Socio-epidemiological and land cover risk factors for melioidosis in Kedah, Northern Malaysia.

Muhammad Radzi Abu Hassan,Edwin Michael,Norasmidar Aziz,Benjamin Mayala,Noraini Ismail,Subhada Prasad Pani,Rose E Donohue,Zainab Shafie,Alfredo G Torres

doi:10.1371/journal.pntd.0007243

Abstract

BackgroundMelioidosis, a fatal infectious disease caused by Burkholderia pseudomallei, is increasingly diagnosed in tropical regions. However, data on risk factors and the geographic epidemiology of the disease are still limited. Previous studies have also largely been based on the analysis of case series data. Here, we undertook a more definitive hospital-based matched case-control study coupled with spatial analysis to identify demographic, socioeconomic and landscape risk factors for bacteremic melioidosis in the Kedah region of northern Malaysia.Methodology/Principal findingsWe obtained patient demographic and residential information and clinical presentation and medical history data from 254 confirmed melioidosis cases and 384 matched controls attending Hospital Sultanah Bahiyah (HSB), the main tertiary hospital of Alor Setar, the capital city of Kedah, during the period between 2005 and 2011. Crude and adjusted odds ratios employing conditional logistic regression analysis were used to assess if melioidosis in this region is related to risk factors connected with socio-demographics, various behavioural characteristics, and co-occurring diseases. Spatial clusters of cases were determined using a continuous Poisson model as deployed in SaTScan. A land cover map in conjunction with mapped case data was used to determine disease-land type associations using the Fisher’s exact test deploying simulated p-values. Crude and adjusted odds ratios indicate that melioidosis in this region is related to gender (males), race, occupation (farming) and co-occurring chronic diseases, particularly diabetes. Spatial analyses of disease incidence, however, showed that disease risk and geographic clustering of cases are related strongly to land cover types, with risk of disease increasing non-linearly with the degree of human modification of the natural ecosystem.Conclusions/SignificanceThese findings indicate that melioidosis represents a complex socio-ecological public health problem in Kedah, and that its control requires an understanding and modification of the coupled human and natural variables that govern disease transmission in endemic communities.

Highlights

Melioidosis, once thought to be restricted to Southeast Asia and northern Australia [1], is increasingly diagnosed in other tropical regions, including across Africa, the Caribbean, and other parts of Asia [2, 3]
We undertook a more definitive hospital-based matched case-control study coupled with spatial analysis to identify demographic, socioeconomic and landscape risk factors for bacteremic melioidosis in the Kedah region of northern Malaysia
Our results indicate that melioidosis in northern Malaysia is significantly associated with gender, race, occupation, co-occurring chronic disease as well as living in risky landscapes, with disease risk increasing and declining non-linearly with the degree of ecosystem modification

Summary

Introduction

Melioidosis, once thought to be restricted to Southeast Asia and northern Australia [1], is increasingly diagnosed in other tropical regions, including across Africa, the Caribbean, and other parts of Asia [2, 3]. Previous work has shown that peninsular Malaysia may be at high risk for the disease, with hospital cases recorded from practically all regions of the country [6,7,8,9,10,11], and calculated annual incidences ranging from 4.3 per 100,000 in the eastern state of Pahang [6] to as high as 16.35 per 100,000 recently reported by us in the northwestern agricultural state of Kedah [7] These studies have highlighted the high fatality rate, as well as provided data suggestive of the myriad social and ecological factors that may govern disease transmission in this region [6,7,8,9,10,11]. We undertook a more definitive hospital-based matched case-control study coupled with spatial analysis to identify demographic, socioeconomic and landscape risk factors for bacteremic melioidosis in the Kedah region of northern Malaysia.

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