Published Date: 2012-06-12 16:16:13
Subject: PRO/EDR> Melioidosis - Australia (03): (NT)
Archive Number: 20120612.1165498
MELIOIDOSIS - AUSTRALIA (03): (NORTHERN TERRITORY)
A ProMED-mail post
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International Society for Infectious Diseases
Date: Tue 5 Jun 2012
Source: Nine MSN [edited]
Acting director of the Centre for Disease Control in the [Northern] Territory, Steven Skov, said there had been 97 cases of melioidosis locally this wet season, resulting in 9 deaths. Dr Skov said the figure was a record number of cases, although not a record number of deaths, which has dropped in recent years due to better treatments and awareness of the disease.
The soilborne disease is thought to lie dormant in the ground for most of the year, but comes to the surface when there is heavy rain during the wet season. Those at risk of catching melioidosis include gardeners who come into close contact with soil and people with compromised immune systems.
During the past 3 years there has been a spike in the number of cases, which researchers had put down to strong wet seasons. But Dr Skov said high numbers of melioidosis cases had continued this wet season despite it not being an unusually heavy rainy period.
"We can't say for a certainty just why we have had this increase over the past 3 years," he said. "When there is heavy rainfall combined with high winds the bacteria can get aerosolized and then people with risk factors might breathe it in and get sick from it. But that is speculation and we can't test that in any sort of scientific way," he said.
[Most of the reports of melioidosis from Australia originate in the Northern Territory; however, the disease is also endemic in Queensland, which is east of the Northern Territory. The disease usually occurs during the rainy season and may be accentuated by extreme flooding from rain and also from tsunamis, as occurred in 2005 in Thailand. A few cases were diagnosed after survivors returned to their home country of Finland.
_Burkholderia pseudomallei_ exists as an environmental saprophyte living in soil and surface water in endemic areas (South East Asia and northern, tropical Australia), particularly in rice paddies. In endemic countries, the organism exists primarily in focal areas and is not equally distributed throughout the landscape. Sporadic cases have been reported to have been acquired in parts of Africa and the Americas. The organism may exist in a viable, non-cultivable state in the environment, interacting with other organisms, particularly protozoa, which might explain its adaptation to an intracellular niche. 2 outbreaks in Australia have also implicated potable water supplies rather than surface water as a potential source of the infection.
Melioidosis is a disease of the rainy season in the endemic areas. It mainly affects people who have direct contact with soil and water. Many have an underlying predisposing condition such as diabetes (commonest risk factor), renal disease, cirrhosis, thalassemia, alcohol dependence, immunosuppressive therapy, chronic obstructive lung disease, cystic fibrosis, and excess kava consumption. Kava is an herbal member of the pepper family that can be associated with chronic liver disease.
Melioidosis may present at any age, but peaks in the 4th and 5th decades of life, affecting men more than women. In addition, although severe fulminating infection can and does occur in healthy individuals, severe disease and fatalities are much less common in those without risk factors.
The most commonly recognized presentation of melioidosis is pneumonia, associated with high fever, significant muscle aches, chest pain, and -- although the cough can be nonproductive -- respiratory secretions can be purulent, significant in quantity, and associated with on-and-off bright, red blood. The lung infection can be rapidly fatal -- with bacteremia and shock -- or somewhat more indolent.
Acute melioidosis septicemia is the most severe complication of the infection. It presents as a typical sepsis syndrome with hypotension, high cardiac output, and low systemic vascular resistance. In many cases, a primary focus in the soft tissues or lung can be found. The syndrome, usually in patients with risk factor comorbidities, is characteristically associated with multiple abscesses involving the cutaneous tissues, the lung, the liver, and spleen, and a very high mortality rate of 80 to 95 per cent. With prompt optimal therapy, the case fatality rate can be decreased to 40 to 50 per cent.
The melioidosis bacillus is intrinsically insensitive to many antimicrobials. It should be noted that bioterrorism strains may be engineered to be even more resistant. _B. pseudomallei_ is usually inhibited by tetracyclines, chloramphenicol, trimethoprim-sulfamethoxazole (SXT), antipseudomonal penicillins, carbapenems, ceftazidime, and amoxicillin/clavulanate or ampicillin/sulbactam. Ceftriaxone and cefotaxime have good in vitro activity but poor efficacy; and cefepime did not appear, as well, to be equivalent to ceftazidime in a mouse model. The unusual antimicrobial profile of resistance to colistin and polymyxin B and the aminoglycosides but sensitivity to amoxicillin/clavulanate is a useful tool to consider in treatment of infection with the organism.
The randomized and quasi-randomized trials comparing melioidosis treatment have been reviewed, and it was found that the formerly standard therapy of chloramphenicol, doxycycline, and SXT combination had a higher mortality rate than therapy with ceftazidime, imipenem/cilastatin, or amoxicillin/clavulanate (or ampicillin/sulbactam). The betalactam-betalactamase inhibitor therapy, however, seemed to have a higher failure rate.
Source: Tolaney P, Lutwick LI: Melioidosis. In: Lutwick LI, Lutwick SM (eds). Bioterror: the weaponization of infectious diseases. Totowa NJ: Humana Press, 2008 pp 145-58.
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