Known as the great mimicker, melioidosis is sometimes confused with tuberculosis or other bacterial diseases — and the stakes are high with as many as half of all cases ending in death, according to the Centers for Disease Control and Prevention.
The infection is transmitted by the bacterium Burkholderia pseudomallei, found in tropical and subtropical regions, but as environmental conditions shift, this gram-negative bacterium contaminating soil and water has now been detected elsewhere.
"We've seen three cases in the last three years in Mississippi in the same county with the same novel strain," Katherine DeBord of the CDC's National Center for Emerging and Zoonotic Infectious Diseases, told Medscape.
This is the first time the bacterium has been found in the continental US, in an area of the Gulf Coast region predicted suitable for the growth of B pseudomallei by environmental modeling studies.
Washing Up on US Shores
Now, scientists are saying melioidosis is probably more widespread than the number of reported cases suggest.
The illness, also known as Whitmore's disease, has recently been recognized as a significant source of illness, with about 165,000 cases worldwide and 89,000 deaths each year around the globe.
Most cases are diagnosed in Southeast Asia and Northern Australia. And Thailand has by far the largest number of culture-confirmed cases with roughly 2500 people diagnosed each year.
In the largest clinical trial of melioidosis to date, the 30-year Darwin Prospective Melioidosis Study included more than 1000 cases. Investigators found that infection correlated with rainfall, with 80% of cases occurring during the wet season (from November to April in endemic areas).
In stormy weather conditions, contaminated water and soil is disturbed and can be inhaled or swallowed. Skin with a small cut or burn can serve as an access point into the body.
A Tier 1 Select Agent
B pseudomallei is a tier 1 select agent and it is a reportable condition to jurisdictions. The World Health Organization lists B pseudomallei as a Risk Group 3 pathogen (high individual risk, low community risk) since it does not normally spread by casual contact from one individual to another, but can still result in serious disease with an increased risk of aerosolized spread.
The incubation period after exposure is usually within 21 days. In a small number of cases, infection can be activated months or years later. But person-to-person transmission is still rare, says Caroline Schrodt, MD, lieutenant commander, US Public Health Service, from the CDC's National Center for Emerging and Zoonotic Infectious Diseases.
"Diagnosis can be tricky and treatment is complicated," Schrodt explains. Treatment includes 2 weeks of intravenous antibiotics during the acute phase of illness followed by oral antibiotics during the eradication phase for at least 3 months. Complicated infections require longer duration of treatment during both phases.
Intravenous ceftazidime or meropenem are used during the intensive phase and even though many patients improve in the acute phase of treatment, Schrodt says, "it's important to continue the entire acute and eradication phases of treatment to decrease risk of relapse or recurrence."
Oral trimethoprim-sulfamethoxazole (Bactrim) is recommended for eradication therapy and should be continued for at least 3 months after, she points out. Simultaneous folic acid supplementation can be considered to help offset the adverse effects associated with the drug's anti-folate influence such as bone marrow toxicity.
Pneumonia Common
In the Darwin Prospective Study, pneumonia was the most common primary diagnosis in more than half of the 1000 cases. Secondary pneumonia developed in approximately 20% of patients with nonpulmonary primary presentations. And skin infection occurred in about 150 people, which were often chronic and lasting for months. Children were more likely than adults to have skin melioidosis.
Another 140 people in the trial had a genitourinary infection, with most of them involving men with prostatic abscesses.
Patients were very sick with more than half developing bacteremia. More than 20% went into septic shock and most required mechanical ventilation.
Scientists are concerned that cases of melioidosis will continue to increase as risk factors such as diabetes and severity of weather-relate events rise.
The gold-standard for diagnosis of melioidosis is a culture of B pseudomallei from any specimen. Anyone suspected to have melioidosis should have blood, sputum, and urine cultures collected. Specimens from all relevant sites of infection such abscesses and skin ulcerations should also be collected. Any time a culture tests positive, the treatment time clock restarts.
The CDC recommends that suspected cases of melioidosis be reported to the local health department. "If you have any questions or suspect a patient may be infected with B pseudomallei, we at CDC's Bacterial Special Pathogens Branch can provide clinical consultation," says Schrodt.
B pseudomallei is a gram-negative, oxidase-positive, motile bacillus with a signature safety-pin appearance on staining. Diagnosis can be challenging as first attempt to culture may be unsuccessful. Serial cultures may be needed for patients with a strong indication of infection.
Risk of melioidosis can be associated with exposure to imported products or animals. One multistate outbreak of melioidosis in recent years was linked to an aromatherapy spray. B pseudomallei infection should still be considered in patients with compatible illness, even if they do not have a history of travel to melioidosis-endemic areas.
To lower the risk for infection, people should drink safe water and protect skin from soil or muddy water. They should avoid walking through flood water after weather events and wear protective boots. Open wounds, cuts or burns should be covered with waterproof bandages. Skin injuries should be washed thoroughly if they come in contact with dirty water or soil.
"This is a high-consequence disease and it's important to recognize and adequately treat," Schrodt says.
Sources:
CDC Melioidosis Webpage – general information
Local endemicity in U.S. HAN 00470
Imported aromatherapy spray–associated melioidosis outbreak
https://www.nejm.org/doi/full/10.1056/NEJMoa2116130
https://emergency.cdc.gov/han/2021/han00456.asp
https://emergency.cdc.gov/han/2021/han00455.asp
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Cite this: Tackle Deadly Melioidosis With Swift, Specialized Care - Medscape - Oct 05, 2023.
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