A 3-Year-Old Boy With Fever and Drowsiness

Gavin Christian K.W. Koh, MB, BChir, MA, MRCP, DTM&H; Richard J. Maude, BSc, MBChB Hons, MRCP, DTM&H; Pramot Srisamang, MD

Disclosures

July 28, 2017

In endemic areas, melioidosis most commonly presents as fulminant sepsis, and the duration of symptoms before presentation is commonly brief. Lesions are usually (but not invariably) found in the lungs (presenting as consolidations or lung abscesses), liver, spleen, kidneys, skin, and joints.[1] The mortality of melioidosis is high (20%-40%), despite adequate and appropriate treatment.[1]

Melioidosis also has a less common indolent form, which presents after an extended period of incubation and may be difficult to differentiate from tuberculosis. This is the form most commonly seen in nonendemic areas (eg, United States, Western Europe), where most cases are imported.[6,7]

Contact with soil or surface water is usually part of the history. Specific occupations, such as rice farming and gardening, are important risk factors for the disease. The most common route of infection is presumed to be translocation via minor abrasions in the skin, but inhalation is probably an important route, including aspiration of contaminated well water; this has also been described in cases of extreme weather events.[1]

Around two thirds of all adult patients with melioidosis have diabetes mellitus as a risk factor, and in endemic areas, melioidosis may be the first presentation of diabetes. As a result, all adult survivors of melioidosis should be evaluated for diabetes after recovery.

Other risk factors for melioidosis include immunosuppression (corticosteroids, methotrexate, cancer chemotherapy), chronic renal impairment or renal calculi, thalassemia major, excessive alcohol use, cystic fibrosis, and cancer.[2] A study of over 500 patients with melioidosis found no association with HIV infection.[8]

Melioidosis in children differs in numerous ways from that seen in adults. In children, the disease is usually a localized abscess, mortality is low, relapse is uncommon, and contact with soil and water are often the only risk factors.[1] Around one third of all cases of pediatric disease present as parotitis.[1]

B pseudomallei is not a normal human commensal, and a carrier state is exceedingly rare. Identification of B pseudomallei in any clinical specimen is diagnostic of melioidosis.[1,9] Specimens of blood, throat, and respiratory secretions (eg, sputum, tracheal aspirate, bronchoalveolar lavage) and urine should be collected from every patient in whom the disease is suspected.[9] In addition, pus from any abscesses or collections and surface swabs from any wounds should be obtained, as should specimens from any other site as clinically indicated. Nasogastric aspirates are useful in young children, who tend to swallow their sputum instead of expectorating it. Throat swabs are a valuable diagnostic tool and are often positive, even in cases where no evidence suggests oropharyngeal or respiratory involvement.[9]

B pseudomallei should be handled in biosafety level 3 conditions because of the risk for laboratory-acquired infection.[10] The specimens listed above would normally only be handled in biosafety level 2 conditions; however, the appearance of melioidosis in the differential diagnosis should prompt the clinician to warn the microbiology laboratory before any specimens are sent.

The classic textbook appearance of an intracellular bipolar-staining rod ("safety pin" appearance) is uncommon, not sensitive, and not dependable for diagnosing B pseudomallei.[11] B pseudomallei is not usually a fastidious organism, allowing for growth in a wide variety of media. Early discussion with the microbiology laboratory permits the use of techniques that maximize the chances of identifying the organism.

For blood cultures, lysis centrifugation improves the time to identification, but it requires the blood to be collected because special specimen containers (eg, isolator blood culture tubes) may be required.[12] Specimens obtained from nonsterile sites (eg, sputum and throat swabs) are prone to overgrowth by commensal bacteria, thereby obscuring the presence of B pseudomallei. The use of selective media maximizes the chance of isolating B pseudomallei from these specimens.[13] In endemic areas, Ashdown agar (which contains crystal violet and gentamicin as selective agents) and tryptic soy broth with crystal violet and colistin are routinely used for this purpose. These media are cheap and easy to manufacture, and the ingredients are readily available. Commercially available selective medium for Burkholderia cepacia is an acceptable substitute for microbiology laboratories that no longer make their own media.[14]

The colonial morphology of B pseudomallei (classically described as looking like cornflower heads [Figure 2]) is exceedingly variable and may look like environmental contaminants; other environmental species (eg, Pseudomonas, Burkholderia) may produce colonies that are similar in appearance.

Figure 2.

The laboratory may erroneously report colonies of B pseudomallei as being of no clinical significance, unless appropriately notified. This is unlikely to occur in cases with a heavy, pure growth of the organism from a sterile site (eg, blood or an intraoperative specimen), but it is possible when growth is meager and the specimen is from a nonsterile site. Even if the isolate is recognized as significant, identification of the organism is not straightforward because some commercial systems may erroneously identify the organism as other Burkholderia species, Chromobacterium violaceum, or Pseudomonas species.[15] A 16S polymerase chain reaction assay may be required to properly identify the organism.[16] In the United States, help with identification is available from the Centers for Disease Control and Prevention (CDC).

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