Chapter 3Infectious Diseases Related To Travel

David D. Blaney, Jay E. Gee, Theresa L. Smith

INFECTIOUS AGENT

Burkholderia pseudomallei is a saprophytic, gram-negative bacillus widely distributed in tropical soil and water.

MODE OF TRANSMISSION

Human infection with B. pseudomallei usually occurs by inhalation or subcutaneous inoculation, or occasionally by ingestion; person-to-person transmission is rare via contact with the blood and body fluids of an infected person.

EPIDEMIOLOGY

Melioidosis is an infectious disease endemic in Southeast Asia, northern Australia, Papua New Guinea, much of the Indian subcontinent, southern China, Hong Kong, and Taiwan. It is considered highly endemic in northeast Thailand, Malaysia, Singapore, and northern Australia (Map 3-12). In northern Australia and northeast Thailand, melioidosis accounts for 20% of all community-acquired septicemias. Melioidosis is the most common cause of severe community-acquired pneumonia in northern Australia.

Melioidosis has been reported in Puerto Rico, suspected in El Salvador, and may be underdiagnosed in India, Africa, the Caribbean, and Central and South America. In 2009, an imported case from Aruba was identified in the United States. In northern Brazil, clusters of melioidosis have recently been recognized and are associated with periods of heavy rainfall.

Travelers of all ages are at risk for infection when visiting areas endemic for melioidosis. The highest risk for melioidosis exists for military personnel, adventure travelers, ecotourists, construction and resource extraction workers, and other people whose contact with contaminated soil or water may expose them to the bacteria. B. pseudomallei has been isolated from ill troops of all nationalities who served in areas with endemic disease, with a latency of as long as 62 years.

As much as 85% of cases occur during the rainy season, when exposure to the organism is believed to be highest. Melioidosis has been diagnosed among travelers who contracted the disease while staying in endemic areas during the rainy season. After the 2004 Southeast Asian tsunami, an increase in the number of melioidosis cases was observed among repatriated tourists. Risk factors for systemic melioidosis include diabetes, excessive alcohol use, chronic renal disease, chronic lung disease (such as associated with cystic fibrosis and chronic obstructive pulmonary disease), thalassemia, and malignancy or other non-HIV-related immune suppression.

CLINICAL PRESENTATION

Melioidosis may occur as a subclinical infection, localized infection (such as cutaneous), pneumonia, meningoencephalitis, sepsis, or chronic suppurative infection. The latter may mimic tuberculosis, with fever, weight loss, productive cough, and upper lobe infiltrate, with or without cavitation. The incubation period is generally 1–21 days, although it may extend for months or years. With a high inoculum, symptoms can develop in a few hours. More than 50% of cases present with pneumonia. Without appropriate treatment, case-fatality ratio may reach 90% within 48 hours of developing symptoms. Morbidity and mortality of melioidosis are higher in people with underlying diseases such as diabetes mellitus, renal dysfunction, chronic pulmonary disease, or compromised immune system. However, HIV infection does not appear to be a major risk factor for developing melioidosis.

DIAGNOSIS

Culture of the organism may be done from blood, sputum, pus, urine, synovial fluid, peritoneal fluid, and pericardial fluid. The most widely used serologic test for melioidosis is the indirect hemagglutination assay (IHA). Diagnostic assistance, including IHA serology and molecular, biochemical, and genetic characterization of isolates, is available through the CDC Zoonoses and Select Agent Laboratory (http://www.cdc.gov/nczved/divisions/dfbmd/bzb/lab_submission.html#zsal).

TREATMENT

Melioidosis often requires long courses of antimicrobial therapy. Some of the more common antibiotics used are ceftazidime, imipenem, meropenem, trimethoprim-sulfamethoxazole, and doxycycline. Relapse may be seen in patients, especially those who do not complete a full course of recommended eradication-phase therapy.

PREVENTIVE MEASURES FOR TRAVELERS

No vaccine is available to protect against melioidosis. In areas of endemic disease, skin lacerations, abrasions, or burns that have been contaminated with soil or surface water should be immediately and thoroughly cleaned.

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