Phenotypic Diagnosis and Characterization of Fungaemia using Conventional Blood Culture

Abstract

Background: Fungaemia is highly associated with immunocompromised populations as a results of long hospital stays, intensive care unit admissions and oncology. Blood culture is the most reliable conventional method in the diagnosis of bloodstream infections. We wanted to estimate the prevalence of fungaemia in order to determine the exact burden by origin for mitigation measures to be put in place; Thus blood specimens were collected from patients in health facilities across Uganda. Not so much emphasis has been put on strengthening fungal diagnostic methods especially fungaemia given the length of time it takes to obtain a BACTEC positive results for fungi in comparison to severe disease conditions of these patients. Sabaroud dextrose agar (SDA) is the most routinely used culture media for suspected fungal infections but few studies have critically looked at the length of time it takes from culturing to first evidence of growth. This study aimed at determining the proportion of fungaemia in blood samples of patients from different health facilities across Uganda by species and origin. We also intended to approximate how long it would take for a fungal culture on sabaroud dextrose agar (SDA) to grow from positively flagged BACTEC results for fungi. We analysed one hundred and ten (110) blood culture specimens flagged as ‘positive’ by an automated BACTEC 9120 blood culture system for bloodstream infections. To classify pathogens into different categories, gram stain was performed. To identify fungal pathogens, the BACTEC positive blood specimens were sub-cultured on SDA; biochemical identification tests including sugars, Lactophenol cotton blue, chromogenic agar for candida, germ tube and cornmeal agars were used. Our study findings show the prevalence of fungaemia was 4.0% from health facilities across Uganda, with Candida albicans being the most prevalent of all the fungal species; Cancer patients were at higher risk of developing fungaemia with 75% of fungal isolates coming from their wards; it takes an average of 48 hour to observe the earliest growth on SDA. Our study prevalence is relatively lower than that of researchers who carried out their studies in other clinical set ups except in different populations with better socioeconomic status. Candida albicans was still the most prevalent from other studies although C.tropicalis and C.glabrata are on the rise. Our time to SDA positive results was in agreement with similar studies done in other parts of Africa except there are those whose growth appeared as early as 24 hrs. Burden of fungaemia among immunocompromised patients are being under estimated in Uganda