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. 2012 Aug 8:12:185.
doi: 10.1186/1471-2334-12-185.

Analyzing the spatial and temporal distribution of human brucellosis in Azerbaijan (1995 - 2009) using spatial and spatio-temporal statistics

Rakif Abdullayev  1 , Ian Kracalik, Rita Ismayilova, Narmin Ustun, Ayden Talibzade, Jason K Blackburn
Affiliations

Analyzing the spatial and temporal distribution of human brucellosis in Azerbaijan (1995 - 2009) using spatial and spatio-temporal statistics

Rakif Abdullayev et al. BMC Infect Dis. .

Abstract

Background: Human brucellosis represents a significant burden to public and veterinary health globally, including the republic of Azerbaijan. The purpose of this study was to examine and describe the spatial and temporal aspects of the epidemiology of human brucellosis in Azerbaijan from 1995 to 2009.

Methods: A Geographic information system (GIS) was used to identify potential changes in the spatial and temporal distribution of human brucellosis in Azerbaijan during the study period. Epidemiological information on the age, gender, date, and location of incident cases were obtained from disease registries housed at the Republican Anti-Plague station in Baku. Cumulative incidences per 100,000 populations were calculated at the district level for three, 5-year periods. Spatial and temporal cluster analyses were performed using the Local Moran's I and the Ederer-Myer-Mantel (EMM) test.

Results: A total of 7,983 cases of human brucellosis were reported during the 15-year study period. Statistically significant spatial clusters were identified in each of three, five year time periods with cumulative incidence rates ranging from 101.1 (95% CI: 82.8, 124.3) to 203.0 (95% CI; 176.4, 234.8). Spatial clustering was predominant in the west early in the study during period 1 and then in the east during periods 2 and 3. The EMM test identified a greater number of statistically significant temporal clusters in period 1 (1995 to 1999).

Conclusion: These results suggest that human brucellosis persisted annually in Azerbaijan across the study period. The current situation necessitates the development of appropriate surveillance aimed at improving control and mitigation strategies in order to help alleviate the current burden of disease on the population. Areas of concern identified as clusters by the spatial-temporal statistical analyses can provide a starting point for implementing targeted intervention efforts.

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Figures

Figure 1
Figure 1
Total number of newly reported cases of human brucellosis seropositives by year during the period 1995 to 2009 shown by the black bars and incidence per 100,000 indicated by the red line.
Figure 2
Figure 2
Map A shows Azerbaijan grouped into dummy regions: Nakchivan (light blue), West (dark green), Central (dark blue), and East (light green). Map B displays the total number of human brucellosis seropositives by district during the time period 1995 to 2009 with the Central region overlain with cross-hatching. The capital Baku is represented by a star in map B.
Figure 3
Figure 3
Spatial distribution of cumulative incidence estimates during the study period 1995 to 2009. Cumulative estimates were calculated for three equal 5-year periods. The maps display period 1 (1995 to 1999), period 2 (2000 to 2004), and period 3 (2005 to 2009). Insets A refer to crude cumulative incidence estimates for each time period and insets B refer to Empirical Bayes smoothed (EBS) estimates for each time period. Cross-hatching overlain on maps depicts the Central dummy region of Azerbaijan. During period 1 cumulative incidences ranged between 0 to 415.0 cases per 100,000 persons with the highest rate occurring in Bilasuvar (95%CI : 368.9, 465.4), period 2 cumulative incidences that ranged between 0 to 386.5 cases per 100,000 persons with the highest rate occurring in Gobustan (95%CI : 324.5, 456.9), and period 3 Cumulative rates during period 3 ranged between 0 to 283.4 cases per 100,000 persons with the highest incidence again occurring in Gobustan (95%CI : 232.2, 342.8).
Figure 4
Figure 4
Boxplots are displaying the crude cumulative incidence rates per district in each of the time periods, [period 1 (1995 to 1999), period 2 (2000 to 2004), and period 3 (2005 to 2009)] paneled by the dummy region: Central, East, Nakchivan, and West. Crude estimates were calculated for each period using the total number of reported cases during a 5-year period as the numerator and the median year population as the denominator.
Figure 5
Figure 5
Local Moran’s I clusters across Azerbaijan with red portraying High-High areas, dark blue Low-Low areas, light blue Low-High areas, and pink High-Low areas. During period 1 (1995 to 1999) High-High clusters were identified in Gor (Goranboy), Imi (Imishli), Kha (Khanlar), Saa (Saatly), and Tar (Tartar). During period 2 (2000 to 2004) Abs (Absheron) was identified as a High-High cluster and Khi (Khizi) was identified during period 3 (2005 to 2009). The star represents the location of the capital Baku and cross-hatching represents the Central region.
Figure 6
Figure 6
Total number of human brucellosis cases by month and season. Winter months (n = 1,000) are shown in the graph by cross-hatched bars, Spring months (n = 2,228) are displayed by the solid black bars, Summer months (n = 3,131) are represented by dotted bars, and Fall months (n = 1,624) are displayed by the solid grey bars.
Figure 7
Figure 7
Results from the Ederer-Myer-Mantel’s (EMM) test displaying significant temporal clusters during period 1 (1995 to 1999) shown in light grey, period 2 (2000 to 2004) shown in dark grey, and period 3 (2005 to 2009) shown in black.
Figure 8
Figure 8
Age distribution of human brucellosis cases in men illustrated by the black bars and women displayed by the grey bars.
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