Analysis of 21 Years’ Data on Melioidosis Pneumonia Patient Outcomes
By Amesh A. Adalja, MD, FACP, November 18, 2011
Melioidosis, a Category B biothreat caused by the bacterium Burkholderia pseudomallei, is a common cause of community acquired pneumonia in the endemic regions of Southeast Asia and northern Australia. The bacterium, which is acquired by inhalation or inoculation, sometimes has a long latency period, like TB. Although most exposures are asymptomatic, when clinical disease does occur, fulminant pneumonia and severe sepsis can ensue.1,2 Because of its importance as a community acquired pathogen and its varied presentations, studying the outcomes of large cohorts of melioidosis patients is valuable to guide clinical management. Toward that end, Meumann and colleagues recently published the results of their study of a database containing 21 years (1989–2010) of prospectively collected data on melioidosis cases treated at the Royal Darwin Hospital in Australia.1
Between 1989 and 2010, there were 624 culture confirmed cases of melioidosis at the Royal Darwin Hospital. Notable characteristics included the following:
Median age was 49.5 years
69% of cases were male
51% of cases were primary pneumonia due to inhalation
19% of cases acquired by inoculation developed secondary pneumonia
More than 90% of primary pneumonia cases had acute or subacute presentations (ie, symptoms for less than 2 months)
Reactivation of prior infections was considered possible in 4% of acute and subacute cases.1
Morbidity and Mortality
As would be expected, patients with acute or subacute pneumonia more likely to develop bacteremia and septic shock and died (22% vs. 4%) more often than patients with chronic presentations. Lower-lobe and multilobar involvement on chest radiography was also more likely.1
Among patients with extrapulmonary involvement, 31% developed secondary pneumonia, which was more likely to occur in those with positive blood cultures. However, secondary pneumonia cases were found to have much lower rates of septic shock (16% vs. 47%) and death (27% vs. 8%) than those with bacteremic primary pneumonia.1
Risk Factors for Primary Pneumonia
The researchers conducted a multivariate analysis to delineate the following risk factors that predispose patients to developing primary pneumonia rather than extrapulmonary disease.
Rheumatic heart disease
Congestive heart failure
Chronic obstructive pulmonary disease
Interestingly, they found that kava use was predictive of extrapulmonary presentations. People ingest the roots of the kava plant to obtain an anxiolytic effect. The use of this substance has previously been linked, without a clear explanatory mechanism, to prostatic melioidosis abscess formation. In this study, kava use was associated with statistically fewer primary pneumonic processes.1
Melioidosis as a Bioweapon
Because it can cause fulminant disease and because of its environmental ubiquity in endemic regions, melioidosis has been studied as a potential bioweapon by several countries in the past.2 Additionally, it is naturally resistant to many antimicrobials, such as first and second generation cephalosporins and aminoglycosides, and the bacterium can be engineered to enhance its resistance profile. The standard treatment is a 2-week course of intravenous ceftazidime followed by 3 months of oral trimethoprim-sulfamethaxazole. During a bioattack with melioidosis, aerosol dispersal would be the expected route of exposure and primary pneumonia—the most fulminant type of presentation—would result. The present study is an important collection of the type of clinical data that would prove essential in such an event.2
- Meumann EM, Cheng AC, Ward L, Currie BJ. Clinical features and epidemiology of melioidosis pneumonia: results from a 21-year study and review of the literature. Clin Infect Dis 2011; Nov 4. [Epub ahead of print].
- Vietri NJ, Deshazer D. Meliodosis. In: Textbook of Military Medicine: Medical Aspects of Chemical and Biological Warfare. Washington, DC: Office of the Surgeon General at TMM Publications; 2007. Available at: http://www.bordeninstitute.army.mil/published_volumes/biological_warfare/biological.html. Accessed November 15, 2011.