil Abstract In Brazil, as in the rest of the world, dengue has become the most important arthropod-borne viral disease of public health significance. Roraima state presented the highest dengue incidence coefficient in Brazil in the last few years (224.9 and 164.2 per 10,000 inhabitants in 2000 and 2001, respectively). The capital, Boa Vista, reports the highest number of dengue cases in Roraima. This study examined the temporal and spatial distribution of dengue in Boa Vista during the years 1999- 2001, based on daily notifications as recorded by local health authorities. Temporally, dengue notifications were analysed by weekly and monthly averages and age distribution and correlated to meteorological variables. Spatially, dengue coefficients, premises infestation indices, population density and income levels were allocated in a geographical information system using, Boa Vista 49 neighbourhoods as units. Dengue outbreaks displayed distinct year-to-year distribution patterns that were neither periodical nor significantly correlated to any meteorological variable. There were no preferences for age and sex. The derived maps showed that premises infestation indices, population density, income and dengue incidence were concentrated along a central horizontal east-west axis. Major risk areas of transmission during the three consecutive years were the central neighbourhoods. These neighbourhoods are of the highest income population in the city. Keywords: Dengue, spatial information, Roraima, Brazil. #For correspondence: [email protected] † This work was supported by the Brazilian Council for Science and Development-CNPq (521176/98-0), the Oswaldo Cruz Institute-FIOCRUZ and the Roraima Federal University-UFRR Dengue Bulletin – Vol 27, 2003 63 Dengue in Boa Vista, Roraima, 1999-2001 Introduction This study examines the temporal and spatial dengue notification data in Boa Vista, The state of Roraima is located in the Roraima, for the years 1999-2001, taking Amazon region at the border of Guyana and into account some meteorological, Venezuela. An outbreak with 12,000 dengue entomological and demographic factors. cases (incidence rate of 1,160/10,000 inhabitants) was registered in 1981-1982 in Boa Vista, Roraima(1,2). It was during this Materials and methods outbreak that dengue was diagnosed in Brazil by laboratory tests and isolated from Place of study human hosts and mosquito vectors for the 2 (3) Roraima has an area of 225,116 km and a first time . Currently, dengue is reported in population of 321,397(12). The rural all the 27 states in Brazil; 87% of these are population density is 1.4/km2, while the situated in the south-eastern and north- population density of its capital, Boa Vista, is (4) eastern regions . Even though these regions 26/km2 (38% of the state population)(12,13,14). report the largest number of cases, the Approximately 85% of the Roraima state is importance of Roraima is due to the fact that under forest, with the remaining 15% this state alone presented the country’s covered by savanna(15). The capital, Boa Vista highest coefficients of dengue incidence, i.e. (02049’11”N, 60040’24”W), with an area of 224.9 and 164.2 (per 10,000 inhabitants) for 122,000 km2, is located by the Branco river (4) the years 2000 and 2001, respectively . (Figure 1). Savanna is the predominant Dengue is also assumed to display a seasonal ecological environment in Boa Vista. The variation in Brazil, with the majority of the climate is tropical humid with an average cases occurring in the rainy season (February temperature of 27.80C (10-year average)(16) to May). However, in Boa Vista, it may peak and an average rainfall of 429 mm (4-year either in the rainy (April-November) or dry average)(16) with low annual variation. The (December-March) seasons. This reflects the climate presents two distinct seasons, a rainy fact that hosts, parasites, vectors and season between April and November, with environmental factors are all dynamic factors high rainfall indices during the months of that vary temporally and spatially in an June and July, and a dry season from (5,6,7) epidemiological system . December to March(17). The city has 49 neighbourhoods (bairros) (Law 483 of 9 Temporal changes in the environment December 1999). Formerly, these are driven mostly by meteorological variables neighbourhoods were 19 in number. The that determine the relationship between Census 2000 data, available at the IBGE hosts, parasites and vectors(8). Variables Internet site(12) contains old neighbourhoods. linked to the human population such as This re-division makes the comparison density and socioeconomic status have also between the old and new data difficult, since been considered important(9,10). Analyses and some new neighbourhoods encompassed projection of geographical data allow spatial the areas of old ones. Many streams visualization in relation to physical maps and (igarapés) and rivers cross the city. Most facilitate comparisons of longitudinal urban lakes were drained and land filled to investigations(11). avoid becoming mosquito breeding sites. 64 Dengue Bulletin – Vol 27, 2003 Dengue in Boa Vista, Roraima, 1999-2001 The main river is the Branco, which crosses are linked to the city water system and have the city in the north-westerly direction. routine trash collection(12). There are four Approximately 90% of the homes have general hospitals and 13 health units. sanitary installations (even though most of Around 69% of the population is literate. them are not linked to the sewage system), The average annual income is US$ 714(12). Figure 1. Brazil, Roraima and Boa Vista neighbourhoods Branco River BOA VISTA VENEZUELA RORAIMA GUYANA Amazon Boa Vista BRAZIL Dengue Bulletin – Vol 27, 2003 65 Dengue in Boa Vista, Roraima, 1999-2001 Dengue notifications Meteorological data Compulsory notification for dengue was Meteorological data registered daily for the started in 1996 in Boa Vista. The dengue period 1999-2001, rainfall(mm), data from 1982 to 1998 were not humidity(%), temperature(°C), wind comprehensive and were therefore excluded direction(°), wind velocity (knot) and from this study. From 1999 onwards dengue atmospheric pressure (hpa) were provided notifications were registered daily by both by the Boa Vista Air Force Base (June 1999 the municipal and state health secretariats data was based on monthly averages) (Secretaria do Estado de Saúde de Roraima- (Serviço Regional de Proteção ao Vôo de SESAU and Secretaria Municipal de Saúde- Manaus, Relatório Climatológico Diário, SEMSA). Our data refers to people reporting unpublished data). dengue-related symptoms such as high fever, headache, myalgia, arthralgia and dizziness. Dengue notifications were analysed daily, Census data and weekly and monthly averages were The demographic data used in the analyses, calculated from these daily values. based on the census performed on 31 July/1 Epidemiological weeks were used for August 2000(12) were age, sex, population averaging (epidemiological weeks were and income. The population density and counted from Sunday to Saturday). Age and income were analysed according to sex of individuals reporting dengue were also neighbourhoods(14). analysed to establish their distribution throughout the period and in relation to the normal population curve. From the daily Spatial analyses notification reports, the following data were used: date, epidemiological week of report, Dengue coefficients, premises infestation age and neighbourhood of residence. Age indices, meteorological values and census was analysed in ranges to facilitate a data were integrated in the Geographical comparison with the age census data that Information System Arc View 3.2-based uses this format. software using Boa Vista map layers (Multispectral). Spatial analyses units were the 49 neighbourhoods of the capital, Boa Entomological data Vista. The dengue incidence per Premises infestation indices for Aedes aegypti neighbourhood (per 10,000 inhabitants) was were collected by FUNASA-RR. Indices were plotted using the dot tool (1 notification = 1 partial, available for the year 2001 and for a dot, spread by chance in the polygon area). certain number of neighbourhoods only. The premises infestation indices and average Aedes albopictus was not found in Boa Vista income per neighbourhood were plotted (FUNASA-RR, unpublished data). using the gradient tool. 66 Dengue Bulletin – Vol 27, 2003 Dengue in Boa Vista, Roraima, 1999-2001 Results meteorological values shifted four days backwards (time of report delay Temporal analyses corresponding to the average intrinsic incubation period) (data not shown). Daily analysis of dengue notifications is liable to error due to the unequal distribution of Table 1. Correlation between premises infestation, population density, income and dengue notifications. Notifications on meteorological variables and dengue weekends and holidays were minimal (Figure incidence for the period 1999-2001 in Boa 2). For that reason, dengue notifications Vista, Roraima, Brazil were analysed by weekly averages. Dengue outbreaks displayed distinct year-to-year Dengue incidence distribution patterns (Figure 3) that were Variable 1999 2000 2001 neither periodical nor significantly correlated to any meteorological variable (Figures 4 and Premises infestation - - -0.10 5) (Table 1). During the period of this study, Population density -0.01 0.28 0.14 the average wind velocity was 3.5 m/s. Income 0.40 0.44 0.40 Correlation between dengue and population density and income varied from -0.01 to 0.44 Rainfall 0.12 0.03 -0.18 (Table 2).