10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Melioidosis from Aerosolization of the Environmental Bacterium Burkholderia Pseudomallei
BART CURRIE, Menzies School of Health Research & Royal Darwin Hosp., AU
Abstract Number: 480 Working Group: Infectious Bioaerosol
Abstract Melioidosis is caused by infection in humans and animals with the soil and water bacterium Burkholderia pseudomallei. While traditionally endemic in Southeast Asia and northern Australia, improvements in surveillance and diagnostics have increasingly unmasked cases of melioidosis and the presence of B. pseudomallei in local environments in the tropics and subtropics globally, including in the Americas and most recently Puerto Rico.
The Darwin Prospective Melioidosis Study has enrolled all culture-confirmed cases of melioidosis from the tropical Top End of the Northern Territory of Australia since October 1st 1989. With 1052 cases over 28 years, annual incidence rates are strongly influenced by rainfall and wind, being over 50/100,000 in some recent years with concomitant rates in the Indigenous population of over 100/100,000. Around 85% of cases present with acute illness, with the likely infecting event being increasingly identified through informed patient history and occurring within the 3 weeks prior to symptom onset. Recognised examples of exposure events that have been documented include inhalation or percutaneous inoculation during high pressure hosing or while mowing lawns or using a whipper-snipper (weed-whacker). Pneumonia is the presentation for half of cases, overall bacteremia rates are 60% and septic shock occurs in 21% of all cases, with most requiring ventilation in the ICU. With current treatment guidelines relapsed melioidosis is now very uncommon and mortality in Darwin has fallen from initially over 30% of all cases to around 10% in recent years. Nevertheless mortality from melioidosis remains over 40% in many regions globally where there are no or limited diagnostic laboratory capabilities, lack of the antibiotics required for optimum therapy (ceftazidime and meropenem) and no state-of-the-art hospital facilities for managing patients with severe sepsis.
What remains totally unclear is the proportion of cases that are from aerosol inhalation of B. pseudomallei in comparison to percutaneous inoculation or ingestion, with clinical (e.g. mediastinal disease) and epidemiological data from the Darwin study supporting but not proving a shift to inhalation during severe monsoonal weather. While activation from a latent focus is a rare occurrence, the proportion of those asymptomatic but seropositive to B. pseudomallei who have latent bacteria still present with the potential for later activation (the “Vietnamese Time Bomb”) also remains entirely unclear.
Air sampling studies have only occasionally successfully cultured B. pseudomallei from samples taken during weather events. In one Darwin case of severe melioidosis with pneumonia and mediastinal mass, whole genome sequencing of a positive air sample B. pseudomallei isolate collected outside the patient’s accommodation was closely matched to the sequence of the clinical isolate from the patient’s blood culture.
Various rodent and primate animal models have been used to study the aerosol route of infection with B. pseudomallei. They provide support to the proposition that deliberate release of manufactured B. pseudomallei aerosols in a high density city population could have catastrophic consequences analogous to those from anthrax and justifying the listing of B. pseudomallei as a Tier 1 Select Agent.