Environmental detection ofBurkholderia pseudomalleiand associated melioidosis risk: a molecular detection and case-control cohort study
Authors: Pakdeerat Sukritpong , Chomkatekaew Chalita , Boonklang Phumrapee , Wongprommoon Arin , Angchagun Kesorn , Dokket Yaowaret , Faosap Areeya , Wongsuwan Gumphol , Amornchai Premjit , Wuthiekanun Vanaporn , Changklom Jirameth , Siriboon Suwatthiya , Chamnan Parinya , Peacock Sharon J , Corander Jukka , Day Nicholas PJ , Thomson Nicholas R , Uttamapinant Chayasith , Wongpalee Somsakul Pop , Chewapreecha Claire 
Published: November 2024

Background

Environmental acquisition ofBurkholderia pseudomalleican cause melioidosis, a life-threatening yet underreported disease. Understanding environmental exposure is essential for effective public health interventions, yet existing tools are limited in their ability to quantify exposure risks.

Methods

We conducted two complementary studies across a 15,118 km2area of northeast Thailand to improve detection methods and investigate risk factors for melioidosis. In the first study, we compared a newly developed, equipment-light CRISPR-based assay (CRISPR-BP34) with conventional culture methods using both spiked samples and real water samples from household and community sources (November 2020 - November 2021). The second study involved a case-control analysis of 1,135 participants (October 2019 - January 2023) to evaluate the association between environmental exposure toB. pseudomallei(detected in Study 1) and melioidosis risk.

Findings

The CRISPR-BP34 assay demonstrated improved sensitivity (93.52% vs 19.44% for conventional methods) and specificity (100% vs 97.98%), allowing for more accurate detection ofB. pseudomalleiand exposure risk quantification. Environmental exposure toB. pseudomalleiin water sources within a 10 km radius of participants’ households was significantly associated with increased melioidosis risk (OR: 2.74 [95% CI 1.38-5.48]). This risk was also heightened by known factors: occupational exposure among agricultural workers (4.46 [2.91-6.91]), and health factors like elevated hemoglobin A1c, indicating diabetes (1.35 [1.19-1.31]).

Interpretation

Our findings underscore the impact of environmental contamination on melioidosis risk. The robust association between contaminated water sources, including piped water systems, and clinical cases highlights the urgent need for improved water sanitation to mitigate melioidosis risk.

Funding

Wellcome Trust

Evidence before this study

We conducted a PubMed search, without language restrictions from database inception to 11 September 2024, using the following search terms: (“Burkholderia pseudomallei” AND “environment* sampl*”) or (“Burkholderia pseudomallei” AND “spatial”), yielding 172 research and review articles. Several studies attempted to link the detection ofB. pseudomalleiin the environment with melioidosis risk through case-control and case-only designs. However, none demonstrated a statistically significant relationship between environmental presence ofB. pseudomalleiand infection risk (case-control) or clinical severity (case-only). The main challenges included low detection rates in environmental samples, inconsistent sampling methodologies, and outdated guidelines, which restricted the use of individual analyses or meta-analyses across combined studies. While soil is widely considered the natural reservoir forB. pseudomallei, its distribution varies significantly across soil textures, moisture levels, and depths, often leading to inconsistent or inconclusive data. These variations complicate efforts to establish a reliable link between soil contamination and melioidosis risk. Water sampling has been suggested as a viable alternative due to its more homogenous nature and simpler collection methods. Water also directly reflects human exposure risk, as people are regularly in contact with natural water bodies and treated water systems. However, detectingB. pseudomalleiin water is challenging due to its low abundance. Molecular techniques such as PCR, following an enrichment process, have shown the highest sensitivity for detectingB. pseudomallei. The enrichment step enhancesB. pseudomalleigrowth while suppressing competing microorganisms. For example, in a study conducted in a disease hotspot in Laos, positive detection rates improved from a median of 50% (IQR 42.5 - 53.8%) using conventional culture inspection methods, to 55% using PCR alone, and 75% with PCR following enrichment. While this approach is promising, it requires access to PCR equipment, which is often unavailable in resource-limited, melioidosis-endemic regions. These challenges create gaps in current detection methods and hinder the ability to accurately quantify environmental exposure risks and identify high-risk areas.

Added value of this study

Our study addressed these gaps by developing an equipment-light device capable of detectingB. pseudomalleiin environmental samples after enrichment. This approach eliminates the need for complex PCR equipment while maintaining high sensitivity and specificity, comparable to qPCR. Our findings established a statistically significant link between environmental exposure toB. pseudomalleiwithin a 10 km radius of households and 2.74-fold increased odds [95% CI: 1.38-5.48] of acquiring melioidosis. This risk remains significant even after adjusting for confounding factors such as underlying health conditions (e.g. diabetes) and occupational exposures.

Implications of all the available evidence

Our results confirm thatB. pseudomalleican be detected in both natural water reservoirs and publicly treated piped water systems in endemic regions, and that its presence is positively associated with the occurrence of melioidosis. The detection ofB. pseudomalleiin treated water systems emphasises the urgent need for improved water sanitation measures. These results highlight the importance of environmental monitoring and targeted interventions to reduce melioidosis risks in the endemic areas.