Melioidosis, caused by the environmental bacterium Burkholderia pseudomallei, is a deadly and often overlooked infectious disease, historically linked to Southeast Asia and northern Australia. Known as the “great mimicker,” it can masquerade as pneumonia, tuberculosis, or sepsis, confounding diagnosis and delaying treatment.
While once thought confined to tropical zones, B. pseudomallei has now been confirmed in the soil and water of the southern United States. Its appearance here marks a shift with profound implications. As climate change accelerates extreme weather and reshapes ecosystems, conditions across parts of the U.S. may increasingly mirror those of endemic regions.
A growing concern is drinking water safety. Although boiling reliably kills B. pseudomallei, disinfection with chlorine or UV light may only reduce its numbers. In contrast, reverse osmosis (0.001 µm) and ultrafiltration (0.01 µm) systems provide effective physical removal of the bacteria.
This article traces the rising threat of melioidosis in the U.S., from ecological emergence to clinical risks. Drawing on climate modeling, regional outbreak data, and lessons from Australia, it examines how a once foreign pathogen is becoming a domestic concern.
Emergence of Melioiodosis in the USA
For decades, melioidosis has remained neglected by global health authorities, despite mortality rates rivalling those of dengue and measles. Global estimates suggest as many as 165,000 new infections and 89,000 deaths annually, a number likely underreported due to low awareness and inadequate diagnostics, especially in rural or under-resourced settings (Wiersinga et al., 2018).
Until recently, endemicity was largely restricted to Southeast Asia and northern Australia. However, recent studies and outbreaks have confirmed the pathogen’s presence in the Americas, including the continental United States.
The transformation from importation to local transmission was first hinted at by sporadic cases in Vietnam War veterans. For years, these infections were considered latent reactivations from Southeast Asia. The longest documented latency period was 29 years (Chodimella et al., 1997; Meumann et al., 2024).
But the paradigm shifted in 2022, when B. pseudomallei was isolated from the environment in Mississippi after several U.S. residents with no international travel history fell ill. Genomic analysis confirmed the environmental strain matched clinical isolates, validating the pathogen’s naturalization in U.S. soil (CDC 2022).
Ecological Foundations and Climate-Driven Expansion
B. pseudomallei is a versatile and resilient organism. It thrives in acidic, nutrient-poor soils, particularly in association with grasses and surface water. It has been recovered from bore water, puddles, and even domestic taps, as seen in both Australia and Thailand. During the rainy season, it rises from deeper soil layers to the surface, where it can become airborne or waterborne. It can survive in distilled water for over 16 years (Wiersinga et al., 2018), and outbreaks have often been linked to periods of flooding, construction, or water chlorination failure (Inglis et al., 1999).
These environmental traits make B. pseudomallei sensitive to climate dynamics. In Australia, the disease shows a marked seasonal trend, with sharp increases in cases during the wet season.
A recent outbreak in northern Queensland, Australia, offers a grim case study: by mid-May 2025, 31 deaths and 221 reported cases had occurred, which is an increase of 163 compared to the same time in 2024. Towns like Cairns and Townsville in Far North Queensland were heavily affected following record-breaking rainfall and severe flooding in February 2025, illustrating how climatic extremes convert endemic bacteria into public health crises.
The situation is poised to repeat in the United States. Climate models project that by mid-century, southern states including Texas, Louisiana, Mississippi, Alabama, and Florida will increasingly resemble the melioidosis-prone climates of Southeast Asia. These regions already experience high humidity, seasonal storms, and rising groundwater. These are ideal conditions for the activation and spread of B. pseudomallei (Meumann et al., 2024).
Waterborne Transmission and Public Health Infrastructure
Though skin inoculation and inhalation have been considered primary routes of infection, mounting evidence suggests ingestion of contaminated water is a major but under appreciated pathway.
In a 2014 study in Thailand, Limmathurotsakul and colleagues isolated B. pseudomallei from 7% of household drinking water samples, including public tap water. In two cases, clinical and waterborne strains were genetically identical, providing direct evidence of infection via ingestion of tap water. This is not only plausible but likely in rural areas with poor chlorination, leaky infrastructure, or reliance on unprotected water sources.
In Western Australia in 1997, an acute outbreak struck a remote coastal community. Seven cases occurred over a six-week period, with three deaths. The outbreak coincided with construction work that disrupted soil, failures in water chlorination, and unusually acidic water from boreholes. Investigators isolated B. pseudomallei from a domestic tap, genetically identical to clinical isolates.
This incident emphasized the importance of potable water safety, particularly in regions undergoing development or infrastructure repair (Inglis et al., 1999).
Many communities in the United States, particularly in the Gulf Coast, face heightened vulnerability to melioidosis due to their reliance on shallow wells and aging water infrastructure. These systems are often poorly protected and prone to contamination, especially during heavy rainfall or flooding.
As climate models predict more frequent and intense storms, these less protected water sources may increasingly serve as conduits for the spread of Burkholderia pseudomallei as well as other waterborne pathogens.
Size of Burkholderia pseudomallei
The size of an B. pseudomallei varies between strain, of which there are many!
To know if a specific type of water filter can physically remove it or not, then we need to know how SMALL B. pseudomallei are.
Being bacteria, they are longer than they are wide.
Sagripanti et al., (2011) compared the size of 5 different strains of B. pseudomallei, and found the smallest diameter was around 0.35 to 0.42 micron (µm). So a water filter, purifier or RO system that has pore sizes smaller than this will be able to filter them out.
| Strain | Length Range (µm) | Diameter Range (µm) |
| ATCC 23343 | 0.92–3.22 | 0.39–0.98 |
| NCTC 13177 | 1.10–2.90 | 0.42–1.02 |
| BCC15 | 0.88–2.97 | 0.40–0.98 |
| BCC21 | 1.04–2.78 | 0.38–0.87 |
| 78-3 | 1.05–2.85 | 0.35–0.86 |
Water Purification Technologies that can Remove or Kill B. pseudomallei
Several water purification technologies can reduce or eliminate B. pseudomallei from drinking water:
Chlorination
Chlorination remains the most widely used and cost-effective method used by municipal facilities to disinfect water.
Free chlorine residuals of between 0.5-2.0 ppm provide effective continuous disinfection in water distribution systems, and the CDC considers chlorine concentrations up to 4 ppm (4 mg/L) safe for drinking water (CDC 2024b).
Given the proven survival of B. pseudomallei in unchlorinated, low-chlorinated or untreated drinking water (CDC 2024a), chlorination remains an important defense.
However, chlorine has its limitations as a biodefence disinfectant against B. pseudomallei, and certain strains are more tolerant of chlorine than others. For example, some endemic strains from Australia were exposed to very high chlorine disinfection (1,000 ppm), but still regrew within two days (Howard & Inglis 2003)!
So, chlorine can certainly reduce the number of B. pseudomallei in your drinking water, but there is no guarantee they will ALL be killed.
Reverse Osmosis and Ultrafiltration
For point-of-use applications, RO and ultrafiltration units provide a non-chemical barrier that avoids issues of residual disinfectants and pH sensitivity.
Reverse osmosis (RO) systems provide one of the best physical barriers to B. pseudomallei. Many RO filters are NSF-58 certified and use pore sizes as small as 0.001 μm, far below the small bacterial diameter of 0.35–0.86 μm (strain 78-3) (Sagripanti et al., 2011).
Ultrafiltration water systems typically have pore sizes in the range of 0.01 μm and are also effective at removing B. pseudomallei.
Even membrane filters with 0.22 to 0.45 μm pore sizes have been used in studies to recover and concentrate B. pseudomallei from water for research purposes (e.g., Limmathurotsakul et al., 2012). Filters of this size are also effective at removing many of the organisms during actual water purification.
Boiling
Though not always practical, boiling remains universally effective.
B. pseudomallei is readily inactivated by temperatures exceeding 140°F (60°C), and full sterilization is achieved by boiling at 212°F (100°C) for at least 1 minute. For emergency scenarios or households without access to filtration or chlorination, boiling remains a gold standard.
UV Sterilization
Ultraviolet (UV) light can effectively reduce Burkholderia pseudomallei in clear water, but the bacterium is not highly sensitive to UV compared to other microbes.
Laboratory studies show that a UV dose of 120 Joule per square meter (J/m²) is required to achieve a 99.99% reduction in B. pseudomallei, while lower doses have limited effect (Inglis & Sagripanti 2006).
In the real world, however, its protective outer structures and ability to form biofilms or reside within protozoa cysts (e.g., Acanthamoeba spp.) can shield it from UV exposure and chemical agents.
UV effectiveness is also significantly reduced in turbid or particulate-laden water. Therefore, UV treatment should be used in combination with other methods, such as ultra- or micro-filtration (such as RO) or chlorination.
Clinical Complexities and Diagnostic Gaps
Diagnosing melioidosis remains a challenge. The disease mimics a range of infections from tuberculosis to abscesses to septic shock.
In endemic regions like Australia, patients typically present with pneumonia (in 50% of cases) or sepsis (in 20%) (Currie 2015).
About 11% of cases develop chronic infection, often manifesting as abscesses in the liver, spleen, or prostate (Currie 2015).
Mortality rates range from 10% to over 40%, depending on timeliness of treatment and healthcare access (Wiersinga et al., 2018).
Unfortunately, melioidosis is often misidentified in non-endemic areas. The bacterium grows slowly and may be dismissed as a contaminant.
In the U.S., lack of familiarity and absence of routine testing means many cases go undetected or are misdiagnosed. No vaccine currently exists, and treatment requires a long dual-phase antibiotic regime initially, followed by three to six months of oral eradication therapy.
Endemicity in the United States
The 2022 detection of B. pseudomallei in Mississippi was a watershed moment. Environmental sampling recovered B. pseudomallei from soil and puddles on private property, and whole-genome sequencing linked isolates from patients and environmental samples. This represents a shift in disease paradigm: melioidosis is now a domestic threat for the United States.
Genomic surveillance indicates that the strains found in the U.S. are distinct from those in Southeast Asia or Australia, aligning more closely with other Western Hemisphere isolates. This suggests an independent environmental establishment rather than recent introduction via travel or trade.
Lessons from Australia
Australia offers a rich case study in melioidosis management. It has invested heavily in surveillance, environmental testing, water safety, and public education. In Darwin (northern Australia), community awareness campaigns and early antibiotic initiation have reduced case fatality from over 50% in the 1980s to below 15% in recent years (Currie 2015). Routine testing of drinking water supplies and risk communication during the wet season have been critical.
The United States could emulate these strategies, particularly in southern states that are prone to hurricanes and floods.
Surveillance, Prevention, and Policy
Melioidosis remains underdiagnosed, underreported, with little attention from public health agencies. It is not currently listed as a neglected tropical disease by the WHO.
In the U.S., no routine testing is performed for B. pseudomallei in drinking water, nor are standard clinical protocols widely distributed outside infectious disease circles, potentially leading to misdiagnosis.
References:
Centers for Disease Control (CDC) and Prevention. Bacteria that Causes Rare Disease Melioidosis Discovered in U.S. Environmental Samples. CDC https://archive.cdc.gov/www_cdc_gov/media/releases/2022/p0727-Melioidosis.html (2022).
Centers for Disease Control (CDC) and Prevention. About Melioidosis https://www.cdc.gov/melioidosis/about (2024a)
Centers for Disease Control (CDC) and Prevention. About Water Disinfection with Chlorine and Chloramine. https://www.cdc.gov/drinking-water/about/about-water-disinfection-with-chlorine-and-chloramine.html (2024b).
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