Quantitative cerebrospinal fluid (CSF) cultures provide a measure of disease severity in cryptococcal meningitis. The fungal clearance rate by quantitative cultures has become a primary endpoint for phase II clinical trials. This study determined the inter-assay accuracy of three different quantitative culture methodologies. Among 91 participants with meningitis symptoms in Kampala, Uganda, during August-November 2013, 305 CSF samples were prospectively collected from patients at multiple time points during treatment. Samples were simultaneously cultured by three methods: (1) St. George's 100 mcl input volume of CSF with five 1:10 serial dilutions, (2) AIDS Clinical Trials Group (ACTG) method using 1000, 100, 10 mcl input volumes, and two 1:100 dilutions with 100 and 10 mcl input volume per dilution on seven agar plates; and (3) 10 mcl calibrated loop of undiluted and 1:100 diluted CSF (loop). Quantitative culture values did not statistically differ between St. George-ACTG methods (P = .09) but did for St. George-10 mcl loop (P < .001). Repeated measures pairwise correlation between any of the methodswas high (r≥0.88). For detecting sterility, the ACTG-method had the highest negative predictive value of 97% (91% St. George, 60% loop), but the ACTG-method had occasional (~10%) difficulties in quantification due to colony clumping. For CSF clearance rate, St. George- ACTG methods did not differ overall (mean -0.05 ± 0.07 log10CFU/ml/day; P = .14) on a group level; however, individual-level clearance varied. The St. George and ACTG quantitative CSF culture methods produced comparable but not identical results. Quantitative cultures can inform treatment management strategies.
Bibliographical noteFunding Information:
This research was made possible through support from the Fogarty International Center and National Institute of Neurologic Diseases and Stroke (R01NS086312, R25TW009345) and National Institute of Allergy and Infectious Diseases (U01AI089244, T32AI055433). This work was supported in part by the Doris Duke Charitable Foundation through a grant supporting the Doris Duke International Clinical Research Fellows Program at the University of Minnesota. Jonathan Dyal is a Doris Duke International Clinical Research Fellow. Tihana Bicanic was funded by a Wellcome Trust Intermediate Fellowship (WT 089966). We thank Tonny Luggya for laboratory work; Jane Francis Ndyetukira, Cynthia Ahimbisibwe, Florence Kugonza, and Alisat Sadiq for patient care.