Determinants of Recurrent Melioidosis

Limmathurotsakul, Direk (2008). Determinants of Recurrent Melioidosis. PhD thesis The Open University.



Recurrent melioidosis represents relapse following failure to eradicate bacteria responsible for the primary infection or re-infection with a new strain. The first results chapter (chapter 3) evaluates the proportion of recurrent melioidosis due to relapse versus re-infection. Isolates from the same patient with an identical genotype were considered as relapse and those with a different genotype as re-infection. Three quarters of recurrent cases were due to relapse and one quarter were due to re-infection. There are two ways in which this approach could be confounded. First, ‘re-infection’ could actually represent relapse if primary infection was caused by simultaneous infection with multiple B. pseudomallei strains, followed by chance selection of different strains from the two episodes for genotyping. The chance of this mistake occurring is based on the rate of polyclonal B. pseudomallei infection. Chapter 4 describes the rate of polyclonal infection in a large group of unselected patients in northeast Thailand, which was very low (2/133 cases, 1.5%). Second, ‘relapse’ could actually represent reinfection in the event that re-infection was caused by a B. pseudomallei strain that was by chance identical to the primary strain. The probability of this happening is based on the degree of genetic diversity of B. pseudomallei in the environment. Chapter 5 demonstrates that the population of B. pseudomallei in even a small sampling site is extremely diverse. Thus, it is unlikely that the assessment of the causes of recurrent melioidosis contained significant errors due to polyclonal infection or low genetic diversity of the organism. Chapter 6 examines specific risk factors of relapse and reinfection. Duration and choices of antibiotics used for the primary episode were major determinants of relapse. Chapter 7 compares the clinical manifestations of relapse and re-infection and develops a simple scoring index to predict relapse or re-infection in patients presenting with recurrent melioidosis.

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