Misdiagnosing melioidosis.

To the Editor: Melioidosis is endemic in southern and Southeast Asia and northern Australia. Although relatively few indigenous cases are recognized in the Indian subcontinent, a substantial proportion of cases imported into the United Kingdom originate there, probably reflecting patterns of immigration and travel, and underdiagnosis within the Indian subcontinent (1-3).

A 33-year-old woman spent 3 months in India. Shortly after arriving there, fever, myalgia, rigors, pharyngitis, and tender cervical lymphadenopathy developed. After she received antimicrobial agents, her symptoms initially improved, but in September 2005, 1 week after returning to the United Kingdom, she visited her general practitioner with recurrent fever and increasingly painful cervical lymphadenopathy. She was given a course of oral co-amoxiclav 625 mg 3x daily. However, the following week she visited the emergency department of her local hospital with left-sided suppurative cervical lymphadenitis. Pus aspirated from the lymph node grew an aminoglycoside-resistant "pseudomonad" identified as Pseudomonas fluorescens (API20NE profile 1056554), assumed to be a contaminant. She was discharged home to complete a further 10-day course of co-amoxiclav.

One month later, the patient again went to the emergency department, this time with a submental abscess. An otolaryngology consultation was sought, and the abscess was incised and drained. Although tuberculosis was suspected, no acid-fast bacilli were identified, and cultures were negative for mycobacteria; histologic examination showed noncaseating granulomata. Culture of fluid from the submental collection again yielded an aminoglycoside-resistant pseudomonad, however. At this point misidentification was suspected, and the isolate, which had a characteristic colony form on Ashdown's Medium, microscopic appearance (Figure, panel A), API20NE profile (1556574), and fatty acid profile, was identified as Burkholderia pseudomallei, the etiologic agent of melioidosis.

[FIGURE OMITTED]

The patient had no relevant past medical history. Before immigrating to the United Kingdom 3 years earlier, she had lived in Tanjore, a rice-farming area of Tamil Nadu. She had stayed with family there during her recent trip, which coincided with the monsoon season, but she denied rural travel, fresh water contact, or skin abrasions. On examination, she was obese with acanthosis nigricans and tender cervical lymphadenopathy. Blood tests showed a mild microcytosis, low ferritin level, and erythrocyte sedimentation rate 40 mm/h; serum biochemistry and levels of C-reactive protein, fasting glucose, and hemoglobin by electrophoresis were nor mal. Two blood cultures were negative. Results of chest and abdominal imaging were normal. The patient was treated with intravenous ceftazidime for 10 days and oral co-trimoxazole for 4 months. She remains well.

B. pseudomallei serologic tests, performed subsequently, showed negative results by ELISA against the standard laboratory strain (204). However, when the assay was repeated using the patient's own isolate, the result was positive (immunoglobulin G titer 4,000). Comparison of lipopolysaccharide (LPS) antigens from the 2 strains by sodium dodecyl sulfate--polyacrylamide gel electrophoresis and immunoblotting showed that they differed in O-repeating units (Figure, panel B).

B. pseudomallei is an aerobic, gram-negative, environmental saprophyte ubiquitous in soil and surface water (e.g., paddy fields) in disease-endemic areas. Acquisition may occur through skin abrasions, aspiration of fresh water, inhalation, and possibly ingestion and may occasionally occur in the laboratory. An association between severe respiratory melioidosis and heavy monsoonal rains suggests that inhalation has previously been underrecognized as a route of infection (4); this is the likely mode in this case.

Many infections are initially subclinical but may result in latency and delayed manifestations, even after several decades. Clinical signs and symptoms include septicemia, cavitating pneumonia, bone and soft tissue infections, disseminated abscesses, mycotic aneurysms, lymphadenitis, and childhood parotitis. Most patients have an underlying predisposition to infection, especially diabetes, renal disease, alcoholism, and thalassemia, but in the largest Indian case series 50% patients had no traditional risk factors, as with our patient (5). B. pseudomallei is a category B potential bioterrorism agent.

Limited awareness of the disease, confusion with other conditions such as tuberculosis, and laboratory constraints all probably contribute to underdiagnosis of melioidosis in many areas (6). However, accurate diagnosis is important because septicemic melioidosis may be rapidly fatal, B. pseudomallei is intrinsically resistant to many antimicrobial agents, and prolonged treatment is usually required to minimize relapse. Diagnosis is usually by culture from sterile sites. Laboratory misidentification is not uncommon and occurred in this case because the diagnosis was not considered. Isolation of aminogly-coside-resistant pseudomonads in patients from disease-endemic areas should always prompt consideration of melioidosis and accurate identification. PCR is an emerging diagnostic tool not yet extensively validated (7).

The role of serology in diagnosis is limited by high background seropositivity rates in disease-endemic areas. No standardized serologic test is inter nationally agreed upon. This case illustrates another potential pitfall in melioidosis serodiagnosis. Most isolates express a conserved LPS antigen, which allows use of a single reference strain for determination of anti-LPS antibodies (8). However, because some strains express different LPS antigens, serologic tests must be performed with the patient's own strain.

This case illustrates potential pitfalls in diagnosing melioidosis, which requires clinical and laboratory awareness and knowledge of its geographic distribution. LPS-based serologic assays should use a range of isolates representative of known LPS types.

Acknowledgment

We are grateful to the patient for permission to publish this case report.

References

(1.) Dance DA, Smith MD, Aucken HM, Pitt TL. Imported melioidosis in England and Wales. Lancet. 1999;353:208.

(2.) John TJ, Jesudason MV, Lalitha MK, Ganesh A, Mohandas V, Cherian T, et al. Melioidosis in India: the tip of the iceberg? Indian J Med Res. 1996;103:62-5.

(3.) John TJ. Melioidosis, the mimicker of maladies. Indian J Med Res. 2004;119:vi-viii.

(4.) Currie BJ, Jacups SP. Intensity of rainfall and severity of melioidosis, Australia. Emerg Infect Dis. 2003;9:1538-42.

(5.) Jesudason MV, Anbarasu A, John TJ. Septicaemic meliodosis in a tertiary care hospital in south India. Indian J Med Res. 2003;117:119-21.

(6.) Dance DAB. Melioidosis: the tip of the iceberg? Clin Microbiol Rev. 1991;4:52-60.

(7.) Novak RT, Glass MB, Gee JE, Gal D, Mayo MJ, Currie BJ, et al. Development and evaluation of a real-time PCR assay targeting the type III secretion system of Burkholderia pseudomallei. J Clin Microbiol. 2006;44:85-90.

(8.) Pitt TL, Aucken H, Dance DA. Homogeneity of lipopolysaccharide antigens in Pseudomonas pseudomallei. J Infect. 1992;25:139-46.

Address for correspondence: Andrew J. Brent, Nuffield Department of Infectious Diseases & Microbiology, John Radcliffe Hospital, Headington, Oxford, United Kingdom OX3 9DU; email: [e-mail]

Andrew J. Brent, * Philippa C. Matthews, * David A. Dance, ([dagger]) Tyrone L. Pitt, ([double dagger]) and Rupert Handy ([section])

* John Radcliffe Hospital, Headley Way, Headington, Oxford, United Kingdom; ([dagger]) Health Protection Agency (South West), Plymouth, Devon, United Kingdom; ([double dagger]) Laboratory of HealthCare Associated Infection, London, United Kingdom; and ([section]) Heatherwood and Wexham Park Hospitals, Wexham, Slough, United Kingdom

A. J. Brent and R. Handy had clinical responsibility for the patient. R. Handy and P.C. Matthews made the initial microbiologic diagnosis of melioidosis, and T.L. Pitt confirmed the isolate as Burkholderia pseudomallei. T.L. Pitt performed the serology and SDS-PAGE analysis of lipopolysaccharide antigens. All authors contributed to preparation of the manuscript. A.J. Brent is guarantor for the article, had full access to all the clinical and microbiologic data, and had final responsibility for the decision to submit for publication.